GB1578740A - High-voltage circuit breakers - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO HIGH-VOLTAGE CIRCUIT-BREAKERS (71) We, NORTHERN ENGINEER ING INDUSTRIES LIMITED, a British company of NEI House, Regent Centre, Newcastle-upon-Tyne, NE3 3SB, 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: This invention relates to high-voltage circuit-breakers, and concerns a hydraulic energy absorber which may be employed in conjunction with such a circuit-breaker to produce an energy absorbing effect to control the movement of an external dynamic system such that the motion of the system is substantially independent of changes in the magnitude of the system forces.

The invention is particularly although not exclusively applicable to high-voltage circuit-breakers of the type employing interrupters of the puffer-type, which use SF6 gas as the insulating and arc quenching medium.

In this context a puffer-type interrupter is a piston-and-cylinder device whose cylinder is filled with the arc-extinguishing fluid medium and which is driven by the actuating mechanism which separates the interrupter contacts to direct a flow of the arc-extinguishing medium, compressed by the piston in the cylinder of the device, at the gap between the separating contacts in operation of the circuit-breaker, for cooling and extinguishing an arc drawn between the contacts.

A fundamental problem occurring with such circuit-breakers is that the pressure rise of the gaseous medium within the puffer cylinder of the interrupter is dependent upon the magnitude of the current being interrupted. This rise in pressure exerts a retarding force upon the moving contacts of the circuit-breaker thereby causing a reduction in velocity and thus causes a variation in the displacement versus time characteristic of the contacts. For consistent short-circuit interruption it is desirable that the displacement versus time characteristic is fairly consistent throughout the whole range of currents to be interrupted. Previous attempts to solve this problem fall into two categories: (a) by imposing a constant retarding force on the contacts which is larger than the force due to the pressure rise so that the variation in force is relatively small; (b) by increasing the mass of the moving contacts so that variation in the kinetic energy due to the rise in pressure is small in relation to the kinetic energy of the contacts.

The shortcoming of method (a) is that the energy of the prime mover must be increased to allow for the high constant retarding force, whilst (b) requires much larger initial accelerating forces in order to drive the contacts to the desired velocity and also increases stress levels in drive linkages etc., whilst retarding the contacts at end of travel.

An object of the invention from one aspect is to obtain a consistent time versus displacement characteristic irrespective of the magnitude of the current being interrupted, without fundamentally increasing the accelerating forces and hence the energy output required by the operating mechanism or prime mover.

In accordance with the present invention å circuit-breaker having one or more interrupter units of the puffer type as herein defined, includes a hydraulic energy absorber which is coupled to the operating mechanism of the circuit-breaker, the hydraulic energy absorber comprising a liquid-filled piston-and-cylinder unit coupled to the operating mechanism of the circuit-breaker so that operation of the latter drives the piston linearly in the cylinder to produce a pressure change therein, which pressure change reacts through the piston on the operating mechanism and is regulated by means of a spring-biased self-amplifying valve as defined below which regulates the rate of flow of liquid, produced by the said pressure, through a discharge outlet in the cylinder wall.

In this context a self-amplifying valve is a pressure-responsive valve with positive feedback such that movement of the movable valve member against its biassing spring under an actuating pressure has the effect of increasing that pressure, and hence increasing the resultant valve movement, and vice versa.

In one construction embodying the invention, the energy absorber comprises a piston slidable within a cylinder for linear reciprocation therein, the piston and cylinder being housed within an outer container which is partially filled with liquid, and at least one spring-biased selfamplifying valve is provided at one or each end of the cylinder, said valve controlling the flow area through a discharge passage connecting the interior of the cylinder to a chamber within the container in response to changes in pressure generated within the cylinder by the piston movement, whereby to produce an energy absorbing effect which is substantially independent of the force applied to the piston by the associated mechanism, so that the rate of energy absorption is substantially constant.

The cylinder of the energy absorber preferably includes further passages connecting the cylinder with the chamber within the container so as to produce a dashpot effect towards each end of piston travel.

