Is it possible to run HT motor through LT VFD (LT VFD supply given to Transform

Is it possible to run HT motor through LT VFD (LT VFD supply given to Transformer LT side and transformer HT side connected to motor)

Question Posted / rp_amarlapudi

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Is it possible to run HT motor through LT VFD (LT VFD supply given to Transformer LT side and trans..

Answer / kingshuk dey

To start with, let's get our concepts correct. The motor supply comes from the VFD, which in turn is connected to the power supply from a board (or LT side of transformer, in your case).

Supply(TRF) --> VFD --> Motor

First off lets assume your VFD type is less than or equal to this LT supply. (LT/HT for TRF is subjective, Lt can be 220V when HT is 460V, or 460V when HT is 1000V etc). But a 460V VFD will burn its fuses if connected to 1000V.

Anyway, if you connect the VFD to LT side, and the motor is HT (meaning it's rated for a heavy current like 32KV), the motor will try to pull more and more current to start from the VFD, ultimately exceeding the current setting of the VFD and it will trip with an Overload or Overcurrent (OH, OC) fault on its display. If the current is enough to start the motor, it will rotate, but with very less speed (like if the motor is not connected to any load).

Just as a matter of interest, if you connect the LT side of TRF to VFD, and HT side of TRF to motor, "nothing" will happen as there is no current source (both VFD and motor are current consuming equipments) :P

Motor --> TRF HT -- TRF LT --> VFD (LOL!)

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