The weakest link in the relay protection system is the transformer in the power system voltage. In the voltage loop, it is easy to malfunction during operation. The transformer in the voltage plays a very important role in the normal operation of the power system. Function, although there are not too many devices in the secondary circuit process of the voltage transformer, and the wiring process is not very complicated, there will always be such and other faults in the process. The faults that occur in the secondary circuit of the voltage transformer cannot be ignored, and may even cause more serious consequences, such as the malfunction and refusal of the protection device. According to the past situation, the secondary circuit of the voltage transformer is in the process The failures are mainly reflected in the following aspects:
1. The point grounding method of the secondary circuit of the voltage transformer is different from the normal situation. The secondary circuit of the voltage transformer shows no secondary grounding or multi-point grounding. The secondary grounding is also called secondary virtual grounding. The main reason for this is in addition to the problem of the grounding grid in the substation, the more important problem lies in the process of wiring. The secondary grounding of the voltage sensor will generate a certain voltage between it and the ground grid. This voltage is determined by the degree of imbalance between the voltages and the resistance generated by contact with each other, and the voltage generated by contact with the ground grid At the same time, it will also be superimposed between the voltage of each protection device, which will cause a certain amplitude value change of each phase voltage and related phase fluctuations to a certain extent, which will cause the impedance and directional components to malfunction and refuse to move. .
2. The voltage of the open triangle of the voltage transformer is abnormal in the loop. The voltage of the open triangle of the voltage transformer will be disconnected in the loop. There are mechanical reasons. The occurrence of a short circuit at the same time is largely related to certain usage habits of electricians. In order to achieve the fixed value of the zero-sequence voltage, under the protection of the transformer and the electromagnetic bus, the current-limiting resistance of the relay in the voltage is short-circuited. Some people even use a relatively small-scale relay. The result is It will greatly reduce the blocking phenomenon of the open delta voltage in the loop. However, when there is a grounding fault inside the substation or at the outlet, the zero sequence voltage will be relatively large, and the impedance of the loop load will be relatively small. The current will be larger, and the coil of the current relay will overheat, which will cause the insulation to be damaged, and then a short circuit will occur. If the short-circuit condition lasts for a long time, it will cause the coil to burn out. It is not uncommon for the voltage transformer to break at the burnt coil.
3. Secondary voltage loss of voltage transformers The secondary voltage loss of voltage transformers is a classic problem that often occurs in voltage protection systems. The main reason for this problem is that the performance of various types of breaking equipment is not perfect. . And the imperfection of the secondary loop process.
4. Use correct inspection methods
4.1 Sequential inspection method This method is to use inspection and debugging methods to find the root cause of the fault. It is carried out in the order of external inspection, insulation inspection, fixed value inspection, power supply performance test, protection performance inspection, etc. This method is mainly applied to the failure of microcomputer protection. It is in the process of handling accidents where there is a problem with movement or logic.
4.2 Use the whole set of test method The main purpose of this method is to check whether the action logic and action time of the protection device are normal, and it can often take a short time to reproduce the fault. And identify the root cause of the problem, if there is an abnormality, then combine other methods to check.
4.3 Reverse sequence inspection method If the incident record of the microcomputer relay protection tester and the electric fault recorder cannot find the root cause of the accident in a short time, attention should be paid to the result of the accident. Look forward from level to level until the root cause is found. This method is often used when the protection malfunctions.
4.4 Make full use of the fault information provided by the microcomputer relay protection tester, and follow the correct steps.
(1) Make full use of the fault recorder and time record. The event record, fault recorder graphics, and device light display signal of the microcomputer relay protection tester are important basis for accident handling. Making correct judgments based on useful information is the key to solving the problem.
(2) After some relay protection accidents occur, the cause of the failure cannot be found according to the signal instructions on the spot. Or there is no signal indication after the circuit breaker trips, and it is impossible to (define) a man-made accident or an equipment accident. This situation is often caused by insufficient attention of the staff, inadequate measures, and other reasons. Man-made accidents must be truthfully reflected in order to analyze and avoid wasting time.
Post time: Dec-29-2021