Analysis of the discharge circuit of the bus diffe

Analysis of discharge circuit of bus coupler current phase comparison bus differential protection

Abstract: bus coupler current phase comparison bus differential protection is widely used in plants and stations with 110kV and above double bus connection. In order to prevent unexpected reclosing, the outlet of 220kV bus differential protection is connected to the direct jump terminal of phase separation operation box, and 110kV bus differential is discharged by discharge relay to line reclosing. By analyzing the discharge circuit of bus differential protection based on bus coupler current phase comparison, it is pointed out that this circuit can not reliably discharge in some designs, and the discharge circuit should be improved or the discharge relay should be replaced

key words: bus differential protection reclosing improvement Untitled Document bus coupler current phase comparison bus differential protection (SMC type) is widely used in plants and stations with 110kV and above double bus connection in Hebei Province and the country. According to incomplete statistics, there are about 100 sets in operation in Southern Hebei. This bus differential protection principle has simple wiring and slow operation speed, and can meet the requirements of general 110kV and 220kV plants and stations for bus differential protection, except that the double bus will refuse to operate in case of successive faults

it is worth noting that in some faults, the unexpected behavior of bus differential protection action and line switch reclosing occurred. When the 110kV bus of Xiazhuang 110KV, Diantou 110kV and Shijiazhuang thermal power plant failed, the line switch reclosed. The post accident inspection found that the relay used to discharge the line reclosing operated slowly, which was the main reason for the false reclosing. 1. Principle and current situation of discharge circuit according to the principle of SMC bus differential protection, start an intermediate relay to discharge the reclosing of line switch at the same time of the action outlet of bus differential protection. According to the current investigation, the outlet of 220kV bus differential protection is connected to the direct jump terminal of the phase separation operation box, and the reclosing is released through the discharge circuit in the operation box. The 110kV bus differential can also be more complicated for users according to the new experimental standards. From the perspective of discharge circuit wiring, there are the following forms

a. the discharge relay is connected in parallel with the bus coupler outlet (Class A, see Figure 1). Figure 1 class a parallel wiring diagram B. discharge relay is connected in parallel with other outlets (class B, see Figure 2). Figure 2 class B parallel wiring diagram C. the discharge relay and other outlets are the same intermediate relay, using the contact of MCJ for discharge (Class C, as shown in Figure 3). Figure 3 class C wiring diagram D. the discharge relay is activated by the outlet relay (Class D), which can be divided into two types: self holding or not

from the perspective of relays used, there are delay reset relays and fast intermediate relays. 2 Analysis of discharge circuit 2.1 reliable starting of discharge relay

it can be seen from the above that the wiring of discharge circuit and the experimental speed and height of the experimental machine used should be selected according to the performance of the product to be tested, and the relay is diverse. If it is analyzed only from the principle wiring, since the general switching action time is 40 ~ 60ms (oil switch), if the same relay (Class C) is used, the discharge process time can make the reclosing circuit not reclose

when the outlet is connected in parallel with the bus coupler (Class A), the action time of the phase comparison relay (40ms) plus the action time of the line switch (40ms) is equal to 80ms. If the discharge relay adopts the delayed reset relay, its action time is about 80 ~ 90ms, which may compete with the tripping of the line switch, and the discharge is unreliable. If the line switch is SF6 switch, the action time is 30ms, and the discharge is more unreliable. The discharge relay of Handan bureau adopts dz-12b with the damping coil removed, and its action time is about 10ms, which can ensure reliable discharge

adopt the discharge mode of parallel connection with the outlet of line switch (class B) or restart the discharge relay by MCJ (Class D). If the fast intermediate relay is adopted, there should be no discharge problem; However, if the time-delay reset relay is used, the discharge is more unreliable than Class A

2.2 reliable discharge completion problem

another strength area of Jinan Zhongchuang Industrial Test System Co., Ltd. is to confirm the performance of composites in very warm environment This requires the accurate control of the temperature of the fixture and tooling samples to ensure the reliability of the performance under different temperature settings, and it is easy to operate the delay reset relay or holding mode, and there is no problem after the discharge. The fast intermediate relay is adopted. Generally, because its action time is 10ms, there is always more than 20ms from the start to the switch jumping off and the relay returning, and it should be able to discharge (it should be confirmed by the test to ensure that there is a margin in the discharge time)

2.3 single/double bus discharge problem

if the FDJ is started in parallel with the bus coupler outlet or by two MCJ in parallel, the reclosing discharge of all line switches on the double bus shall be carried out. It should be said that there is no big problem. If there is no continuous fault, the line reclosing on the faultless bus can still be recharged

of course, the better way of double bus should be to judge the fault bus and discharge the reclosing circuit of the bus outlet at the same time at the outlet of the fault bus, so as to prevent the instantaneous fault of the sound bus. It should be noted that if the holding mode is adopted, it must be reset in time to make the line reclose and charge. 3 improvement scheme according to the above analysis, several improvement schemes are recommended

a. the bus differential outlet is connected to the permanent jump terminal of the operation box. If the line switch operation box has a permanent jump terminal, the bus differential outlet can be connected to this terminal, and the locking reclosing task can be completed inside the operation box

b. self hold, manual or automatic reset. Two sets of discharge relays are started by two sets of busbar differential protection outlet relays, which are self maintained by the discharge relay. Both busbar differential protection outlet relay and discharge relay adopt fast intermediate relay. When using manual reset, special attention should be paid to the on-site operation, and the discharge must be reset in time, following the rise in the price of billets nationwide on the 2nd

c. replace the current commonly used electromagnetic damping principle time-delay reset discharge relay. The time-delay reset relay is changed into a fast intermediate relay, but it must be verified by test that it can reliably discharge the reclosing of each line. Alternatively, the electromagnetic damping relay is changed into a static time-delay reset relay. The relay must be verified by test