How does a VFD calculate torque?
A VFD cannot increase the voltage above its supply voltage. This causes the current to decrease as frequency increases, thus decreasing the available torque. Theoretically, torque is reduced by the ratio of the base speed divided by the higher speed (60 hertz / 90 hertz = 67%).
How does VFD control motor torque?
When the speed of an AC motor is controlled by a VFD, HP or torque will change depending on the change in frequency. At 60 hertz (base motor speed), both HP and torque are at 100 percent. When the VFD reduces frequency and motor speed, it also reduces voltage to keep the volts/hertz ratio constant.
What is Torque Control in VFD?
Torque control mode allows for the VFD to directly control motor torque instead of motor speed. This is necessary for any application where torque takes priority over speed. Winder, rewinders, capping, and web applications are some good examples of when torque control is utilized.
Does a VFD provide constant torque?
Constant torque is achieved because the VFD is increasing the voltage to the motor as it increases the speed. This relationship keeps the current and torque to the motor relatively constant. Typical applications are: Traction Drives, Compressors, Conveyors, Mixers, and Hoists.
What should the constant torque be on a VFD?
Check with the manufacturer. A 2:1 constant-torque duty rating (in your case, 25-50Hz speed range) is not unusual for inverter-duty motors, and if you’re not using an inverter-duty motor, you should be. If (as others have also noted) your load does not require 100% torque at reduced speed, heating may not be an issue.
What is the efficiency of a VFD motor?
As mentioned previously, the efficiency of a motor will change when operated at reduced speed or torque. Figure 6.4 shows typical efficiency/speed curves for a VFD-driven, high-efficiency-type motor with a nominal efficiency of 95 percent at different percentage torque loads (T/Tn) and speeds.
What is the RPM of a gohz VFD?
RPM of the motor is 2800 / 3360 at 50 / 60 Hz. It is now running on 50 Hz. I need a RPM of 1400 to 1500 which means I will need to run the motor on 25 Hz which is not a problem with the GoHz VFD. But how much does it affect the motor torque?
How are VFDs used in variable speed pumps?
Motor efficiency versus speed (nominal 95% efficient motor) (Courtesy of Hydraulic Institute) For more information on applying VFDs to pump motors, refer to HI’s newly published Application Guideline for Variable Speed Pumping at www.pumps.org.