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Accident analysis of xx station on March 28th.

On March 28th, 2008, the 3 1 1 incoming line 35kv vacuum circuit breaker and 30 1 35kv vacuum circuit breaker of xx35kv substation failed, resulting in unexpected power failure of xx station and wharf station.

I. Accident at xx Station

On March 28th, around 18: 30, the switch of xx substation was seriously discharged due to the rain. 1 13, the dispatcher immediately ordered them to 10KV, 50 1, 30 1 out. Open the circuit breakers 50 1-4, 30 1-3, 31-3, 31-2. Because it was raining, we had to pull the circuit breaker 3 1 1-2. 18: 47, breaker 3 1 1-2 of xx station was disconnected. After further inspection, the two-phase CT of switch 30 1 in xx station was seriously discharged, and the three-phase CT of switch 3 1 1 C was cracked, so it could not be put into operation.

At 08: 35 on the 29th, the 35KV3# bus at xx Station was connected to the outlet of circuit breaker 3 1 1-2. After checking that all the equipment was normal, the power was transmitted by using 3 14 tower water line. During power transmission, it was found that the switch xx3 12 CT was too loud to be put into operation. The site decided to jump the 35KV3# bus of xx station to the lower opening of 3 12-2 breaker, and the load of 5 18xx of xx station fell to the power supply scheme of 5 12xx line of xx station. 16: 59 Tashui 3 14 for power transmission, and all terminal stations resumed power transmission. 17: 13xx Station 5 12xx Line resumed power transmission. After the accident was handled, it was reported to the company leader.

First, the cause analysis of the accident

The 35kv vacuum circuit breakers currently used in xx Station are four products of Beijing Dianyan Huayuan Electric Power Technology Co., Ltd., the model is ZW24-40.5. The equipment that caused the accident this time is 3 1 1, 3 12, 30 1 switch. The accident phenomenon is the same, and the external current transformer discharges the junction box of the bottom secondary line.

(a), the main cause of the accident is due to the rain xx station 30 1, 3 1 1 switch CT external insulation caused by serious flashover. The important factors of flashover are:

1, the CT insulation seal of the switch is poor, which leads to the reduction of insulation in bad weather and the primary winding discharges to the skin;

2. The defective design of the insulation layer of the current transformer of the switch is the main reason why the primary winding of the current transformer discharges the weak point of the insulation of the secondary winding and sheath.

(2) The CT external insulation of 30 1 switch in 2)xx Station was severely burned at the bottom of phase B and phase C, and the secondary terminal box at the bottom of phase A showed discharge traces. After the technicians of the switch manufacturer opened it, the internal wiring of the junction box was in good condition.

1. If a single-phase grounding fault occurs in one of the two-phase windings B and C of the 30 1 switch CT, 1# main transformer will not trip differentially due to the "CT disconnection locking differential protection" of xx station (allowing grounding operation for 2 hours). The 35KV PT phase voltage of xx station should show that the fault phase voltage is 0V, and the other two-phase voltages will rise to 35KV line voltage. The tower station, Xu Liying station, ×× station and Chengbei station connected to the system should have the phenomenon of phase voltage change and "35KV bus grounding signal", but the dispatching station did not have "35KV bus grounding signal". Therefore, the possibility of single phase grounding is ruled out.

2. If a single-phase grounding fault occurs in phase B and phase C of CT winding of 30 1 switch, it is a phase-to-phase short circuit. The differential protection of xx station 1# main transformer should be put into operation, with a fixed value of 0.83A (equivalent to a differential current of 33.2A). There is no action in the field differential. If there is a problem with the differential protection device of 1# main transformer at that time, resulting in differential failure, then the high-voltage backup protection of 1# main transformer should act. However, due to the failure of CT itself, the short-circuit fault can no longer be correctly reflected, so it is necessary to start the 3 14 overcurrent protection action (fixed value 1 1A, 03 seconds, CT transformation ratio of 500/5) of the upper switch of xx station to trip. However, when the accident happened, the tower water of 3 14 tower station did not act and tripped.

(3) The 3 1 1 switch of 3)xx Station is cracked.

3 1 1 CT C phase secondary junction box has cracks and discharge traces. After the jumper switch 3 1 1 was implemented, the power supply of line 3 12xx resumed, and it was found that the CT of switch 3 12 also discharged.

(4) If 3 1 1 and 30 1 switches are subjected to overvoltage, the insulation will be damaged. By looking at the voltage curve of xx station of dispatching automation, no significant voltage fluctuation was found, and the overvoltage hazard was basically eliminated.

Therefore, it is unlikely that there will be problems with the two sets of protection devices at xx Station and Tashang Station. Therefore, according to the above analysis, it is preliminarily determined that the external insulation of 3 1 1 switch CT and 30 1 switch CT occurred partial flashover when the accident occurred, but the metal grounding or interphase short circuit did not occur in time. The dispatcher and the operation team took power failure measures in time to avoid the accident expansion caused by switch insulation breakdown.

Two. Measures and suggestions

1. It is suggested that the substation work area start to check the secondary part of the comprehensive automatic control equipment of xx station to ensure that the protection device is normal and the setting value is calculated correctly.

2. Through this accident, three 35KV switches at xx Station appeared flashover. Relevant departments should be organized to carefully test and analyze this type of turnout to determine the cause of the accident. If it is a switch quality problem, replace such switches if necessary.

3. In view of the accident at xx station, the operation group of substation work area should increase the number of special inspections of all outdoor switches, especially the equipment of the same model as that at xx station. The dispatcher of dispatching station strengthens the patrol in bad weather through remote monitoring system.

4. Strengthen spare parts management and prepare sufficient spare parts.

5, according to the company's power grid emergency plan, formulate a reasonable accident handling process, implement the post, clear responsibility, in the event of an accident, all departments should work together to restore power transmission as soon as possible.