Phase failure protection of the hottest three-phas

Lack of phase protection of three-phase motor

Abstract: in the operation of three-phase motor, due to various reasons, such as the fuse of three-phase power supply is blown, or the contact of contactor is burned, resulting in poor contact of one phase, or the disconnection of one phase due to installation and maintenance, it will cause the lack of phase operation of three-phase motor. If it is not found in time, the motor will be burned for a long time, causing equipment damage, affecting the continuity of production, and causing heavy losses to industrial and agricultural production

key words: three phase motor phase loss protection Untitled Document with the rapid development of economy and the further enhancement of the industrialization of social production, motors are more and more widely used in industrial and agricultural production. Especially three-phase motor, because of its large power, stable operation, simple control, easy to use, has been widely used in factories and enterprises. Almost all drag devices, especially pumps and fans, must meet the requirements of a] and b] as much as possible, and they are inseparable from the motor. When the tensile curve of the motor reaches the peak e, the requirements are becoming higher and higher. 1. The purpose of setting protection is that during the operation of three-phase motor, due to various reasons, such as one phase of fuse of three-phase power supply is blown, or the contact of contactor is burnt out, resulting in poor contact of one phase, or one phase disconnection caused by installation and maintenance, the three-phase motor will run without phase. If it is not found in time, it will burn the motor with high accuracy for a long time, causing equipment damage, affecting the continuity of production, and causing heavy losses to industrial and agricultural production. In order to ensure the safe operation of the motor, so that it can stop the operation of the motor in time in case of phase failure, and avoid the motor burning accident, generally important motors are equipped with various protective devices, especially phase failure protection. 2 basic principle at present, most of the motor phase loss protection circuits adopt microcomputer protection or electronic protection devices, with many components, complex lines and low working reliability. When problems occur, they often lose the protection function, or work abnormally, resulting in motor protection failure or failure to switch on, which has an adverse impact on production. The protection device introduced in this paper has the characteristics of simple principle, few components, reliable operation and basically no maintenance. And through the appropriate configuration of components, it can play the role of reactive power compensation. The principle of the protection device is: the neutral point of three-phase star connection, when the three-phase load is balanced, the potential is very low, which is basically equivalent to the ground potential. When the three-phase power supply lacks phase, the neutral point potential will rise to the phase voltage. Using this feature, the power supply of the power supply is monitored, so as to play the role of phase failure protection. 3 wiring Description: the three capacitors are connected into a star, the capacitor terminals are connected to three-phase power supplies a, B and C respectively, the neutral point is connected to the coil of the voltage relay, and the other end of the coil is grounded. The normally closed contact of voltage relay shall be connected in series with the control circuit of AC contactor. When any phase a, B and C is disconnected, the neutral point potential rises to phase voltage, and the voltage relay acts to disconnect the control circuit of the AC contactor and cut off the motor power supply. The proportion of capacitor renewable energy in this circuit is also increasing. The capacitor capacity does not need to be too large, but the withstand voltage level is sufficient. When selecting the withstand voltage value, it should be noted that since the voltage is AC voltage, its peak value and a coefficient should be considered to leave room. If the power factor of the motor is low, the appropriate capacitance value can be selected in combination with the power and power factor of the motor when selecting the capacitor capacity, so that the protection device can play the role of reactive power compensation at the same time. The selection of voltage relay mainly considers that its setting range can meet the requirements of the actual maximum voltage. The above is mainly considered for low-voltage motors. For high-voltage motors, they are generally large-scale equipment, and their protection devices are relatively perfect, which will not be repeated here. The protection device has simple wiring and is easy to realize. It is suitable for all kinds of three-phase induction motors and other places that need phase failure protection. When installing, it can be installed directly with the control circuit, which basically does not occupy space, but it should ensure a safe distance. In addition, the normally open contact of the voltage relay can also be used to install an alarm device according to needs, which is convenient for operation and management. This problem involves specific control loops and practical applications, which will not be discussed here