Cat generator fluctuating

Status
Not open for further replies.
C

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I had a service call yesterday to one of our big farms that didn't have power and the Siemens SWBD with integral ATS wouldn't switch over to generator. It uses the typical 2 wire start. Right when I pulled up I noticed the generator RPM's were fluctuating quite a bit, probably several hundred RPM along with the voltage and Hz. I'm sure the ATS didn't like what it was getting and wouldn't transfer.

I proceeded to flip the ATS into "manual" and shut the generator down. It was in the "auto start" mode on the selector switch. I gave it a minute or two and restarted it in the "manual start" mode. It came up to speed at a steady 480v 60hz. Gave it a minute or two again and manually opened the utility main and then closed in the gen main. The whole facility was now running on gen power without an issue.

Any ideas why the generator would fluctuate like that on an auto start?

I asked the customer to call the Cat dealer to come out and take a look. Thought maybe someone on here had seen this before...
 
Cow said:
I had a service call yesterday to one of our big farms that didn't have power and the Siemens SWBD with integral ATS wouldn't switch over to generator. It uses the typical 2 wire start. Right when I pulled up I noticed the generator RPM's were fluctuating quite a bit, probably several hundred RPM along with the voltage and Hz. I'm sure the ATS didn't like what it was getting and wouldn't transfer.

I proceeded to flip the ATS into "manual" and shut the generator down. It was in the "auto start" mode on the selector switch. I gave it a minute or two and restarted it in the "manual start" mode. It came up to speed at a steady 480v 60hz. Gave it a minute or two again and manually opened the utility main and then closed in the gen main. The whole facility was now running on gen power without an issue.

Any ideas why the generator would fluctuate like that on an auto start?

I asked the customer to call the Cat dealer to come out and take a look. Thought maybe someone on here had seen this before...
Click to expand...

Just a guess there is a problem with the governor on the generator.

As for the reason the ATS would not transfer to the generator, the ATS controls are designed to look at the voltage line to line and line to neutral, if the ATS is a 4 wire. It will have over voltage as well as under voltage perimeters. It also looks/may look at the frequency.

When you first showed up on the scene you said you could hear the generator's engine rpm's fluctuating quite a bit. That means the generators output voltage as well as frequency was swinging up and down with the rpm of the engine. Voltage could have been swinging well over 500V and or well under 480V. The ATS was doing its' job protecting its' load from the generator by not transferring the load to the generator source.
 
Last edited:
Jamesco said:
Just a guess there is a problem with the governor on the generator.

As for the reason the ATS would not transfer to the generator, the ATS controls are designed to look at the voltage line to line and line to neutral, if the ATS is a 4 wire. It will have over voltage as well as under voltage perimeters. It also looks at the frequency.

When you first showed up on the scene you said you could hear the generator's engine rpm's fluctuating quite a bit. That means the generators output voltage as well as frequency was swinging up and down with the rpm of the engine. Voltage could have been swinging well over 500V and or well under 480V. The ATS was doing its' job protecting its' load from the generator by not transferring the load to the generator source.
Click to expand...
My thoughts as well. The fact it worked after shutting down and then switching to manual mode was probably more related to something resetting on shutdown more so then it being a manual vs auto problem. The governor controlling the engine shouldn't care if ATS is in manual or auto.
 
Diagnostic visit

Diagnostic visit

I would have Cat come and put their laptop on the generator and look for start events and see if the GCM (generator control module) had any codes.
 
kwired said:
My thoughts as well. The fact it worked after shutting down and then switching to manual mode was probably more related to something resetting on shutdown more so then it being a manual vs auto problem. The governor controlling the engine shouldn't care if ATS is in manual or auto.
Click to expand...

The governor controlling the engine shouldn't care if ATS is in manual or auto.
Click to expand...

Agree.
The generator doesn't even have the ability to know if the ATS is in auto or manual transfer mode.

The governor should, when it sees the load, the ATS has transferred to the generator, quickly react and adjust the engine rpm accordingly to maintain the set point voltage and frequency. ( As you know voltage and frequency go hand in hand)

My guess is when the generator was shut down the governor somehow, short term, corrected its' malfunction. (If it happened once good chance it's going to happen again.)

Probably time for a new governor.

Worth noting, when the OP restarted the generator engine and the governor seemed to be operating properly, the OP then selected manual transfer at the ATS. The ATS still looks at the line to line and line to neutral, (If neut is used) and the voltage must still fall within the set perimeters before it will transfer the load to the generator.

Worth noting, once the ATS has transferred the load to the generator, and normal power is not restored to the ATS, IF the generator governor screwed up again The ATS remains connected to the generator. What's the connected load? What happens if the voltage swings above, say, 550V ????


.
 
Last edited:
kwired said:
did it work again in auto? May have reset whatever was malfunctioning when you shut down.
Click to expand...

I never tested it in auto after that. It's for a dairy and they had cows stuck on the carousels, my main mission was to get the carousels turning again since the cows had been standing in place for quite a while. Once it was in manual and running, I left it there. The power company was just pulling in as I was leaving, so they may not have had it running on the generator for to long after I left.

Jamesco said:
Agree.
The generator doesn't even have the ability to know if the ATS is in auto or manual transfer mode.

The governor should, when it sees the load, the ATS has transferred to the generator, quickly react and adjust the engine rpm accordingly to maintain the set point voltage and frequency. ( As you know voltage and frequency go hand in hand)

My guess is when the generator was shut down the governor somehow, short term, corrected its' malfunction. (If it happened once good chance it's going to happen again.)

Probably time for a new governor.

Worth noting, when the OP restarted the generator engine and the governor seemed to be operating properly, the OP then selected manual transfer at the ATS. The ATS still looks at the line to line and line to neutral, (If neut is used) and the voltage must still fall within the set perimeters before it will transfer the load to the generator.

Worth noting, once the ATS has transferred the load to the generator, and normal power is not restored to the ATS, IF the generator governor screwed up again The ATS remains connected to the generator. What's the connected load? What happens if the voltage swings above, say, 550V ????
Click to expand...

The connected load showed around 675 amps on the generator display. I can't recall if the voltage was swinging high, but it was swinging very low.

I will keep everyone's comments in mind. It sounds like it may be the governor and that it's most likely to happen again.

Thanks for the help everyone.
 
I'm not familiar with that generator, however I have seen some engines that the mechanical governor gets into a swing at no load and causes the surging. Usually however the application of a load will smooth it out. given that, I'd venture a guess that something made it stumble on initial startup and got into the swing and was never able to recover until you shut it down.
 
Status
Not open for further replies.
Top