Phase sensitive short circuit protection for wire and cable equipment
Time of issue:
2020-01-07
The basic starting point of phase sensitive short circuit protection for wire and cable equipment is to detect not only the line current of wire and cable equipment, but also the impedance angle change of short circuit circuit circuit of wire and cable equipment
The basic starting point of phase sensitive short circuit protection for wire and cable equipment is to detect not only the line current of wire and cable equipment, but also the impedance angle change of short circuit circuit circuit of wire and cable equipment. Generally speaking, the power factor of the motor is lower when it starts, but higher when it is short circuited. Based on this, the starting current and short circuit current can be distinguished by detecting the phase angle of current lag voltage. However, when the motor is located at the secondary outlet side of the transformer, or the power supply cable is short, it is difficult to distinguish the starting current from the short-circuit current from the phase angle. Therefore, the phase sensitive short-circuit protection can not protect the short-circuit fault at the outlet of the transformer, and there is a certain "dead zone".
In addition, whether the motor starts or short-circuit fault occurs, the line current of wire and cable equipment has to go through the transition process. The current waveform is not a sine function, so it is difficult to detect the phase angle. Therefore, phase sensitive short-circuit protection generally has delay, which is inconsistent with the principle of fast sampling, so it can not be used for fast short-circuit detection and protection.
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