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Precautions for using loop resistance tester

time:2020/9/26   source:华天电力  reading:744 time

(1) The voltage loop of the loop resistance tester 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 it is an abnormal test line of the instrument voltage loop. If there is not enough field test experience, it may misjudge the tester’s problem. Interrupt the test and replace or repair the instrument. Delaying the time of power outage brings unnecessary trouble to the test work.

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(2) The voltage circuit contact of the loop resistance tester is poor. In most cases, the terminal of the circuit breaker will produce an oxide film or oil film on the outer surface of the terminal after long-term operation. When the loop resistance voltage test clamp is connected to such a terminal strip, it may produce bad contact, and even the voltage test clamp itself should produce a certain contact resistance. When the contact resistance is equal to the internal resistance of the voltage sampling circuit, the test result Will be severely affected.

(3) The voltage circuit of the loop resistance tester is open or poorly connected (the contact resistance R1 is infinite when it is open), and there is strong electromagnetic interference at the test site. For example, if the bus is charged, the charged bus passes through the air as the medium capacitor, which interferes with the two voltage test lines of the tester. Due to the interference, the differential mode voltage appears at both ends of the voltage collection line of the loop tester.

If the interference is large, the loop resistance tester will display a value much larger than the resistance value of the product under test. At this time, if the tester has sufficient field test experience, the abnormality of the test result can be judged. As a result, everyone’s attention was drawn and the correct test results were finally obtained. However, if the tester does not have enough experience, he may misjudge that the resistance of the switch circuit exceeds the standard, and may use power outage repair methods to deal with defects, causing unnecessary losses to power production. .

If the interference intensity is not great, the instrument indicates that the value is just within the range of the qualified resistance of the circuit breaker. This is the same as the result of "(2) Poor contact of voltage circuit", which can also lead to misjudgment.

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