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Update: Drive OEM informed a 690 V drive cannot be used for 415 V input because of capacitor charging capability. Their recommendation is a 3-winding D/D-Y isolation transformer with 30 deg phase shift for 12 pulse firing for harmonics reduction. Or go for an AC to AC drive eliminating all...

Wye secondary with grounded neutral it is. I have an old 250 KVA trafo which I will rewind for 415 Delta and 690 V Wye with a 415 V tap.

Thanks, gr8. So it would be a delta/wye transformer? Any reason why the VFD input should be a wye? Bill. Yes, I had the same idea. 415/690-415 trafo. Since the drive is 690 V rated, I guess there is a better safety factor (in terms of voltage) when it is used in 415 V?

This week, we trialed a 125 KW VFD for testing LV motors in decoupled condition. During the trials, I noticed our LED lights started flickering even though they were switched off. When asked, the OEM drive guru said there will be harmonics fed into the system, and we need to install an...

Plenty of ingenuity in that era.

great info, System Protection and maparentau.

Thanks, Jeff. Forget PM synch motor, last week I asked to demo a 125 KW drive (reputed Japanese brand) for no-load testing of four normal cage motors with no-load currents varying from 90 to 250 Amps in my shop and the drive dealer team couldn't do it for any of them without the drive tripping...

Their so-called manual has more disclaimers and caveats than actual usage info. I wouldn't touch it even with a 20 ft pole.

I have a few Fluke and reputed Japanese make clamp meters of various current ratings. None of them is rated over 2000 V. Post more details and photos of your meter. As Bill asks, are you willing to risk your life with such a meter?

Stator core of that era will be hot rolled silicon steel with higher loss than the later day low loss cold rolled steel. So, core was most likely changed. I doubt the 300 RPM rotor can withstand centrifugal forces at 720 RPM, so possible new rotor, bearings and bearing supports. Stator winding...

"The rest of section 7.6.5 indicates that some hydro units remain online without excitation for long enough to manually restore the excitation system." Manually intervene is the key point here. If your machine ran for 15 minutes with no operator action, better to check the rotor health.

Now you get 1000 W in total.

IEEE 492 7.6.4 Asynchronous operation (field maintained) - (I have personally seen a 50 MW hydro machine completely destroyed in this operating condition) Operation of a generator out-of-synchronism with partial or full-field excitation maintained, places the most severe type of duty on the...

OP said 4 x 240 V x 1000 W heaters with 3 terminals suitable either for 240 V or 120 V. If there is another connection possible for both 240 V and 120 V, please post here. Yes, 62.5 W for each heater and 250 W in total. Which is what I find in large motors. It's enough to keep the motor warm.

jpts - I don't have the voltages in open loop and closed loop, only the currents. iop - It's embedded round PM rotor.

This is not an eddy current brake. It plain old fail-safe spring activated mechanical brake found in hoists.

V/Hz is set correctly in open loop. Drive is set for PM synch motor mode. In open loop, the motor had odd electromagnetic noises on top of high current. In closed loop, low current and smooth running. Guess, PM synch motors are odd beasts.

The brake operates mechanically by springs in case of power loss/stop to hold the hoist in position. The DC supply releases the brake (by pulling in the springs) when the hoist is moving up/down. After seeing the excellent performance of my new 60 ton EOT crane which came with VFD's for...

Lionel - Yes, the custom designed drive is set for PM mode. Bill - The very idea of VFD is to have constant flux density V/Hz through the entire speed range.