poltergeist

[mshields]

At a hospital I do alot of work for, they've recently lost their backup generator. Not their only generator but the one that backs up the Level 1 Emergecy Generator. Since they deem this backup of the backup as essential, they've gone out and gotten a temp unit. THe temp unit is a 500kW. THe existing unit is a 350KW.

There are some obstacles to replacing the dead generator, they're going to live with this arrangement for the next, maybe 6 months but they're having a strange problem. When they last tested the temp and permanent generator they simulated the stationary generator dying and switched over to the temp. All went according to plan - no problem. So then they switch back to the existing generator and circuit down stream breakers tripped. a 100A-3P was the largest but also a 50A-3P and several 20A-1P. I've not yet investigated to find out exactly which breakers these are but I'm told they're all fairly down stream in the distribution.

The question is what could possibly be causing this to happen. If you switch from utility to the 350kW generator nothing happens. Why would these breakers be tripping when they switch from the temp generator to the old. All transitions by the way are open transitions.

Any thoughts

 

[roger]

How long is the open transition? Is there any in-phase monitoring between the two generators?

Roger

 

[mshields]

your response

your response

No Roger there isn't. But why would you need it for an open transition?

 

[steve66]

No Roger there isn't. But why would you need it for an open transition?

An open transition may only last 1/10 of a second or so. If the ATS supplies any motors, then they will still be coasting, and acting as small generators.

Then bang, a different generator comes online, and its not inphase with the motors, so you get a surge. And anytime there is a surge, there is a chance a breaker will trip.

If I understand correctly, there is a generator that backs up a generator that backups a utility? Is that correct?

I'm not sure how much luck you will have if you try to turn on the in-phase monitoring. If they don't both have electronic controls, they may not match frequency close enough to synch.

 

[zbang]

Then bang, a different generator comes online, and its not inphase with the motors, so you get a surge. And anytime there is a surge, there is a chance a breaker will trip.

Exactly what I was thinking. That's why there are often delays built into the cut-over; so motors can spin down and be sequentially restarted.

 

[templdl]

That?s my opinion also. If the TS has a TDN (time delay neutral) set a delay. Remember that there had to have been a delay when the power was lost until the time the generator stated and the switch over to the emergency source. As such there would be no issues with a short delay transferring back to normal. When you don't let the motor loads settle down a bit they will generate enough counter EMF because they are more often than not out of phase with the normal source that you will get a current spike which acts like a short circuit and the breaker will trip instantaneously.

 

[hurk27]

H'mm never heard of this kind of problem with motors but big time with transformers, which was what I was going to guess?, generally most motors will have the delay of a few cycles from the starter contactor pulling back in and or other controls. but I will say most of the times I have had this problem was the ATS returning back to the utility not another generator?

 

[roger]

An open transition may only last 1/10 of a second or so. If the ATS supplies any motors, then they will still be coasting, and acting as small generators.

Then bang, a different generator comes online, and its not inphase with the motors, so you get a surge. And anytime there is a surge, there is a chance a breaker will trip.

If I understand correctly, there is a generator that backs up a generator that backups a utility? Is that correct?

I'm not sure how much luck you will have if you try to turn on the in-phase monitoring. If they don't both have electronic controls, they may not match frequency close enough to synch.

That is where I was going with my questions.

Roger

 

[Joethemechanic]

they're going to live with this arrangement for the next, maybe 6 months

Just curious why it is going to take 6 months to repair/replace a little 350 KW unit? I've had them that I had to disassemble/reassemble to get into buildings but 6 months seems way way long on the time to complete the project. What could this thing be? A KT Cummins or a 92 series Detroit?

 

[hurk27]

I guess I should explain my response in post 7 as it is because of my lack of not having the experience with ever finding a problem like this that was because of motors just means I have never run across this type of problem before, and as I posted most of problems like this was attributed to transformers being fast transition back into the utility too fast which results in blowing fuses protecting the transformer.

So I started a new thread so not to take this one sideways that maybe we can discuss the science behind motors on a poly-phase systems so I can get my brain to wrap around this to better understand this problem a little better.

Heres a link to the new thread: CLICK HERE

 

[socalelect]

Just curious why it is going to take 6 months to repair/replace a little 350 KW unit? I've had them that I had to disassemble/reassemble to get into buildings but 6 months seems way way long on the time to complete the project. What could this thing be? A KT Cummins or a 92 series Detroit?

joe you never cease to amaze me with the old school engines you name off , its been a while since i have seen the old kt's or kta's
i however have disassembled and reassembled a monster of a generator with twin 8v92ta's on it , that thing was a trip the 2 engines were side by side connected to the generator with a 2 bellhousing housing , i cant remember what it was called i think it had a clutch in it as well , when i started it earplugs werent near enough :happysad:

 

[Joethemechanic]

"The Roundhouse" (poliece headquarters) here in Philly has a 16V-92 Detroit that was installed in the mid 90's. It's basically a pair of 8V-92 blocks end to end. I'm thinking it is rated 900KW at a 0.8 PF.

