High voltage circuit breaker preventive test method

In order to correctly judge the state of the high-voltage circuit breaker through the analysis of preventive test data, the basis for the state maintenance of the circuit breaker is provided by a simple, safe and effective test method. In the following, several commonly used preventive test analysis methods are introduced to make judgments on the insulation characteristics, mechanical characteristics and wear of the circuit breaker.

1. Measurement of conductive loop resistance

The conductive loop resistance test is a common test for the circuit breaker to judge whether the contact is in good contact, and it is also the main item of the circuit breaker preventive test. The measurement method is to add a current greater than 100A when the circuit breaker is closed, and obtain the resistance by measuring the voltage across the circuit. With the use of enclosed busbars and GIS, it is difficult for testers to measure near the circuit breaker, often with a long busbar or through a grounding knife. In addition, different testers may use different places to measure the voltage, which makes the test data often unable to reflect the state of the device. Before conducting the test of the conductive loop resistance, the tester must first understand the position of the voltage measured by the previous test. The grounding knife gate should be measured to ensure good contact with the grounding knife. When the test data is obtained, the temperature at the time of measurement is recorded, and the test data is converted to a standard resistance at 75 degrees. Only the data thus measured can be compared with the previous data, and it is more effective to judge whether the contact contact is good. When the values ​​differ by more than the specified value, the cause should be analyzed or the repair should be arranged to eliminate equipment hazards.

2. Measurement of circuit breaker opening and closing time parameters

The circuit breaker opening and closing time parameter is the primary indicator of the circuit breaker's operating performance. Circuit breakers of different manufacturers have different switching and closing times, but they all require quick action. The time parameters include the closing time, the opening test and the different time periods. The opening time of the circuit breaker includes the two parts: the inherent opening time and the arc-extinguishing time, so it is also called the full opening time. In order to ensure that the acquired data can be reliably used for analysis and judgment, it should be ensured that the voltage applied to the test is a standard power supply, and the action circuit is the same as the previous test, and the energy storage mechanism is at the same level during the test. In the data analysis, the trend of the time parameter should be judged by combining the previous test data. Through the analysis of the test data, it can effectively judge whether the mechanical structure of the circuit breaker is loose, deformed and worn, whether the energy storage mechanism is normal, and whether the energy storage spring is deformed by stress and deformation.

In particular, when measuring the opening and closing time of the three-phase linkage high-voltage circuit breaker on site, the test wiring should be connected to the connection terminal of the relay protection switching operation to avoid wiring directly at the opening and closing coil of the circuit breaker. The test is carried out, otherwise it is difficult to find the problem that the opening and closing time exceeds the standard, which leads to the impact on the safe and stable operation of the power grid in the field application. When used for the pre-conduction time measurement of the synchronizing device, the closing voltage should also be added to the monitoring system closing relay terminal, so as to ensure accurate and reliable measurement time.

3. Measurement of the operating voltage of the circuit breaker's split and closing electromagnet

The measurement of the operating voltage of the circuit breaker operating mechanism is an important part of the circuit breaker characteristic test. In addition to verifying that the circuit breaker coil is sensitive and reliable, it can also test the performance of the entire operating mechanism under non-rated operating voltage. When the voltage of the operating mechanism should be kept within the rated voltage range of 80% to 110% according to the regulations, the circuit breaker should be able to be reliably closed. When the voltage of the operating mechanism should be kept within the rated voltage range of 65% to 120%, the circuit breaker should be able to reliably open. When the coil voltage is lower than the rated voltage of 30%, the circuit breaker should be reliably rejected.

The action of the circuit breaker is mainly accomplished by the action of the opening and closing coil. When the secondary DC system is poorly insulated and high-resistance is grounded, the induced low-voltage DC voltage will be generated at both ends of the circuit breaker closing coil, and the circuit breaker works in a strong electric environment, which easily causes strong electromagnetic interference if the coil If the operating voltage is too low, the circuit breaker will be erroneously opened, so the regulation stipulates that the circuit breaker must not operate when the rated voltage is lower than 30%. In the event of an accident in the power system, in order to ensure that the circuit breaker can operate reliably, the power system will not be protected due to the failure of the circuit breaker. Therefore, it is stipulated that the voltage of the operating mechanism should be maintained within the rated voltage range of 65% to 120%. When inside, the circuit breaker should be able to reliably open.

Through the circuit breaker operating voltage test, we can find problems such as the DC electromagnet core pin, the DC electromagnet working gap is too large, and the coil turns short. Special attention is paid to the fact that many circuit breakers often measure the operating voltage of the split and closing electromagnets often at a much lower value than the specified voltage. This is because the equipment manufacturer uses a voltage divider resistor on the loop when configuring the electromagnet. Therefore, in this case, the operating voltage of the split and closing electromagnets cannot be directly measured, and the voltage dividing resistors should be measured together to ensure the accuracy of the test data.

4, dynamic resistance test

The breaker contacts consist of a main contact and an arc contact. When the switch is closed, the main contact of the arc contact is closed after the arc-extinguishing is closed; when the switch is opened, the main contact is first separated by the arc after the contact is separated. During the circuit breaker switching and closing process, the main circuit resistance is changed. The arc contact mainly protects the main contact from arc ablation and wear. In order to check the degree of wear of the arc contact, we test the resistance change during the opening process through the dynamic resistance, because the sudden change of the resistance from infinity to the arc contact resistance during the closing is difficult to measure, and the instantaneous DC when the arc contact is just closed Produces harmful noise and does not take measurements.

When the circuit breaker is opened, the current on the main contact is transferred to the arc contact after the main contact is separated. The time is taken as the node, and the time to the arc contact is defined as the “arc contact time”. The contact time of the arc contact corresponds to the degree of ablation and wear of the arc contact. As the degree of wear increases, the arc contact becomes shorter and shorter, and the contact time of the arc contact is shortened. If the arc contact wears too much, after the main contacts are separated, the current cannot be effectively transferred to the arc contact, and the generated arc will directly ablate the main contact, causing the main contact to be damaged or even an accident. It can be seen that the dynamic resistance test obtains the contact time of the arc contact by measuring the change of the resistance of the conductive loop, and evaluates the degree of ablation and wear of the arc contact.
For circuit breakers that frequently cut off large current circuits, especially for pumped-storage unit outlet circuit breakers, the degree of ablation and wear of the arc contacts is the main basis for the state maintenance judgment. It is recommended that the measurement be performed once a year.

5, closing resistance test

The closing resistor is designed and installed to force the operation overvoltage generated when the high voltage level circuit breaker is reclosed. When the circuit breaker receives the closing order, the closing resistor is put in advance and the circuit is turned on. About 10ms, the main contact of the circuit breaker is closed, the closing resistor is separated and used, and the circuit breaker is closed. If the closing resistance is damaged, the main contact of the circuit breaker will be directly closed, which will cause the operating overvoltage generated when the circuit breaker is reclosed, which will damage the operation of the equipment.

At present, the commonly used measurement method is to add a voltage source and a resistor at both ends of the circuit breaker, and record the change of the measured voltage during the closing process through the oscillograph, and directly calculate the resistance value of the closing resistor through the data analysis software. Determine the operating state of the short-circuiting closing resistor, and check whether the closing resistor resistance and input time meet the design requirements.