US1990348A - Electric switch - Google Patents

Description

Invent-Or: David Cl rfi Ce,

5 H m/v7 8,8

His Attorne g.

Patented 5, 1935 UNITED STATES ELECTRIC SWITCH David 0. Prince, Swarthmore,

Pm, assignor to General Electric Company, a corporation of New York Application October 26, 1933, Serial No. 695,242

6 Claims.

. and forming a part of this specification.

Referring to the drawing, the single figure thereof is an elevational view, partly in section of a liquid break or oil switch embodying the present invention. e

The switch illustrated comprises a sealed or pressure-confining tank 1 forming the switch casing, a suitable arc extinguishing liquid 2, as

. oil for example, completely filling the casing 1,

. of the switch.

and relatively movable contact structure im-.

mersed in said liquid comprising stationary contacts 3 and 4 carried at the enclosed ends of the lead-in conductor stud bushings 5 and 6 respectively, and a movable contact structure for interconnecting the stationary contacts 3 and 4 in the closed circuit position of the switch. The oil tank may be permanently sealed as by suitable oiltight Joints 1' for the bushings, etc. since no packing glands for exterior moving parts are necessary. 1 1

The movable contact structure is actuated in accordance with 'variation 01' the oil pressure within the casing 1, a substantial increase in pressure effecting circuit opening movement of the movable contact structureand a decrease in the oil pressure to the normal value effecting the circuit closing operation; To this end the movable contact structure may comprise a plura lity of hollow, sealed, expansible members 7 which contain a suitable compressible fluid, as air. Each. expansible member 'I, which may be constructed of suitable conducting material, as copper, in the manner of the well known metallic bellows, is normallyin the expanded or circuit closing position. In order to insure positive return of the expansible members to the circult closing position in response to decrease of the exterior oil pressure a central compression spring 8 may be provided as illustrated.

The actual contact portions of the member 7- may comprise raised or button-like conducting portions 9 which coact with the stationary contacts 3 and 4 and with the contact portions of intermediate expansible contact members to complete the circuit betwee the terminals 5 and 6 The oil'pr ssure within the tank 1 may be'varied in any .suitable manner as by a flexible wall portion ormetallic bellows 10 forming a lateral extension of the casingl. The bellows 10 is connected to an operating rod 11 and a compression spring 12 which is seated between the outer face of the bellows and a stationary support 12.

As illustrated, the metallicbellows 10 is filled with oil and communicates with the interior of the tank 1 so that pressure acting on the bellows tending to compress the same results in increase of the oil pressure within the switch tank which is of substantially constant volume. Normally the oil within the switch tank is under no appreciable pressure, the operating rod 11 which is attached to the free end of the bellows being latched against'the tension of spring 12 by latching means 13 co-acting with a tripping or releasing solenoid 14. a

In this position the switch is in readiness to be tripped which may be accomplished in the usual manner as by imparting a tripping impulse to the tripping solenoid 14, causing in turn release of the latch 13 and bias of the operating rod 11 and bellows 10 towards the right under the influence of the compression spring 12. The oil pressure within the switch tank is immediately increased, the magnitude of the pressure rise depending on the tension of the spring 12 with the result that each of the hollow contact members 7 is instantly compressed to separate the contact portions 9 with respect to the co-acting contact portions. Accordingly a plurality of breaks are formed simultaneously within the oil tending to quickly interrupt arcing at these points.

Closing of the switch is effected by decrease of the oil pressure which is accomplished by return movement and latching of the operating rod 11, thereby transferring the spring pressure to the latching means and permitting the members to expand into contact engagement.

The supporting means for the movable hollow contact members 7 may comprise any suitable arrangement as lateral supports 15 and an interconnecting structure 16. For the purpose of equalizing the voltage impressed across each break, thereby minimizing arcingat the contacts and greatly reducing the pressure generated within the tank and substantially eliminating voltage surges, as in the interruption of high tension direct current circuits each break is in parallel with a suitable resistance. To this end the lateral supports 15 are formed of conducting material and are interconnected at the fixed ends thereof by a suitable resistance material 17 forming part of the structure 18. In the present instance the supporting structure 16 comprises a main supporting post 18 rigidly connected to and insulated as at 19 with respect to the lateral conducting supports 15. The lateral conducting supports 15 are spaced by and electrically connected to discs of resistance material 17, the elements being clamped into good conducting engagement by the central supporting post 18. Each break formed by a pair of contacts is accordingly shunted by a circuit including a resistance or suitable impedance, the characteristics of which may be chosen in accordance with the desired interrupting performance of the switch. A synthetic resistance material, known to the trade as Thyrite, may be used as a specific instance.