During test runs it seriously made my teeth itch.

Somebody around here has a KT or KTA Cummins powered unit is their sewer plant. I'm thinking South Jersey. That KTA was good for a bit over 800HP in factory trim @ 1800 so it may be a little overkill for a 350KW unit.

But seriously, why 6 months, unless they are doing extensive upgrades.

I'd love to know how somebody killed a backup, to a backup. I'll bet it never saw an hour put on it that wasn't put on it during exercise.

 

[socalelect]

probably maintence related , if it is indeed a backup to a backup . i see it alot around here with the back ups that that the fire depts have at their stations , we reccomend service annualy , oil, filter , test coolant blah blah the response we get is well it only runs like a hour a week the power goes out rarely it should be fine , maybee next year there mostly 45 kw kohlers , the latest problem we have had is the rats move in and eat the wiring , have had a couple start fires when the ran thru there excersize cycle due to rat problems

i CANT stand detroits , the company i used to work for had a fleet of tractors with the " buzzin dozen" 12v71 those things are scary when they suck the blower seals :thumbsdown::thumbsdown:

 

[Joethemechanic]

To me 2 stroke Detroits aren't old. Buda, Allis Chalmers and Waukesha are "a little" old lol

As far as newer units I like, John Deere makes a first class generator engine, and Hino makes a pretty good engine. the First Police district has a Hino Powered Generator in the basement. I'm thinking somewhere around 150KW.

A lot of people swear by Cat, and there are some good Cat units, but all those 3406 series that leaked around the crevice seals because somebody didn't want to keep the coolant addiditive levels right. Next thing you know you have an otherwise perfectly good running engine with coolant in the lube oil. And it is a seriously expensive fix

 

[steve66]

That is where I was going with my questions.

Roger

Yes, I figured that's were you were going. I didn't mean to hijack the discussion - hope you didn't mind me jumping in.

I've had breaker trip even when phase monitoring is enabled. Those usually seem to be the smaller branch circuit breakers. Not sure what the reasoning behind that is. I guess some things just don't like the power on, power off, and power back on 0.1 sec. later.

 

[roger]

hope you didn't mind me jumping in.

Not at all, I'm glad you did.

Roger

 

[socalelect]

To me 2 stroke Detroits aren't old. Buda, Allis Chalmers and Waukesha are "a little" old lol

As far as newer units I like, John Deere makes a first class generator engine, and Hino makes a pretty good engine. the First Police district has a Hino Powered Generator in the basement. I'm thinking somewhere around 150KW.

A lot of people swear by Cat, and there are some good Cat units, but all those 3406 series that leaked around the crevice seals because somebody didn't want to keep the coolant addiditive levels right. Next thing you know you have an otherwise perfectly good running engine with coolant in the lube oil. And it is a seriously expensive fix

crevice seals , you talkin liner o-rings ? anything CAT is expensive you ever seen when effed up coolant does to liners ?
im actually a fan of the MQ generators they have always been good to us and ( we have a fleet of i think 12 or 14 ranging from 45kw to like 250kw
alot of our customers dont want to buy a gen but they will set up a dock for them and then when the power goes out like it did a couple months ago call in a panic and not care about the cost of a rental
we have a couple of 150 kw gens with cummins 8.3's or ISC's as they call emm now they are near bulletproof

 

[Joethemechanic]

crevice seals , you talkin liner o-rings ? anything CAT is expensive you ever seen when effed up coolant does to liners ?

Exactly what I'm talking about. You know how many 3406 Cats I have torn apart that were low hours and otherwise perfect. Now give me a 1693 and I'm good

 

[Open Neutral]

H'mm never heard of this kind of problem with motors but big time with transformers,

A motor is a transformer with a primary winding & a mechanical secondary.

 

[mshields]

answer to questions

answer to questions

This in indeed a generator backing up a generator backing up the utility. The first generator is a temp 500kW with the existing generator it is backing up being a 350kW.

I understand the back EMF comments. But the thing of it is, that doesn't, correct me if I'm wrong explain why it only happens in one direction. From the 500kW to the 350kW.

If you go from the 350kW to the 500kW it never happens. THat's what really threw me off.

As for the delay in getting this unit replaced it is related to the fact that the units are inaccesible. So it's more than just the lead time of getting a replacement unit. It's finding it a new home. Even if we could put it where the old one is, we don't want to.

Thanks for all the input.

Mike