Study on AC-Impact Superposition Voltage Test Platform Method

Author： GOZ Electric Time：2024-09-25 09:34:47 Read：22

The hidden dangers of internal insulation of high-voltage electrical equipment pose a serious threat to its safe and stable operation. On-site withstand voltage test is an important item in the on-site handover test procedures, including power frequency withstand voltage test and impulse withstand voltage test. With the large-scale construction and commissioning of ultra-high voltage and ultra-high voltage transmission lines in China in recent years, actual operation experience has found that electrical equipment that has passed the withstand voltage test still has insulation faults during operation, and electrical equipment that has passed the AC withstand voltage test has flashover during the impulse withstand voltage test.

Using impulse voltage test to diagnose insulation faults has always been a hot topic of research at home and abroad. Scholars have always hoped to not only obtain the overall insulation condition of the equipment, but also hope to find possible local insulation defects. In recent years, domestic and foreign scholars have conducted a large number of experimental studies and theoretical analyses on the local discharge characteristics of electrical equipment insulation materials under power frequency overvoltage or impulse overvoltage, and have achieved fruitful research results. In the past, the research on the partial discharge characteristics of high-voltage power equipment such as GIS, power transformers, power cables and their accessories mainly focused on the case where the electrical equipment was subjected to a single power frequency voltage or impulse voltage. There was little research on the partial discharge characteristics of electrical equipment under the action of AC superimposed impulse voltage. However, in addition to the normal power frequency AC voltage, the high-voltage electrical equipment in actual operation will inevitably be subjected to the action of operating overvoltage and lightning overvoltage. At this time, the insulation of the electrical equipment will be subjected to the combined action of the two voltages at the same time, which seriously threatens the insulation performance of the equipment. Through the above analysis and discussion, it can be seen that the study of the partial discharge characteristics of insulation defects of electrical equipment such as GIS, power transformers, power cables and their accessories under the action of AC superimposed impulse voltage has important practical engineering significance, and it is also of great significance for the insulation optimization of electrical equipment.

In order to study and analyze the partial discharge characteristics of insulation defects of electrical equipment under AC-impact superimposed voltage, a set of AC-impact superimposed voltage test platform with controllable superposition phase was designed in this paper. The voltage and current distribution of each device during the superposition of the two voltages was analyzed by theoretical calculation combined with circuit simulation. The type and parameters of the impulse voltage generator and the power frequency test transformer protection device were selected to avoid damage to the equipment during the superposition of the two voltages. A high-voltage ball gap synchronous trigger circuit is designed to control the high-voltage ball gap to conduct at any phase of the power frequency.

Test platform design

IEC 60060-1:2010 proposes that combined and synthetic voltages can be used for equipment insulation testing. Based on this, a method for applying AC superimposed impulse voltage is designed. The AC-impact superimposed voltage test platform designed in this paper is shown in Figure 1. It mainly consists of a 100kV impulse voltage generator, a 100kV/10kVA AC test system, protection devices, a measurement system, and a phase synchronization trigger device. The power frequency phase synchronization trigger can control the high-voltage ball gap to conduct at any phase of the power frequency, generating AC-operation impulse superimposed voltage and AC-lightning impulse superimposed voltage with fully controllable and adjustable superimposed phases, and the superimposition error is less than 5%. Reasonable protection device design effectively avoids damage to the test equipment during the superposition of the two voltages and ensures the reliability of the test platform. The effectiveness of the test platform designed in this paper is verified by simulation and experiment.

Figure 1

Conclusion

1) The AC-Impact Superposition Voltage Test Platform circuit was designed to realize the superposition of AC voltage and operating impulse voltage, and AC voltage and lightning impulse voltage.

2) Theoretical calculation and circuit simulation were combined to design the impulse voltage generator and AC test transformer protection circuit to avoid damage to the test device during the superposition of the two voltages.