The device, however, is not limited to a resistance having particular characteristics. For example, the resistance across each gap may be chosen so that in the case of the heaviest cur- ;rents to be interrupted the voltage drop across the resistance will not exceed that which can be instantly cleared by the individual break. The voltage across each break is regulated by the voltagedrop in the resistance material 1'7, so that, knowing the voltage rating of a single break, the voltage across the switch terminals can be increased indefinitely by a pro rata increase in the number of breaks. Such an increase in the number of breaks does not complicate the construction of the switch mechanism since the oil pressure is communicated simultaneously to each contact member '7. Likewise, any difierence in time between the opening of difierent breaks is unimportant since the voltage across the gap is determined by the voltage drop in the resistance material.

In response to the tripping operation above described the simultaneous opening of the movable contacts efiects practically instantaneous transfer of the current to the resistance material with the result that there is practically no arcing and consequent deterioration of the oil. Since the contacts are operated by oil under pressure, the oil furthermore is at the maximum dielectric strength while the contacts are being separated. As no explosion or generation of high arcing pressure is involved it is not necessary to make a switch casing larger than the insulation requirements demand.

Under certain load interrupting conditions, a small amount of gas may be generated due to slight arcing. Since there is no appreciable pressure on the oil when the switch is closed, the oil may breathe freely into an expansion chamber, thereby freeing the oil of occluded gases and providing for variations in the oil volume due to temperature changes. It will be apparent that suitable means as a simple check valve op erated by fluid pressure may be used for closing the opening to the expansion chamber when the switch is operated. The metallic bellows 10 likewise provides for limited variations in the oil volume in both the open and closed circuit positions.

Obviously there will be a comparatively small follow-current flowing through the resistance material 1'7. Such current is relatively easily interrupted as by a conventional disconnecting switch or the like since the current through the high resistance is at a'comparatively high power factor. It is likewise apparent that voltage surges due to switching operations would not occur with the present switch by reason of the damping effect of the resistance material.

It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:-

1. An electric switch comprising a pressureconfining casing completely filled with an arcextinguishing liquid, said casing having a flexible wall portion, relatively movable contacts immersed in said liquid, a hollow pressure actuated member immersed in said liquid operatively related to said contacts, and means exterior of said casing cooperating with said flexible wall portion for varying the pressure of said liquid, thereby causing actuation of said contacts.

2. An electric switch comprising a pressureconfining casing containing an arc-extinguishing liquid, stationary and movable contact structure immersed in said liquid so that arcing at said contact structure is interrupted within said liquid, said movable contact structure including a hollow gas-filled flexible member, and means for efiecting variation in pressure of said liquid so that said hollow member is actuated to cause circuit opening and closing movement thereof.

3. An electric switchcomprising a casing containing an arc-extinguishing liquid, relatively movable contact structure immersed in said liquid and arranged to form a plurality of breaks in series, said structure including a plurality of hollow compressible gas-filled members normally in contact engagement, and means for increasing the pressure of said liquid for compressing said members and eliecting opening of the circuit within said liquid at a plurality of points.

4. An electric switch comprising a pressureconfining casing containing an arc-extinguishing liquid, stationary and movable contact structures immersed in said liquid, said movable contact structure including a hollow gas-filled compressible member, increase in pressure of said liquid causing compression of said member and circuit opening movement of the movable contact structure so that arcing at said structure is interrupted within said liquid, means resiliently biasing said hollow member towards expanded closed circuit position, and means exterior of said casing for effecting variation in the pressure of said liquid.

5. An electric switch comprising a switch casing containing an arc-extinguishing liquid, relatively movable contact structure including a plurality of compressible members forming a plurality of breaks in series immersed in'said liquid, said members actuated in response to variation of liquid pressure within said casing, and means including a resistance element in shunt with each break connected to said contact structure.

6. An electric switch comprising a pressureconfining casing filled with an arc-extinguishing liquid, said casing having a flexible wall portion, relatively movable contacts immersed insaidliquid arranged so that arcing between said contacts is interrupted by said liquid, means responsive to pressure created in said liquid for separating said contacts, a, spring coacting with said flexible wall portion for creating pressure in said liquid, a

latch for maintaining said spring under tension

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