Secondary 480-240 Delta-Delta voltages

[radioperson]

Hi!

I have an application whereby I'm using a 3-phase 480-240 transformer to power a Variable Frequency Drive (VFD) for an AC motor, using the secondary 3-phase 240 VAC of the transformer for the Drive's power connection. However, since the secondary of the transformer is connected as Delta, I'm not only seeing 240 volts AC phase-to-phase, but also voltages of 100, 150 and 170 from each phase of the secondary to the ground connection of the VFD. Should I be concerned of these phase-to-ground voltages, or will the VFD just be looking at the 240 volt potential between each of the phases? Thanks!

Bill K.

 

[ScottyUK]

If the delta is ungrounded then the voltages you measure to ground are meaningless because they are as a result of the interaction of your meter and whatever stray capacitances are present. The drive will work with 240V between phases.

However! General wisdom is to avoid running drives on ungrounded sources. Most are designed for use on a solidly grounded supply; unpredictable and generally bad things can happen when used on other supplies. See what the drive manual says about supply characteristics, or call the OEM tech support.


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