Generator shutdown

keynotez · Aug 1, 2011

Hi Folks! Wanna ask some help. I have a KOMATSU Generator with capacity of 350KVA, 220V, 3phase. When I was recording the data from a HOIKI power analyzer, I noticed that sometimes the current reading on the GROUND line reaches to 40Amperes. What could be the cause of that measurement? Before I started the recording of the power analyzer, the generator shut downs and the main breaker of the load also tripped. That is why I am gathering the data of the generator using the power analyzer. What could be the cause of the shutdown? Is it the leakage current to the ground line? I did the insulation resistance testing on the windings of the alternator and have a minimum measurement of 3 Mega-ohms. Please help me about my analysis. Thanks a lot guys!

malcolmsanford · Aug 1, 2011

40amps to ground that is some leakage.

What type of installation is this generator supplying?

Knobhead · Aug 1, 2011

All I can suggest at this time with the information given, is you have a neutral / earth fault external to the generator. The outgoing ACB does it trip on E/F or REF?
Without the information it’s pure guess work on our part.

Lighthouse Phil · Aug 1, 2011

Lets not get into anything heavy here yet..
are you recording the data because of unexplained shut downs ?
How often are the shut downs ?
Have you checked the AVR (Automatic Voltage Regulater) for correct output voltages ?
If all 3 phases are in use, are they balanced ?
What is the genset suppling ?
Is the Earth and Neutral linked in side the alternator box?
is the Genset on a Mains failure set up or constant running ?
Just a little more info please

keynotez · Aug 2, 2011

Good day folks! Uhm, actually the shut down only happened once. When we check the ACB/ATS of the main load during the shutdown, it also tripped. The Genset is supplying a Semi-conductor Company. The three-phases are all loaded but Line 2 draws 10-20Amperes less than Line 1 & 3. The earth and neutral are not linked inside the alternator box. Voltage output of all the lines are constant during the whole recording period. Same with the power factor.
P.S. Thanks for all the replies, I just don't want to happen again the shutdown that's why I am making an analysis.

Engineer54 · Aug 2, 2011

As a starter, you need to earth that generator neutral, there are only a very few circumstances where you would not... Your supply is too all intents and purposes balanced..... What and/or how are you providing the gen-set with it's earthing?? I hope that the ATS is a 4 pole type, 3 pole with jointed neutral link can give you all sorts of stray current problems....

When you say the generator is loaded, are you saying it's running at or near capacity?? Whatever the loading is, make absolutly sure that any adjustable parameters on both the ACB and ATS (if also present) are set to suitable protection levels. Check them anyway, the company may have added more equipment since the Generators protection was last set up!!!

As Tony commented on, most modern Generator protection systems will indicate what protection function actually tripped the gen-set out. You may have to scroll through on some types of multi function protection relay modules.

Lighthouse Phil · Aug 2, 2011

Its a good sign that the voltage is constant, that rules out any over/under voltage relays coming into operation and causing a shut down. As E54 has stated, has any new equipment been added since the safety parameters were set, ?? More loading will trip an over current relay, again causing shutdown.
You say this only happened once, ,,how long was the genset running before shut down ?
Was it within seconds or minutes, or an hour or more ? Is the genset due a service ? Low oil pressure / over heating will shut it down. Low oil pressure will shut it down very soon after starting, look for a oil leak. Over heating could take an hour or more. Depends on dry or wet sump system. In a wet sump the oil will be "stored" in the engine, in a dry sump, the oil will be in a large container under the engine, which normally gives the engine a longer running time and so will take longer to heat up. Air temp around the genset should be kept low if possible, is the genset in a confined space with no air movement.?
We have engines which run for 3 or 4 months at a time (24/7), only to shut down on a oil leak or overheating.
Depending on the control panel, the main breaker could be tripped by the controls, a safety feature in case the genset starts again, the main breaker would have to be manually reset. (After the electrician is happy to go ahead)
Would like to know how long the genset was running before shutdown..
Interested in this one...

keynotez · Aug 8, 2011

Hi folks! At last the Generator did shut down again and I have the data during the shut down. I am just confused with the "K Factor" at the Neutral Line. Could you please help me analyze with these ones? Thanks a lot. P.S. thanks for your inforamtive replies Lighthouse Phil. Please see those attached files. The shut down occured 9:15AM - 9:45AM. My interval recording was 30 minutes but 1 hour interval on graphical display for presentation purposes. Line 1, 2 and 3 has a maximum K Factor of 4.0 while Neutral Line has almost 200 K Factor. Is it normal to a Neutral Line? Help please.

keynotez · Aug 8, 2011

OMG.. I think it's normal for a Neutral line to have a big "K Factor"...Don't you think so guys? I referred to the other Genset and other recordings, "K Factor" at Neutral line is still big... Seems that it's not the cause of the shut down...hmmm...tsk...tsk...

Electro-tech · Aug 8, 2011

IMO, not a expert, If you have un-balanced phases plus harmonics surely you will get heating of the neutral bar, a higher neutral current.That is why you have to consider the conductor sizing of the neutral to alow for harmonic disturbances.Heating up is usually the failure of most motors etc. Maybe there is a thermal overload .

Knobhead · Aug 8, 2011

Harmonics show worse in the neutral as it’s handling all the harmonics from the 3 phases. Much of the harmonics being created by new VFD’s and IT equipment. It’s got to the stage now that where a designer would specify a 3&½ core cable they now want 4 core.

I often wonder how some of the 3&½ core cables I installed 20+ years ago are fairing, VFD’s were rare things then. It’s causing quite a lot of concern now due to neutrals overheating.

Just as an aside, the first VFD I installed was for a 20hp motor, it was the size of a large wardrobe.

Lighthouse Phil · Aug 8, 2011

your graph is showing that the genset has a near constant load of 20A per phase up until 06:45AM then goes upto 50A per phase after this time. Is your genset running constantly ?. The 50A loading didn't last to long then died away all together, is this the time the genset shut down ?.
The graph for the K factor is from a different time, 8:45pm, this high K factor is at a different time to shut down.

Is the genset capable of delievering 50A per phase for an hour or more, ? Looking at the graph for time/current and then the neutral/K factor, I dont think the 2 are related.

I'm sure if the genset control panel can deliver such good time/current graphs, it should be able to tell you which parameter shut it down. At the moment I'm thinking along the lines of overheating, as the genset runs for an hour before shut down. From the graphs, the genset ran at 55A for 10 to 15 mins before shut down.........Is the maximum current limit being reached and the panel shuts it down, ? or is it working to hard and over heats ??

Engineer54 · Aug 8, 2011

We need to know what protection you have on the gen set, and at what values those breakers and/or protection relays, have been set too. Just providing the logged time and the current the gen set tripped out at, gives us nothing to work with on it's own...

Forget the K factor thing at this time, it's not the cause of your gen set tripping out....