Poor AC Generator power quality

[goboatingnow]

Originally Posted by Adamante

That looks ugly. Yeah, I'd say the problem might be inside the generator. Perhaps a loose winding flopping around under load. Perhaps weakening insulation causing a partial short. Any way for you to megger the generator windings?

What about the voltage regulator? Does your unit have an active voltage regulator? Any way to replace it or to check its operation with a diagnostic procedure?

Nope looks like a generator to me.

[FlyingCloud1937]

A couple of quick questions.

I notice that when you scoped shore power it;s 50 hz, to be expected in OZ. Now I also see from the scopes that the gen is running at 60 hz, what is the Hz of the compressor?

Also what is the Hz for the air.con?

A couple of thoughts here, First have a look at the trace for the resistive hot water heater, notice how the the current trace is in sync with the voltage, no signs of clipping showing at the peak of the sine wave. With no voltage huntingNow lets look at the air.con... notice how the sine wave is not being clipped, and the voltage trace is lagging the current trace.

Now the bat charger we see the voltage lagging the current, and some clipping on the peak voltage.

Now when we look at the compressor, we see the voltage leading way out in front of the current, and a severe clipping of the peak sine wave, with what appears to be a serious amount of hunting both in the hz, and voltage.

If this compressor is a 50z machine that will be part of the problem, but not all of it VAR is almost equal to the load, not quite but way up there. So we know most of the issues are with the compressor, both from a reactive load that has poor power factor coupled with distortion from the VFD. It looks like you need to add some run caps. Or just maybe there are already run caps installed in the compressor that have failed/are failing.

Lloyd

[Poozer]

Originally Posted by FlyingCloud1937

A couple of quick questions.

I notice that when you scoped shore power it;s 50 hz, to be expected in OZ. Now I also see from the scopes that the gen is running at 60 hz, what is the Hz of the compressor?

Also what is the Hz for the air.con?

A couple of thoughts here, First have a look at the trace for the resistive hot water heater, notice how the the current trace is in sync with the voltage, no signs of clipping showing at the peak of the sine wave. With no voltage huntingNow lets look at the air.con... notice how the sine wave is not being clipped, and the voltage trace is lagging the current trace.

Now the bat charger we see the voltage lagging the current, and some clipping on the peak voltage.

Now when we look at the compressor, we see the voltage leading way out in front of the current, and a severe clipping of the peak sine wave, with what appears to be a serious amount of hunting both in the hz, and voltage.

If this compressor is a 50z machine that will be part of the problem, but not all of it VAR is almost equal to the load, not quite but way up there. So we know most of the issues are with the compressor, both from a reactive load that has poor power factor coupled with distortion from the VFD. It looks like you need to add some run caps. Or just maybe there are already run caps installed in the compressor that have failed/are failing.

Lloyd

Hi Lloyd,

Here are responses to your questions:

The air compressor VFD can take either 115 or 230v input at 50-60Hz. There is a jumper wire on the VFD circuit board that sets the VFD to the correct input voltage. The VFD takes single phase input and outputs 208v 3-phase to drive the 2hp 3 phase motor. It seems to start at about 30Hz and 8amps and runs at full speed of 60Hz and 20amps. This is controlled by the VFD.

I have load tested the generator and it will deliver up to 45amps before the voltage and frequency start to drift.

The air conditioning compressor is 115v 60Hz.

There are no run caps in this system.

The VFD air compressor is replacing a single phase 115v 60Hz cap start motor driven compressor that had no VFD. My genset has never had a problem starting this motor for the past 12 years, although recently the motor has started overheating and tripping off on the internal thermal overload. This was one of the main reasons I decided to replace the compressor.

I really appreciate your help!

