Loop-gap resonator

A loop-gap resonator (LGR) is an electromagnetic resonator that operates in the radio and microwave frequency ranges. The simplest LGRs are made from a conducting tube with a narrow slit cut along its length. The LGR dimensions are typically much smaller than the free-space wavelength of the electromagnetic fields at the resonant frequency. Therefore, relatively compact LGRs can be designed to operate at frequencies that are too low to be accessed using, for example, cavity resonators. These structures can have very sharp resonances (high quality factors) making them useful for electron spin resonance (ESR) experiments, and precision measurements of electromagnetic material properties (permittivity and permeability).
Background.
Loop-gap resonators (LGRs) can be modelled as lumped-element circuits. The slit along the length of the resonator has an effective capacitance formula_1 and the bore of the resonator has effective inductance formula_2. At, or near, the resonance frequency, a circumferential current is established along the inner wall of the resonator. The effective resistance formula_3 that limits this current is, in part, determined by the resistivity formula_4 and electromagnetic skin depth formula_5 of the conductor used to make the LGR. It is, therefore, possible to model the LGR as an formula_6 circuit. Since the LGR current is a maximum at the resonant frequency, the equivalent circuit model is a series formula_6 circuit. This circuit model works well provided the dimensions of the resonator remain small compared to the free-space wavelength of the electromagnetic fields.
One advantage of the LGR is that it produces regions of uniform electric and magnetic fields that are isolated from one another. A uniform electric field exists within the slit of the LGR and a uniform magnetic field exists within the bore of the resonator. The uniform magnetic field makes the LGR a good source of microwave magnetic fields in ESR experiments. Furthermore, because the electric and magnetic fields are isolated from one another, one can use the LGR to independently probe the electric and magnetic properties of materials. For example, if the gap of the LGR is filled with a dielectric material, the effective capacitance of the LGR will be modified which will change the frequency formula_8 and quality factor formula_9 of the resonance. Measurements of the changes in formula_8 and formula_9 can be used to fully determine the complex permittivity of the dielectric material. Likewise, if the bore of the LGR is filled with a magnetic material, the effective inductance of the LGR will be modified and the resulting changes in formula_8 and formula_9 can be used to extract the complex permeability of the magnetic material.
Resonant Frequency and Quality Factor.
Resonance frequency.
The capacitance of the gap of the LGR is given by
where formula_15 is the permittivity of free space, formula_16 is the thickness of the bore wall, formula_17 is the gap width, and formula_18 is the length of the resonator. The resonator bore acts as a single-turn solenoid with inductance given by
where formula_20 is the permeability of free space and formula_21 is the inner radius of the LGR bore. For a high-formula_9 resonator, the resonant frequency is, to an approximation, given by
where formula_24 is the vacuum speed of light. Therefore, the resonant frequency of the LGR is determined from is geometry and is, to first approximation, independent of its length.
Quality factor.
For a highly underdamped series formula_6 circuit, the quality factor, which determines the sharpness of the resonance, is given by
The effective resistance of a LGR can be estimated by considering the length of conductor through which the current travels and the cross-sectional area available to it. The relevant conductor length is the circumference formula_27 of the conductor's inner surface. The depth that the current penetrates into the inner surface of the LGR bore is determined by the electromagnetic skin depth formula_5. Therefore, the cross-sectional area through which charge flows is formula_29. Combining these results gives an effective resistance
where formula_4 is the resistivity of the conductor. The effective capacitance, inductance, and resistance then lead to a simple expression for the expected quality factor of the LGR
where, for a good conductor, the electromagnetic skin depth at the resonance frequency is given by
and formula_34. For an aluminum resonator with formula_35 and formula_36 the above analysis predicts formula_37.
Radiative losses.
In practice, the measured quality factor a cylindrical LGR, without additional electromagnetic shielding, will be much less than the predicted value of formula_38. The suppression of the quality factor is due to radiative power loss from magnetic field lines that extend out of LGR bore and into free space. An order-of-magnitude estimate of the effective radiation resistance can be made by treating the LGR as a conducting loop. In the limit that the wavelength of the radiation is much larger than the loop radius formula_21, the radiation resistance is
and can be much larger than the resistance formula_41 due to the resistivity of the LGR conductor.
The radiative losses can be suppressed by placing the LGR inside a circular waveguide. Provided that the cutoff frequency of the lowest TE11 waveguide mode is well above the resonant frequency of the LGR, the magnetic field lines will be prevented from propagating into free space. The presence of the electromagnetic shield will alter the resonant frequency and quality factor of the LGR, but typically by only a few percent.
Toroidal LGR.
In some applications requiring high quality factors, the electromagnetic shielding provided by a concentric circular waveguide surrounding a cylindrical LGR can be bulky and awkward to work. A toroidal LGR can be used for high-formula_9 measurements without requiring additional electromagnetic shielding. In the toroidal geometry the two ends of a cylindrical LGR are joined to form a completely closed structure. In this case, the magnetic field is completely confined within the bore of the resonator and there is no radiative power loss. The toroidal LGR consists of two halves that are bolted together along the outer diameter of the structure.
Like the cylindrical LGR, the toroidal LGR can be modelled as a series formula_6 circuit. In general, the effective capacitance, inductance, and resistance of the toroidal LGR will differ from the expressions given above for the cylindrical LGR. However, in limit that the radius of the torus is large compared to the bore radius formula_21, the capacitance, inductance, and resistance of the toroidal LGR are approximated by the expressions above if one takes formula_18 to be equal to the circumference of the torus.
The toroidal LGR is particularly convenient when characterizing the electromagnetic properties of liquid samples or particles suspended in a liquid. In these cases, the bore of the toroidal LGR can be partially filled with the liquid sample without requiring a special sample holder. This setup allows one to characterize the magnetic properties of, for example, a ferrofluid. Alternatively, if the liquid sample is nonmagnetic, the entire toroidal LGR can be submerged in the liquid (or gas). In this case, the dielectric properties of the sample only modify the effective capacitance of the resonator and the changes in formula_8 and formula_9 can be used to determine the complex permittivity of the sample.
Coupling to a LGR.
Inductive coupling loops are typically used to couple magnetic flux into and out of the LGR. The coupling loops are made by first removing a length of outer conductor and dielectric from a semi-rigid coaxial cable. The exposed centre conductor is then bent into a loop and short-circuited to the outer conductor. The opposite end of the coaxial cable is connected to either a signal generator or a receiver. In the case of a signal generator, an oscillating current is established in the coupling loop. By Faraday's law of induction, this current creates and oscillating magnetic flux which can be coupled into the bore of the LGR. This magnetic flux, in turn, induces circumferential currents along the inner wall of the LGR. The induced current, once again by Faraday's law, creates an approximately uniform oscillating magnetic field in the bore of the LGR. A second coupling loop, connected to a receiver, can be used to detect the magnetic flux produced by the LGR. Alternatively, using a vector network analyzer (VNA), a single coupling loop can be used to both inject a signal into the LGR and measure its response. The VNA can measure the ratio of the forward and reflected voltages (formula_48, or reflection coefficient) as a function of microwave frequency. Far away from resonance, the magnitude of the reflection coefficient will be close to one since very little power is coupled into the LGR at these frequencies. However, near the resonance frequency formula_8, the magnitude of the reflection coefficient will fall below one as power is transferred into the LGR. The coupling between the external circuits and the LGR can be tuned by adjusting the relative positions and orientations of the coupling loop and LGR. At critical coupling, impedance matching is achieved and the reflection coefficient approaches zero.
It is also possible to capacitively couple electric fields into and out of the gap of the LGR using suitably-fashioned electrodes at the end of a coaxial cable.
Multi-Loop, Multi-Gap LGRs.
Multi-loop, multi-gap LGRs have also been developed. The simplest of these is the two-loop, one-gap LGR. In this case, magnetic field lines form closed loops by passing through each of the bores of the LGR and the currents on the inner walls propagate in opposite directions - clockwise in one bore and counterclockwise in the other. The equivalent circuit, neglecting losses, is a parallel combination of inductors formula_2 and formula_51 in series with capacitance formula_1. If formula_53, then the resonant frequency of the two-loop, one-gap LGR is formula_54 times greater than that of the conventional one-loop, one-gap LGR having the same bore and gap dimensions. It is also worth noting that, since magnetic field lines pass from one bore to the other, radiative power losses are strongly suppressed and the resonator maintains a high quality factor without requiring additional electromagnetic shielding.
The multi-loop, multi-gap LGRs with more than two loops have more than one resonant mode. If the central bore is singled out as having inductance formula_51, then one of the resonant modes is one in which all of the magnetic flux from each of the external loops of inductance formula_2 is shared with the central loop. For this mode, the resonant frequency of an formula_57-loop, formula_58-gap LGR is given by
where it has been assumed that all loops have the same inductance formula_2.
LGRs and superconductivity.
Loop-gap resonators have been used to make precise measurements of the electrodynamic properties of unconventional superconductors.
Most notably, a LGR was used to reveal the linear temperature dependence of the magnetic penetration depth, characteristic of a d-wave superconductor, in a single crystal of YBa2Cu3O6.95.
In these experiments, a superconducting sample is placed inside the bore of a LGR. The diamagnetic response of the superconductor alters in the inductance of the LGR and, therefore, its resonant frequency. As described below, tracking the change in the resonant frequency as the temperature of the sample is changed allows one to deduce the temperature dependence of the magnetic penetration depth.
Theory.
The inductance of the LGR can be expressed as formula_61, where formula_62 is the volume of the LGR bore. Since the resonant frequency formula_8 of the LGR is proportional to formula_64, a small change in the effective volume of the resonator bore will result in a change in the resonant frequency given by
Due to the Meissner effect, when a superconducting sample is place in the bore of a LGR, the magnetic flux is expelled from the interior of the sample to within a penetration depth formula_66 of its surface. Therefore, the effective volume of the resonator bore is reduced by an amount equal to the volume from which the magnetic flux has been excluded. This excluded volume is given by
where formula_68, formula_69, and formula_70 are the sample dimensions along the three crystallographic directions and formula_71 is the sample volume formula_72. In the above expression, it has been assumed that the microwave magnetic field is applied parallel to the formula_69-axis of the sample. Since the presence of the superconductor reduces the LGR volume, formula_74 and
Solving this expression for the formula_68-axis penetration depth yields
Generally, it is not possible to use LGR frequency-shift measurements to determine the absolute value of the penetration depth because it would require knowing the sample thickness formula_70 very precisely. For example, in fully doped YBa2Cu3O7, formula_79 at low temperature.
Therefore, to use the LGR measurement to determine formula_80 to within 10%, one would have to know the value of formula_70 with an accuracy of formula_82 which is typically not possible.
Instead, the strategy is to track the changes in frequency as the sample temperature varies (while keeping the LGR at a fixed temperature). The absolute penetration depth can be expressed as
where formula_84 is temperature, formula_85 is the experimental base temperature, and formula_86 is the change in penetration depth as the sample temperature is increased above the base temperature. One can, therefore, express the change in penetration depth as
Finally, defining formula_88, one has
This final expression shows how the LGR shifts in resonant frequency can be used to determine the temperature dependence of the magnetic penetration depth in a superconducting sample.
Experimental details.
In a d-wave superconductor, the penetration depth typically changes by a few ångströms per degree kelvin, which corresponds to formula_90 for a formula_91 platelet sample in a LGR with a bore volume of formula_92. Measuring such small changes in relative frequency requires an extremely high-formula_9 resonator. The ultrahigh quality factors are obtained by coating the LGR surfaces with a superconducting material, such as a lead-tin alloy. The resonator is then cooled below the superconducting transition temperature of the coating using a bath of superfluid liquid helium. Quality factors of formula_94 have been achieved using copper LGRs coated with lead-tin and cooled to formula_95.
Measuring permittivity and permeability.
This section describes how LGRs can be used to determine the electromagnetic properties of materials. When there are no materials filling either the gap or bore of the resonator, the impedance formula_96 of the LGR can be expressed as
where formula_98. Re-expressed in terms of the resonant frequency formula_99 and quality factor formula_9, the impedance is given by
A measurement of the frequency dependence of the impedance of an empty LGR can be used to determine formula_99 and formula_9. The impedance measurement is most easily done using the vector network analyzer (VNA) to measure the reflection coefficient formula_48 from an inductively-coupled LGR. The impedance and reflection coefficient are related by
where formula_106 is the output impedance of the VNA (usually, formula_107).
Complex permittivity.
Now suppose that the gap of resonator has been completely filled with a dielectric material that has complex relative permittivity formula_108. In this case, the effective capacitance becomes formula_109 and the impedance of the LGR is given by
Separating the real and imaginary terms leads to
This expression shows that a nonzero formula_112 enhances the effective resistance of the LGR and, therefore, lowers its quality factor. A nonzero formula_113, on the other hand, alters the imaginary part of the impedance and modifies the resonant frequency. Written in terms of the empty-resonator resonant frequency and quality factor, the above impedance can be expressed as
Provided that formula_99 and formula_9 are known before hand, a measurement of the frequency dependence of formula_117 can be used to determine formula_118 and formula_112 of the material filling the gap of the LGR. This analysis gives the values of formula_118 and formula_112 at the resonant frequency of the filled LGR.
Complex permeability.
Next, suppose that the bore of a LGR is filled with a magnetic material have complex relative permeability formula_122. In this case, the effective inductance becomes formula_123 and the impedance of the LGR is given by
Separating formula_125 into its real and imaginary components and writing the impedance in terms of formula_99 and formula_9 of the empty LGR yields
Once again, formula_129 contributes additional dissipation which lowers the quality factor of the filled resonator and formula_130 shifts the resonant frequency. A measurement of the frequency dependence of formula_125 can be used to extract the values of formula_130 and formula_129 at the resonant frequency of the filled LGR.


