How do you check for good clean generator power output?

Kilowatt Crusher said:

Besides checking the voltage and frequency from your multimeter, how could you determine if the generator output is clean. I haven't used an o-scope since trade school, and wouldn't know what to look for, but I do have access to a decent one. It's a 1750 kw genset powered by a cat and just recently when testing it the ats was slow to sync.

First time poster, but long time follower.

Any thoughts?

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When using a scope test under load. I compared to the building power. Just make sure to have the scope plugged into the generator power because the neutral or grounds are tied together in the scope

dronai said:

When using a scope test under load. I compared to the building power. Just make sure to have the scope plugged into the generator power because the neutral or grounds are tied together in the scope

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Good point. Would you just look for some ripple or deviation in the frequency? I assume looking at it line to line rather than line to neutral as the ats is a 3 pole and the neutral is tied to the utility. Or would it be better to test line to neutral?

I was getting a false reading for HZ on a hand held meter. So I used the scope to check. Generator company told me to test under load.

Kilowatt Crusher said:

Good point. Would you just look for some ripple or deviation in the frequency? I assume looking at it line to line rather than line to neutral as the ats is a 3 pole and the neutral is tied to the utility. Or would it be better to test line to neutral?

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Unless you isolate the AC scope power, testing line to line will create a short because the ground clip on the probe is tied to ground. You could test line to neutral or line to line with 2 probes and not connect the ground clips though. It's a bit dangerous unless you are sure of what you are doing.

That being said, it is difficult to accurately measure 60hz with a scope and I wouldn't even bother using a scope on that generator. You could look at the waveform but it's probably not going to tell you why the ATS was slow switching over.

dronai said:

I was getting a false reading for HZ on a hand held meter. So I used the scope to check. Some ET members told me to test under load but I didn't listen to them.

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fify

We perform full load test utilizing a Fluke 1750, or an RPM, with resistive load banks to step load the system.

8V71 said:

fify

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Some ET members told me to test under load but I didn't listen to them.
fify


Sorry, I will give you credit also :laughing: But I did talk to a tech from the Generator company who confirmed what you said.

Dronai, was this an idling generator or a inverter type generator?

Big John said:

Dronai, was this an idling generator or a inverter type generator?

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Standby idling type. I also checked with my portable Honda at home, and the same result. With my hand held the reading was at 180 HZ, and 60HZ in the wall outlet ?

The scope shows a dashed sine wave but the measurements look the same. I didn't test under load, but next time I will, as it's supposed to clean up what I'm seeing.