Motor protector to fault signal sampling method - Database & Sql Blog Articles

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1) Sampling of overload and short circuit fault signals. The overload and short-circuit faults in the starting operation of the motor are reflected in the abnormally increasing current value flowing through the winding of the motor. Generally, the motor protector circuit uses three current transformers to sample the running current signal, and the sampling signal is compared with the current reference signal. Compare, judge whether it is in the overload or short-circuit fault state, and output the stop signal when the fault occurs. The circuit collects and processes the analog voltage signal—the current signal output by the current transformer is converted into a signal voltage through the load resistor, and is sent to the voltage comparator circuit to obtain the fault signal output.

When the sampling of the single-phase short-circuit fault signal is generated, it can be obtained by the zero-sequence current transformer, and the principle is the same as the leakage safety device. Or sample the motor casing voltage to obtain the leakage signal.

2) Sampling of the phase failure fault signal. As mentioned above, the phase failure of the motor is manifested as different faults such as power phase loss, motor cable disconnection, and motor winding open circuit. If the method of sampling the three-phase power supply voltage is used, only the power phase loss fault can be protected. The completion of the detection of the latter two phase failures is not a method. The fundamental method is to use the method of sampling the three-phase current to judge the phase loss fault, and can accurately respond to the three phase failure faults, take corresponding technical measures, and make judgments on the three-phase current imbalance.

Generally, the judgment of the phase loss operation is not focused on the magnitude of the current signal amplitude, but on the presence or absence of the three-phase current signal, and comparing the presence or absence of the three-phase current signal to obtain a phase failure fault signal. Therefore, the current detection signal is usually processed into a digital signal, and a phase failure fault protection signal is obtained through a logic operation.