What are the hazards of shaft current to the operation of variable frequency motors?

Update:19 Oct 2020
Summary:

The motor is one of the most common machinery. It is a […]

The motor is one of the most common machinery. It is a device that converts electromagnetic energy into mechanical energy. It is widely used in various fields. During the energy conversion process of the motor, some simple and complex factors may cause the motor to change to varying degrees. Shaft currents, especially high-power variable-frequency motors, high-voltage variable-frequency motors and ordinary variable-frequency motors, sometimes cause the bearing of the variable-frequency motor to burn out due to the shaft current.

The necessary conditions for generating current are voltage and closed loop. To eliminate the shaft current, from a theoretical perspective, one measure is to control or eliminate the shaft voltage, and the other is to cut off the closed loop; in actual production, different motor manufacturers , According to different operating conditions, the measures taken are not the same. According to the way of cutting off the circuit, use insulated bearing sleeves, insulated end covers, insulated bearings, or measures to insulate the bearing position.

In order to fundamentally reduce the hazard of shaft current, the rationality of the motor design plan of the variable frequency motor manufacturer and the conformity of the manufacturing process to the design are very necessary. The design plan and the lean control of the process manufacturing are more economical and more economical than the various later measures reliable.

Do variable frequency motors need to install an encoder?

Does the variable frequency motor need to install an encoder? This is not necessary. If you need to measure the actual speed of the motor or control the motor for positioning operation, you must install an encoder to detect the position of the motor in real time, and the motor does not need it here It must be a variable frequency motor, so how does the encoder detect the position signal?

The encoder is generally installed on the motor shaft or the shaft of the reducer to rotate synchronously with the motor, so that we can detect the angle signal of the motor's rotation, and control whether it is speed measurement or positioning. We can convert the rotation signal into a linear position movement signal to achieve positioning. For example, the motor drives the screw rod to rotate. The screw thread pitch is 8mm and the encoder resolution is 1000p/r. Then the signal corresponding to one pulse of the encoder is 0.008mm, the encoder is connected to the plc to output pulses, and the plc counts and converts into a specific position signal, so that the encoder can feedback the position of the motor movement in real time to realize positioning control. If it is speed measurement, it is also converted into the motor speed (r/min) according to the pulse frequency.

The encoder is a pulse detection device. If you need to get the rotation signal of the motor, you can add an encoder. Whether it is a normal motor or a variable frequency motor, you can add it for positioning or speed measurement. The variable frequency motor with an encoder can achieve a servo motor-like Function, can not only adjust speed, but also feedback position information.

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