Aldo R. Boccaccini

Aldo Roberto Boccaccini (born 2 September 1962 in San Rafael, Argentina) is a nuclear engineer and material scientist. He is currently a Professor of Biomaterials and Head of the Institute of Biomaterials at the Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Erlangen, Germany.
Biography.
Boccaccini studied 2 years of electromechanical engineering at Universidad Tecnologica Nacional, in San Rafael, Argentina, and earned his engineering degree in Nuclear Engineering at Instituto Balseiro, S. C. de Bariloche, Argentina in 1987. He then moved to Germany and carried out his doctoral studies at RWTH Aachen, where he earned his doctoral degree (Dr.-Ing) in 1994. He then held postdoctoral positions in the UK at University of Birmingham, School of Metallurgy and Materials and in the USA, University of California, San Diego. In 2001 Boccaccini received his habilitation at Technical University Ilmenau, Germany. In 2000 Boccaccini joined the Department of Materials at Imperial College London (UK), where he was appointed Professor of Materials Science and Engineering in 2008. In 2009 Boccaccini moved to Germany as Professor for Biomaterials and Head of the Institute of Bomaterials at University of Erlangen-Nuremberg. He was appointed chair of the Department of Materials Science and Engineering from 2017 to 2019.
Academic work.
The fields of research of Boccaccini in the broad field of materials science and engineering focus on biomaterials for a variety of biomedical applications. In particular his research focuses on bioactive glasses and composites, bioactive coatings, tissue engineering scaffolds and drug delivery systems. He is also a pioneer of the field of electrophoretic deposition applied to biomedical and functional materials. Boccaccini is also member of the Advisory Board of the Network of Argentine Scientists in Germany and an international advisor to the Ministry of Science, Technology and Innovative Production of Argentina since 2008.
Boccaccini is also on the council of the European Society of Biomaterials (ESB) and the Federation of European Materials Society (FEMS). Since 2018, he has also been a full member of the .
Publications.
Prof. Boccaccini is the editor-in-chief of the journal Materials Letters and the founding editor-in-chief of the Open Access journal Biomedical Glasses (launched in 2014). He has published more than 900 research papers, he has co-edited 5 books, more than 20 book chapters. Boccaccini is a highly cited researcher, according to the Highly Cited 2014 list published by Thomson Reuters. To date (February 2020) he has been cited more than 52.000 times and has an h-index of 102 as listed in Google Scholar. In 2018, Boccaccini was again included in Clarivate Analytics' list of the most cited scientists.


North Sea Link

The North Sea Link is a 1,400 MW subsea high-voltage direct current electricity cable under construction between Norway and the United Kingdom. When completed, it will be the longest subsea interconnector in the world.
Route.
The cable will run from Kvilldal, Suldal, in Norway, to Blyth in the United Kingdom.
Its converter station in England will be located near to the cable landfall in East Sleekburn village and it will be connected to the National Grid at the Blyth substation.
Technical description.
The cable will be long. It has a planned capacity of 1,400 MW. It is estimated to cost €2 billion and become operational in 2021.
The offshore cable will be supplied by Prysmian. The cable will be manufactured at the Arco Felice factory in Naples, Italy, and it will be installed by the cable-laying vessel "Giulio Verne". Cable for the fjord, tunnel and lake sections, and the onshore connection in Norway, will be supplied by Nexans and manufactured at Nexans' plant in Halden, Norway. It will be laid by using Capjet trenching system and the cable-laying vessel "Skagerrak". The HVDC converter stations will be built and installed by the ABB Group.
Ownership.
It is a joint project of the transmission system operators Statnett and National Grid plc.
Current status.
As of February 2020, the UK on-shore cable has been installed between the landfall at Bucca headland and the converter station site at East Sleekburn. The converter station is under construction. As of January 2021, the converter station in Suldal has been connected to the grid.
Future plans.
The cable is due to be completed in 2021.
The interconnection may also connect the North Sea wind farms as well as offshore oil and gas platforms, becoming the backbone of the proposed North Sea Offshore Grid.
Project history.
The project was first proposed in 2003 when Statnett and National Grid prepared a 1,200 MW interconnector between Suldal in Norway and Easington, County Durham, in the United Kingdom. This project was suspended.
On 6 October 2009, Statnett and National Grid announced they were conducting a feasibility study of the cable. According to the pre-feasibility study the project will be economically and technologically feasible. It will be a commercial cable jointly owned by Statnett and National Grid NSN Link Limited, a subsidiary of National Grid.
National Grid quotes various groups in favor of more interconnections.
The route survey of the offshore section was conducted by MMT in 2012.
In March 2015, Statnett and National Grid announced a decision to "start the construction phase", a month after announcing the "Nemo link", a similar connection between the United Kingdom and Belgium. Along with Viking Link from Denmark, they would increase the UK's electricity interconnection level (transmission capacity relative to production capacity) from the 6% it was in 2014.
Economy.
Once completed the North Sea Link will give the UK access to the south Norway bidding area (NO2) of Nord Pool Spot with an annual transmission capacity of 12.3 TWh. According to the analysis by the United Kingdom market regulator Ofgem, in the Base case scenario the cable would contribute around £490 million to the welfare of the United Kingdom and around £330 million to the welfare of Norway. According to the analysis, over the 25-year cap and floor regime (a regulation for how much money a developer can earn once the interconnector is in operation) the benefit of the United Kingdom consumers is expected to be around £3.5 billion under the Base case scenario. Once the cable is completed the average domestic consumer bill in the United Kingdom would be around £2 less.
According to Auke Lont, CEO of Statnett, Norway may use the interconnector to import electricity at times of peak supply in the United Kingdom, which could temporarily reduce hydroelectricity output in Norway and shift Norwegian hydroelectricity production to peak demand times.
In 2014 the Norwegian energy service provider Markedskraft analyzed the impact of two interconnectors under construction from Norway, the North Sea Link and NorGer a submarine cable of identical capacity connecting Norway with Germany. The electricity will at any moment flow towards the country with the highest price and these price differentials generate income for the interconnector whether the electricity flows one way or the other. Markedskraft estimated that while the Norwegian import and export via NorGer will zero out in 2020, the annual net export to the UK via North Sea Link is projected to be about the 10 TWh, i.e. almost all of the interconnector's annual capacity. Markedskraft go on to estimate that the increased demand for Norwegian electricity via North Sea Link will increase the price of electricity in Norway by 25 NOK/MWh (ca. 2.6 €/MWh). A 2016 study expects the two cables to increase price in South Norway by 2 øre/kWh, less than other factors.


