The selection of supporting equipment for cable fault testers should be based on the actual conditions of the unit. For units that mainly test high-voltage cables, in addition to the main unit requiring high reliability and stable performance, the configuration of accessories should follow the following principles. The relationship between the length of the cable under test and the capacitance configured: since the cable's own capacitance increases with the length of the cable, during high-voltage cable fault testing, the high-voltage capacitor plays a very important role. When the sphere gap discharges, the energy stored in the high-voltage energy storage capacitor will be transferred to the cable through the discharge process. The longer the cable, the larger the distributed capacitance, the stronger the cable's ability to absorb energy, and the lower the voltage reaching the fault point. When the voltage is lower than the discharge voltage at the fault point, the fault point cannot be broken down, and no effective discharge can occur, so the test point cannot collect the correct test waveform. The only way to improve this is to increase the energy of the storage capacitor. The general configuration requirement is: 1.5uf per kilometer. The withstand voltage of the capacitor should be greater than or equal to 30kV. Recommended configuration: 2uf/35kV pulse capacitor. For low-voltage cables (400V level), since the impulse voltage cannot exceed 10000V (commonly 5000-8000V), a capacitor of 8uf or larger capacity should be configured, and a withstand voltage of 15kV is sufficient.
Selection of high-voltage impulse transformer: For general testing, a 2kVA transformer is sufficient. For special faults, sometimes it is necessary to burn through the faulty cable, and in this case, a larger capacity power transformer with a protective operation box should be used for control. It is best to reach above 5KVA, but such situations are relatively rare. Users can choose according to actual conditions.
Regarding the integrated high-voltage test power supply, it is an integrated high-voltage impulse flash power supply designed to cooperate with cable fault testing. It can generally be divided into low-voltage type and high-voltage type. The low-voltage type is generally designed for testing cables below 6kV, with an output voltage between 10000-15000V, and is equipped with a larger pulse discharge capacitor inside the instrument. The high-voltage type is mainly designed for high-voltage cable testing, with an output voltage up to 35kV during fault testing, and is generally equipped with a capacitor of 1-2uf internally. The biggest advantage of the integrated test power supply is that it combines the high-voltage PT, capacitor, and control system into one unit, which has a series of advantages such as convenient operation, safety, and reliability, but it also has disadvantages such as heavy weight, inconvenient transportation, and small internal capacitor configuration. Therefore, users should decide based on actual conditions when selecting. Recommended configuration: for low-voltage cables, an integrated device can be chosen, while for high-voltage power supplies, it is best to choose loose parts for on-site wiring and use, which offers greater flexibility.
