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Phase loss protection of three-phase asynchronous motor
Release time:
2024-07-05
At present, most motor phase protection circuits adopt microcomputer protection or electronic protection devices, which have many components, complex circuits and low reliability. When problems occur, they often lose their protection function or fail, resulting in motor protection rejection or failure to shut down, which adversely affects production. The protection device introduced in this paper has the characteristics of simple principle, few parts, reliable operation and small maintenance. With proper component configuration, it can act as a reactive power compensation.
九洲封头
Basic principles:
At present, most motor phase protection circuits adopt microcomputer protection or electronic protection devices, which have many components, complex circuits and low reliability. When problems occur, they often lose their protection function or fail, resulting in motor protection rejection or failure to shut down, which adversely affects production. The protection device introduced in this paper has the characteristics of simple principle, few parts, reliable operation and small maintenance. With proper component configuration, it can act as a reactive power compensation.
The principle of the protection device is: the neutral point of the three-phase star connection, the potential of the three-phase load balance is very low, which is basically equivalent to the ground potential. When the three-phase power supply is out of phase, the neutral point potential will rise to the phase voltage. Using this characteristic, the power supply situation of the power supply is monitored, and the phase difference protection is played.
Wiring instructions:
The three capacitors are connected in a star shape, the capacitor terminals are respectively connected to the three-phase power supply A,B and C, the neutral point is connected to the voltage relay coil, and the other end of the coil is grounded. The normal and closed contacts of the voltage relay shall be connected in series with the control circuit of the AC contactor. When any phase A,B and C is disconnected, the neutral point potential rises to the phase voltage, and the voltage relay is used to open the control circuit of the AC contactor and cut off the power supply of the motor. In this circuit, the capacity of the capacitor does not need to be too large, and the withstand voltage level is mainly sufficient. When selecting the withstand voltage value, pay attention to the peak value of the AC voltage and consider the coefficient to leave room for it. If the power factor of the motor is low, when selecting the capacitor capacity, the appropriate capacitor value can be selected in combination with the power and power factor of the motor, so that the protection device can also play the role of reactive power compensation. The choice of voltage relay mainly considers that its setting range can meet the actual voltage requirements.
The above is mainly to consider the low-voltage motor. For high-voltage motors, they are generally large-scale equipment, and their protection devices are relatively complete, which will not be repeated here.
This protection device is simple and easy to operate, and is suitable for various three-phase induction motors and other occasions that require phase gap protection. The installation can be installed directly with the control circuit, basically does not take up space, but to ensure a safe distance.
In addition, the alarm device can also be installed on the normally open contact of the voltage relay for convenient operation and management. This problem involves specific control loops and practical applications and will not be discussed here.
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