GB1604060A - Circuit interrupter using dielectric liquid with energy storage - Google Patents

Description

(54) CIRCUIT INTERRUPTER USING DIELECTRIC LIQUID WITH ENERGY STORAGE (71) We WESTINGHOUSE ELECTRIC CORPORATION of Westinghouse Building, Gateway Center, Pittsburgh, Pennsylvania, United States of America, a corporation organised and existing under the laws of the State of Pennsylvania, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a high-voltage circuit interrupter using liquid dielectric for arc extinction purposes.

Liquified gas circuit interrupters are known from the specification of U.S. Patent 3,150,245 which discloses a fluid such as sulphur hexafluoride and provides driving means for forcing the liquified gas at high pressure toward the arc zone when the contacts of the interrupter are parted. One of the problems pointed out in this is maintaining a high enough pressure especially during the low temperature ambient operation for effective arc extinguishing. In order to maintain an adequate Injection pressure, this proposes three techniques which are (1) the use of a mechanically operated impulse device, (24 the use of an accumulator with gas such as nitrogen in one end and sulphur hexafluoride in the other, and (3) the use of sulphur hexafluoride and a heater to maintain a high enough temperature.

A problem with the above design is the remarkable rise in the fault current interrupting requirements in the past decade. For example, this is directed to interrupting perhaps 50,000 amperes with pressures which are generally less than 1,000 psi. In contrast with a current of for example 120,000 amperes, as much as 2,000 psi may be required. With the required high pressure, two problems are presented. One is that when an arc is formed upon separation of the contacts, the arc in essence shuts off the flow of interrupting fluid and causes an incipient high pressure maximum. This pressure may be much higher in fact than the required arc extinguishing pressure and subjects the entire interrupter device to severe mechanical stress. On the other hand, when the arc is near current zero, the arc diameter reduces, thus allowing the liquid to flow out the orifices more rapidly. This tends to reduce the pressure below an acceptable level in which an arc might be reestablished. In other words, a low-pressure minimum may be produced by rapidly increasing flow area while the pump has a slow response to these changing conditions.

In the specification of U.S. Patent 3,406,269, it is disclosed in Figures 5 and 6 techniques (including an accumulator) for maintaining sufficient pressures. However, since the systems are closed, there is no pressure minimum problem.

An object of the present invention is to provide an improved circuit interrupter which is capable of effectively operating at relatively high fault currents, and to produce an interrupter where pressure variations are minimized.

According to the present invention, a high-voltage circuit interrupter uses a dielectric liquid introduced into the interrupter at a high pressure to extinguish an arc formed when current is interrupted, said interrupter comprising movable and fixed contacts retained in at least a partially confined enclosure, means for introducing said dielectric liquid into said enclosure at a predetermined initial high pressure, energy storage means responsive to said high pressure liquid and to changes in said liquid flow for smoothing the resultant pressure of said liquid, by reducing any maximum and increasing any minimum in said pressure, said enclosure including a first nozzle formed by said fixed electrical contacts converging to a narrow throat and a second electrical insulating nozzle having a narrow throat opposite said throat of said first nozzle, said movable contact normally in its closed condition, extending through said throat of said second nozzle and into said throat of said first nozzle to make electrical contact with said fixed contacts, said enclosure including an entrance port for introduction of said liquid between said throats of said nozzles, said moving contact in said closed condition effectively closing said port, said moving contact when opening being withdrawn from both of said nozzle throats to provide a bidirectional flow path for said liquid in opposite directions with a primary flow path through the narrow throat and a diverging portion of said second nozzle and a secondary flow path through said narrow throat and a diverging portion of said first nozzle.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a simplified diagram of a circuit interrupter; Figure 2 is a set ot curves illustrating the operation of the interrupter of Figure 1 and its improvement over the prior interrupters; Figure 3 is a graph showing interrupter pressure requirements; Figure 4 is a more detailed cross-sectional view of an interrupter embodying the invention which is patterned after Figure 1; and, Figure 5 is a cross-sectional view of an alternative embodiment of the circuit interrupter.