The moving contacts of the interrupter unit are connected to the piston via a linkage system giving a desired velocity ratio. Separating movement of the interrupter contacts causes the piston to move, thereby creating a pressure within the cylinder and causes the hydraulic fluid to flow through overlapping regulating orifices in the cylinder wall and in the movable valve member. Increase in piston velocity causes an increase in the pressure in the cylinder and vice versa. The pressure causes a force to be exerted on the face of the valve member, acting in opposition to the spring force acting on the valve member. The valve member remains stationary against a stop until the force due to the pressure is greater than that exerted by the spring when the valve member will start to move. Movement of the valve causes a reduction in the effective flow area of the regulating orifices, thereby causing a further increase in pressure, thus causing further valve movement until either the pressure force equals the spring force or until the valve is shut.

In either case the pressure in the cylinder acts upon the piston causing a retarding force to be exerted upon the contacts, thus causing a reduction in contact velocity and piston velocity and thereby reducing the cylinder pressure; this reduction continues until the spring force is greater than the pressure force on the valve, when the valve starts to open thus increasing the orifice area and causing a further pressure reduction etc., thus reducing the retarding forces acting on the contact until they are less than the accelerating forces due to the prime mover.

The pressure versus displacement characteristic of the valve for a given piston velocity is determined by the shape and size of the overlapping valve orifices, and the force and rate of the valve spring(s) over a wide range.

The mass of the movable valve member determines the response time of the system and also its dynamic characteristics, by allowing sufficient time lag to occur, coupled with the kinetic energy of the valve to ensure positive feedback throughout its travel (in both directions).

Overshoot of the valve and consequent time delay in the closed position are minimised by arranging for the valve member to open an orifice in the spring chamber and equalise the fluid pressure on both sides of the valve, after a predetermined travel of the movable valve member. The total spring force is then used to bring the valve to reset almost instantaneously, thus allowing immediate reversal of valve movement.

When the piston approaches the end of its travel it shuts off flow to the valve and also to orifices in the cylinder wall thus causing an additional pressure rise, dashpotting of the piston and contact occurring as further cylinder wall orifices are shut off.

The above description applies to the operation of the hydraulic energy absorber when the accelerating forces due to the prime mover are greater than those due to the pressure rise in the puffer cylinder, i.e.

when the current being interrupted is low.

When interrupting large currents the contact velocity is not sufficient to cause the valve to operate and only a small amount of energy is absorbed.

Intermediate currents cause accelerations which are lower than those previously described and thus operation of the valve has a relatively greater retarding effect upon the contacts, thus the valve only partially closes before reversing direction.

The invention may be carried into practice in various ways, but one specific embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a part sectional elevation of one phase of an SF6 circuit-breaker of the metal-clad dead-tank type; Figure 2 is an end elevation of the circuitbreaker shown in Figure 1; Figure 3 is an alternative arrangement of the circuit-breaker shown in Figures 1 and 2; and Figure 4 is a sectional elevation of a hydraulic energy absorber in accordance with the invention for application to the circuit-breaker operating mechanism shown in Figures 1, 2 and 3.

Figures 1, 2 and 3 illustrate one single phase of a three-phase circuit-breaker arrangement for high-voltage operation in a three-phase circuit.

Each phase comprises a twin interrupter tank 10--10 formed in two interconnected parts and filled with an insulating medium, for example SF6 gas at super-atmospheric pressure, and each tank portion is of earthed metal and houses a pair of puffertype interrupters 1 lA, 1 lB and may be of the type described in our British Patent Application No. 44231/74 (Case AR/988) or similar and comprise fixed and moving contact assemblies. The mechanical operating drive to the moving contact assemblies is provided by a pair of insulated rods 14 which are each connected to the moving contacts and to separate operating mechanisms 21 described in greater detail below.

The interrupting units ll, IlA and 11B respectively comprise a fixed contact housing~ 12A or 12B, and a co-operating moving contact assembly 13A or 13B mounted for vertical movement from a housing 15A or 15B. The interrupters, which are not shown in detail but whose co-operating contacts are shown in dotted-line form, each have a fixed tubular contact in the housing 12A or 12B, with a larger-diameter spring contact cluster co-axial with and surrounding the tubular contact. The moving contact assembly 13A, or 13B, of each interrupter unit has an insulating nozzle orifice mounted on the end of a tubular conducting puffer cylinder.