List of wave power stations

The following page lists most power stations that run on wave power. Wave farms are classified into 8 types based on the technology used, such as Surface-following attenuator, Point absorber, Oscillating wave surge converter, Oscillating water column, Overtopping/Terminator, Submerged pressure differential, Bulge wave device, and Rotating mass.


Maryland power plant research program

The Maryland Power Plant Research Program (PPRP) is a government program within the Maryland Department of Natural Resources and is charged with addressing power plant licensing issues. PPRP was established under the Power Plant Siting and Research Act of 1971. This legislation provided a model for addressing power plant licensing issues which several other states have adopted. PPRP is housed within DNR’s headquarters in Annapolis, Maryland.
Mission and functions.
PPRP functions to ensure that Maryland meets its electricity demands at reasonable costs while protecting the state's valuable natural resources. It provides a continuing program for evaluating electric generation issues and recommending responsible, long-term solutions.


Alan Parkinson (engineer)

Alan Parkinson is a mechanical and nuclear engineer who lives in Canberra, Australia. He is also a whistleblower who wrote the 2007 book, "" which exposed deficiencies in the clean-up of the British atomic bomb test site at Maralinga in South Australia.
Maralinga clean-up.
In 1993, Parkinson became the key person on the Maralinga clean-up project, representing the then federal Labor government (through the Department of Primary Industry and Energy). By 1997, however, there was much cost-cutting involved in the project, and differences of opinion about how the project should proceed, which led to the sacking of Parkinson by the new Howard government.
The clean-up, which involved simply burying untreated long-lived radioactive debris in holes in the ground, was totally unsatisfactory according to Parkinson. He exposed the situation through the Australian Broadcasting Corporation, provoking a strong rebuttal from the government, composed of scientific distortion and personal abuse.
The plan was to collect some of the contaminated soil and bury that soil in a specially prepared trench 15 metres deep. Several thousand tonnes of debris contaminated with plutonium was to be treated by a process of in situ vitrification. After collection and burial of the soil, the project moved to the second phase - the treatment of 21 pits by vitrification. Against the advice of Parkinson, the government department extended the contract of the project manager, even though that company had no knowledge of the complex process of vitrification. At that stage Parkinson was removed from the project. The government and the project manager then embarked on a hybrid scheme in which some pits would be exhumed and others treated by vitrification. After successfully treating 12 pits, there was an unlucky thirteenth during which something in the pit exploded and severely damaged the equipment. The government then cancelled the vitrification and simply exhumed the remaining pits, placed the debris in a shallow pit and covered it with clean soil.


Champlain Hudson Power Express

The Champlain Hudson Power Express (CHPE) is a proposed high-voltage direct current (HVDC) submarine power cable project linking the Montreal area to the New York City neighborhood of Astoria, Queens. If approved, the line is expected to be commissioned in 2021.
The venture, being developed by Transmission Developers Inc. (TDI), a Blackstone Group, L.P. (Blackstone) portfolio company, would carry clean energy - hydropower and wind power from eastern Canada - and feed it directly in the New York City electricity market. Construction costs for this project are estimated at US$2.2 billion for the section located in the State of New York.
The Quebec section of the line would be built and operated by TransÉnergie, the transmission arm of Hydro-Québec.
Background.
Power rates in the New York metro area and Long Island have long been among the highest in the U.S. and according to the U.S. Department of Energy, the city is the "epicenter" of grid congestion in the eastern United States. The congestion problem in the New York City area and on Long Island is compounded by the fact that the area uses two-thirds of the state's electricity while most generation and import capacity is located upstate and near the Great Lakes.
Over the years, a number of proposals to increase transmission capacity to the New York City and Long Island markets have encountered hostile reactions and determined opposition from environmental groups and communities along the planned paths. For instance, construction of the Cross Sound Cable, a 328-MW submarine DC cable linking Connecticut to Long Island via the Long Island Sound, was authorized in 2002, but its commissioning was delayed for a year because of a dispute involving the promoter and the state of Connecticut. Another project, the Neptune Regional Transmission System has been operational since 2007. The 500 kV cable connects New Jersey and Long Island. It runs buried in the Atlantic Ocean and has a capacity of 660 megawatts. A proposed HVDC line, West Point Partners, that would have interconnected the grid from a substation in Athens, New York to a substation near the Indian Point Energy Center was tabled when the landowner where the southern converter station would be located, Con Edison, sold the land to the Village of Buchanan. The Village of Buchanan then sold the rights to use the land to the natural gas company Spectra for their new proposed natural gas pipeline.
However, a 400 kilovolts DC line between the Rock Tavern substation, 60 miles north of New York, and the Marcy hub in central New York, has been marred by controversy. Launched in 2006, the proposed "New York Regional Interconnect" (NYRI) had a 1,200 megawatts capacity. It was shelved by its developers in early 2009 after two years of staunch opposition from several groups concerned by the impact of pylons along the proposed route.
Project.
TDI, whose board is chaired by former Ontario Premier David Peterson, is backed by Blackstone and was announced on February 23, 2010. Since then, the CHPE Project has made significant progress in terms of securing the governmental approvals. The Federal Energy Regulatory Commission authorized the Project developers to sell transmission rights at negotiated rates in July 2010. Less than a year later, the New York State Department of State issued its Coastal Zone Consistency determination for the project.
Settlement.
On February 24, 2012, the parties participating in the detailed review of the project being conducted before the New York State Public Service Commission (PSC) announced that they had reached a settlement of all of the issues in the proceeding. On April 18, 2013, the New York State Public Service Commission granted the CHPE project a Certificate of Environmental Compatibility and Public Need.
The CHPE project tries to avoid difficulties encountered by other proposals by presenting itself as an "environmentally benign" solution. By avoiding overhead wires and 10 story high towers, the promoter hopes to avoid the fate of previous projects, such as NYRI. The initial project involved two 1,000 MW lines, the first one to New York, and the second going all the way to Connecticut, via the Long Island Sound. The construction cost for the two lines and converter stations in the U.S. was estimated at $3.8 billion. The line to Connecticut was cancelled in July 2010.
According to the company's president and CEO, Donald Jessome, choosing an underwater route avoids " disrupt[ing] communities with overhead transmission". The developer says that the cable also provides economic and environmental benefits to the state, bringing low-cost and clean power to critical load centers.
Opposition to Project.
According to the Atlantic chapter of the Sierra Club, some towns in Rockland had called on Governor Cuomo to press then-President Obama to stop this agreement. As this is an agreement with a foreign country, his approval was needed. In continuation, as of September 2017 the newly elected Donald Trump administration has also not addressed this issue. Part of Iona Island which contains a bird sanctuary is to be blasted to make way for CHPE project. Three planned CHPE cooling stations are to be located in a state park in the Haverstraw/West Haverstraw vicinity. Residents of this area are also concerned about property seizures under eminent domain.
There is also opposition from New York labor unions because most construction jobs will go to workers from out of State.
The Atlantic chapter of the Sierra Club has asked its members to oppose this project. New York wind energy producers currently cannot get their electricity carried to the New York City. It is the Sierra club's contention that CHPE will stop any chance of New York City getting locally produced wind power and in general dampen the market for local alternative energy production.
Route.
The proposed cable would have a length of approximately between the Canada-U.S. border and its southern terminal, in New York City. The two cables would be buried at varying depths of under Lake Champlain and the Hudson River, Harlem, and East Rivers.
The cables would cross the border under Lake Champlain and would run southward to the Town of Dresden north of the Village of Whitehall. On its way to the Hudson, the cables would be routed briefly taken along State Route 22 and then parallel the Delaware & Hudson Railroad right-of-way to Rotterdam, at which point it accesses the right-of-way of a CSX Transportation rail line, continuing southwards until it enters the Hudson River in the Town of Catskill.
Once the cables are in the Hudson River, they continue south to the Town of Stony Point, where the CSX railroad right-of-way is again relied on until the cables re-enter the Hudson in the Town of Clarkstown. The cables next make landfall in the Harlem River Intermodal Yard in the Bronx, traverses the East River to reach Queens, and terminates at a converter station on the large energy campus in the Astoria neighborhood in the New York City borough of Queens.
Economics, emission levels, and reliability.
In an economic analysis filed on behalf of the promoter to the New York Public Service Commission in July 2010, London Economics International estimates that the projected line would save New York customers $8.1 billion (2010) on their electricity bills over the first 10 years of operations, between 2015 and 2024. In addition, the proposed cable would have positive impacts on the electricity grid, since power carried by the cables could force the retirement of older, uneconomic power plants in New York.
The planned line, which would carry 7.64 terawatt-hours of renewable electricity per year, would lower emissions by 6,800 tonnes, emissions by 10,800 tonnes and emissions by nearly 37 million tonnes during the first decade of operation.
A study released by TDI in February 2012 concludes that the CHPE will create hundreds of jobs directly and thousands of indirect and induced jobs. The Project will also reinforce the reliability of New York's bulk power delivery system.
The proposed CHPE project has applied to the U.S. Department of Energy for a Presidential Permit, and to the U.S. Army Corps of Engineers for permits issued pursuant to the federal Clean Water Act and Rivers and Harbors Act, and hence, is subject to the requirement that an Environmental Impact Statement (EIS) be prepared. The CHPE EIS is of an Environmental Impact Statement currently under preparation.
Hydro-Québec's position.
According to the promoter, the Quebec section of the line would start at a DC conversion station to connect with Hydro-Québec TransÉnergie's Hertel substation (735-315 kV) near La Prairie, and would reach the junction point at the international border in Lake Champlain.
The initial reaction of Hydro-Québec (HQ)and the Quebec government to the CHPE project was first met with some skepticism, considering the 400 to 500 million Canadian dollars price tag for the Quebec section of the line. In addition, the CHPE could be seen as competing with a proposed 1,200 MW HVDC line to be built by the company in association with NSTAR and Northeast Utilities, which is expected to increase exports of Quebec hydropower to New England. Reflecting on the project in April 2010, Hydro-Quebec's CEO, Thierry Vandal, stated that it was technically "very complex" and "very costly".
Despite its mixed initial reaction, the Quebec utility intervened in support of the proposal before the FERC in May 2010, and the PSC in March 2012.[18] In the March 2012 letter, HQ cited the CHPE project's potential to bring large quantities of renewable energy to downstate New York at no cost to New York ratepayers and the CHPE project's progress before the PSC as the reasons for entering into "active discussions" with TDI.
Late in January 2013, Hydro-Québec formally filed a project notice to build the Quebec part of the line to the Quebec Minister of Sustainable Development, Environment, Wildlife and Parks, Yves-François Blanchet. The ±320 kV power line would start at the Hertel transmission station, near La Prairie, to reach the US border on the shore of lake Champlain. The project includes the deployment of a DC terminal at Hertel TS, but in contrast to the US part of the line, Hydro-Québec excludes running the line in the Richelieu riverbed.


