Home » FAQ » Is a Contactor Required between VFD and Motor?

Is a Contactor Required between VFD and Motor?

1. When a VFD controls a motor and does not need to switch between the power supply, an output contactor is not needed to be connected between the variable frequency drive and motor. The main reason is that: if an output contactor is connected, the motor may be started directly when the output frequency of VFD is high. As a result, a large starting current would be generated, which may lead to trip of VFD.

2. The output contactor has to be connected in following two cases.
  • When a VFD controls several motors, each motor shall have an independent controlling contactor, as shown in figure a.
  • Switch between variable frequency and power frequency. When the motor is connected to the power frequency power supply, it must disconnect from the VFD. So the contactor is necessary between the motor and VFD, as shown in figure b. 


Similar to output contactor, when a VFD controls only one motor and doesn’t need to switch with a power frequency, there’s no need to connect the thermal relay as the VFD has thermal protection function itself. However, when a VFD connects with several motors, the capacity of each motor is much smaller than that of VFD, VFD can’t provide thermal protection for each motor. On this basis, each motor can only be protected by its own thermal relay. When the motor needs to be switched between variable frequency and power frequency, as the VFD can’t provide thermal protection for motor when running at power frequency, the thermal relay is necessary.

Post a Comment:

    
Plz Calculate (8 * 1) =
(Your comment will show after approved.)

You may also like:


Variable Frequency Drives
Sales Email info@variablefrequencydrive.net



Featured Articles
Variable Frequency Drive for Fans Variable Frequency Drive for FansFan is a kind of machine that compresses and conveys gas. If the pressure of exhausted air is quite low, the fan plays a role of ...
Variable Frequency Drive for Food ... Variable Frequency Drive for Food ConveyorNowadays the food machinery industry has been rapidly developed. As the motor drive, variable frequency drive will change the ...
Can I Run a 60Hz Motor on 50Hz by ... Can I Run a 60Hz Motor on 50Hz by Using a VFD?We are often asked “can the motor with a rated frequency of 60Hz operate at 50Hz (vice versa)?” When the motor is operated at a ...
How Does Variable Frequency Drive ... The rotating speed of inductor type AC motor (hereinafter referred to as motor) is determined by the number of pole and ...
What is a Variable Frequency Drive What is a Variable Frequency DriveVariable frequency drive (VFD) is an adjustable speed drive used for motor drive system, control the speed and torque of the AC ...