Referring to Figure 1, an interrupter 10 is shown having fixed contacts 11 and a movable contact 12. These contacts are contained in at least a partially confined enclosure which will be shown in greater detail below. The enclosure has a secondary flow path 15b formed by the parting of contact 12 from fixed contacts 11 (which form a nozzle) and a primary flow path 15a in an opposite direction to path 15b. An entrance port 13 of the interrupter is connected to a source 14 of dielectric liquid such as sulphur hexafluoride (SF6). Liquid source 14 is pumped by air operator 16 driven by high-pressure air from the reservoir 17 through an air valve 18. The operator 16 includes a cylinder 19 containing a piston 20 having a head 21 which pumps source 14.

Air valve 18 is operated or placed in an open condition when the moving contact 12 of the interrupter is parted from fixed contact 11.

Intermediate the entrance port 13 and the dielectric fluid source 14 is energy storage means or accumulator 23. It includes a floating piston 24 and a reservoir of high-pressure nitrogen 26. Floating piston 24 obviously has an effective mass much less than that of pump piston 20. In operation accumulator 23 acts effectively as a pressure surge protector. It tends to resist any pressure change in fluid system. This is accomplished by storing potential energy in the accumulator 23 as the system pressure tends to rise (as for example where the arc is clogging or blocking the flow of liquid) and giving up energy as the system pressure tends to drop (as for example when the arc is small and the flow area is increased and the parted contact allows a hydrodynamic surge of the liquid or gas out of the interrupter as shown by the flow paths 15a and 15b).

The accumulator therefore reduces pressure peaks and increases pressure minimums. It is a pressure leveler as clearly illustrated in Figure 2 where the curve 27 designated "100 kA arcing with accumulator" shows a variation of approximately 300 psi whereas in comparison in curve 28 without the accumulator 23 there would have been a variation of 3,000 psi. The graph of Figure 2 charts the operation of the interrupter through a time interval of three current head 21 which pumps source 14. A typical high pressure of about 1500 psi leads to current heads that occur at intervals and are produced by pumped source 14.

The graph of Figure 2 charts the operation of the interrupter through a time interval of three current zeros as indicated which occur at half-cycle intervals. These occur at intervals of 8-1/3 milliseconds assuming the frequency is 60 Hz and the current is symmetrical. At the time 29 moving contact 12 parts and the wide oscillation in curve 28 is caused by the arc blocking the flow of dielectric and the high inertia of the pump piston 21 of Figure 1. An improvement provided by the present invention is the increase of pressure at the second current zero from 700 to 1,700 psi. The pressure was also greatly re reduced from 3,700 psi to 2,200 psi. As discussed above, two advantages are obtained. The increase in pressure at current zero where interruption takes place will improve interruption. Secondly, the reduced peak pressures between current zeros will reduce the mechanical stresses on the interrupter and the interrupter support structure.

Figure 3 is a set of curves illustrating the liquid sulphur hexafluoride pump accumulator pressure capability 31 and the necessary interrupter pressure requirement curve 32 for various current ratings shown on the horizontal line of the graph with actual current and interrupting ratings being indicated. Thus, the pump accumulator pressure capability (which corresponds to the current zero pressure of curve 27 of Figure 2 de depending on the current to be interrupted should be designed accordingly.

In addition, the accumulator system should be optimized for each respective interruption current rating by varying the nitrogen pressure behind the accumulator piston 24.

Nonoptimum accumulator pressure will cause the piston to respond too quickly or too slowly. Either of the foregoing situations can allow the liquid dielectric pressure to drop below the maximum at current zero. The various interrupting currents and optimum nitrogen fill have the following typical values: Accumulator Interrupting Charge Current Pressure 120 kA 2,000 psig 100 kA 1,900 psig 80 kA 1,800 psig 63 kA 1,700 psig Accumulator 23 of Figure 1 can be varied in design such as using a spring instead of nitrogen as the energy storage means. In addition, a rubber bladder or metal bellows could be used in place of the floating piston. Finally, the design could allow the liquid sulphur hexafluoride to be in direct contact with the nitrogen with no separator being used.

