RU2020688C1 - Arcing short circuit protective gear for metalclad switchgear - Google Patents

Abstract

FIELD: short-circuit protection of switchgear installations. SUBSTANCE: metalclad switchgear protective system depends for its operation on combining direct-acting current relay and arc-protection relay responding to changes in light intensity within switchgear cubicles. Supply circuits are connected to rectifier bridge of intermediate current transformer. Auxiliary relay coil is also connected to rectifier bridge and its transfer contacts are inserted in direct-action relay coil circuit. EFFECT: improved design. 1 dwg

Description

 The invention relates to electrical engineering and is intended for relay protection of switchgear cubicles of indoor and outdoor installations from short circuits (short circuit), accompanied by an electric arc.

 Known devices for protecting switchboards from an electric arc KZ containing working and brake photosensors, a comparison circuit, a threshold element, an executive body (FRG patent N 1126011, French patent N 2087348).

 A technical solution of a similar purpose is also known (AS USSR N 815544, N 997175, N 1111224, N 1415320, N 1453518, N 1545287). Their common drawback is that they are compatible, as a rule, with the relay protection of the switchgear performed on the relay of the indirect principle of operation and are practically unsuitable for switchgear cells equipped with direct current relays (such as RTM, RTV [1,2]), since In the latter case, a direct-acting relay is a measuring and executive body.

 The arc protection relay requires operational power and therefore there is no direct effect on the circuit breaker tripping. The closest in technical essence (prototype) is the execution scheme based on direct current relays of the RTV or RTM type [1, p. 78, Fig. 4-17], containing measuring current transformers, in series with whose windings the RTV relay windings and RTM.

 The disadvantages of this solution are the low speed and reliability when disconnecting internal short-circuit through an electric arc. This is because the direct current relay has a dependent time-current characteristic, regardless of whether it is an internal short circuit or external. Slowing down the operation of the protection can lead to the development of an accident and the transition of the electric arc to the busbars or to adjacent cells.

 The use of previously known arc protection relays is complicated by the lack of a constant operating current source and the need for special switching contacts capable of switching CT circuits without breaking the circuit.

 The purpose of the invention is to increase reliability, speed and reduce the amount of damage.

 The goal is achieved by the fact that in the device for protecting the complete switchgear from arc short circuits with direct-acting relays, containing measuring current transformers, the secondary circuits of which include the windings of the direct current relays, additionally, intermediate current transformers, the secondary winding of which is connected to the capacitor, are added to the terminals of which are connected by a rectifier bridge, to the positive and negative poles of which an arc protection relay is connected, the photosensor of which is located in sections of the complete switchgear, and its output contact is connected to the positive pole of the rectifier bridge and to the intermediate relay coil, the second terminal of which is connected to the negative pole of the rectifier bridge, the open contact of the intermediate relay is connected to the part of the direct current relay winding, and the closed contact to the whole winding.

 All elements of the claimed device are used for their intended purpose and are known in the practice of relay protection of power systems, but the combination of these elements in their connection distinguishes the proposed device from similar devices and to obtain positive qualities are not inherent in the prototype device.

 The drawing shows the protection circuit of switchgear with direct current relay in two-phase design.

 The following notation is adopted on the diagram: 1,2 - current transformers; 3 - intermediate current transformer; 4 - capacitor; 5 - rectifier bridge; 6 - arc protection relay, photosensors 7 of which are located in the compartments of the switchgear cell; 8 - closing contact of the arc protection relay; 9 - winding of an intermediate relay with switching contacts 10; 11 - winding of a direct current relay; 12.13 - protection kits installed in two or three phases of switchgear and consisting of the listed elements (2,4,5,8,9,10,11).

 In the initial state (in the absence of currents in the CT), the windings of the intermediate relay 9 and the direct current relay are not currented and they are in an unused state. The contacts 8 of the relay 6 of the arc protection are open, the opening contacts 10 of the intermediate relay 9 are closed, and the closing contacts, respectively, are open. A feature of the intermediate relay 9 is the switching of contacts 10 without opening the circuit. The arc protection relay is in an unused state, since the photosensor is in dark mode.

 The operation of the protection device can be explained in the following modes.

 With external short circuit, i.e. when a fault occurs outside the protected cell, the arc protection relay 6 is in an idle state and its contact 8 is open, the intermediate relay 9 is in an idle state and therefore open contact 10 is closed, which causes current to flow from the CT 1 through a part of the winding of the direct current relay 11 . If the short-circuit current exceeds the setpoint current of the relay 11, then it trips, which leads to the circuit breaker tripping by the relay 11. If the short-circuit current does not exceed the tripping current of the relay 11, then it does not work.

 If a short circuit occurs through an arc inside the protected cell, this leads to the operation of the relay 6 of the arc protection, which closes its contact 8, which leads to the operation of the intermediate relay 9. Relay 9 closes the closed contact 10, which ensures the flow of current from the CT through the entire relay winding 11, increasing the magnetomotive force compared to the previous case. Given this, with internal short circuit, the direct relay operation is ensured in the independent part of the time-current characteristic [1], ie in this case, the duration of the protection is reduced. The supply of the arc protection relay is provided from an intermediate transformer 3 loaded on a capacitor 4 and a rectifier bridge 5, which ensures high reliability of the protection, since the operation of the arc protection relay is possible only if there is a current of sufficient magnitude.

 Thus, the introduction of additional elements into the protection circuit led to the following results: increased reliability due to the supply of an arc protection relay from an intermediate current transformer enclosed in the secondary circuit of the CT of the protected connection; increases the speed of protection, as it ensures forced disconnection of the direct current relay, that is, its operation in the independent part of the time-current characteristic; the amount of damage is reduced by reducing the response time of the switchgear protection, i.e. localization of the accident in the volume of one cell.

 The proposed protection can be implemented on the basis of serial devices, for example, the elements (3,4,5,9) represent an intermediate alternating current relay of the RP-341 type, with a contact gain of 10, switching without breaking the circuit. The direct current relay can be based on relays of the RTM and RTV type (with a practically independent and time-dependent time delay, respectively).

 Conducted laboratory and field tests in a 10 kV network by simulating a short circuit confirmed the high efficiency and positive qualities of the proposed device.

Claims (1)

 DEVICE FOR PROTECTING COMPLETE DISTRIBUTION DEVICES FROM ARC SHORT CIRCUITS, comprising a measuring current transformer, the first terminal of the secondary winding of which is connected to the first terminal of the winding of the direct current relay, characterized in that an additional intermediate current transformer is introduced, the primary winding of which is connected to the second terminal to the second current, another terminal through the make contact of the newly introduced intermediate relay - to the second terminal of the direct current relay winding I, the secondary winding of the additional intermediate current transformer is loaded on a capacitor, to the terminals of which a rectifier bridge is connected to the positive and negative poles of which an arc protection relay is connected, whose photosensor is located in the compartments of the complete switchgear, and its output contact is connected to the positive pole of the rectifier bridge and to winding of an intermediate relay, the second output of which is connected to the negative pole of the rectifier bridge, breaking contact in between The relay is connected to a part of the winding of a direct current relay.

Images