Within the puffer cylinder there is contained a tubular contact which cooperates with the fixed contact to make or break the high voltage circuit. The puffer cylinder also contains a puffer piston which is fixed relative to the cylinder, and the arrangement is such as to generate and direct a flow of arc-extinguishing blast of pressurised gas onto the interrupter contacts during circuit-breaking operation.

Insulation and separation between the fixed and moving contact assemblies of the interrupters 11A and 11B is provided by insulating tubes or rods 19 which also act as structural support members. The fixed contact 12A of the upper interrupter unit 11A is carried by an end fitting 17, and the housing 15B is mounted on support insulation posts 16, or alternatively on an insulating tube 18 provided with a stress relief shroud 18A. The common operating rod 14 for each pair of interrupter units I IA and 11 B extends vertically up centrally in the respective tank portion 10, and is connected to the moving contact assemblies 13A and 13B. When it is necessary to incorporate capacitors for voltage grading or circuit-interrupter purposes, the capacitor units may conveniently be housed within the tubes 19.

The current path for the circuit-breaker shown in Figures 1 and 2 is from a first electrical connector 30 supported within an insulated bushing 31 in a flanged housing 32 at the left-hand portion of the tank 10, through the two interrupter units 11 therein to the lower housing 15 and thence through a pair of separate connectors 33 within a flanged housing 34 which joins the two parts of the twin tank 10--10 to a similar arrangement in the right-hand portion tank 10 to its associated second connector 30. If the flanged housing 34 and the housings 32 are similarly dimensioned then it is possible to rotate each portion 10 of the tank through 1800 around its vertical axis of symmetry in order to obtain an arrangement with low-level external connections 30 and a high level interconnection 33--33 between adjacent tank portions 10.

An isolating switch is provided between the two intermediate connectors 33 and consists of a bridging contact 36 which is mechanically driven via an insulating rod 40 from housing 34 by a mechanism 41, or alternatively via an insulating rod 42 by a mechanism 43. This isolating switch would have the facility to break only residual capacitive currents.

In the circuit-breaker shown in Figures 1 and 2 the connectors 30 within the flanged housings 32 are connected through metal clad busbar trunking 44 to associated isolators, etc., in the known metalclad fashion. Current transformers 45 are housed within the trunking 44 as shown on the lefthand side of Figure 1 or outside the trunking 44 as shown on the right-hand side of Figure 1. In the latter case a capacitive voltage transformer is also shown and comprises an outer electrode 46 which is capacitively connected to the conductor 30. The capacitive current is led via an insulated lead 47 to measuring and protective apparatus, not shown.

In the arrangement shown in Figure 3 the connectors 30 are directly coupled to insulated bushing terminals 50 through elbow chambers 51; in this arrangement the connectors 33 described in Figure 1 are directly coupled, and the isolator mechanism 36 etc. described with referance to Figure 1 may, if required, be incorporated within the bushing terminals 50.

The arrangement of Figure 3 also makes provision for a closing shunt resistor 52 which may be contained within a housing 53 above the tank 10--10 or else external to and alongside the tank 110; in the former instance, as illustrated, the resistor is supported by insulators, not shown, and is electrically connected across the cylinders by means of an isolating switch gap 55 to the end connector 17 on the other side of the interrupter tank. The gap 55 is opened and closed either by a linkage off the main contact drive or by a seperate drive, not shown. The function of such a shunt resistor is to reduce the likelihood of over-voltages caused by directly closing on to a length of transmission line, and it is switched into the circuit some milliseconds prior to the main (low impedance) interrupter contacts closing.

All the earthed-metal housings 10, 32, 34, 44, 53 etc., thus described are connected together in a fluid-tight manner through sealed flanges, and the interiors of the housings contain SF6 gas at a pressure above atmospheric.

The mechanical power required to operate the interrupters 11 both in the Figures 1 and 2 arrangement and the Figure 3 arrangement is provided by two pneumatic actuators 21, one for each pair of interrupters, which are synchronised by a common operating solenoid 60. The actuators 21 are connected to cranks 61 which are coupled to the interrupter operating rods 14 and are also connected to energy absorbing units 62 which are each fixed at one end to the circuit-breaker supports. Further details of the energy absorbers 62 will be described with reference to Figure 4. In Figure 2 the compressed-air supply tank 63 is shown for connection to the actuators 21 via pipes 64, 65. The operating mechanism assembly is connected to the circuit-breaker through rotary shaft seals which retain the integrity of the pressurised tanks 10.

