Bill
% slip is the same for all frequencies/speeds. In your example, the speed at 10 Hz will be 293 RPM, not 260 RPM.
Motor output power is proportional to speed and hence the constant torque. (torque/speed/power equation)
My personal experience with DG KVA and DOL start vs VFD start.
Our 10 ton hoist has two winding two speed motor rated 415 V, 12/4 HP, 16/14 A, 1440/465 RPM.
I use a 50 KVA DG when other shop load is low or a 125 KVA DG when shop load is high.
With DOL start on high speed, the inrush current...
The capital and running costs of a larger DG purely from starting KVA point can be better spent on well-designed VFD's (with bypass contactor, if needed) which offer stress-free multiple starts of the motors in addition to speed control benefits, if needed.
I tested a 3000 RPM motor on no-load today. The starting inrush current was 60 A (with the final no load steady state current of 12 A). During the run-up starting from 500 RPM to 2500 RPM, I switched off and on with 1 sec, 2 sec, 3 sec, 5 sec and 10 sec delay between off and on. The inrush...
Lionel. Our all copper electrical system, designed and executed by professional engineers like my dad and me, has been in place for over 45 years with zero issues, not even a fuse blowout. So, the VFD is the issue here, not our electrical system.
Bill. The motors were hardly 5 feet away from...
There is no 're-gen' in a motor with no power supply. Since the motor is already spinning via the load, it will have a shorter inrush current period than when it is started from zero speed. Just make sure the motor rotates in the same direction as it is being spun by the load. Otherwise, the...
2U+1 AC HV test is a requirement for new motors and rewound motors and the full responsibility lies with the OEM/rewinder.
Partly rewound machines and overhauled machines are AC HV tested at their appropriate values as per standard, but the risk is under the customer. As a rewinder, I advise...
Thanks Lionel. Yes, input current was very low in decoupled run but my LED lights were flickering even they were switched off and a few failed when the drive was test run. Drive supplier said we need the isolation transformer to avoid harmonics and LED light flickering and failure.
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...
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...
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...
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?
