Gas circuit breaker pressure connection for high and low pressure driers
United States Patent 11 1 Tschannen et al.  
 [ 1 Apr. 22, 1975 GAS CIRCUIT BREAKER PRESSURE CONNECTION FOR HIGH AND LOW PRESSURE DRIERS [75] lnventors: Christian Tschannen.  
 Unterentselden. Switzerland: Henry G. Meier. Glendale. Calif.  
 [73] Assignee: [TE Imperial Corporation, Spring House. Pa.  
 [22] Filed: Sept. 19, [973 [ll] Appl. No.: 398,872  
 [52] U.S. Cl 200/[48 E; 200/148 B [51] Int. Cl. H0lh 33/57 [58] Field of Search ZOO/I48 E. 148 B. 148 R [56} References Cited UNITED STATES PATENTS 3.566.062 2/l97l Mcier et ul 200/148 E 10W pflfjjfi/ef&#39; ale/5e U/V/T L&#39;flMPflfJfO/i 0/! Jz&#39;fflflflmi F/QOM- A 63672 GUM/&#34;55508 Cl? 4 NIT 6/455 3.793.499 2/1974 Wagner et al ZOO/I48 B Primary Examiner-Robert S. Macon Attorney. Agent. or Firm-Ostrolenk. Faber. Gerb &amp; Sofi&#39;en [57] ABSTRACT The high pressure drier of a two pressure circuit breaker is placed at high pressure only during the time that the compressor is operating. The high pressure of the drier bleeds back to the low pressure system through a calibrated orifice in the oil return line to the compressor. The normal pressure of the high pressure drier is low enough that gas heaters are not needed to protect against liquefaction of sulfur hexafluoride gas.  
 8 Claims, 5 Drawing Figures awenv Ca l/&#34;1265271? OFF/64770 a/vzy CAM/664720 V4/F/ E /A 0/4 ,&#39;&#39;rme/v L/A/A? PATENTED APR 2 2IS1&#39;5 SEiLET 2 0F 4 PATENTED Z B 3.879.591  
 sum 3 er 4 GAS CIRCUIT BREAKER PRESSURE CONNECTION FOR HIGH AND LOW PRESSURE DRIERS BACKGROUND OF THE INVENTION This invention relates to two pressure gas circuit breakers and more specifically relates to a novel gas control system which eliminates the need for heating the high pressure drier of the system.  
  A gas control system for two gas pressure circuit breakers is shown in US. Pat. No. 3,566,062 entitled &#34;Heater Arrangement for SF Circuit Breakers&#34; in the name of Henry G. Meier and George Y. DeSeve, dated Feb. 23, l97l and assigned to the assignee of the present invention.  
  The gas control system shown in this patent has a drier in the high pressure system which will contain gas such as sulfur hexafluoride at pressures greater than 10 atmospheres. Therefore, a heater must be added to prevent liquefaction of the gas at these pressures.  
  The present invention provides a novel arrangement which eliminates the need to heat the high pressure gas drier.  
 BRIEF SUMMARY OF THE INVENTION In accordance with the present invention a novel calibrated orifice is provided in the oil return line from the oil separator and drier combination to the compressor. This calibrated orifice is sufficiently large to insure appropriate return of oil to the compressor and further allows leakage of high pressure gas from the high pressure drier back to the low pressure system so that the high pressure drier is at high pressure only while the compressor is operating. Thus under normal conditions, the compressor is not operating, and the high pressure drier will be at a low pressure, for example, three atmospheres so that the high pressure drier need not be heated to prevent liquefaction of the gas at low temperature ambients.  
  As a further feature of the present invention, the compressor is operated directly in response to the measured pressure in the high pressure gas system without temperature compensation. Thus prior art controls use a temperature compensated pressure switch so that the compressor will be operated to maintain a constant gas density in the high pressure system. It has been found that a fixed pressure rather than a constant density can be used in the high pressure system for both compressor operation of a low pressure arrangement and conventional low pressure lockout controls.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation of a circuit breaker of the type to which the present invention may apply.  
 FIG. 2 is a side view of the circuit breaker of FIG. 1.  
  FIG. 3 schematically illustrates a prior art gas system for a typical phase of the circuit breakers of FIGS. 1 and 2.  
  FIG. 4 schematically illustrates prior art heaters applied to the high pressure reservoirs of FIGS. 1 to 3, and further schematically illustrates the prior art gas system of FIG. 3.  
  FIG. 5 schematically illustrates the novel modified compressor and drier arrangement of the present invention.  
 DETAILED DESCRIPTION OF THE DRAWINGS Referring first to FIGS. I and 2, there is shown therein a three phase gas circuit breaker which consists of three low-pressure tanks I0, 11 and I2, one for each phase, where each tank is provided with two terminal bushings. Tank in FIGS. 1 and 2 is seen to have terminal bushings I3 and 14, while the terminal bushings l5 and 16 are seen in FIG. 1 for tanks 11 and I2. A control cabinet 17 is provided. as shown in FIGS. I and 2, and provides the various controls and compressors, and the like. required for the operation of the interrupters contained within tanks I0, II and I2 and for the operation of the gas system as will be described later.  