Heywood interconnector

The Heywood interconnector is a 275 kV overhead electricity transmission line with two circuits connecting the electricity grids in South Australia and Victoria, two states of Australia. Both are part of the National Electricity Market. The nominal capacity of the interconnector is 650 MW since an upgrade in 2016. The interconnector was commissioned in 1988 and was the first connection between the two state electricity grids.
Routing.
The Victorian end of the interconnector is the substation at Heywood. The South Australian end is the South East substation near Mount Gambier. When constructed, the Heywood Interconnector project created the new 275 kV links from South East substation through the Tailem Bend substation to the Para Substation at Gould Creek on the outskirts of Adelaide as Para was the closest 275 kV substation to Heywood at the time. The 2016 upgrade included a new substation named Black Range at Willalooka (half way between the South East and Tailem Bend substations) with series compensation to improve transmission efficiency.
Function.
When the Heywood interconnector was built in 1988, the primary purpose was to move cheaper coal-powered electricity from Victoria to South Australia. In later years, it has been used to an increasing degree to transport wind-powered electricity from South Australia to Victoria.
The 2016 South Australian blackout occurred, because multiple windfarms reduced power during a major thunderstorm, after a tornado caused multiple towers on transmission lines to collapse<https://reneweconomy.com.au/aemo-report-into-sa-blackout-raises-questions-answers-none-55986/ref>. The Heywood interconnector became overloaded, as the missing generation was automatically drawn from Victoria. The tripping of the interconnector lead to an islanding of the SA power system, which fell into a rapid frequency decline.


GD Power Development

GD Power Development Company, or Guodian Power Development Company, the subsidiary of China Guodian Corporation, engages in the generation and supply of electric power and heat. It was founded in 1992 and was listed on the Shanghai Stock Exchange in 1997. It is headquartered in Beijing, China.


EL84

The EL84 is a thermionic valve of the power pentode type. It is used in the power output stages of audio amplifiers, most commonly now in guitar amplifiers, but originally in radios. The EL84 is smaller and more sensitive than the octal 6V6 that was widely used around the world until the 1960s. An interchangeable North American type is the "6BQ5" (the RETMA tube designation name for the EL84).
The EL84 was developed to eliminate the need for a driver tube in radios, so it has rather more gain than is usual in a power pentode. Eliminating a preamplifier triode in radios made them cheaper. Manufacturers were quick to adopt it in general use, and they are found in many old European valve radios and other audio equipment. A single EL84 was used in low-cost equipment, and a push–pull pair for lower distortion and higher power.
In common with all 'E' prefix tubes, using the Mullard–Philips tube designation, it has a heater voltage of 6.3 V. It can produce 17 W output in Class AB1 in push–pull configuration. Many guitar amplifiers routinely run EL84 tubes in excess of 400 VDC, with the Traynor Guitarmate reportedly putting out 25 W RMS with 2 EL84s in a push–pull configuration and a B+ between 400–420 VDC.
Developed by Philips in 1953, and used in the British Mullard 5-10 amplifier circuit, the EL84 came to prominence when used in Watkins (and later the Vox) amplifiers preferred by many British Invasion bands of the 1960s.
N709, 6BQ5/EL84/6P15, and other exact equivalents.
The 1959 "Miniwatt" Technical Data book from Philips lists the 6BQ5 as the R.E.T.M.A. (American) name for the EL84 in its "Type Number Cross Reference", and hence an "exact" substitute. American and Japanese manufacturers might label their versions of the EL84 as "EL84/6BQ5" or "6BQ5/EL84" or simply "6BQ5" Other manufacturers followed with their versions, such as the N709 from General Electric Co. Ltd. of England and the 6P15 from UK brand Mazda, that were designed to be "drop-in" substitutes. The CV2975 is the military designation (Common Valve) for EL84.
Other equivalent tubes are the 7189 and 7189A, an extended-ratings version of the tube for industrial applications, E84L (7320) long life, professional version with more than 10000 hours expected lifetime and the directly equivalent 6P14P (Cyrillic: 6П14П) produced in the USSR by the Reflektor plant. a slightly modified version of the 6P14P was manufactured in Russia for Sovtek. An extended-ratings version of the 6P14P is also available - 6P14P-EV (Cyrillic: 6П14П-ЕВ) and is known among US guitar players as "EL84M" or the "Russian military EL84". While not necessarily a true "military version" of the tube (in fact it is more comparable to the 7189), 6P14P-EVs are known for their low noise and durability. Large NOS (New Old Stock) supplies of the tube are available.
The 6GK6 has nearly equivalent operating characteristics with a different pinout.
 the tube was manufactured in Russia (Sovtek and Electro-Harmonix brands), Slovakia- Čadca (JJ Electronic), and Serbia- Niš (Ei). The Sovtek EL84 is often sold under their own brand name by other well-known electric guitar and guitar amplifier manufacturers - such as Fender or Mesa Boogie.
Also see 6P1P.
PL84, UL84 and EL86.
Although RCA and Sylvania produced the 8BQ5 and 10BQ5 as exact equivalents to the 6BQ5/EL84 other than heater voltage/current, most variants of the EL84 (e.g. the 15CW5/PL84) for series-heater applications such as television receivers (where it was most economical to directly-rectify the mains) made slight changes to the geometry of the original EL84 design to optimise performance for the slightly lower power supply voltages. When a 6.3V heater version of the PL84 was needed, the type number EL86 was assigned; the EL86 and PL84 are therefore very similar to, but "not exactly identical" to, the original EL84.
Characteristics.
Note: Specifications given for the EL84, PL84 and UL84 are from Philips; RCA and Sylvania list slightly higher voltage ratings for Va and Vkf and lower for Vg2 for the xCW5 series - the 6CW5/EL86, 8CW5/XL86, 10CW5/LL86, 15CW5/PL84, and 30CW5/HL84.


List of power stations in China

The following page lists some power stations in China divided by energy source and location.
By location.
The following pages list the major power stations in China by province:


