Hi. I am an indrustrial electrical service technician and was hoping someone here could help me with a question I have.

Just now I attended a job where a 7.5KW ABB Drive was the problem.

Input amps were 23-24A Per phase, Output was 14-15 A Per phase.

Because of the high current draw on the load side of the Drive, it was tripping the upstream TOL.
I was wondering why this happened ? Where are the extra Amps going to?

I am 99% sure the problem is something stuck in the pipe system as I can hear a lot of cavitation noise when it ramps up to full power (50Hz)

 

Are you absolutely sure of those numbers? Typically, the input amps are LESS than the output amps on a VFD. How are you reading current? A cheap meter on a VFD will not give you accurate readings. The harmonic content distorts the meter's reading unless the meter has some sophisticated filtering algorithms in it, and you don't often see that capability in meters that cost less than a month's pay...

Why do you have a TOL upstream of the VFD? Most TOLs also have difficulty with the high harmonics in a VFD circuit and will nuisance trip because the harmonics cause additional heating in the sensing elements.

Cavitation is a very dangerous thing in pumps and can destroy it in short order. Are you running the pump to full speed against a closed head? Because otherwise, if the pump was designed right, there should be no cavitation.

 

I am absolutely sure. This is why I posted in here. The input amps were read via my Fluke 376. The upstream TOL was set to 16 A and it was tripping.

The 15A downstream was taken from the VFD panel and also my meter, They matched.

Can you provide some documentation so I can read about harmonics?