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Dear sir's, pl advise, In a 100MVA, BHEL make Tx, found IR value between C-F , C-T is Zero, internal inspection was carried out no fault like shorting between core to frame & core to tank found, in this Tx. As pet design Frame & Tank is on same potential. After that a cable lead connected from...

Actually I have checked the trends of dc voltage vs current but when the discharge line is ok then everything remains constant but at times when their is minor fluctuations of rpm of motor say 30 rpm the current dips and dc voltage shoots up, I just want to know the reason of this rpm fluctuations.

it is a positive displacement(poston diaphragm pump) pump with pulsation dampners, so back pressure is probably being controlled, isn't it??

issue not yet resolved, the chocking in slurry line(discharge of the pd pump) resulted in repeated trippings due to dc overvoltage, but the pump is designed for max discharge pressure of 167 bar and the dc overvoltage occuring at any discharge pressure, the pump has 3 cylinders,I have changed...

Replaced the capacitor bank with new one but the problem still persists, can you give some light on how speed and current loop gain are calculated and the importance of these parameters in vfd...

The I/P voltage is 694V.

The capacitors are rated 1100V so the upper limit is set.

The drive is 7 years old and the issue for 3 drives (total installed qty. :06),the drive is houaed indoor in clean environment qith avg room temp. 26 degrees)

All speed signal and reference cable has been checked, and pd is piston diaphragm pump, one kind of positive displacement pump, How to nullify this regenerative effect in vfd, wihout connecting a braking resistor or chopper.

How to check capacitors(995mfarad) as on physical inspection those looks good and we have total of 6 such vfd, and problem is coming in three of them.

I am facing problem with my 690V,1500kw vfd unit which is 7 years old(make:Nelco),It is a 12 pulse rectifier unit driving a PD pump(Make:Geho) for dense slurry disposal with output pressure upto 160bar.It has functioned well till three months before the vfd started tripping on HV DC LINK BUS...