Also, although liquid sulphur hexafluoride is the preferred liquid, other liquids may be used.

The operator 16 driving liquid source 14 must have a relatively high mass in order to provide the necessary high forces required to provide the high pressure necessary to arc interruption. With such a high mass, naturally the response is relatively slow compared to the accumulator 23 (for example, the floating piston may have a weight of two pounds); since its effective mass is typically 1/10 or less than that of the pump system, it responds to changes in the flow condition much more rapidly, thus minimizing swings in pressure. Thus, in general, the energy storage means in the form of accumulator 23 must be designed with piston 24 having an effective mass much less than the effective mass of the liquid dielectric introducing means which includes the pump 20 and 21 and source fluid 14. Such introducing means must generate as much as 200,000 hp for 20 milliseconds.

Figure 4 illustrates a practical embodiment of the theoretical configuration of Figure 1 where an insulating nozzle 33 receives moving contact 34 and the metal fingers 35 which form the fixed contact. An entrance port 13 is formed in nozzle 33 to allow passage of the dielectric fluid in its secondary flow path 15b only when the moving contact 34 is being parted. This effectively retains the fluid in close proximity to the contact area. On removal of contact 34 the fluid flows in two opposite directions 15a and 15b through nozzle 36 formed by the fixed contact 35 and through insulating nozzle throat 37 to extinguish the arc 38. Coupled to entrance port 13 is the insulating cylinder 39 having the pump piston 40.

Cylinder 39 is connected to a liquid sulphur hexafluoride storage unit 41 by pipeline 42.

Cooling coils 43 are provided for storage unit 41.

Accumulator 23 is connected at a port 44 the upper portion of cylinder 39.

Figure 5 is an alternative embodiment of the interrupter where stationary or fixed contacts 44 are normally engaged by the moving contact 46 which moves, in an insulating nozzle 47 for example made of TEFLON (Registered Trademark). In an annular space 48 on one side is a dielectric liquid pump system 49 and on the other an accumulator 23'. A high-pressure tube 51 surrounds the entire apparatus. Accumulator 23' includes the free-floating piston 24'. The double-flow paths 15a and 15b are indicated by arrows. The initial liquid level of SF6 covers up to and including the narrow throat of nozzle 47.

If desired, the annular space 48 can accommodate an additional pump and accumulator for greater interrupting capacity.

WHAT WE CLAIM IS: 1. A high voltage circuit interrupter using a dielectric liquid introduced into the interrupter at a high pressure to extinguish an arc formed when current is interrupted, said interrupter comprising movable and fixed contacts retained in at least a partially confined enclosure, means for introducing said dielectric liquid into said enclosure at a predetermined initial high pressure, energy storage means responsive to said high pressure liquid and to changes in said liquid flow for smoothing the resultant pressure of said liquid, by reducing any maximum and increasing any minimum in said pressure, said enclosure

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   current rating by varying the nitrogen pressure behind the accumulator piston 24.

   Nonoptimum accumulator pressure will cause the piston to respond too quickly or too slowly. Either of the foregoing situations can allow the liquid dielectric pressure to drop below the maximum at current zero. The various interrupting currents and optimum nitrogen fill have the following typical values: Accumulator Interrupting Charge Current Pressure

   120 kA 2,000 psig

   100 kA 1,900 psig

   80 kA 1,800 psig

   63 kA 1,700 psig Accumulator 23 of Figure 1 can be varied in design such as using a spring instead of nitrogen as the energy storage means. In addition, a rubber bladder or metal bellows could be used in place of the floating piston. Finally, the design could allow the liquid sulphur hexafluoride to be in direct contact with the nitrogen with no separator being used.

   Also, although liquid sulphur hexafluoride is the preferred liquid, other liquids may be used.

