Sharing of Fault Examples of Vacuum Circuit Breakers, After Watching You Can Also Do

1.Fault discovery

At 9:10 on April 8, 2007, when a 110kV fully automatic substation of Shixing Power Supply Bureau was making a routine inspection of the equipment during the shift shift, it was found that the 35KV 321 vacuum circuit breaker made anintermittent abnormal "squeak" sound . After further observation, it was confirmed that It is phase C that makes the sound. The staff on duty used an infrared thermometer to check the C-phase electrical connection point, TA and the circuit breaker body. The temperature was about 16.5°C, which was the ambient temperature. No other abnormality was found in the appearance inspection of the circuit breaker. After that, the 321 vacuum circuit breaker was disconnected from the power grid and put out of operation, and at the same time, the engineering and technical personnel were notified to check and test on the spot, so as to ensure that the fault was solved in the shortest time and the normal power supply mode was restored.

2.Analysis of failures

2.1 Visual inspection and vacuum degree test

The model of the vacuum circuit breaker is ZW7-40.5 with built-in LZZBJ4-35 current transformer. It was put into operation in June 2005. The technicians first tested the vacuum circuit breaker for insulation resistance, vacuum degree and contact resistance. The vacuum interrupter of the circuit breaker, the lower end insulating sleeve, and the built-in current transformer have good insulation resistance, and the vacuum degree and contact resistance are also qualified. It can be seen from the results of the infrared thermometer that the electrical connection points are in good contact and there is no heating phenomenon. They continued to inspect the insulating rod, horizontal rod and box of the circuit breaker. No fracture, corrosion, discharge, etc. were found. In the case of broken pins, foreign objects or parts falling off, the components of the fixed connection parts are not loose, the insulation is not damaged or stained, the sealing rubber ring is not aged, the silicon steel sheet screws of the current transformer core are also tight, and the vacuum circuit breaker Is the intermittent "squeaking" abnormal sound caused by the open circuit of the secondary circuit of the current transformer or the loose connection line? Carry out multiple manual opening and closing operation tests, free tripping tests, and electric opening and closing operation of the circuit breaker. In the test, no abnormality was found in the circuit breaker, and there should be no problem with the spring energy storage control mechanism and mechanical transmission system of the circuit breaker.

2.2 Pressure test

In order to find out the specific location of the abnormal noise from the C-phase of the vacuum circuit breaker, follow the principle of not expanding the damage scope of the equipment and not aggravating the damage degree of the equipment, and apply the rated voltage 22.5 to the single-phase segment when the circuit breaker is open. kV test, no abnormal noise was found.

In order to more truly reflect the fault, find out the specific location of the abnormal noise as soon as possible, and carry out no-load power transmission to the circuit breaker (that is, only close the isolating switch and circuit breaker on the bus side). Squeak "discharge sound, the specific part of the sound is between the lower insulating sleeve and the current transformer. The sound of the current transformer in the box is particularly obvious, and the discharge sound is getting louder and louder as time goes on, and it seems to feel at any time there is a possibility of breakdown.

The vacuum degree test cannot replace the power frequency withstand voltage test. Due to the limitation of the test range, the vacuum degree test must cooperate with the power frequency withstand voltage test to make a correct diagnosis of the vacuum interrupter, especially for the complete leakage of the vacuum bubble, the test value will be close to the value when the vacuum degree is good, and it is easy to cause a wrong judgment. Therefore, it was decided to carry out the preventive power frequency withstand voltage test according to the regulations in the breaking state of the circuit breaker.

First, the lower end of the insulating sleeve is grounded, and only the upper end of the vacuum arc chamber is applied with voltage. After the voltage rises to 95kV/1min, no abnormality is found.

Next, apply voltage to the lower insulating bushing (including the current transformer). When the voltage rose to 58kV, an abnormal crackling sound suddenly occurred, and the high-voltage test instrument tripped.

Tested with a megohmmeter, the insulation resistance of the upper vacuum interrupter is 2500MΩ, and the insulation resistance of the lower insulation bushing is 0MΩ, which is obviously broken down. The lower insulation bushing includes current transformers, insulating rods, bushings and current transformers. Insulating silicone grease filled between them, but no traces of discharge and breakdown were found in various parts of the lower insulating sleeve by visual inspection. Since the current transformer is built-in, it is inconvenient to dismantle, so first untie the insulating rod to test step by step. The edge power of the lower end of the insulating sleeve is 2500MΩ, and the edge power of the edge rod is 0MΩ. It seems that the fault point has finally been found, and the problem lies in the insulation pull rod. After completely removing the edge pull rod, it was found that there was a layer of carbonized powder in the entire protective cover under the insulating pull rod.