Electricity sector in China

China's electric power industry is the world's largest electricity producer, passing the United States in 2011 after rapid growth since the early 1990s. In 2019, China produced more electricity than the next three countries—U.S., India, and Russia—combined.
Most of the electricity in China comes from coal, which accounted for 65% of the electricity generation mix in 2019. By the end of 2019, China's installed capacity for renewable energy was about 795 GW, while coal power capacity was 1040 GW. In 2020, China added 48GW of solar power and 71GW of wind power, and 13GW of hydropower, thus bringing the total installed renewable capacity to more than 900 GW. As of 2020, China's installed capacity for solar power was 252GW and wind power was 281 GW—the latter generated by more than 135,000 turbines. Coal-fired electricity production declined from 2013 to 2016 coinciding with a major boom in renewable energy, and a decline in GDP growth. In 2020, Chinese Communist Party general secretary Xi Jinping announced that China aims to go carbon-neutral by 2060.
China has two wide area synchronous grids, the State Grid and the China Southern Power Grid.
The northern power grids were synchronized in 2005.
Since 2011 all Chinese provinces are interconnected. The two grids are joined by HVDC back-to-back connections.
China has abundant energy with the world's third-largest coal reserves and massive hydroelectric resources.
There is however a geographical mismatch between the location of the coal fields in the north-east (Heilongjiang, Jilin, and Liaoning) and north (Shanxi, Shaanxi, and Henan), hydropower in the south-west (Sichuan, Yunnan, and Tibet), and the fast-growing industrial load centers of the east (Shanghai-Zhejiang) and south (Guangdong, Fujian).
History.
In April 1996, an Electric Power Law was implemented, a major event in China's electric power industry. The law set out to promote the development of the electric power industry, to protect legal rights of investors, managers and consumers, and to regulate generation, distribution and consumption.
Before 1994 electricity supply was managed by electric power bureaus of the provincial governments. Now utilities are managed by corporations outside of the government administration structure.
To end the State Power Corporation's (SPC) monopoly of the power industry, China's State Council dismantled the corporation in December 2002 and set up 11 smaller companies. SPC had owned 46% of the country's electrical generation assets and 90% of the electrical supply assets. The smaller companies include two electric power grid operators, five electric power generation companies and four relevant business companies. Each of the five electric power generation companies owns less than 20% (32 GW of electricity generation capacity) of China's market share for electric power generation. Ongoing reforms aim to separate power plants from power-supply networks, privatize a significant amount of state-owned property, encourage competition, and revamp pricing mechanisms.
It is expected that the municipal electric power companies will be divided into electric power generating and electric power supply companies. A policy of competition between the different generators will be implemented in the next years.
South China from the Changjiang valley down to the South China Sea was the first part of the economy to liberalize in the 1980s and 1990s and is home to much of the country's most modern and often foreign-invested manufacturing industries. Northern and north-eastern China's older industrial base has fallen behind, remains focused on the domestic economy and has suffered relative decline.
In recent history, China's power industry is characterized by fast growth and an enormous installed base. In 2014, it had the largest installed electricity generation capacity in the world with 1505 GW and generated 5583 TWh China also has the largest thermal power capacity, the largest hydropower capacity, the largest wind power capacity and the largest solar capacity in the world. Despite an expected rapid increase in installed capacity scheduled in 2014 for both wind and solar, and expected increase to 60 GW in nuclear by 2020, coal will still account between 65% and 75% of capacity in 2020.
In Spring 2011, according to "The New York Times", shortages of electricity existed, and power outages should be anticipated. The government-regulated price of electricity had not matched rising prices for coal.
Production and capacity.
China Energy Portal publishes Chinese energy policy, news, and statistics and provides tools for their translation into English. Translations on this site depend entirely on contributions from its readers. 2020 electricity & other energy statistics (preliminary)
The official Statistics available in English are not up to date (latest 2018). Numbers are given in "(100 million kw.h)" which equals 100 GWh or 0.1 TWh.
Sources.
Coal power.
China is the largest producer and consumer of coal in the world and is the largest user of coal-derived electricity. However, coal has been falling as a percentage of the energy mix, from over 80% in 2007 to 64% in 2018. Coal electricity generation has also declined in absolute terms since 2014.
Domestic coal production has declined even further, dropping 9% year on year in 2016. Further declines in production were announced in July 2016 when the commission in charge of state-owned enterprises, SASAC, ordered companies under its supervision to cut coal mining capacity by 10% in 2 years and by 15% in 5 years.
Despite the cuts to coal production and falling percentage of coal in the energy mix, electricity consumption is expected to grow by 3.6-4 percent over 2016 to 2020 according to the Thirteenth Plan (2016–2020).
According to the same five-year plan, coal power capacity will be expanded from 960 GW to under 1,100 GW by the end of 2020 to meet some of the continued growth in electricity demand. In the first two months of 2016, China added 22 GW of capacity, 14 GW of which was coal, according to the China Electricity Council.
To curtail the continued rapid construction of coal fired power plants, strong action was taken in April 2016 by the National Energy Administration (NEA), which issued a directive curbing construction in many parts of the country. This was followed up in January 2017 when the NEA canceled a further 103 coal power plants, eliminating 120 GW of future coal-fired capacity, despite the resistance of local authorities mindful of the need to create jobs. The decreasing rate of construction is due to the realization that too many power plants had been built and some existing plants were being used far below capacity.
In 2019, reports show that approvals for new coal mines had increased fivefold over approvals in 2018, and the China State Grid Corporation forecast that total coal power plant capacity would peak at 1,230-1,350 GW, an increase of about 200-300 GW.
The think tank Carbon Tracker estimated the average loss was about US$4/MWh and that about 60% of power stations were cashflow negative in 2018 and 2019.
In 2020 Carbon Tracker estimated that 43% of coal-fired plants were already more expensive than new renewables and that 94% would be by 2025. According to a 2020 analysis by Energy Foundation China, in order to keep warming to 1.5 degrees C coal plants without carbon capture must be phased out by 2045.
Hydropower.
Hydroelectricity is currently China's largest renewable energy source and the second overall after coal.
China's installed hydro capacity in 2015 was 319 GW, up from 172 GW in 2009, including 23 GW of pumped storage hydroelectricity capacity.
In 2015, hydropower generated 1,126 TWh of power, accounting for roughly 20% of China's total electricity generation.
Due to China's insufficient reserves of fossil fuels and the government's preference for energy independence, hydropower plays a big part in the energy policy of the country.
China's potential hydropower capacity is estimated at up to 600 GW, but currently the technically exploitable and economically feasible capacity is around 500 GW. There is therefore considerable potential for further hydro development.
The country has set a 350 GW capacity target for 2020.
Hydroelectric plants in China have a relatively low productivity, with an average capacity factor of 31%, a possible consequence of rushed construction and the seasonal variability of rainfall. Moreover, a significant amount of energy is lost due to the need for long transmission lines to connect the remote plants to where demand is most concentrated.
Although hydroelectricity represents the largest renewable and low greenhouse gas emissions energy source in the country, the social and environmental impact of dam construction in China has been large, with millions of people forced to relocate and large scale damage to the environment.
Wind power.
With its large land mass and long coastline, China has exceptional wind resources: it is estimated China has about 2,380 GW of exploitable capacity on land and 200 GW on the sea. At the end of 2014, there was 114 GW of electricity generating capacity installed in China, more than the total nameplate capacity of China's nuclear power stations, (although capacity of wind power is not on par with capacity of nuclear power) and over the year 115,000 gigawatt-hours (GWh) of wind electricity had been provided to the grid. In 2011, China's plan was to have 100 GW of wind power capacity by the end of 2015, with an annual wind generation of 190 terawatt-hours (TWh).
China has identified wind power as a key growth component of the country's economy; researchers from Harvard and Tsinghua University have found that China could meet all of their electricity demands from wind power through 2030.
Nuclear power.
In terms of nuclear power generation, China will advance from the moderate development strategy to accelerating development strategy. Nuclear power will play an even more important role in China's future power development. Especially in the developed coastal areas with heavy power load, nuclear power will become the backbone of the power structure there. China has planned to build up another 30 sets of nuclear power generator within 15 years with total installed capacity of 80 GW by 2020, accounting for about 4% of China's total installed capacity of the electric power industry. This percentage is expected to double every 10 years for several decades out. Plans are for 200 GW installed by 2030 which will include a large shift to Fast Breeder reactor and 1500 GW by the end of this century.
Solar power.
China is the world's largest market for both photovoltaics and solar thermal energy.
Of the 7,623 TWh electricity produced in China in 2020, 261.1 TWh was generated by solar power, equivalent to 3.43% of total electricity production.
This was a 289% increase since 2016, when production was 67.4 TWh, equivalent to an annual growth rate of 40.4%.
China has been the world's leading installer of solar photovoltaics since 2013 (see also growth of photovoltaics), and the world's largest producer of photovoltaic power since 2015.
In 2017 China was the first country to pass 100 GW of cumulative installed PV capacity.
Solar water heating is also extensively implemented, with a total installed capacity of 290 GWth at the end of 2014, representing about 70% of world's total installed solar thermal capacity. The goal for 2050 is to reach 1,300GW of Solar Capacity. If this goal is to be reached it would be the biggest contributor to Chinese electricity demand.
Transmission infrastructure.
The central government has made creation of a unified national grid system a top economic priority to improve the efficiency of the whole power system and reduce the risk of localised energy shortages. It will also enable the country to tap the enormous hydro potential from western China to meet booming demand from the eastern coastal provinces. China is planning for smart grid and related Advanced Metering Infrastructure.
Ultra-high-voltage transmission.
The main problem in China is the voltage drop when power is sent over very long distances from one region of the country to another.
Long distance inter-regional transmission have been implemented by using ultra-high voltages (UHV) of 800 kV, based on an extension of technology already in use in other parts of the world.
Companies.
In terms of the investment amount of China's listed power companies, the top three regions are Guangdong province, Inner Mongolia Autonomous Region and Shanghai, whose investment ratios are 15.33%, 13.84% and 10.53% respectively, followed by Sichuan and Beijing.
China's listed power companies invest mostly in thermal power, hydropower and thermoelectricity, with their investments reaching CNY216.38 billion, CNY97.73 billion and CNY48.58 billion respectively in 2007. Investment in gas exploration and coal mining follow as the next prevalent investment occurrences.
Major players in China's electric power industry include:
The five majors, and their listed subsidiaries:
The five majors are all SOEs directly administered by SASAC. Their listed subsidiaries are substantially independent, hence counted as IPPs, and are major power providers in their own right. Typically each of the big 5 has about 10% of national installed capacity, and their listed subsidiary an extra 4 or 5% on top of that.
Additionally two other SOEs also have listed IPP subsidiaries:
Secondary companies:
Nuclear and hydro:
Grid operators include:
Territorial differences.
China consists of three largely self-governing territories: the mainland, Hong Kong, and Macau. The introduction of electricity to the country was not coordinated between the territories, leading to partially different electrical standards. Mainland China uses type A and I power plugs with 220 V and 50 Hz; Hong Kong and Macau both use type G power plugs with 220 V and 50 Hz. Inter-territorial travelers may therefore require a power adapter.