   The operator 16 driving liquid source 14 must have a relatively high mass in order to provide the necessary high forces required to provide the high pressure necessary to arc interruption. With such a high mass, naturally the response is relatively slow compared to the accumulator 23 (for example, the floating piston may have a weight of two pounds); since its effective mass is typically 1/10 or less than that of the pump system, it responds to changes in the flow condition much more rapidly, thus minimizing swings in pressure. Thus, in general, the energy storage means in the form of accumulator 23 must be designed with piston 24 having an effective mass much less than the effective mass of the liquid dielectric introducing means which includes the pump 20 and 21 and source fluid 14. Such introducing means must generate as much as 200,000 hp for 20 milliseconds.

   Figure 4 illustrates a practical embodiment of the theoretical configuration of Figure 1 where an insulating nozzle 33 receives moving contact 34 and the metal fingers 35 which form the fixed contact. An entrance port 13 is formed in nozzle 33 to allow passage of the dielectric fluid in its secondary flow path 15b only when the moving contact 34 is being parted. This effectively retains the fluid in close proximity to the contact area. On removal of contact 34 the fluid flows in two opposite directions 15a and 15b through nozzle 36 formed by the fixed contact 35 and through insulating nozzle throat 37 to extinguish the arc 38. Coupled to entrance port 13 is the insulating cylinder 39 having the pump piston 40.

   Cylinder 39 is connected to a liquid sulphur hexafluoride storage unit 41 by pipeline 42.

   Cooling coils 43 are provided for storage unit 41.

   Accumulator 23 is connected at a port 44 the upper portion of cylinder 39.

   Figure 5 is an alternative embodiment of the interrupter where stationary or fixed contacts 44 are normally engaged by the moving contact 46 which moves, in an insulating nozzle 47 for example made of TEFLON (Registered Trademark). In an annular space 48 on one side is a dielectric liquid pump system 49 and on the other an accumulator 23'. A high-pressure tube 51 surrounds the entire apparatus. Accumulator 23' includes the free-floating piston 24'. The double-flow paths 15a and 15b are indicated by arrows. The initial liquid level of SF6 covers up to and including the narrow throat of nozzle 47.

   If desired, the annular space 48 can accommodate an additional pump and accumulator for greater interrupting capacity.

   WHAT WE CLAIM IS: 1. A high voltage circuit interrupter using a dielectric liquid introduced into the interrupter at a high pressure to extinguish an arc formed when current is interrupted, said interrupter comprising movable and fixed contacts retained in at least a partially confined enclosure, means for introducing said dielectric liquid into said enclosure at a predetermined initial high pressure, energy storage means responsive to said high pressure liquid and to changes in said liquid flow for smoothing the resultant pressure of said liquid, by reducing any maximum and increasing any minimum in said pressure, said enclosure

   including a first nozzle formed by said fixed electrical contacts converging to a narrow throat and a second electrical insulating nozzle having a narrow throat opposite said throat of said throat of said first nozzle, said movable contact normally in its closed condition, extending through said throat of said second nozzle and into said throat of said first nozzle to make electrical contact with said fixed contacts, said enclosure including an entrance port for introduction of said liquid between said throats of said nozzles, said moving contact in said closed condition effectively closing said port, said moving contact when opened being withdrawn from both of said nozzle throats to provide a bidirectional flow path for said liquid in opposite directions with a primary flow path through the narrow throat and a diverging portion of said second nozzle and a secondary flow path through said narrow throat and a diverging portion of said first nozzle.
2. 2. A circuit interrupter as claimed in Claim 1 where said energy sotrage means includes a floating piston movable in a cylinder filled with gas.
3. 3. A circuit interrupter as claimed in Claim 1 or 2 where said fluid is liquid SF6.
4. 4. A circuit interrupter as claimed in any one of Claims 1 to 3 where said energy sotrage means has an effective mass much less than said introducing means.
5. 5. A circuit interrupter as claimed in Claim 4 where said partially confined enclosure provides a primary flow path for said fluid in a nozzle formed by the parting of said movable contact from said fixed contact and a secondary flow path at least partially formed by said fixed contact.
6. 6. A circuit interrupter as in Claim 5 where said fluid flows are directed in opposite directions.
7. 7. A circuit interrupter, constructed and adapted for use, substantially as hereinbefore described and illustrated with reference to the accompanying drawings.