Utility Voltage Increasing throughout day

[Electrical_Tiger]

I am working with a Hospital trying to figure out why a chiller for an MRI keeps shutting down. Well, the chiller is going into a "under/over/no-voltage" alarm and shutting down. I have reviewed our metering trends and found that the voltage on the utility is steadily rising from 6Pm to 3AM and then it decreases back to a good nominal voltage during the day.

Does anyone know what would cause this voltage increase?

I have spoken to the utility and they say that they put capacitors on the line 6 weeks ago. This is the third day in a row the voltage has risen and knocked out the chiller.

Thanks

 

[dereckbc]

I have spoken to the utility and they say that they put capacitors on the line 6 weeks ago. This is the third day in a row the voltage has risen and knocked out the chiller.

There is your answer. What is happening after 6 PM the load is decreasing as the day cools off and HVAC load decreases raising the voltage. POCO switch in PF capacitors in the Summer as load increses to keep the voltage up.

 

[charlie]

. . . I have spoken to the utility and they say that they put capacitors on the line 6 weeks ago. . .

Complain to their Engineering Department and talk to an engineering supervisor (not to a run of the mill complaint taker and definitely not an automated system). They can move the Capacitor bank to alleviate the problem. If you do not get results, file with the public service commission in your state. :smile:

 

[Electrical_Tiger]

The utility says they located the problem this morning. They had a blown fuse in the regulator controller in the substation. As a result, the voltage was not stepping properly.

I will post again as soon as I confirm the voltage does not rise over the night.

Thanks for all of the help!

 

[bob]

You might want to ask the utility about changing the taps on the transformer.
Check and see what the voltage would be increasing the taps by one position.
If the tap setting is on the center position, changing it one step would reduce the voltage by 2 1/2%. The problem with this change is that during the peak loads you may get a low voltage condition.

 

[charlie]

You might want to ask the utility about changing the taps on the transformer.

Unless we can't do anything else to fix a problem, we will not do that since a failed transformer would be replaced with the taps in the middle position. That would not be good for a 3? bank to have one of transformers replaced and the taps not match.

 

[bob]

Unless we can't do anything else to fix a problem, we will not do that since a failed transformer would be replaced with the taps in the middle position. That would not be good for a 3? bank to have one of transformers replaced and the taps not match.

Charlie
Good point. I have never done the tap change on a 3 pot bank. I was thinking
pad mount transformer. Done it numerous time on a PMT.

 

[djohns6]

If the tap changer control is working properly now , I'll bet your problem is solved .

 

[mxslick]

Ummmm..

Ummmm..

Unless we can't do anything else to fix a problem, we will not do that since a failed transformer would be replaced with the taps in the middle position. That would not be good for a 3? bank to have one of transformers replaced and the taps not match.

(Bold added by me.)


Charlie, would it not be standard practice for a utility crew to check the taps on a damaged pot in a three-pot bank before installing a new one? Seems that it would be very dangerous to assume that all the pots are in the middle tap position.

I do know that a failed transformer is nasty smelling, but it would be a lot worse to have a second failure happen....

 

[djohns6]

(Bold added by me.)


Charlie, would it not be standard practice for a utility crew to check the taps on a damaged pot in a three-pot bank before installing a new one? Seems that it would be very dangerous to assume that all the pots are in the middle tap position.

I do know that a failed transformer is nasty smelling, but it would be a lot worse to have a second failure happen....

They should check the taps and the nameplate on the replacement pot . Impedance , polarity , etc . Does it ALWAYS get done ? Well ....... usually .

 

[charlie]

1. They should check the taps and the nameplate on the replacement pot . Impedance , polarity , etc.
2. Does it ALWAYS get done? Well ....... usually.

1. Absolutely!
2. Exactly!

And that is all I have to say about that. :grin:

 

[mxslick]

Do I detect a bit of an "oops" factor here? :grin:

Seriously though, having watched our POCO guys do repairs under some really bad conditions, and do a lot of it live, I have a lot of respect for them.