Williamson amplifier

The Williamson amplifier is a four-stage, push-pull, Class A triode-output valve audio power amplifier designed by D. T. N. Williamson during World War II. The original circuit, published in 1947 and addressed to the worldwide do it yourself community, set the standard of high fidelity sound reproduction and served a benchmark or reference amplifier design throughout the 1950s. The original circuit was copied by hundreds of thousands amateurs worldwide. It was an absolute favourite on the DIY scene of the 1950s, and in the beginning of the decade also dominated British and North American markets for factory-assembled amplifiers.
The Williamson circuit was based on the 1934 "Wireless World Quality Amplifier" by Walter Cocking, with an additional error amplifier stage and a global negative feedback loop. Deep feedback, triode-connected KT66 power tetrodes, conservative choice of standing currents, and the use of wide-bandwidth output transformer all contributed to the performance of the Williamson. It had a modest output power rating of but surpassed all contemporary designs in having very low harmonic distortion and intermodulation, flat frequency response throughout the audible frequency range, and effective damping of loudspeaker resonances. The 0.1% distortion figure of the Williamson amplifier became the criterion for high fidelity performance that remains valid in the 21st century.
The Williamson amplifier was sensitive to selection and matching of passive components and valves, and prone to unwanted oscillations at infrasonic and ultrasonic frequencies. Enclosing four valve stages and an output transformer in a negative feedback loop was a severe test of design, resulting in a very narrow phase margin or, quite often, no margin at all. Attempts to improve stability of the Williamson could not fix this fundamental flaw. For this reason, and due to high costs of required quality components, manufacturers soon abandoned the Williamson circuit in favour of inherently more stable, cheaper and efficient three-stage, ultralinear or pentode-output designs.
Background.
In 1925 Edward W. Kellogg published the first comprehensive theory of audio power amplifier design. Kellogg proposed that the permissible level of harmonic distortion can reach 5%, provided that distortion rises smoothly rather than abruptly, and that it generates only low-order harmonics. Kellogg's work became the de facto industry standard of the interwar period, when most amplifiers were employed in cinemas. Early sound film and public address requirements were low, and customers were content with crude but efficient and affordable transformer-coupled, class B amplifiers. The best theatre amplifiers, built by Western Electric around their 300A and 300B power triodes, far exceeded the average level but were expensive and rare.
By the middle of the 1930s Western Electric and RCA improved performance of their experimental audio equipment to a level approaching modern understanding of high fidelity, but none of these systems could be commercialized yet. They lacked sound "sources" of matching quality. Industry leaders of the 1930s agreed that the improvement of commercial amplifiers and loudspeakers would make sense only after the introduction of new physical media surpassing low-quality AM broadcasting and shellac records. The Great Depression, World War II and the post-war television boomconsecutively delayed this goal. Development of commercial audio equipment came to a standstill; the few enthusiasts seeking higher level of fidelity had to literally do it themselves. American DIYers experimented with novel beam tetrodes. Australians preferred traditional push-pull circuits built around directly-heated triodes and complex, expensive interstage transformers.
British school of thought led by Walter Cocking of "Wireless World" leaned to push-pull, class A, RC-coupled triode output stages. RC coupling, as opposed to transformer coupling, argued Cocking, extended the amplifier's bandwidth beyond the required minimum of 10 kHz and improved its transient response. Tetrodes and pentodes were undesirable due to higher harmonic distortion and higher output impedance that failed to control fundamental resonance of the loudspeaker. Cocking wrote that Kellogg's 5% distortion limit was too high for quality amplification, and outlined a different set of requirements - the first definition of high fidelity. Instead of Kellogg's single figure of merit (harmonic distortion), Cocking set three simultaneous targets - low frequency distortion, low harmonic distortion, and low phase distortion. In 1934 Cocking published his first "Quality Amplifier" design - a two-stage, RC-coupled triode class A amplifier that achieved no more than 2–3% maximum distortion without using feedback. Feedback appeared in his 1943 "Wartime Quality Amplifier", built around American 6V6 beam tetrodes; however, both the input stage and the output transformer were placed outside the feedback loop. Cocking's "Quality Amplifier" family became the foundation of post-war British and Australian audio industry, including the Williamson amplifier.
Development.
In 1943, in the middle of World War II, twenty-year-old Scotsman Theo Williamson failed mathematics exam and was discharged from the University of Edinburgh. Theo was not physically fit for military service, so instead the authorities drafted him for mandatory civilian work at Marconi-Osram Valve. In April 1944 Williamson transferred from production line to Applications Laboratory of the company, where he had enough free time for his own DIY projects. Management did not object, and by the end of 1944 Williamson had conceived, built and tested the amplifier that would soon be known as the "Williamson amplifier". Another wartime projects, a novel magnetic cartridge, would be commercialized in 1948 as the Ferranti ribbon pickup.
Design targets.
Following Cocking's ideas, Williamson devised a different, much stricter set of fidelity requirements:
Williamson reviewed contemporary amplifier configurations, and, just like Cocking, settled on a low distortion push-pull, class A, triode output stage. Unlike Cocking, Williamson believed that such a stage can deliver high fidelity sound only when the amplifier is governed by 20–30dB deep negative feedback loop (and thus the complete amplifier must have 20–30dB higher open loop gain to compensate the effect of feedback). Deep feedback inevitably causes sudden, harsh onset of distortion at overload but Williamson was content with this flaw. He argued that it is a price worth paying for an improvement in linearity at medium and high power levels. On the contrary, wrote Williamson, slow but steady rise of distortion to 3–5%, as advocated by Kellogg, is distinctly unwanted in a high fidelity system.
Prototypes and tests.
Valve complement of the original Williamson amplifier was determined by scarce supply in wartime Britain. The two suitable and available output valves were either the PX25 triode, or a triode-connected KT66 beam tetrode. Williamson initially used the PX25, an already obsolete directly-heated triode introduced in 1932. In his second prototype, Williamson used the more efficient KT66, which became the valve of choice in post-war period. Powered from +500 V power supply, the KT66 prototype delivered 20 Watts at no more than 0.1% distortion. A less costly +425V power supply enabled 15 Watt output power at no more than 0.1% distortion; this arrangement became standard for the Williamson amplifier and defined its physical layout. The complete prototype system, including the amplifier, the experimental magnetic pickup and a Goodmans full-range speaker in an acoustical labyrinth enclosure, has proven to Williamson that a low distortion, deep feedback amplifier, indeed, sounded superior to amplifiers without feedback. The difference was particularly audible with the best available shellac records, despite the physical limitations of this low-fidelity format.
The prototypes impressed the Marconi management, who granted Williamson unlimited access to the company's test facilities and introduced him to the people from Decca Records. The latter provided Williamson with precious, exclusive test material - sample records of the experimental Decca ffrr system, the first true high fidelity medium in the United Kingdom. These records, which exceeded any preexisting media in sound quality, helped Williamson with fine-tuning his prototypes. He was certain that he was now firmly on the right track, but neither Marconi, nor its parent the General Electric Company were willing to invest in mass production of amplifiers for the civilian market. The design was not interesting to company lawyers either, because it did not contain anything patentable. Williamson merely put together well-known circuits and solutions.
Publication.
In February 1946 Williamson left Marconi, moved to Edinburgh and joined Ferranti. A few months later a senior Marconi salesman, who sought new means of promoting the KT66 to general public, noticed Williamson's 1944 report about his amplifier prototypes, and sent it for publication to "Wireless World". Chief editor H. F. Smith knew Williamson for his earlier contributions; he contacted the author directly and requested a detailed article written specifically for the DIY readers. Williamson promptly responded, but for unknown reasons the publication, originally slotted for 1946, was delayed until April–May 1947. While the paper was waiting for print, the magazine had published the new version of Cocking's "Quality amplifier". Cocking, as the technical editor of "Wireless World", certainly had precedence; according to Peter Stinson, he was sceptical about the Williamson amplifier, believing that his own design needed no further improvements.
By 1947 British industry had already released two amplifiers of comparable sound quality. Harold Leak announced production of his Leak Point One in September 1945;
 later in the same year Peter Walker published the first sketch of his distributed-load output stage that would become the Quad II production model. Leak and Walker tried to commercialize their ideas on the meagre post-war British market; their achievements were practically unknown outside of the United Kingdom. Williamson did the opposite: he donated his design to worldwide DIY community, thus securing lasting popular following.
In August 1949 Williamson, responding to letters from the readers, published the "New Version" of this amplifier. The article dealt extensively with construction, tuning and troubleshooting issues, however, its main objective was to address stability issues reported in letters from the readers. Apart from the additional frequency compensation network, a biasing potentiometer and a new, indirectly-heated rectifier valve that was not available in 1947, the circuit remained the same. In October 1949 - January 1950 and May 1952 Williamson published a series of articles on matching preamplifier stages and brief "Replies to Queries" concerning assembly and testing. A collection of articles published by Williamson in 1947-1950 was printed as a standalone 36-page brochure in 1952, with a second edition in 1953. The Williamson amplifier itself, as described in the August 1949 issue of "Wireless World", remained unchanged.
Reception.
The Williamson amplifier was an instant success. The publication coincided with the resumption of television broadcasting, the beginning of FM broadcasting, the release of the first high fidelity gramophone records (Decca "ffrr" and the LP record), and the "discovery" of the captured German "Magnetophon". The high fidelity media that did not exist in the 1930s became a reality, and the public wanted playback equipment of matching quality. Off-the-shelf amplifiers available in 1947 were not fit for the task. At the same time, electronic components markets were flooded with military surplus, including cheap American 6L6 and 807 power valves. For a while, DIY construction was the only way to obtain high fidelity amplification. Thousands of amateurs began copying the Williamson design; the required transformers and chassis were soon provided by industry.
In September 1947 Australians R. H. Astor and Fritz Langford-Smith adapted the Williamson circuit for American 6SN7 and 807 valves; a 6L6 variant followed soon. British and Australian press was unanimously enthusiastic: "by far the best we have ever tested ... extraordinary linearity and lack of harmonic and intermodulation distortion", "amplifier to end [all] amplifiers", "absolute tops for obtaining natural reproduction" and so on. America lagged behind by about two years: first reviews appeared in the second half of 1949, and were just as complimentary. American companies adapted the circuit to locally available components, and soon began importing "premium" British valves and transformers, thus launching the market for British hi-fi in the United States. By the end of 1949 the Williamson amplifier became a universally recognized reference design, and a starting point for all valve designs employing global feedback.
The spread of DIY construction and the abundance of publications addressed to the amateurs had a solid economic reason: factory-made electronics of the 1940s were too expensive. The industry has not yet reorganized for mass production of affordable consumer products. Home construction of valve electronics was relatively simple and promised considerable savings. The number of home-made Williamson amplifiers is estimated at least in hundreds of thousands; they absolutely dominated the DIY scene in English-speaking countries. Stereo has not been commercialized yet; almost all surviving Williamson amplifiers are monaural. Each one differs in minor details, assembly quality is usually inferior to factory-made models. In the 21st century these monaural amplifiers are commonly sold at online auctions, but finding a matching pair is almost impossible.
Small-scale factory production in the United Kingdom began in February 1948; first big manufacturer, Rogers, announced production in October 1948. In the early 1950s the Williamson amplifier dominated factory production in both the United Kingdom and the United States; John Frieborn of Radio-Electronics wrote in 1953 that "since Williamson published the first description of his "High-Quality Audio Amplifier", other audio designers had two apparent choices, beating him [Williamson] or joining him."
Design features.
Topology.
The Williamson amplifier is a four-stage, push-pull, class A triode valve amplifier built around a high quality, wideband output transformer. Its second (concertina-type phase splitter, V1B), third (driver, V2A and V2B) and fourth (output, V3 and V4) stages follow Cocking's "Quality Amplifier" circuit. The added first stage (V1A) is a dedicated error amplifier, which compensates for the loss of gain caused by negative feedback. Williamson optimized operating points of each stage for best linearity with sufficient overload reserve. The output stage is biased into pure class A; traditionally it used triode-connected beam tetrodes or pentodes. With American 807 or British KT66 valves (Williamson recommended the latter type) and specified power supply the amplifier delivered 15 Watts of output power. Further increase in output, according to Williamson, required use of four output valves; his 1947 article mentions construction of a 70-Watt prototype.
The plate of the first stage and the grid of the phase splitter are connected directly. This configuration, known since 1940, was still uncommon in 1947; American designers considered it a novelty even in the early 1950s. Phase splitter, driver and output stage are capacitively coupled. Cathode bypass capacitors are absent: Williamson, like Cocking before him, tried to linearize open-loop performance of each stage, and deliberately sacrificed gain for linearity; he was also concerned with potential low-frequency instability introduced by added capacitances. The circuit in either 1947 or 1949 variant contains no electrolytic capacitors; its power supply uses a CLC filter with two 8 uF paper capacitors, with a further LC filter feeding the first three stages.
