Motor starting surge on a generator?

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zbang

Senior Member
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Roughly 5346 miles from Earls Court
We're working over an event site problem-

One of the caterers has a soft-serve ice cream machine (which we Have Opinions about). When they serve the "twist" of both flavors, it appears that the starting current of both auger motors together (my guess- 2HP each) causes the generator governor to try pulling up the voltage, which then spikes once the start surge slacks off. This is causing pretty much every LED in that area (100s of them) to flicker and is really bothering a lot of people. It may have caused some damage but there are no hard examples.

Presently, that site is on a 75(?) KVA diesel with Deep Sea electronic governor. We're thinking that swapping the 75 for an otherwise-identical 150 KVA unit might lessen the apparent problem due to the larger size and rotating mass of the generator itself. Does this make sense or are we just rationalizing a solution? (We're going to make the swap anyway so folks can see that we're trying to deal with the issue.)

Any other thoughts on the matter?
 
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Unless the auger motors are 3-ph, soft start/vfd won't help. A capacitor at the machine might help.

Am thinking there is either a problem with the machine and/or a problem with the governor. Amp draw on the machine both when starting and running might indicate a problem. There may be many settings on the governor that could be adjusted, too. Read the manual or contact the manufacturer.
 
Other possibilities that measuring voltage, current and hertz might point out:

  • Voltage drop at machine due to long, undersized, conductors causing a larger surge in starting current.
  • Generator lightly loaded so that the percent increase in load demand is high and engine cannot respond quickly.

Something often done on ships is to increase the hertz a bit to lessen the surge on sudden load increases. This would play havoc on clocks that rely on 60hz to keep time. Rarely a problem nowadays, I'd think.
 
A 2 HP 240 volt single phase motor draws between 11 & 12 amps. A 75 KVA 240 volt three phase generator.produces approximately 180 amps. The two 2 HP motors appear to only use 7.5% ( 24 amps ) if the available 180 amps that the 75 KVA generator. How long does it take these motors to obtain name p!ate RPM? .I did a Google search and several companies make soft starters & VFD'S for 240 volt 2 HP single phase motor. You should consult a reputable soft starter manufacturer and ask if it would solve the flickering if LED lamps.Have you taken ampere readings on all three generator legs. If you go with VFD'S might have to adjust start ramp up time to. reduce high inrush current. Assuming both motors are single phase : If motor #1_was on A & B phase & #2 motor was on B & C phase then you might want to try to have more LED'S,on A & C phase. Some tines this helps. If both motors are on a single cord then place a higher # of LED'S on the phase motors are not on.
 
garbo said:
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I did a Google search and several companies make soft starters & VFD'S for 240 volt 2 HP single phase motor. ...
Click to expand...
Can you give links to these site? I have looked at some single phase motor VFD options and they required modifications to the motors, which didn't seem a very good idea.
 
I wonder if a mechanical solution would work: modify the lever so that the twist option starts one auger and then the other in sequence rather than both at exactly the same time.

Also: the LEDs may be flickering on small phase errors rather than on gross voltage changes.

Jonathan
 
Just an idea, but if you had a small constant voltage transformer (aka a CVT such as a Sola) you could try it on some of the LED lights. If the problem is due to a voltage spike, such a transformer might help. If the problem is caused by phase "glitches" such as Jon mentioned, then it's less likely to help.
If a CVT reduces the flickering enough, you could consider a larger one for all of the lights if that's feasible.

A CVT is not very efficient, but compared to a larger generator it could be a better option.
 
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You could be all within the rated load, but one person jumping on a 10 person boat can rock the boat such that others definitely feel it. The shifting of one person is considerable relative to the size of the boat and this is how it works with abrupt load swing relative to the system size.

One person jumping around on a ship wouldn't be noticeable due to the much larger inertia, which is akin to grid power.

If you have the resources to swap a 75kVA for a 150kVA, you might try putting the problematic load on a separate 5-10kVA generator.
 
Alternatively, you could use a small inverter generator on the lighting like they do to power up those tripod puffer lights for road construction. You said 100s of LEDs. If they're like 10W ea, that's just a few kWs.

I can't comment more since I don't know the event setup but having to wire all the lights to a separate source is likely more costly than just putting the problem load on its own small generator.
 
zbang said:
that site is on a 75(?) KVA diesel with Deep Sea electronic governor
Click to expand...

Are you sure about this? Usually the governor is internal to the engine, usually an ECM these days (like a car or truck) and very tight governing.

Usually the voltage regulator is internal to the generator itself or at least a separate component.

The Deep Sea controller just monitors speed and voltage and oil pressure and stuff, and controls the starting and stopping mostly.

Anyway it sounds like an overshoot after starting the motors. But that is rare on modern electronic engines, especially this size. What specific engine is in it?

You might try a different 75 kw genset temporarily, and see if it has the same problem.

You might simply stage start the motors by a few seconds. Put a delay in one of them.

LEDs are pretty bad for flickering on supplies like this.
 
Deltaforce said:
If it governor issue, generator speed not steady constant load or even no load.
That also to check
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I'm sure there is a tach, or scanner, or even a laptop with the right software to plug in that ecm and get someone to start these ice cream augers while you check.

Those 2 hp motors suldn't cause the govoner to droop. There is way too much rotating mass. And remember the govonor only senses load on the engine The engine dosen't feel the reactive current, so the engine only feels active power. If it was a PF problem it wouldn't put any additional load onto the engine. Well actually will load the engine a tiny bit to the energy loss of the I2R heating of the conductors.

I'm thinking this is a power quality problem, like a spike, large inrush, harmonic maybe
 
Joethemechanic said:
I'm sure there is a tach, or scanner, or even a laptop with the right software to plug in that ecm and get someone to start these ice cream augers while you check.

Those 2 hp motors suldn't cause the govoner to droop. There is way too much rotating mass. And remember the govonor only senses load on the engine The engine dosen't feel the reactive current, so the engine only feels active power. If it was a PF problem it wouldn't put any additional load onto the engine. Well actually will load the engine a tiny bit to the energy loss of the I2R heating of the conductors.

I'm thinking this is a power quality problem, like a spike, large inrush, harmonic maybe
Click to expand...
In step by step troubleshooting procedure
First step
Check fuel, air, mechanical connections
 
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