  Two elongated tanks are then contained within enclosures 20 and 21 which receive high-pressure gas which is to be connected to the interrupters contained within tanks 10, 11 and 12 and which are heated in accordance with the present invention. Details of the construction of the interrupters are disclosed in US. Pat. No. 3,526,734, entitled Dead Tank Gas Blast Circuit Breaker With Interrupter Structure Immersed in Low Pressure of Dead Tank, in the name of Daniel H. McKeough, and assigned to the assignee of the present invention.  
  FIG. 3 schematically illustrates high-pressure tank which might be contained within one of housings 20 or 21 in connection with the housing 10 for the first phase of the circuit breaker of FIGS. I and 2. The arrangement of FIG. 3 (and of FIG. 4) is also described in US Pat. No. 3,566,062. It will be noted that the tank 10 contains two schematically illustrated interrupters 31 and 32 which are connected to the schematically illustrated bushings l3 and 14. In FIG. 3, the darkened regions represent high-pressure gas while lightly colored regions represent low-pressure gas. The gas system includes a compressor having a high-pressure side connected to an oil filter and trap 41 and a gas drier 42. From the gas drier 42 the high-pressure gas flows through shut-off valve 43 which is normally open and into the main tank 30. The high-pressure gas from drier 42 is normally isolated from the low-pressure system by the normally closed shut-off valves 44 and 45.  
  Gas blast valves of the type described in US. Pat. No. 3,526,734 are provided for interrupters 31 and 32 to normally terminate the high-pressure below interrupters 31 and 32. The low-pressure system extends the interior of tank 10 through the normally open shut-off valve 46 through a filter-drier 47&#39;and back to the compressor 40. A service connection 48 is also provided which is connected to the system through valve 44 and a valve 49 in the low-pressure system. Safety relief valves 50 and 51 are also provided as shown.  
  FIG. 3 further schematically shows resistance heaters 52 and 53 which cooperate with the main gas reservoir 30 to keep the gas above its condensation temperature. Thermostats 54 and 55 are provided for heaters 52 and 53, respectively.  
  During the operation of the circuit breaker, the gas blast valve associated with interrupters 31 and 32 are opened (not shown), thereby connecting high-pressure gas to the interrupter chambers in order to force gas through the separating contacts of the interrupters (not shown). This gas is shut off by the closing of the blast valve after the interruption of the circuit, with compressor 40 maintaining the desired pressure differential between the high and low-pressure gas systems.  
  FIG. 4 schematically illustrates heaters for tanks 60 and 61 which are contained within housings and 21 of FIGS. 1 and 2. Note that appropriate insulation may be provided between the housings 20 and 21 and the main high-pressure tanks and 61. In FIG. 4, the tanks 10, 11 and 12 are schematically illustrated as are the interruptcrs 31-32 of tank 10 and the interrupters 62-63 of tank 11 and the interrupters 64-65 of tank 12.  
  The heavy solid lines of FIG. 4 indicate high-pressure gas connections. Thus it is seen that interruptcrs 31 and 32 are connected to tanks 60 and 61, respectively, by high-pressure connectors 66 and 67, respectively. Similar high-pressure connectors 68 and 69 make highpressure connection between tank 60 and interrupters 62 and 64, while connectors 70 and 71 connect the high-pressure gas of tank 61 to intcrrupters 63 and 65.  
  The gas system shown in FIG. 4 corresponds generally to that shown in FIG. 3 wherein compressor 40 has its high-pressure side connected through oil filter and trap 41, drier 42, valve 43, and thence to the interior of tanks 60 and 61. The low-pressure side of compressor 40 is connected through the filter-drier 47, valve 46, to a low-pressure conduit which is connected to the interiors of tanks 10, ]1 and 12. The novel heater arrangement then consists of circular band heaters -91 disposed on either side of the connection to conduit 71; hand heaters 92-93 connected on either side of the connection to conduit 70; and band heaters 94-95 connected on either side of the connection to conduit 67. These band heaters consist of any desired electrical resistance heater which may be connected to power supply 96 as schematically illustrated. The power supply 96 is then actuated from a suitable thermostat 97 or from a plurality of thermostats disposed along the length of the tank 61 so that power is applied to the various band heaters 90 to as required by ambient temperature conditions. It will be apparent that this placement of band heaters in regard to their axial displacement along the length of the tank will insure uniform heating of the gas within the tank.  
  A similar disposition of heaters is provided for tank 60 and includes the band heaters 100 to and their respective power supply 106. Power supply 106 is operated from thermostat 107. If desired, it is possible to drive heaters 90-100, 92-102 and 94-104 from one power supply and the other band heaters from the sec ond power supply, This will insure proper heat distribution even though one power supply may fail. It will also be observed that the circular band heaters are wrapped completely around the exterior surface of the high pressure tanks and are accessible for maintenance without the need for obtaining access to the interior of the high-pressure tanks.  
