I have problem with two 230/460v 15 kw 30hp (56amps) pumps. The service is 208/120Y 3 phase and the two pumps are 230v 3 phase. I installed a 75kva transformer to step up the voltage to 230v, and two VFD's to control the pumps and amperage draw. The transformer I got was an Acme transformer (TP-53364-4S) which I backfed and didn't not ground the XO terminal. One pump motor that was rebuilt recently burned up which may have been due to the bearings that wern't replaced. The VFD's have 230-234 volts on line and load sides. The amperage which should be 56amps per VFD is going waaay down to around 28 amps when both pumps are running at the same time. They are set up for lead lag and usualy don't run together. My question is why would the ampacity drop down to half with both pumps running? The tech said that the voltage isn't changing when they are on together.
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