One of the energy absorbers 62 is shown in greater detail in Figure 4 and consists of a sealed housing 70 one end of which is sealed off by a connecting-end lug plate 71, which is attached to the circuit-breaker supports.

A drive rod lug 72 for connection to one of the drive shafts 14 of Figure 1 is carried by a piston rod 73 whose piston 74 is reciprocable within a cylinder 75 defined in the interior of the housing 70 by a tubular partition wall 75a. At the lower end of the cylinder 75 there is a plug 76 whose axial bore contains a self-amplifying valve comprising a cup-shaped valve member 77 which is spring-biased by a stack of constant-rate dished annular plate springs 78 housed within a chamber 79 at the lower end of the plug 76. The valve member 77 and cylinder plug 76 are formed with cooperating radial ports 80, 81 respectively which provide a variable flow path from the interior of the valve 77 to an annular-section chamber 82 surrounding the cylinder 75 in the housing 70. Orifices 83 and 84 are also provided through the wall 75a at opposite ends of the cylinder 75. The piston 74 carries a downwardly-protecting skirt 74a secured to it by a bolt 74b, the skirt 74a entering the bore of the plug 76 as a close fit in its rim flange 76a as the piston 74 approaches its lowermost position in the cylinder 75.

As applied to the circuit-breaker in Figures 1, 2 or that in Figure 3, the axis of the energy absorber 62 is vertical, and in this attitude the interior is almost completely filled with hydraulic fluid to a level 85, introduced through a filling hole closed by a screw 86. If the absorber is required to be used in a horizontal position a reservoir 87, shown dotted, is employed. Alternatively an inclined attitude may be adopted, with or without a reservoir.

The drive rod 14, Figure 1 connected to the moving contacts of 13A, 13B and puffer pistons of one pair of interrupters I IA, 1 lB is connected to the drive rod lug 72 of the piston rod 73 via a linkage system giving a desired velocity ratio. The linkage system comprises the crank 61 of Figure 1, to opposite arms of which the respective piston rod lug 72 and the ram of the respective actuator 21 are connected and which is coupled by a crank case mechanism 68 to the rod 14, so that rotation of the crank 61 by the actuator 21 moves the rod 14 vertically in opposition to the action of the absorber 62. Thus the separating movement of the contacts of the interrupters I IA, 11 B caused by downward movement of the rod 14 causes the absorber piston 74 to move downwardly in Figure 4, thereby creating a fluid pressure within the cylinder 75 and causing the hydraulic fluid to flow through the orifices 84 in the cylinder wall 75a, 80 in the valve member 77 and 81 in the plug 76. Increase in piston velocity causes an increase in the pressure in the cylinder 75 and vice versa. The pressure in the cylinder 75 causes a downward force to be exerted on the upper face of the valve member 77, acting in opposition to the force of the spring stack 78 acting upon the opposite face of the valve 77. The valve member 77 remains pressed upwardly and stationary against a stop 88 on the plug 76 until the force due to the fluid pressure exceeds that exerted by the springs 78, when the valve member will start to move downwardly.

Movement of the valve member 77 downwards causes a reduction in the flow path through the overlapping orifices 80, 81 thereby causing a further increase in the pressure thrust on the upper face of the valve, and thus causing further valve movement until either the pressure force again equals the spring force or the valve is shut.

In either case the pressure in the cylinder 75 reacts upon the piston 74 causing a retarding force to be exerted via the linkage 61, 66, 67, 14 upon the interrupter contacts, and thus causing a reduction in contact velocity and piston velocity and thereby reducing the cylinder pressure; this reduction continues until the spring force is greater than the pressure force on the valve, when the valve starts to open thus increasing the orifice flow area 80, 81 and causing a further pressure reduction etc., thus reducing the retarding forces acting on the contacts until they are less than the accelerating forces due to the prime mover 21.

The pressure versus displacement characteristic of the valve 77 for a given piston velocity is determined by the shape and size of the orifices 80, 81 and the strength and rate of the valve springs 78 over a wide range.