  FIG. 4 shows the further placement of blanket-type heaters 110-111 for tank 60 and 112-113 for tank 61. The use of such blankets further improve the distribu tion of heat to the length of the tanks 60 and 61, with these blankets being appropriately driven from power supplies 96 and 106.  
  FIG. 5 illustrates the manner in which the control system of FIGS. 3 and 4 is modified in accordance with the invention to eliminate the need for heaters for the oil separator 41 and high pressure drier unit 42.  
  In FIG. 5, as the compressor 40 operates, gas flows from the low pressure conduit 200 connected to low pressure drier 47 to the intake of the compressor 40. High pressure gas then flows into high pressure output conduit 201 of the compressor 40 and through oil separator 41 to the high pressure drier 42. Gas from the high pressure drier 42 then flows through a check valve 202 and charges the high-pressure system of the breaker and the main tank 30 of FIG. 3.  
  During this operation, oil collects in the bottom of oil separator 41. In the prior art arrangements, this oil had to pass through a float controlled valve and was returned through oil return line 203 to the crank case of compressor 40 which is at the same pressure as the lowprcssurc system of the breaker.  
  In accordance with an important feature of the present invention, the prior art float valve is eliminated and an orifice or permanently open restriction 204 is installed in oil return line 203. Orifice 204 is large enough to pass the required rate of oil flow from the separator 41 but is sufficiently small to permit the formation of a large pressure differential across the orifice 204 while the compressor 40 is operating. Thus high pressure can be developed in conduit 201 and drier 42 when compressor 40 operates. However, when the compressor 40 shuts off, the high pressure in oil separator 41 and in high-pressure drier 42 drains through the orifice 204 in oil return line 203 until the pressure equalizes with the pressure of the low pressure system. Typically, the low-pressure system will be at about 3 atmospheres while the high-pressure system will be at about l5 atmospheres. At the 3 atmosphere pressure, the SF gas will not liquefy under the lowest possible breaker ambient temperature and therefore no heaters are required to heat the drier unit 42. Thus, considerable savings are obtained through the use of the present invention.  
  As another feature of the present invention, the highpressure gas system and the operation of compressor 40 are controlled in response to the direct meansurement of the pressure of the high-pressure system. The heaters and heater controls on the high pressure reservoir 30 of FIG. 3 and the equivalent reservoirs in FIG. 4 are set to maintain some minimum temperature which is related to the saturation temperature of the gas at the normal operating high pressure.  
  It has been found that the compressor, the lowpressure alarm system and the low-pressure lock-out controls can be controlled in response to direct pressure measurements rather than constant density measuremcnts as in the past with considerable savings in the control circuitry. This mode of operation is based on the recognition that the interrupter performance will be dependent upon gas pressure in the high-pressure system rather than the gas density of the high-pressure system.  
  Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of the invention be limited not by the specific disclosure herein, but only by the appended claims.  
  The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:  
  l. A gas pressure control system for a two pressure circuit breaker; said two pressure circuit breaker having a relatively high gas pressure region filled with a given dielectric gas and a relatively low gas pressure region filled with a given dielectric gas; said gas pressure control system including a compressor. and a high pressure drier unit and an oil separator; said compressor having a low pressure connection and a high pressure connection; said low pressure connection being connected to said low gas pressure region; said high pressure connection being connected through said oil separator to an inlet port of said high pressure drier; said high pressure drier having an outlet port connected to said high gas pressure region. and an oil return line connected from said oil separator to a low pressure region of said compressor; said oil return line having a fixed restriction therein of sufficient size to permit oil flow therethrough and to permit a substantial pressure differential thereacross when said compressor operates.  
  2. The gas pressure control system of claim 1 which further includes heater means for heating the high pressure gas in at least portions of said high pressure gas region to prevent liquefaction of said gas at low ambient temperatures; said high pressure drier unit being at a temperature lower than the temperature of said heated portions of said high pressure gas region.  
  3. The gas control system of claim 1 which further in cludes a low pressure drier connected between said low pressure connection and said low pressure gas region.  
 4. The gas control system of claim I which further includes a check valve connected to said outlet port of said high pressure drier.  
  5. The gas control system ofclaim 1 wherein said gas at least includes sulfur hexafluoridc as a component thereof and wherein said high gas pressure region is at a pressure greater than about ten atmospheres. and said low gas pressure region is at a pressure lower than about three atmospheres.  
  6. The gas pressure control system of claim 4 which further includes heater means for heating the high pressure gas in at least portions of said high pressure gas re gion to prevent liquefaction of said gas at low ambient temperatures; said high pressure drier unit being at a temperature lower than the temperature of said heated portions of said high pressure gas region.  
  7. The gas control system of claim 6 wherein said gas at least includes sulfur hexalluoride as a component thereof and wherein said high gas pressure region is at a pressure greater than about ten atmospheres. and said low gas pressure region is at a pressure lower than about three atmospheres.  
  8. The gas control system of claim 7 which further includes a low pressure drier connected between said low pressure connection and said low pressure gas region.