Regards,
Doug

[FlyingCloud1937]

Originally Posted by Poozer

Hi Lloyd,

Here are responses to your questions:

The air compressor VFD can take either 115 or 230v input at 50-60Hz. There is a jumper wire on the VFD circuit board that sets the VFD to the correct input voltage. The VFD takes single phase input and outputs 208v 3-phase to drive the 2hp 3 phase motor. It seems to start at about 30Hz and 8amps and runs at full speed of 60Hz and 20amps. This is controlled by the VFD.

I have load tested the generator and it will deliver up to 45amps before the voltage and frequency start to drift.

The air conditioning compressor is 115v 60Hz.

There are no run caps in this system.

The VFD air compressor is replacing a single phase 115v 60Hz cap start motor driven compressor that had no VFD. My genset has never had a problem starting this motor for the past 12 years, although recently the motor has started overheating and tripping off on the internal thermal overload. This was one of the main reasons I decided to replace the compressor.

I really appreciate your help!

Regards,
Doug

Now we get the rest of the story.

I think you have Digital Frequency Drive problems, a quick search of google shows that there are a number of failures.

How about the intake air filtration system have you given that a check or service.

And as was mentioned by others running this thing on 120 is going to likely be out of balance with the other leg, which will cause some of that peak sine wave clipping, especially as you reach the the max amps. From the traces posted you can see over 30 amps at start up, and it also shows the saturation requirement of the motor in the current trace, the reason for such a large VAR.

Lloyd

[Poozer]

Originally Posted by FlyingCloud1937

Now we get the rest of the story.

I think you have Digital Frequency Drive problems, a quick search of google shows that there are a number of failures.

How about the intake air filtration system have you given that a check or service.

And as was mentioned by others running this thing on 120 is going to likely be out of balance with the other leg, which will cause some of that peak sine wave clipping, especially as you reach the the max amps. From the traces posted you can see over 30 amps at start up, and it also shows the saturation requirement of the motor in the current trace, the reason for such a large VAR.

Lloyd

The air filter is clean, the genset appears to be running prefectly aside from the issues with this compressor.

It seems that the best next step is to configure the genset for 240V and see if that makes a difference. At least I can compare that with the 240V shore power which is working fine, so it would rule out the drive itself as the cause of the problem.

I've also asked the compressor manufacturer to confirm whether they have ever run this compressor on a 6kW Northern Lights generator.

[downunder]

I presume your compressor is a Model YP25/YP35, t he Light Duty YachtPro™.

When I made enquires to Brownies as to what size genset I would need to run a Bauer junior they replies 8KVA.

I am still convinced a NL 5kva (240V/50hz 1500 rev model) with a Vitron Quattro inverter charger with boost would do the job.

Hope you can sort your problem.

[Poozer]

Originally Posted by downunder

I presume your compressor is a Model YP25/YP35, t he Light Duty YachtPro™.

When I made enquires to Brownies as to what size genset I would need to run a Bauer junior they replies 8KVA.

I am still convinced a NL 5kva (240V/50hz 1500 rev model) with a Vitron Quattro inverter charger with boost would do the job.

Hope you can sort your problem.

Yes, it's the Brownies YP25DF (dual filter). They assured me that my 6KW 120V 60Hz generator would work fine, but it does not. They believe my generator is faulty and there is nothing wrong with their compressor. It's a pretty frustrating situation. These compressors cost $15,000 and mine is worthless to me as it currently stands. Hopefully the 240V setting for the generator will work.

[transmitterdan]

If you can get a schematic diagram of the variable frequency drive it might tell a lot. From the pictures it appears that the drive (not the compressor) is not power factor corrected (or it's a really bad implementation of PFC). It is probably a universal input that uses a voltage doubler when running on 115V so the rest of the circuit can run on 230V internally. A doubler can be very non-linear leading to harmonic distortion. I will bet the input circuit draws a lot of current at the tops (and bottoms) of the sine wave and almost no current the rest of the time. For whatever reason, the generator cannot produce these high peak current demands so the voltage waveform clips off the tops. The variable frequency drive senses the voltage drop and slows down. The voltage clipping goes away and the drive becomes more happy and tries to increase the speed and the voltage clips once again. Now it is caught in an infinite loop from which it cannot escape.

