At present, the neutral point of the power supply in China's distribution system is generally not directly grounded. Therefore, when a single-phase ground fault occurs on a line, the current flowing through the fault point is actually the capacitive current generated by the line-to-ground capacitance.
According to statistics, a large proportion of faults in distribution networks are caused by the inability to self-extinguish the arc due to excessive capacitance during single-phase ground faults. Therefore, China's power regulations stipulate that when the capacitive current of 10kV and 35kV systems exceeds 30A and 10A respectively, arc suppression coils should be installed to compensate for the capacitive current. This requires measuring the capacitive current of the distribution network to make decisions.
In addition, the coordination of the line-to-ground capacitance and PT parameters in the distribution network can cause PT ferromagnetic resonance overvoltage. To verify whether PT resonance will occur in the distribution system and what kind of resonance it is, it is also necessary to accurately measure the line-to-ground capacitance value of the distribution network.
Traditional methods for measuring the capacitive current of distribution networks include the direct method of single-phase metal grounding and the indirect method of adding external capacitance. These methods all require contact with primary equipment, thus posing test hazards, complex operations, and low work efficiency.
The YTC750 automatic capacitance current tester measures the capacitive current of the distribution network directly from the secondary side of the PT. Compared with traditional test methods, this instrument does not need to interact with the primary side, so there is no test hazard, no need for complex safety measures, and no need to wait for lengthy dispatching commands. Simply connect the measurement line to the open delta terminal of the PT to measure the capacitive current data.
Since a weak heterodyne test signal is injected from the open delta of the PT, it neither affects the relay protection nor the PT itself, and it avoids the 50Hz power frequency interference signal. At the same time, the output terminal of the tester can withstand 100V AC voltage. If a single-phase ground fault occurs in the system during measurement, it will not damage the PT or the tester, so no special safety measures are required, making this work safe, simple, and fast, with accurate, stable, and reliable test results.
This tester features a large-screen LCD display, Chinese menu, and is very easy to operate. It is small in size, light in weight, and convenient to carry for outdoor operations. The wiring is simple, the test speed is fast, and the data accuracy is high, greatly reducing the labor intensity of test personnel and improving work efficiency.
Common Faults
Fault Phenomenon | Fault Cause and Solution |
No display on the screen after power-on | 1. Poor contact of AC220V power supply 2. Power fuse damaged |
During measurement, the voltage and current waveforms are extremely unstable, and the test results vary greatly | 1. Check whether the open delta voltage of the PT is greater than 5V 2. Check whether the test line is well connected |