I was going to work for our local POCO, passed the lineman's written exam (way back in 1980) with an 85% score...but for one minor (literally) detail... I was only 16 at the time. (My friend's step dad worked for them, and got me the test just for fun. When I passed with such a high score, they contacted me to work for them...then got a trifle upset with my friend's step dad when they found out my age.)

Since then I have found out a few other things which would make me a less than good lineman:

• I hate heights, so no climbing or bucket truck for me..
• I would use a solid link instead of a fuse to burn a fault clear if I can't find it...
• And I'm the guy who, at a pole fire, would let it burn while roasting hot dogs.

 

[Sierrasparky]

Since then I have found out a few other things which would make me a less than good lineman:

• I hate heights, so no climbing or bucket truck for me..
• I would use a solid link instead of a fuse to burn a fault clear if I can't find it...
• And I'm the guy who, at a pole fire, would let it burn while roasting hot dogs.

What is burn a fault clear?
Is that like letting it blast away so you can find the bad spot..

What if the poor connector failed way ahead of the fault......

 

[djohns6]

What is burn a fault clear?
Is that like letting it blast away so you can find the bad spot..

What if the poor connector failed way ahead of the fault......

I remember " back in the day " , we would put the breaker on NON RECLOSE , close into the fault and look for the flash . This was SOP on lines with really bad right of way , at night .

 

[beanland]

VOltage Rise as Load Drops

VOltage Rise as Load Drops

If the voltage regulator was stuck, the voltage would be inverse with load. The load peaks at 3:00 p.m. so the voltage is lowest then. As the load drops toward 3:00 a.m., the voltage will rise. If the regulator cannot lower the voltage, they will run over their 125V limit. Since this is not normal operations, but caused by an equipment failure, not much anyone can do but find the problem and fix it.

 

[mxslick]

My sick idea of fun, lol.

My sick idea of fun, lol.

I remember " back in the day " , we would put the breaker on NON RECLOSE , close into the fault and look for the flash . This was SOP on lines with really bad right of way , at night .

I have heard of this being done, and am told (and understand how and why) it is sometimes necessary.

I would be the one getting a good laugh out of the resulting fireworks.

I do have a sadistic side when it comes to electricity....just ask the Yamaha audio amp that bit me just how far I'll go.

 

[mxslick]

What is burn a fault clear?
Is that like letting it blast away so you can find the bad spot..

What if the poor connector failed way ahead of the fault......

Yes, that's exactly what it means. You intentionally remove circuit protection and either wait for the fault to burn itself into an open circuit condition, or for the conductors to glow, or the transformer to burn out.

And if the connector failed first, well it would make a heck of a bang.

And remember..don't try this at home. :grin:

While in the Air Force, we had an avionics tech hold in a circuit breaker on an F-4. He found the black box causing the problem, but also burned up the main wiring harness in the plane. A very costly mistake.


Edited to add:


Back on topic, I have noticed here in my own palatial estate that my line voltage peaks at about 128volts until midnight, when it shifts back down to around 120-121volts, with a few visible blinks of the lights. Methinks my POCO will soon be replacing the tap changer on that regulator soon.

 

[76nemo]

After #12,16&17, you have me worried MX. Jeffrey Dahmer started off with road kill. Do you see a pattern here?:grin::grin: :grin:

Just kidding. There's a couple of good shows on YouTube where sub-stations let go, they're saved in my favorites:grin:

 

[mxslick]

Am I perhaps a serial electrical killer?

Am I perhaps a serial electrical killer?

After #12,16&17, you have me worried MX. Jeffrey Dahmer started off with road kill. Do you see a pattern here?:grin::grin: :grin:

Just kidding. There's a couple of good shows on YouTube where sub-stations let go, they're saved in my favorites:grin:

LOL not to fear, I only go after electrical devices that tick me off...I've destroyed a fair bit of gear in my day that crossed me the wrong way. :grin:

Yeah, I have found a wealth of electrical destruction videos on YouTube.

One of the most dramatic, and a prime example of "Electricity Gone Wild", can be found HERE.

It all starts with a dropped tree limb, and then throw in a POCO's failed protection scheme...what a mess.