Poor AC Generator power quality

[ebaugh]

The back end on my NL 9K can be wired for 240V operation. The specs of the current small genset indicates the same. If all else fails you could try that configuration. Generally speaking though I was advised by my NL dealer, the genset is better off in the single 120V 50A configuration with a boat that strictly uses 120V, so this might be a last resort sort of measure.

Set for 240V, You can get split phase that way and still have 120V available, but the 120V loads have to be balanced. You get 2 legs of 120V, each good for 25A, plus a 240V also good to 25A. The sum of the power used still can't exceed 6kW. If you have 240V/50A USA style shore power system, or a dual 120V/30A system this is an easy change.

If you have a single 120V/30A USA style system it's not suggested at all.

[Poozer]

Here's the latest on this problem:

The compressor manufacturer (Brownies) believed that the fact that our generator neutral is floating could be the cause, so we grounded the neutral output of the generator but it made no difference to the operation of the air compressor.

I purchased a Fluke 345 power quality scope meter and did some testing. The output waveforms from the generator when running the compressor are quite distorted. The total harmonic distortion ranges from 12% to 40%! This seems to be way higher than acceptable for a modern genset. Here's a link to a PDF with photos of the waveform coming from the genset. I'm waiting to hear back from Northern Lights, and Brownies on next steps.

[Adamante]

Have you tested the generator with a purely resistive load? I'd be inclined to load it with a couple of small space heaters at 1.5 KW each, or maybe some cheap electric hotplates. The idea would be to load it down to a similar KW output without having the reactive load components presented by the compressor. If you see a waveform distortion with a purely resistive load, I'd suspect the generator might be faulty.

[Poozer]

Originally Posted by Adamante

Have you tested the generator with a purely resistive load? I'd be inclined to load it with a couple of small space heaters at 1.5 KW each, or maybe some cheap electric hotplates. The idea would be to load it down to a similar KW output without having the reactive load components presented by the compressor. If you see a waveform distortion with a purely resistive load, I'd suspect the generator might be faulty.

That's good advice, thanks. I'm going to do just that. I'll also capture waveforms running an inductive load (Air Conditioning). I'll post the waveform pics when I'm done.

[Poozer]

Here's a link to the waveform and harmonic readings for different load types on the boat. In all cases, the harmonic distortion is quite high.

[Adamante]

Originally Posted by Poozer

Here's a link to the waveform and harmonic readings for different load types on the boat. In all cases, the harmonic distortion is quite high.

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?

[justlearnin]

If you have 2 120 windings on your gen ...when running the compressor on one try putting some load on the other to help balance the gen and see what happens?

[Lake-Effect]

The solid-state relays shouldn't be a problem. Worst-case, maybe a tiny switching transient if the input was under-driven.

Have you sent your waveform and THD readings to the genny manufacturers? Do they claim to provide true sinusoid into rated load at low distortion?

Any other equipment on the boat acting up when powered by the genny? As rough as the waveforms looked, I bet most generators might have as much as 10% THD without it affecting the typical loads too much.

[Poozer]

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?

There was a big 63Amp relay that the manufacturer installed to automatically switch between shore and generator power (shore on N.C. contacts and Genset on N.O. contacts, relay coil energized by Genset output power) which is a terrible idea. It fused about a year ago and blew out the AVR. I replaced the AVR with a new one, and replaced the contactor with a manual changeover switch. It's very possible that when the contactor blew, it damaged the windings.

Does anyone know how feasible it is to replace the entire generator section on a Northern Lights? The Lugger engine runs like a champ!

[Poozer]

Originally Posted by Lake-Effect

The solid-state relays shouldn't be a problem. Worst-case, maybe a tiny switching transient if the input was under-driven.

Have you sent your waveform and THD readings to the genny manufacturers? Do they claim to provide true sinusoid into rated load at low distortion?

Any other equipment on the boat acting up when powered by the genny? As rough as the waveforms looked, I bet most generators might have as much as 10% THD without it affecting the typical loads too much.

I sent the waveform readings to Northern Lights today. Hopefully they will respond. I'll call their Australian reps tomorrow. They do not provide THD specifications unfortunately, so it's a bit hard for me to determine if they are acceptable or way off spec. I'll also contact Westerbeke tomorrow and see if they have some THD specs they can provide me as an alternative option.

[Poozer]

One other thought about this. My generator has brushes, that as far as I know, haven't been checked/replaced in a long time, maybe ever. It has done 6,000 hours. Could worn or faulty brushes cause harmonic distortion problems?

[ebaugh]

You guys got out of my depth. I contacted an acquaintance at NL that has always been very helpful. He said:

The Northern Lights 6KW generator should be able to start the compressor without any problems but I'd recommend he power it from the 240 volt output of the generator. All NL generators can provide 120/240 AC simultaneously. There is enough power to start the compressor without a variable frequency drive and that may be inducing enough power factor to cause his problem. There is a wiring diagram in the back of the owners manual showing how to connect the generator outputs for 120/240.
Link for wiring operators manual and wiring diagram: http://www.northern-lights.com/literature/manuals.html

The frequency should be set at 62.5 - 63 Hz with no electrical loads. The engine speed/frequency adjustment is a 10mm bolt and locknut bearing against a lever with a spring on the side of the injection pump. Be sure to verify that the air filter and fuel filters are clean before making any adjustments.

Best regards,
Bob Senter
Northern Lights/Lugger Service Training

I forwarded via PM his email and cell phone. He offered his assistance and is looking for your call or email.

Bob

[goboatingnow]

I was about to say the same thing, I wonder if its power factor corrected. High frequency drive systems can generate poor PF ratings.

As to the neutral earth, it may be that earth isnt connected , how did you test to earth, ie did you connect to the earth wire. ( it could be that earth isnt connected to the neutral of the generator, ( it should but it might not be).

Dave

[Adamante]

Originally Posted by Poozer

One other thought about this. My generator has brushes, that as far as I know, haven't been checked/replaced in a long time, maybe ever. It has done 6,000 hours. Could worn or faulty brushes cause harmonic distortion problems?

Oh wow, I didn't realize this was a brushed set. By all means check the brushes for wear and the brush holder for mechanical integrity.

[Adamante]

Originally Posted by goboatingnow

I was about to say the same thing, I wonder if its power factor corrected. High frequency drive systems can generate poor PF ratings.

Based on the posted traces, he seems to be getting severe AC waveform distortion even with a purely resistive load and a unity power factor.