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Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
EasternVoltageResearch
If the source is Wye or Delta it does not matter, as long as 440 V is Line to Line voltage.
If the motor is 440 V on delta and 440 V is the voltage available, you have the choice of starting it on wye and change to delta. It will bring the surge down. Just be sure to make the change at the right time, otherwise you can make things worse. As 7.5 HP is a small motor I would not bother about it, using a straight contactor on it. An extra contactor or a softstart will be throwing money out of the window.
I think WEG motors are all squirrel cage as I installed 50+ of them and none was not. All of them were Wye Delta (six leads). You are an american, so you might find series - parallel wiring motors. They are always internally connected on Y but you can connect windings both in series or parallel. These will have 9 leads.
I never worried about the surge on the first milliseconds, but I do know most inverters for 600+ HP squirrel cage motors will keep some current through the stators while it is 'ready' to be turned on. It reduces the time-to-start. For a 600 HP that would be anywhere from 100 to 200 A. I am wondering now if that reduces inrush as well =)
Do you have means of posting the current plot? I would be interested on seeing it.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
The wiring of the motor windings, wye or delta, is related only to the supply voltage, whether the supply voltage is wye or delta is unimportant.
The higher voltage rating is wye, typical would be three input phases to the bottom terminals and move the shunts to short the top three terminals.
the lower voltage rating is delta typical would be three input phases to the bottom terminals the three shunts should be top-to-bottom. (haven't looked at your motor, just typical)
A 7.5 hp motor (5.6 kW) motor has significant inertia obviously even more with a load. For efficiency the winding resistances are low, so current consumption is determined mainly by reactance, at startup you have a well coupled shorted turn secondary. It takes a huge lump out of the supply.
Conversely, at 3600 rpm the inertial energy is surprisingly large (e.g. inverters need a 'brake' resistor pwm'd across the main Bus during deceleration, typ here 240/415 ac, 580 Vdc bus, at around 650V Bus voltage the brake resistor is used to limit the Bus e.g. 700 to 800 Vdc.
Trust me, there is enough regen energy from a motor to blow bus caps and/or output bridges ;) (diodes across igbts form a three phase rectifier bridge) This is a normal induction motor, servo (permanent magnet) motors are worse.
At this power level you must have as a minimum a motor starter contactor soft-start units are robust (usually phase-controlled thyristors) and sufficient a motor inverter (drive) with current limit, ramp up/down, speed control, motor thermal control etc. is better, some have virtual plc/nc/drive functionality, some are surprisingly cheap. Using just a contactor you are going to place large repetitive stresses on your equipment/mountings/everything .. a soft-start is worth it. Consider two quadrant (drive FWD/REV) vs four quadrant (drive/brake FWD/REV)
As the factory where I work is now owned by Rockwell I must say that ABB make a fine range of products and can work with you. As can many others.
P.S. this is such a huge market, prices are so low, you shouldn't even consider DIY electronics. P.P.S. 4HV-ers, lots of isolation is required ... don't re-invent this wheel (unless it's your career). P.P.S. if your supply has earth leakage protection (or by any other name) you may have trouble with electronic drives as filters etc. 'leak'.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I have the opposite problem, I just had two 5kW inverters donated to me, a Danfoss VLT and an old IMO Jaguar, but I don't have any 3 phase motors to drive with them. They're also 3 phase input and I don't have a 3 phase supply at home.
EVR, you said the inrush current settles down to 60A. I assumed that the motor then accelerates up to its rated speed and the current goes down to just a few amps. But there are some other posts above that don't make that assumption, they think your motor is drawing 60 amps even after it has got up to speed. That would certainly be bad!
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Steve Conner wrote ...
I have the opposite problem, I just had two 5kW inverters donated to me, a Danfoss VLT and an old IMO Jaguar, but I don't have any 3 phase motors to drive with them. They're also 3 phase input and I don't have a 3 phase supply at home.
EVR, you said the inrush current settles down to 60A. I assumed that the motor then accelerates up to its rated speed and the current goes down to just a few amps. But there are some other posts above that don't make that assumption, they think your motor is drawing 60 amps even after it has got up to speed. That would certainly be bad!
I think we are the only two that read that in EVRs first post. Should settle to 8 but the post says 60.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
klugesmith wrote ...
Found this amusing exchange on a 3 phase forum thread. Q: A:
Wow. The reply just strikes the perfect balance of sarcasm, Internet elitism, OCD and a genuine willingness to help.
I once did some condition monitoring on a giant fan powered by a 640kW squirrel cage motor. The fan wheel was something like 8 feet in diameter, fabricated from steel plate and had huge inertia. To deal with the starting current, they just chose a 3.3kV motor and wired it straight to the nearest substation. No new fangled soft starters required.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Steve,
The motor inrush of 180A occurs for about 60ms. This settles down to about 60A for a second or two, and then finally reaches its steady state current of about 8A.
Thanks for all your comments! Very informative. Will continue reading comments and some research as well.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
Those figures don't sound right. The inrush current in the first tens of milliseconds would normally be several times the steady-state locked-rotor current.
I'd be inclined to agree with Avalanche here about the star-delta starter.
For an induction motor of this size, as a bare minimum you should start it in star (wye) connection and then switch over to delta connection when running. Otherwise the inrush current will be very large if connected directly to the full supply voltage in delta configuration from stand still. An electronic VFD or thyristor soft-starter would be better still as you have more control.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
As an example of no-load running current, I often test small drives (e.g. 1 hp) with large motors (e.g. 5 hp) to simulate a load, as the no load current of a motor is many times lower than at rated power.
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
EasternVoltageResearch wrote ...
Steve,
The motor inrush of 180A occurs for about 60ms. This settles down to about 60A for a second or two, and then finally reaches its steady state current of about 8A.
Thanks for all your comments! Very informative. Will continue reading comments and some research as well.
Thanks again!
Whew! That's better! I did think you were drawing 60 amps the whole time! Someone had also mentioned the start and run switching, that may also help you out but would involve adding some components to accomplish it. If you really need some starting components i may be able to get a few from work for you. We have some powerflex drives sitting on a shelf. They have been collecting dust as long as i have worked there. Let me know, i will help if i can!
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Motor inrush current question
They're also 3 phase input and I don't have a 3 phase supply at home.
