Effect of standby mode operation of some household appliances on disturbance voltage and current in frequency range of 9–150 kHz produced by other equipment in low voltage network
Most household appliances commercially available today on the market are equipped with the inverter technology favoring to its smaller size, advanced performance, and energy efficient. Notwithstanding its benefits, unfortunately, this technology may introduce current disturbance according to its relevant frequency switching and eventually degrades power quality. The switching frequency of inverter for household appliances is generally in the range of 9-150 kHz causing the disturbance and may influence the working performance of other appliances. The voltage and current disturbances in the frequency range of 9-150 kHz are not completely covered and currently subject to standardization work. Some household appliances can be operated in standby mode in order to display the time and setting information or to allow them to operate quickly even though it also gives a drawback regarding to its energy consumed. This study investigates the characteristics of standby mode operation of some appliances and its effect to the voltage and current disturbance in the frequency range of 9-150 kHz. The result shows that the standby mode operation of particular household appliances can filter and significantly reduce the voltage and current disturbance in the low voltage (LV) installation network for specific frequency in the range of 9-150 kHz.
Disturbance Characteristics of the Off-Grid Photovoltaic System in the Frequency Range from 9 - 150 kHz with Changing Solar Irradiance and Shading Area
A solar power plant converts light into electricity using photovoltaics. It uses an inverter to convert DC to AC current to be connected to an AC load. Increasing use of solar panels in household application results in an increase in the use of inverters, in which some might due to the fact that inverters can produce disturbances at a frequency between 9-150 kHz. This study is focused on observing the disturbance characteristics of an off-grid photovoltaic system due to variations of irradiation and shading in the frequency range from 9 -150 kHz. It is expected that the output of this observation can provide a reference for research in determining the effects on electric power system. This observation provided a shading effect of 0%, 25%, 50%, 75%, and 100% of the photovoltaic area and then conducted observation based on two solar irradiation conditions. Based on the observations, it is identified that in general there are 3 frequency ranges of dominant disturbances, they are: 20-25 kHz, 72-73 kHz, and 144-146 kHz. Their voltage disturbance will decrease with increasing shading area, where at shading conditions of 25% and 50% they will have a value voltage disturbance that tends to be the same as that in the 3 dominant frequency ranges.
The Vascular Theory of Migraine‐Resuscitated or More Moribund?
Your decision to publish an important paper on cerebral blood flow (CBF) in migraine1 as the first in Headache for 1989 is to be applauded. But does it clarify or cloud the issue? After 20 years of CBF studies in migraine the results show 1) a reduction of at least 25 30% in classical migraine1, 2) an average increase of 31% in common and classical migraine2, 3) or no change in common migraine3. Now we learn that the measurements need modifying by 40% to allow for scattering of radiation the Compton scatter effect which has led to "an unbalanced interpretation of the data"1 So the results are as contradictory as they can be, the measurements require adjustment, and the interpretation is therefore doubly doubtful. From the clinical point of view the neurological aura, the enlarging scotoma, the scintillations, the migration of the paraesthesiae up the arm or visual disturbances across the visual field, have not been seen in cerebrovascular disease.4 The headache is throbbing in only 47% of 750 patients questioned during a migraine5; but even when the pain is pulsatlie, it throbs for only a portion of the time at the maximum of the headache (Blau unpublished observations). The evidence for a neurological aetiology has been examined6: the most potent argument against a vascular cause is that the common triggers stress, light and hunger go direct to the nervous system, not via blood vessels. No one denies that vascular changes occur in migraine but are they primary or secondary to a neurological disturbance? Sokoloff7 concluded that the stimulated rat and monkey cortex showed increased glucose uptake, and that the increased local blood flow occurred "in response (my italics) to changes in local functional activity". The evidence, therefore, points to an underlying neurological basis with secondary vascular responses. The vascular theory may need resuscitation but who is going to give it the kiss of life?