The mass of the valve member 77 determines the response time of the system and also its dynamic characteristics, by allowing sufficient time lag to occur, coupled with the kinetic energy of the valve, to ensure positive feedback throughout its travel (in both directions).

Eventually in its downward travel the valve member 77 may reach a position in which the orifice 80 opens into the spring chamber 79 and equalises the fluid pressure on both sides of the valve. The unresisted force of the springs 78 is then used to bring the valve to rest almost instantaneously thus allowing immediate reversal of valve movement. Overshoot of the valve and consequent time delay in the closed position are thus minimised.

When the piston approaches the end of its travel its skirt 74a enters and closes off the bore of the plug 76, and the piston then shuts off successive orifices 84 in the cylinder wall 75A thus causing an additional pressure rise in the cylinder 75 which is shut off from the valve 77; a dashpotting action of the piston in the cylinder is thus imposed on the moving contacts as the cylinder wall orifices 84 are successively shut off.

The above description applies to the operation of the hydraulic energy absorber 62 when the accelerating forces on the movable contact assemblies due to the actuator 21 are greater than the deceleration forces due to the breaking of fault current, i.e. When the current being interrupted is low. A large amount of energy is then absorbed by the absorber 62.

When interrupting large currents the contact velocity is not sufficient to cause the valve 77 to operate and only a small amount of energy is absorbed.

Intermediate currents result in contact accelerations which are lower than those previously described, and thus operation of the valve 77 has a relatively greater retarding effect upon the contacts, thus the valve only partially closes before reversing direction.

It should be noted that this invention is not limited by the constructional features described with referance to the accompanying drawings nor to the form or interupter referred to.

WHAT WE CLAIM IS: 1. A circuit-breaker having one more current interrupter units with puffer cylinders as herein defined, which includes a hydraulic energy absorber which is coupled to the operating mechanism of the circuit-breaker, the hydraulic energy absorber comprising a liquid-filled pistonand-cylinder unit coupled to the operating mechanism of the circuit-breaker so that operation of the latter drives the piston linearly in the cylinder to produce a pressure change therein, which pressure change reacts through the piston on the said operating mechanism and is regulated by means of a spring-biased self-amplifying valve as herein defined which regulates the rate of a flow of liquid, produced by the said pressure, through a discharge outlet in the cylinder wall.

2. A circuit-breaker as claimed in Claim 1, in which the energy absorber comprises a piston slidabl within a cylinder for linear reciprocation therein, the piston and cylinder being housed within an outer container which is partially filled with liquid, and at least one spring-biased selfamplifying valve at one or each end of the cylinder, said valve controlling the flow area through a discharge passage connecting the interior of the cylinder to a chamber within the container in response to changes in pressure generated within the cylinder by the piston movement whereby to produce an energy-absorbing effect which is substantially independent of the force applied to the piston by the associated mechanism, so that the rate of energy absorption is substantially constant.

3. A circuit-breaker as claimed in Claim 2 in which the cylinder of the energy absorber is formed with further passages connecting the interior of the cylinder with the chamber within the container and arranged to be

