# How does a VFD limit current?

## How does a VFD limit current?

The maximum current you set on a VFD is the current “limit”. When you hit that limit the voltage will droop (foldback) to prevent more current being drawn and the motor rapidly overheating.

The equation to calculate this is: The actual frequency divided by the potential frequency = X divided by the RPM on the machine nameplate….To reiterate, to calculate the RPM of a VFD, you need:

1. The number on the VFD’s control panel.
2. The standard cycle frequency.
3. The RPM on the motor nameplate.

How is VFD power ratio calculated?

Variable speed AC drives will maintain a constant volts/hertz relationship from 0 – 60 Hertz. For a 460 motor this ratio is 7.6 volts/Hz. To calculate this ratio divide the motor voltage by 60 Hz. At low frequencies the volt- age will be low, as the frequency increases the voltage will increase.

### How does a VFD limit inrush current?

VFDs deliver much higher frequency source power during startup to reduce current due to the increased inductive impedance. This can be advantageous if control is desired after full speed is reached. This control allows for continuing control as the load on the motor is changing.

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What is starting current of VFD?

“Starting Current” is that current which is required by any motor to first start it. When you connect the motor to the power supply, it usually takes a lot of amount of current to start, usually 4 to 6 times the normal operating current.

What is the maximum frequency of VFD?

In Constant Horsepower Area – VFD delivers motor nameplate rated voltage from 60 Hertz to 120 hertz (or drive maximum). Motor horse- power is constant in this range but motor torque is reduced as frequency increases.

## Does VFD have inrush current?

Variable Frequency Drives (VFD) VFDs are a type of power conversion equipment that converts utility supply into variable voltage and frequency (speed). One of the benefits of a VFD is that the inrush current never exceeds the motor FLC.