Derivative designs of the 1950s often deviated from Williamson's recommendations while retaining his four-stage topology. According to Peter Stinson, this alone is not sufficient to be called a Williamson amplifier. A true Williamson amplifier must meet five criteria simultaneously:
Feedback.
The 20 dB (ten-to-one) feedback loop of the Williamson amplifier wraps around all four stages and the output transformer. According to Richard C. Hitchcock, "this is a severe test of design and is one of the outstanding features of the Williamson circuit." Williamson wrote that the depth of feedback can be easily increased from 20 to 30 dB, but the audible improvements of deeper feedback will be diminishingly low.
All frequency compensation components are located in the first and second stages of the circuit: their local smoothing RC filters subtly alter frequency response at infrasonic frequencies. An additional RC-filter in the first stage, introduced by Williamson in the 1949 version, prevents oscillations at ultrasonic frequencies. Feedback voltage divider is connected to the transformer secondary, thus feedback depth is dependent on loudspeaker impedance, and setting it at precisely 20 dB requires altering the divider ratio. The voltage divider is purely resistive, with no capacitive or inductive frequency compensation components. According to Williamson, a capacitor shunting the upper leg of the divider is only necessary for inferior-quality transformers; if the transformer matches requirements set by Williamson, the capacitor is useless.
Transformer.
Williamson was confident that the output transformer is the most critical component in any valve amplifier. Even before applying global feedback, the transformer is liable for at least four types of distortion. Their causes cannot be addressed simultaneously, and the designer must make a compromise between conflicting requirements. Global feedback partially suppresses distortion, but also tightens requirements to the bandwidth of the transformer.
Stability theory predicted that an amplifier built to Williamson's specifications could only be stable if the bandwidth of its output transformer was no less than 2.5...160000 Hz. This was impractically wide for an audio amplifier, requiring an exceptionally large, complex and expensive transformer. Williamson, seeking a working solution, had to decrease phase margin to a bare minimum; even then, the required bandwidth had to be no less than 3,3...60000 Hz. Such a transformer, driven by a pair of triode-connected KT66, had to have primary winding inductance of at least 100 H, and leakage inductance of no more than 33 mH. These were extremely demanding specifications for the period, far exceeding anything available on the consumer market. The "Williamson transformers" had to be heavier, larger, more complex and more expensive than typical audio transformers, and yet they could only guarantee minimally acceptable stability. A wider phase margin, wrote Williamson, was highly desirable but required absolutely impractical values of primary inductance.
Overload behaviour.
Valve amplifiers with capacitive coupling between the driver stage and the output stage do not "clip" in the same manner as transistor amplifiers (e.g. clamping output voltage to one of the supply rails). Instead, they "choke" when large signal swings intermittently attempt to bias the grids of the output valves above zero. Positively-biased grids begin conducting, but the coupling capacitors cannot delivered required current. Grid voltages do not reach target values, output waveform flattens.
Feedback attempts to overcome choking by increasing driver voltage swing, but fails because coupling capacitors cannot physically pass direct current. Resulting distortion pattern, as Williamson proved with photocopies of oscillograms and Lissajous curves, is "of the desirable type", i.e. with abrupt onset of distortion at the extremes of otherwise highly linear response curves.
Stability problem.
The first attempts to build the Williamson amplifier revealed its tendency to oscillate due to very narrow phase margin. Astor and Langford-Smith, who gave the Williamson excellent ratings, reported that "for fairly large outputs at low frequencies a high frequency oscillation about 60 kC/s [kHz] would commence and be accompanied by a pulsed output of some other frequency". The Australians, armed with first-class test equipment, suppressed the 60 kHz oscillation with small capacitors on screen grids, but could not identify and suppress the cause of "some other" oscillations.
Later, technicians of the United States Naval Research Laboratory examined seven different commercially available Williamson amplifiers, and found that all of them oscillated at infrasonic frequencies of 2...3 Hz. Replacement of output transformers affected stability only at audio and ultrasonic frequencies. The best transformers displayed perfectly flat frequency response from 10 to 100,000 Hz, but were also prone to infrasonic "breathing". The worst transformers displayed prominent ultrasonic resonances that, however, did not cause sustained oscillations. Some "ringed" at relatively low frequencies of 30 to 50 kHz, others extended into 500...700 kHz range.
Custom-built "Williamson transformers" were imperfect, but general-purpose, off-the-shelf transformers used by amateurs were far worse. Their resonances could only be tamed by narrowing the amplifier's bandwidth. The extent of stability problem in the DIY community remains unknown: the editors of "Wireless Worlds" were flooded with readers' letters, but preferred to redirect them to Williamson. What is known is that the inventor was compelled to revise and improve the design; he took a leave from his job at Ferranti and presented the second version of the Williamson in 1949. Williamson could not fix the fundamental stability problem; the "New version" was just barely stable. Independent analysis published in December 1950 proved that the revised Williamson amplifier remained prone to both infrasonic and ultrasonic oscillations.
According to the analysis, infrasonic open-loop response of the Williamson amplifier is shaped by three high-pass filters: two interstage RC filters, each with a cutoff frequency of 6 Hz, and the output stage RL filter, formed by the valves' output impedances and the transformer's primary inductance. At zero input signal, the nonlinear RL filter has a cutoff frequency of 3 Hz. This combination of cutoff frequencies, wrapped inside a 2030dB frequency loop, is unstable. Williamson tried to suppress it with a compensation network, also serving as a smoothing filter. The transformer's nonlinearity also improved stability: at high signal currents effective inductance of the primary increased, causing a decrease in cutoff frequency and a rise in phase margin. The simplest solution was to spread apart cutoff frequencies of the RC filters, provided that the output transformer conforms to the Williamson specification. For example, the 1952 "Ultralinear Williamson" by David Hafler and Herbert Keroes had these frequencies set at 1.3 and 6 Hz.
Precise analysis at ultrasonic frequencies is impossible due to the asymmetry of the phase splitter stage, and unknown parasitics and nonlinearities of the output stage. Depending on the chosen analysis model, open-loop response can be roughly approximated with a combination of either four or five low-pass filters. Different authors used different approaches and estimated somewhat different cutoff points of these filters, but in each case at least three of four or five cutoff frequencies were dangerously close to each other, which was a certain sign of instability. Williamson, again, fixed the problem with an RC compensation network, but even then phase margin remained dangerously low. DIYers had to tackle oscillations themselves: some added shunting capacitors to the screen grids, others tweaked layout and wiring, or deliberately narrowed the amplifier's bandwidth, negating the benefits of the original circuit.
Component problem.
The Williamson amplifier was very sensitive to the quality and parameters of passive components and valves. Carbon and composition-type resistors generated excessive noise and caused harmonic distortion; American valves used as substitutes for the British types specified by Williamson, could not match their performance. Williamson warned that the KT66 has no direct substitutes, and should be preferred over any alternatives.
Amateurs who copied the Williamson amplifier were unable to identify and fix its critical weak points. An amateur armed with an analogue multimeter could "see" infrasonic oscillations by watching the instrument needle, but fixing high-frequency issues required an oscilloscope with bandwidth of at least 1 or 2MHz bandwidth. In the 1950s bandwidths of many commercial oscilloscopes were too narrow for the task, and even these models were too expensive for the DIYers.
Articles by professional engineers dealing with analysis and fine tuning of the Williamson amplifier were published relatively late, when the original DIY enthusiasm had already faded - in 1952, 1957, 1961. Martin Kiebert, who built professional-grade Williamson amplifiers for his laboratory at Bendix Corporation, identified five sources of distortion caused by inferior components other than the transformer:
Kiebert rated the design positively but warned the readers that following Williamson's instructions is possible only in a laboratory environment. The amplifier reveals its potential only with expensive, properly matched components that were out of reach of an average amateur. Even a perfectly built and tesrted Williamson amplifier would sooner or later need valve replacement, which would very likely cause an unexpected rise in distortion.
Variants and derivatives.
After 1950 the industry produced numerous derivatives of the Williamson amplifier, often deviating significantly from the principles outlined by its creator. In 1950 Herbert Keroes shunted common cathode resistor of his 807 amplifier with a large electrolytic capacitor which, according to Keroes, significantly reduced distortion at high output power. Contrary to recommendations by Cocking and Williamson, Keroes and his partner David Hafler used cathode shunt capacitors in most of their designs; by 1956 this approach became de facto industry standard. In the same 1956 Hafler used fixed bias in his EL34 Williamson. Later, fixed bias became a staple of Soviet and Russian Williamson-like designs that employed exotic output valves like the 6C4C directly-heated triode, the GU-50 generator pentode or the 6P45S horizontal deflection tetrode.
Throughout the 1950s, as prices of capacitors decreased, designers steadily increased their values. The original Williamson amplifier used paper capacitors; by 1952 Kiebert uses electrolytics; the 1955 reference design by Keroes used at least bypass capacitors; the 1961 budget amplifier by Wright employed a total of . Designers of the commercial Bell2200 amplifier (1953) replaced direct coupling of the first two stages with capacitive coupling; the Stromberg-CarlsonAR-425 (also 1953) use a tetrode-mode output stage in an otherwise familiar Williamson topology. Both Bell and Stromberg-Carson modifications further worsened stability, and required additional frequency compensation. Designers of the BogenDB20 (1953) went even further, and combined global and local negative feedback loops with positive feedback in the output stage.
In December 1951 Hafler and Keroes began promoting the ultralinear stage - a method of distributing load between anode and screen grid of a pentode or tetrode, invented by Alan Blumlein in the 1930s. An ultralinear stage delivered 50% to 100% more output power than the same stage in triode connection, at roughly the same distortion, and cost less than a pure pentode or tetrode stage (the latter required a separate screen grid supply, the ultralinear did not need it). The first "Ultralinear Williamson", employing a pair of 6L6 in a Williamson-like topology, delivered ; their second model, built around more powerful 807 tetrodes, delivered . Very soon the American public acquired taste to high-power amplification, and the industry launched the "race for Watts". By 1955 Hafler and Keroes, now working separately, were offering 60-Watt models employing pairs of 6550 tetrodes or quartets of KT66s. Thus in less than a decade, step by step, the industry abandoned the principles set by Williamson, but continued to use his name as a convenient free trademark. In the 21st century it is even used for amplifiers without global negative feedback; the only thing they have in common with the true Williamson amplifier is the four-stage topology.
Following the success of Hafler and Keroes, American manufacturers like Eico, The Fisher, Harman/Kardon and Marantz disposed with "obsolete" power triodes and switched to ultralinear designs. Mullard, Britain's largest valve manufacturer and provider of reference designs to the European industry, publicly supported the novelty. Williamson's former employer, General Electric Company, followed suit and published a reference "30-Watt Williamson" design built around a pair of ultralinear-connected KT88. The original Williamson amplifier lost the race, just like alternative designs by Peter Walker and Frank McIntosh. In September 1952 Williamson and Walker (then business partners in the development of the Quad Electrostatic Loudspeaker) agreed that the ultralinear stage was, indeed, preferable in mass production. Williamson gradually stepped aside from audio engineering. He made his living by designing milling machines and flexible manufacturing systems, which later earned him election to the Royal Society, and never considered audio design a serious occupation for himself.
In 1956 most production amplifiers in North America followed the "Ultralinear Williamson" template, but in the next few years it was retired, too. The new three-stage reference design combined phase splitter and driver functions in one valve, and thus cost proportionally less than four-stage amplifiers. Hafler's Dynaco Stereo 70, which followed this topology, became the most produced valve amplifier in history. North American consumer market was flooded with millions of similar, almost identical amplifiers and receivers claiming 25 to 20W per channel, as well as clones of less powerful British designs like the Mullard 5-10. Advertisements claimed that these models performed as well as the original Williamson, with higher output power and with guaranteed stability. The customers could not verify these claims, and had to rely to listening tests, hearsay and expert advice. The problem was partially addressed by the concept of subjective listening, advanced by Hafler and Keroes back in 1951: "Excellent measurements are a necessary but not a sufficient condition for the quality of sound. The listening test is one of most importance... the most stringent test of all". By the end of the 1960s subjectivist approach was adopted by the audiophiles and marketing people, who eagerly forgot about the objective principles devised by Williamson in the 1940s.
Objectively, many deep-feedback valve designs of the 1950s matched or exceeded the 0.1% distortion rating of the Williamson amplifier, but none could significantly improve on this figure. Williamson had found that valve amplifier performance was limited mostly by the output transformer. Transistor amplifiers did not have this limitation, and yet it took around 15 years to bring their performance to the level attained by Williamson in 1947.
Comments.
Ferrari Pier Paolo - LEAK Audio Hi-Fi - Sandit Editore -Italy (2014)- Book - ISBN - 978-88-97599-92-0