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

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. member will start to move downwardly. Movement of the valve member 77 downwards causes a reduction in the flow path through the overlapping orifices 80, 81 thereby causing a further increase in the pressure thrust on the upper face of the valve, and thus causing further valve movement until either the pressure force again equals the spring force or the valve is shut. In either case the pressure in the cylinder 75 reacts upon the piston 74 causing a retarding force to be exerted via the linkage 61, 66, 67, 14 upon the interrupter contacts, and thus causing a reduction in contact velocity and piston velocity and thereby reducing the cylinder pressure; this reduction continues until the spring force is greater than the pressure force on the valve, when the valve starts to open thus increasing the orifice flow area 80, 81 and causing a further pressure reduction etc., thus reducing the retarding forces acting on the contacts until they are less than the accelerating forces due to the prime mover 21. The pressure versus displacement characteristic of the valve 77 for a given piston velocity is determined by the shape and size of the orifices 80, 81 and the strength and rate of the valve springs 78 over a wide range. The mass of the valve member 77 determines the response time of the system and also its dynamic characteristics, by allowing sufficient time lag to occur, coupled with the kinetic energy of the valve, to ensure positive feedback throughout its travel (in both directions). Eventually in its downward travel the valve member 77 may reach a position in which the orifice 80 opens into the spring chamber 79 and equalises the fluid pressure on both sides of the valve. The unresisted force of the springs 78 is then used to bring the valve to rest almost instantaneously thus allowing immediate reversal of valve movement. Overshoot of the valve and consequent time delay in the closed position are thus minimised. When the piston approaches the end of its travel its skirt 74a enters and closes off the bore of the plug 76, and the piston then shuts off successive orifices 84 in the cylinder wall 75A thus causing an additional pressure rise in the cylinder 75 which is shut off from the valve 77; a dashpotting action of the piston in the cylinder is thus imposed on the moving contacts as the cylinder wall orifices 84 are successively shut off. The above description applies to the operation of the hydraulic energy absorber 62 when the accelerating forces on the movable contact assemblies due to the actuator 21 are greater than the deceleration forces due to the breaking of fault current, i.e. When the current being interrupted is low. A large amount of energy is then absorbed by the absorber 62. When interrupting large currents the contact velocity is not sufficient to cause the valve 77 to operate and only a small amount of energy is absorbed. Intermediate currents result in contact accelerations which are lower than those previously described, and thus operation of the valve 77 has a relatively greater retarding effect upon the contacts, thus the valve only partially closes before reversing direction. It should be noted that this invention is not limited by the constructional features described with referance to the accompanying drawings nor to the form or interupter referred to. WHAT WE CLAIM IS:

1. A circuit-breaker having one more current interrupter units with puffer cylinders as herein defined, which includes a hydraulic energy absorber which is coupled to the operating mechanism of the circuit-breaker, the hydraulic energy absorber comprising a liquid-filled pistonand-cylinder unit coupled to the operating mechanism of the circuit-breaker so that operation of the latter drives the piston linearly in the cylinder to produce a pressure change therein, which pressure change reacts through the piston on the said operating mechanism and is regulated by means of a spring-biased self-amplifying valve as herein defined which regulates the rate of a flow of liquid, produced by the said pressure, through a discharge outlet in the cylinder wall.

2. A circuit-breaker as claimed in Claim 1, in which the energy absorber comprises a piston slidablè within a cylinder for linear reciprocation therein, the piston and cylinder being housed within an outer container which is partially filled with liquid, and at least one spring-biased selfamplifying valve at one or each end of the cylinder, said valve controlling the flow area through a discharge passage connecting the interior of the cylinder to a chamber within the container in response to changes in pressure generated within the cylinder by the piston movement whereby to produce an energy-absorbing effect which is substantially independent of the force applied to the piston by the associated mechanism, so that the rate of energy absorption is substantially constant.

3. A circuit-breaker as claimed in Claim 2 in which the cylinder of the energy absorber is formed with further passages connecting the interior of the cylinder with the chamber within the container and arranged to be

controlled by the piston so as to produce a dashpot effect towards each end of piston travel.

4. A circuit-breaker as claimed in Claim 2 or Claim 3, in which the moving contact(s) of the circuit-breaker are connected to the piston of the energy absorber via a mechanical linkage system of predetermined velocity ratio.

5. A circuit-breaker as claimed in any one of Claims 2 to 4 in which the valve member of the self-amplifying valve is of hollow sleeve form which is a close sliding fit in a bore in the cylinder, and in which the discharge passage whose flow area is controlled is formed by apertures in the valve sleeve and in the wall of the cylinder which overlap one another to an extent which is varied by the axial movement of the valve sleeve in the cylinder.

6. A circuit-breaker as claimed in Claim 5 in which movement of the sleeve under the force of the liquid pressure in the cylinder is opposed by spring means.

7. A circuit-breaker as claimed in Claim 6 in which the valve sleeve, after a predetermined extent of travel under the force of the liquid pressure in the cylinder against the action of the spring means, is arranged to equalise the liquid pressure on opposite sides of the valve sleeve so as to stop further movement of the valve sleeve in that direction and permit it to be returned by the action of the spring means.

8. A multiphase circuit-breaker substantially as specifically described herein with reference to Figures 1 to 4 or to Figures 1 to 5 of the accompanying drawings.