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Home > Industry Information > Three-phase motor phase loss protection

Three-phase motor phase loss protection

2021-05-23

With the rapid development of the economy, the industrialization of social production has been further enhanced, and the application of electric motors in industrial and agricultural production has become more widespread. Especially three-phase motors, due to their large power, stable operation, simple control, easy to use, have been widely used in factories and enterprises. Almost all the driving devices, especially the loads of pumps and fans, are inseparable from the motors, and the requirements for the motors are also getting higher and higher. 1 The purpose of setting the protection In the operation of the three-phase motor, due to various reasons, such as one-phase Fuse of the three-phase power supply is blown, or the contacts of the contactor are burned, causing a bad contact, or caused by installation and maintenance. Phase disconnection will cause the three-phase motor to run out of phase. If it is found that it is not timely, the motor will be burned for a long time, resulting in 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, it can stop the operation of the motor in the event of a missing phase operation, and avoid the motor burn accident. Generally, important motors are equipped with various protection devices, especially the lack of phase protection. 2 Basic Principles Most of the current motor phase loss protection circuits use microcomputer protection or electronic protection devices, which have many components, complex circuits, and low reliability. When problems occur, they often lose their protective effect or work abnormally, resulting in motor protection rejection. If it cannot be closed, it will have an adverse effect on production. The protection device described in this article has the advantages of simple principle, few components, reliable operation, and basically no maintenance. And through the appropriate configuration of components, can play a role in reactive power compensation. The principle of this protection device is: the neutral point of the three-phase star wiring, the potential is very low when the three-phase load is balanced, and is basically equivalent to the ground potential. When the three-phase power supply loses phase, the neutral point potential rises to the phase voltage. Utilize this characteristic, carry on the monitoring to the power supply situation of the power, thus play the role of lack of protection. 3 Wiring instructions The three capacitors are connected in a star shape. The capacitor terminals are connected to A, B and C three-phase power supply respectively. The neutral point is connected to the coil of the voltage relay. The other end of the coil is grounded. The normally closed contact of the voltage relay should be connected in series with the control circuit of the AC contactor. When one of the phases A, B and C is disconnected, the potential of the neutral point rises to the phase voltage, and the voltage relay operates to disconnect the control circuit of the AC contactor and cut off the power of the motor. The capacitor capacity in this circuit does not have to be selected too large, mainly because the withstand voltage level is sufficient. When selecting the withstand voltage value, it should be noted that because the voltage is AC voltage, the peak value needs to be taken into consideration, and a factor is taken into consideration to leave room for it. If the power factor of the motor is low, a suitable capacitance value can be selected in combination with the power and power factor of the motor when selecting the capacity of the capacitor so that the protection device can simultaneously perform reactive power compensation. The choice of voltage relay mainly considers that its setting range can meet the actual highest voltage requirement. The above is mainly for low voltage motor considerations. For high-voltage motors, generally belong to large-scale equipment, and its protection device is relatively complete, so it will not be repeated here. This kind of protection device has simple wiring and is easy to implement. It is suitable for all kinds of three-phase induction motors and other places where phase protection is needed. When installed, it can be directly installed together with the control circuit. Basically it does not take up space, but it must be ensured a safe distance. In addition, it is also possible to use the normally open contacts of the voltage relay to install an alarm device as required to facilitate operation and management. About this problem involves the concrete control loop and the actual application situation, will not discuss here.
Y series 3-phase cast iron housing induction motor

Y series motor is totally enclosed and fan cooled three phase squirrel cage induction motor. It is newly designed in conformity with the relevant rules of IEC&DIN42673 standards. The Y connection for motor of 3kw and below. And delta connection for 4kw and above.

Application:

Y series motors are widely used in places where there doesn't exist combustible, explosive or corrosive gas, and without any special requirements, such as machine tools, pumps, fans, transport machinery, mixer, agriculture machinery and food machines, etc.

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