If the above scenario is right then about the only thing you can quickly try is to configure the generator to run the variable frequency drive on 230V with appropriate jumper settings on the drive itself. That might not work either but it's worth a try. If you already tried it and I missed that note then apologies in advance.

BTW, if you are running the generator on 115 be sure that you have wired it exactly as the generator installation manual says. I have seen 115/230 generators wired wrong so that they can only deliver 1/2 the rated current to a 115V load. For example, Westerbeke generators have 115 volts made on 2 windings and they should be paralleled before passing through the circuit breaker at the generator. Not sure about NL wiring so check the manual.

I would guess that a proper variable frequency drive with power factor correction would run this compressor just fine from your generator. Talk to the compressor supplier and ask them if any VFD will work. If so, find one that the VFD maker will guarantee to work on a 6KVA generator. Many cheap VFD's will not work on a generator unless drawing less than about 10% of rated KVA capacity. Your load is a little over 1/2 the rated KVA.

[Poozer]

Originally Posted by transmitterdan

If you can get a schematic diagram of the variable frequency drive it might tell a lot. From the pictures it appears that the drive (not the compressor) is not power factor corrected (or it's a really bad implementation of PFC). It is probably a universal input that uses a voltage doubler when running on 115V so the rest of the circuit can run on 230V internally. A doubler can be very non-linear leading to harmonic distortion. I will bet the input circuit draws a lot of current at the tops (and bottoms) of the sine wave and almost no current the rest of the time. For whatever reason, the generator cannot produce these high peak current demands so the voltage waveform clips off the tops. The variable frequency drive senses the voltage drop and slows down. The voltage clipping goes away and the drive becomes more happy and tries to increase the speed and the voltage clips once again. Now it is caught in an infinite loop from which it cannot escape.

If the above scenario is right then about the only thing you can quickly try is to configure the generator to run the variable frequency drive on 230V with appropriate jumper settings on the drive itself. That might not work either but it's worth a try. If you already tried it and I missed that note then apologies in advance.

BTW, if you are running the generator on 115 be sure that you have wired it exactly as the generator installation manual says. I have seen 115/230 generators wired wrong so that they can only deliver 1/2 the rated current to a 115V load. For example, Westerbeke generators have 115 volts made on 2 windings and they should be paralleled before passing through the circuit breaker at the generator. Not sure about NL wiring so check the manual.

I would guess that a proper variable frequency drive with power factor correction would run this compressor just fine from your generator. Talk to the compressor supplier and ask them if any VFD will work. If so, find one that the VFD maker will guarantee to work on a 6KVA generator. Many cheap VFD's will not work on a generator unless drawing less than about 10% of rated KVA capacity. Your load is a little over 1/2 the rated KVA.

I don't think the genset is wired wrong because I load tested it, and it delivered 45A at 120V 60Hz before it started to struggle to maintain it's voltage and frequency settings.

Your thoughts on the VFD design are very interesting. There has to be some trick to get the same drive to handle the two input voltages, so you may be on to something there! Hopefully the 240V configuration will work.

Thanks for your advice!

[Dsanduril]

Does the VFD have an input line reactor? The manual I found for the compressor doesn't include a schematic. Particularly when located near the generation source an input line reactor of up 5% impedance is usually recommended (less than 1% is usually too low, more than 5% will generally decrease voltage output). If you can measure the generator/delivery system impedance (with that fancy new meter) and it is less than/close to 1% then it probably needs a reactor. The impedance helps smooth out the distortion hitting the drive and smooths out the waveform.

Finding a 120V 2HP line reactor might be a little difficult, a 240V 2HP is easy. Given that you're down under any shops I could recommend would have a long shipping distance, but any industrial supply house that sells small VFDs should be able to source a line reactor.

