The DC resistance of each circuit of the circuit breaker includes the resistance of the bushing conductor, the contact resistance between the conductor pole and the contact, and the contact resistance between the contact and the contact. This is actually a measure of the contact resistance of moving and static contacts.
Operating circuit breaker contact resistance increases, the contact will make the normal operating current overheating, especially when the short-circuit current through the fault, the contact may cause local overheating, in severe cases may burn the surrounding insulation and cause contact melting Bonding, thus affecting the tripping time and breaking capacity of the circuit breaker, and even refuse to move. Therefore, the installation of circuit breakers, the size of repair and cover up the fault current after 3 times, are required for this test.
experiment method
Resistors for each phase of the circuit breakers shall be measured between the ends of each of the two bushing tubes under DC voltage. The measurement method is the same as the normal DC resistance measurement method, that is, the bridge method or the voltage drop method can be used.
Precautions
In addition to the general considerations for DC resistance measurement, observe the following characteristics of the circuit-breaker:
(1) Since the DC resistance of the conductive circuit of each phase of the circuit breaker is very small, it is generally measured in micro-ohms. Therefore, when using the bridge method to measure, the double-arm bridge must be used. When measuring with the voltage drop method, Enough capacity DC power supply, while selecting the appropriate millivoltmeter and ammeter.
(2) During the test, special attention must be paid to eliminate the influence of the measuring lead and the resistance of the joint. The lead should have enough cross-sectional area, and should be as short as possible. The current and voltage lead joints must be strictly separated.
(3) The circuit breaker should be tripped several times before the measurement. If it is a circuit breaker with electric closing, it should be measured after the electric closing.
(4) In order to protect the measuring instrument, in the measuring process, the circuit breaker tripping mechanism should be stuck to prevent sudden tripping in the test, damage to the instrument.
(5) Measure at least 3 times per phase, whichever is the average, and if there is any suspicion about the measurement result, test several times.
Analysis of the results to determine
Circuit breaker each phase conductive circuit DC resistance measurement results should be consistent with the provisions of the manufacturer.
The measured results compared with the previous results, if more than doubled, the contacts should be checked; when the difference between the three phases, it should attract attention, you must double-check for processing. If the measurement results exceed the manufacturer's standard, the breaker can be tripped once and re-measured. If it is still too large, the cause should be identified and dealt with.
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