Pepco Holdings

Pepco Holdings was a holding company incorporated in February 2001 for the purpose of effecting the acquisition of Conectiv Power Delivery by Potomac Electric Power Company (better known as "Pepco"). The acquisition was completed on August 1, 2002 at which time Pepco and Conectiv became wholly owned subsidiaries of PHI. Conectiv itself had been formed in 1998 to be the holding company of Delmarva Power & Light Company (DPL, better known as "Delmarva Power") and Atlantic City Electric Company (ACE) in connection with the combination of DPL and ACE. In 2005, PHI resumed the use of the Delmarva Power and ACE brands for purposes of operations, with the result that Conectiv Energy was the only remaining Conectiv brand and was restricted for PHI's energy production facilities. Operations of the various companies controlled by Pepco Holdings take place in the Mid-Atlantic states of the United States. Pepco serves Washington, D.C. and its Maryland suburbs, Delmarva Power serves the Delaware and Maryland portions of the Delmarva Peninsula, and Atlantic City Electric serves South Jersey. In 2008, Delmarva Power sold its service area in the Virginia portion of the peninsula to A&N Electric Cooperative and Old Dominion Electric Cooperative for $44 million. In April 2010, Conectiv Energy was sold to Calpine Corporation.
Pepco Holdings was placed at 283rd on the 2006 Fortune 500, a list of American companies ranked by gross revenue. In 2010, the company paid only 10% of the taxes it had paid in the previous year, dropping from US$104 million to US$11 million. The company experienced a doubling of operating profit in 2011, in part due to approved utility rate increases in the states of Delaware, Maryland, and New Jersey along with Washington, DC.
Merger with Exelon.
Exelon announced the proposed purchase of Pepco Holdings, Inc on April 30, 2014. The merger was rejected by the District of Columbia Public Service Commission in August 2015, though it was approved by other federal and state regulators. On March 23, 2016, the merger with Exelon was approved by the District of Columbia Public Service Commission, under a revised set of terms. The merger was completed on that same day.
Criticism.
In December 2011, the non-partisan organization Public Campaign criticized Pepco Holdings for spending $3.76 million on lobbying and not paying any taxes during 2008-2010, instead getting $508 million in tax rebates, despite making a profit of $882 million and increasing executive pay by 118% to $9.7 million in 2010 for the top 5 executives.
Restatement.
In 2006, Pepco Holdings restated its previously reported consolidated financial statements for the three and six months ended June 30,
2005, to correct the accounting for certain deferred compensation arrangements.


Portland Gas Light Company


Tony Irwin

Tony Irwin is a nuclear engineer and technical director of Australian company, SMR Nuclear Technology. For three decades he worked commissioning and operating nuclear reactors in the UK for British Energy (formerly the Central Electricity Generating Board). He emigrated to Australia in 1999 and took a position with the Australian Nuclear Science and Technology Organisation (ANSTO), where he remained for ten years. Irwin chairs the Nuclear Engineering Panel of Engineers Australia and lectures at the Australian National University and University of Sydney on nuclear science. Irwin has a degree in electrical power engineering.
Nuclear power advocacy.
Irwin is an advocate for nuclear power in Australia and has recommended the deployment of small modular reactors, provided that legislation can be changed to allow for it. In 2014 he told the media:"Small modular reactors with their natural safety based on passive safety systems using gravity, natural circulation and pressurised tanks, represent a game-changer that is particularly suitable for Australian conditions."
He has argued in "Mining Australia" that climate change should lead Australia to reconsider nuclear power as an alternative to burning fossil fuels to generate electricity.
He has featured in media reports on nuclear technology and provided commentary to the Australian Science Media Centre in response to the Fukushima nuclear disaster. He has given public presentations and lectures on SMRs and nuclear power, including some at which opposing viewpoints were presented by anti-nuclear advocates such as Ian Lowe.
In 2011 Irwin contributed a chapter on small modular reactors to "Australia's nuclear options", a policy perspective document for the Committee for Economic Development of Australia.
Memberships.
Irwin is a member of the Institution of Engineers Australia and of the UK Institution of Engineering and Technology, a fellow of the Australian Institute of Energy, and chairman of the Nuclear Engineering Panel of the Sydney division of Engineers Australia. He is a member of ARPANSA's Nuclear Safety Committee.