Working principle of capacitance current tester

　　With the development of today's society, we use electricity all the time in our lives. Without electricity, we will lose light and power, so it is very important to detect the capacitance current. So what is the working principle of the capacitance current tester? Let's talk about it below.

　　Introduction of Capacitance Current Tester

　　At present, the neutral point of the power supply in my country's power distribution system is generally not directly grounded, so when the line is single-phase grounded, the current flowing through the fault point is actually the capacitive current generated by the line-to-ground capacitance. In addition, the combination of the distribution network's ground capacitance and the PT parameters will produce PT ferromagnetic resonance overvoltage. In order to verify whether the distribution system will have PT resonance and what kind of resonance will occur, the distribution network's ground capacitance value must also be accurately measured. Traditional methods for measuring distribution network capacitance current include the direct method of single-phase metal grounding and the indirect measurement method of added capacitance. These methods all require contact with primary equipment, and therefore have disadvantages such as test dangers, complicated operations, and low work efficiency.

　　Since a weak out-of-frequency test signal is injected from the PT opening triangle, it will not have any impact on the relay protection and the PT itself, and avoids the 50Hz power frequency interference signal. At the same time, the output end of the tester can withstand an AC voltage of 100V. If a single-phase grounding fault occurs in the system during measurement, the PT and the tester will not be damaged. Therefore, there is no need to take special safety measures, making this work safe, simple and fast, and the test results are accurate, stable and reliable.

　　Capacitance and current test principle

　　DJCI-H fully automatic capacitance current tester measures the capacitance current of the distribution network from the PT opening triangle side. Its measurement principle is shown in the figure.

　　A current of different frequency (non-50Hz AC current, in order to eliminate the interference of power frequency voltage) is injected from the PT open triangle, so that a current with a reduced transformation ratio is induced on the high-voltage side of the PT. This current is a zero-sequence current, that is, its magnitude and direction are the same in the three phases. Therefore, it cannot flow on both the power supply and load sides, and can only form a loop through the PT and the ground capacitance. The three-phase capacitance value 3CR0R can be measured by detecting the measurement signal, and then the capacitive current of the distribution network system is calculated according to the formula I=3ωCR0 RURφR (URφR is the phase voltage of the system under test).

　　At present, the capacitance and current testers widely used in the market are mainly based on two principles: the neutral point added capacitance method principle and the heterodyne power supply signal injection method principle.

　　The representative of the principle of the neutral point added capacitance method is Musen Electric's MS-500PZ fully automatic capacitance and current tester.

　　The MS-500PZ fully automatic capacitance current tester produced by Musen Electric takes samples from the neutral point of the system and measures the total capacitance of the system to the ground with the high-voltage capacitor in the instrument. Since it is measured from the primary side, the measurement result is accurate. It is particularly suitable for measuring the ground current during single-phase grounding faults in unbalanced neutral point non-effective grounding systems (6-35kV), meeting the measurement requirements of most substation lines.

　　The representative of the principle of the heterodyne power signal injection method is the MS-500P fully automatic capacitance and current tester.

　　The MS-500P fully automatic capacitance current tester measures the capacitance current of the distribution network directly from the secondary side of the PT. There is no need to deal with the primary side, so there is no danger in the test. The capacitance current data can be measured by simply connecting the measuring line to the open triangle end of the PT.

　　Since the weak out-of-frequency test signal is injected from the PT opening triangle, it will not have any impact on the relay protection and the PT itself, and avoids the 50Hz power frequency interference signal, making the test safe and accurate. It is particularly suitable for the grounding current measurement of the single-phase grounding fault in the balanced neutral point non-effective grounding system (6-35kV), meeting the measurement requirements of the new substation line, short line, and three-phase symmetrical system.

　　Through the above introduction, we have learned about the relevant content of the capacitor current tester. Only after testing with the capacitor current tester can we ensure the normal current and thus ensure the supply of electricity.