[FlyingCloud1937]

Originally Posted by Poozer

The air filter is clean, the genset appears to be running prefectly aside from the issues with this compressor.

It seems that the best next step is to configure the genset for 240V and see if that makes a difference. At least I can compare that with the 240V shore power which is working fine, so it would rule out the drive itself as the cause of the problem.

I've also asked the compressor manufacturer to confirm whether they have ever run this compressor on a 6kW Northern Lights generator.

Well, was actually speaking of the intake filter of the Dive Compressor, is this a used/or new compressor?

I believe that it will run a far site better in 220v over 120. If not then we can dissect.

Lloyd

[daddle]

Sounds like a compressor design problem. Not an issue when driven from a low impedance utility service (until the power company gets complaints) - but a crummy design for running from a current limited generator. It's power factor. Like I wrote way above: a simple generator can hardly do anything but put out a nice sine wave. It's what spinning magnetic fields do. But exceed the current (magnetic strength) and the voltage will suffer.

That said there could be a problem with the regulator on the generator. But you kinda need to forgive the designers of that for not anticipating such a crummy (cheap, illegal, irresponsible) power factor.

[FlyingCloud1937]

Originally Posted by transmitterdan

If you can get a schematic diagram of the variable frequency drive it might tell a lot. From the pictures it appears that the drive (not the compressor) is not power factor corrected (or it's a really bad implementation of PFC). It is probably a universal input that uses a voltage doubler when running on 115V so the rest of the circuit can run on 230V internally. A doubler can be very non-linear leading to harmonic distortion. I will bet the input circuit draws a lot of current at the tops (and bottoms) of the sine wave and almost no current the rest of the time. For whatever reason, the generator cannot produce these high peak current demands so the voltage waveform clips off the tops. The variable frequency drive senses the voltage drop and slows down. The voltage clipping goes away and the drive becomes more happy and tries to increase the speed and the voltage clips once again. Now it is caught in an infinite loop from which it cannot escape.

If the above scenario is right then about the only thing you can quickly try is to configure the generator to run the variable frequency drive on 230V with appropriate jumper settings on the drive itself. That might not work either but it's worth a try. If you already tried it and I missed that note then apologies in advance.

BTW, if you are running the generator on 115 be sure that you have wired it exactly as the generator installation manual says. I have seen 115/230 generators wired wrong so that they can only deliver 1/2 the rated current to a 115V load. For example, Westerbeke generators have 115 volts made on 2 windings and they should be paralleled before passing through the circuit breaker at the generator. Not sure about NL wiring so check the manual.

I would guess that a proper variable frequency drive with power factor correction would run this compressor just fine from your generator. Talk to the compressor supplier and ask them if any VFD will work. If so, find one that the VFD maker will guarantee to work on a 6KVA generator. Many cheap VFD's will not work on a generator unless drawing less than about 10% of rated KVA capacity. Your load is a little over 1/2 the rated KVA.

It's not a 6 KVA when its running split phase, and supplying from one leg into the load on only half the phase. Not to mention the VFD is only good for about 2/3rds it 3 phase rating when running from single phase.

Now factor in that it's running on 1 leg out of balance on split phase...that's why we have peak clipping, and so much impressed harmonics. Not to mention the fact that the half phase of the split is near maxed out.

Lloyd

[FlyingCloud1937]

Now I think we need to re-title this topic to- Running poor PF loads from a small generator.

Lloyd

[Poozer]

I talked with Westerbeke today. They have a big presence here in Australia (unlike Northern Lights) and are willing to let me bring my compressor to their factory to test run it on their 120V 60Hz 7.6kW generator. This is a huge relief as it will get me out of the tail chasing mode I'm in now.

I'll try it in 120V mode first and then in 240V mode if that doesn't work. I'll also capture waveforms to compare. We run the tests on Thursday morning, and I'll report back once I have the results.

Thank you all for your generous help and advice during this process!

Regards,
Doug