Special Secondary Transformer Voltage Requirements
Special Secondary Transformer Voltage Requirements
(OP)
We will be installing a specially designed motor that will require a minumum of 460 VAC at the motor terminals. The motor will be controlled by a Variable Frequency Drive. When calculating the volatge drops due to motor leads, supply cable and VFD losses, we need 525 VAC at the line side input of the VFD. Our substation will have a 13.8KV to 480V transformer for the operation of other equipment. Any suggestions on the best way to meet the voltage requirements for the VFD and motor?






RE: Special Secondary Transformer Voltage Requirements
RE: Special Secondary Transformer Voltage Requirements
ANSI C84.1 voltage range is typically 440-504 volts. Pardon my saying, but someone screwed up designing [and consequently buying] equipment that required anything outside of this fairly pervasive standard.
RE: Special Secondary Transformer Voltage Requirements
RE: Special Secondary Transformer Voltage Requirements
RE: Special Secondary Transformer Voltage Requirements
Re "Loss through the VFD is 8%": What is your point by that statement? Do you think this will somehow affect voltage drop? The VFD should actually correct voltage drop to some extent, particularly if the VFD is located near the motor. The voltage going into the VFD has very little to do with the voltage out of it.
If you do in fact have a voltage drop problem (and it's not at all clear that you really do), it would not seem that it would take anything more sophisticated than an oversized feeder conductor or adjustment of transformer tap settings to correct.
RE: Special Secondary Transformer Voltage Requirements
RE: Special Secondary Transformer Voltage Requirements
http://www.actechdrives.com
for MCH Series Installation and Operation Manual,
page 9, MH Series Rating
indicates:
Input Voltage (400/480 VAC, 50-60Hz)
Output Voltage (0-400/460 VAC)
(at nominal current Amps and power kVA)
Therefore, the drive located at the motor will provide 460V output.
The drive input is supposed to have 480V. If the voltage on the drive input is too low, an autotransformer at the drive input may be needed.
RE: Special Secondary Transformer Voltage Requirements
Typically, a solid-state VFD rectifies to DC and then reinverts to AC. The AC output is generated at the VFD and therefore the term "voltage drop through the VFD" is rather meaningless. In fact, many VFD's can and will output a higher voltage than they are receiving (particularly in overspeed applications). They are actually very similar to UPS systems without the batteries. There should be no 38-volt drop across the VFD unless it was programmed to do so.
Do you have this kind of VFD or something else?