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Disadvantages in the test of DC resistance tester

time:2020/12/5   source:华天电力  reading:273 time

Disadvantages in the field test of the DC resistance tester:


1. Problems with existing test methods of DC resistance tester


The DC resistance tester designed according to the conventional design principle found that there is a common problem during field testing: when the tester's voltage wiring DC has poor contact or open circuit, the tester will also display a value, and the following will appear at this time Happening:


(1) The voltage DC is open and there is no strong electric field interference at the test site. In this case, since the differential mode voltage input by the amplifier is basically 0, the test value displayed by the instrument is close to 0. If the tester has sufficient field test experience, It can be judged that the instrument voltage DC test line is abnormal. After the instrument voltage DC test line abnormality is eliminated, the correct test result can be obtained; if the tester does not have sufficient field test experience, it may misjudge that the tester has a problem and interrupt the test , Replace or repair the instrument, delay the power outage time, and bring unnecessary trouble to the test work.


Transformer DC Winding Resistance Tester.png


(2) The voltage and DC contact is poor. In most cases, the wiring terminals of the circuit breaker will have an oxide film or oil film on the outer surface of the terminal block after long-term operation. It may be possible when the voltage test clamp of the DC resistance meter is connected to such a terminal block. In case of poor contact, both the voltage test line clamp itself will also produce a certain contact resistance. When the contact resistance reaches the value equivalent to the internal resistance of the voltage sampling DC, it will have a serious impact on the test results.


(3) The voltage DC is open circuit or poor contact (the contact resistance R1 is infinite when the circuit is open), and there is strong electromagnetic interference at the test site, such as the bus bar is charged. At this time, the charged bus bar passes through the capacitor with air as the medium and interferes with the two parts of the tester. A voltage test line, due to interference, makes a differential mode voltage appear at both ends of the DC tester's voltage collection line. The DC resistance fast tester has high regulation stability, full-scale smooth voltage regulation, and the output voltage regulation adopts imported single multi-turn potentiometer, the boost process is stable, the regulation accuracy is high, and it is designed with coarse and fine adjustment functions. The voltage regulation is better than 0.1%, the voltage and current measurement error is less than 1.0%, and the pulsation factor is better than 0.5%. The DC resistance tester adopts new technologies, new materials and new devices in the 1990s. It has the characteristics of large output power, small size and light weight. It has reliable overvoltage, overcurrent and zero-position closing protection functions, with 0.75 times The voltage lock function is equipped with a time relay, which can set a timing sound alarm during the test. The PWM high-frequency pulse width modulation technology first applied by the transformer resistance tester, closed-loop adjustment, and large voltage feedback, greatly improve the voltage stability. Usable high-power IGBT devices and their driving technology, and according to the electromagnetic compatibility theory, adopt special shielding, isolation and grounding measures. The DC high voltage generator realizes high-quality, portable, and can withstand the rated voltage discharge without damaging the ring.


If the interference is large, the DC resistance tester will display a value much larger than the resistance value of the tested product. At this time, if the tester has enough field test experience, he may be able to judge the abnormality of the test result, which can attract attention and Get the correct test result. However, if the tester does not have sufficient experience, he may misjudge that the switch DC resistance value exceeds the standard, and may use the power outage repair method to deal with the defect, causing unnecessary losses to the power production.


If the intensity of the interference is not great, the value displayed by the instrument is just within the qualified resistance range of the circuit breaker, this situation and situation;


(2) Poor voltage and DC contact; the same result will be produced, which will also cause misjudgment.


2. The DC resistance tester uses an improved four-wire measurement method to solve the above problems.


Based on the analysis of the above problems, the DC resistance tester proposes an improved four-wire measurement method. It uses power supply technology to continuously output large currents for a long time, overcomes the shortcomings of pulsed power supply transient currents, and can effectively break down switch contact oxidation The membrane solves the problems existing in the current traditional DC resistance tester.


The test sample is energized through a high-current constant current source, and the voltage and current values are collected to calculate the resistance value of the sample. The value measured at this time must be the true


The real resistance value prevents the generation of false data. Even if there is strong electric field interference in the field, because the resistance in the voltage DC is very small, the voltage induced to the voltage test terminal is a common mode voltage. This product uses capacitor grounding to reduce the AC common mode interference to a very low level. The test accuracy has an impact.


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