Generator output breaker

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JES2727

Senior Member
Location
NJ
A customer is having a problem with some generators. I'll try and explain:
Two generators are paralleled, I think they are 550kw each. Gen #1 is adjacent to the transfer gear, Gen # 2 is in the next room. Gen #1 is not equipped with an output breaker, the breaker in the ATS is serving that purpose. Gen#2 is equipped with a 1000A output breaker in an adjacent control cabinet in addition to the breaker in the ATS. Either these two units once operated individually, or Gen #1 and the parallel gear were added to the existing Gen#2. I say this because I am told the controls for Gen#2 are "abandoned".

Here's the problem (as it's been explained to me):
When the generators run, #1 goes online first. Before Gen#2 comes online the breaker at the generator trips. This is the breaker whose controls are "abandoned". It would seem that the units are not synchronizing so #2 drops out. Or... the "abandoned" controls for #2 are looking for a signal from the ATS that they're not getting, so the breaker drops out.

Here's the solution that I've been asked to provide:
Eliminate the tripping breaker. Just take it out and make it go away. I can do this easily enough and just splice the conductors, thereby eliminating the local disconnecting means and the overcurrent protection.

Here's some questions:
Am I required to provide a disconnecting means at Gen#2? Sec. 445.18 requires the gen to be "equipped" with a disconnect. If the output conductors enter another room before landing on the breaker, is the gen "equipped" with a disconnect? Maybe I can replace the breaker with a molded case switch, but do the output conductors require overcurrent protection before they leave the room?
Overcurrent protection and the controls are provided by the ATS. If there is a problem with the generators synchronizing then the breaker that remains in the ATS should be the one to react.
What else could be causing this breaker to trip?

Thank you.
 

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
A customer is having a problem with some generators. I'll try and explain:
Two generators are paralleled, I think they are 550kw each. Gen #1 is adjacent to the transfer gear, Gen # 2 is in the next room. Gen #1 is not equipped with an output breaker, the breaker in the ATS is serving that purpose. Gen#2 is equipped with a 1000A output breaker in an adjacent control cabinet in addition to the breaker in the ATS. Either these two units once operated individually, or Gen #1 and the parallel gear were added to the existing Gen#2. I say this because I am told the controls for Gen#2 are "abandoned".

Here's the problem (as it's been explained to me):
When the generators run, #1 goes online first. Before Gen#2 comes online the breaker at the generator trips. This is the breaker whose controls are "abandoned". It would seem that the units are not synchronizing so #2 drops out. Or... the "abandoned" controls for #2 are looking for a signal from the ATS that they're not getting, so the breaker drops out.

Here's the solution that I've been asked to provide:
Eliminate the tripping breaker. Just take it out and make it go away. I can do this easily enough and just splice the conductors, thereby eliminating the local disconnecting means and the overcurrent protection.

Here's some questions:
Am I required to provide a disconnecting means at Gen#2? Sec. 445.18 requires the gen to be "equipped" with a disconnect. If the output conductors enter another room before landing on the breaker, is the gen "equipped" with a disconnect? Maybe I can replace the breaker with a molded case switch, but do the output conductors require overcurrent protection before they leave the room?
Overcurrent protection and the controls are provided by the ATS. If there is a problem with the generators synchronizing then the breaker that remains in the ATS should be the one to react.
What else could be causing this breaker to trip?

Thank you.

First of all I am not sure what kind of a scheme you have there. :confused:You mention two ATS's and transfer gear. By transfer gear do you mean paralleling switchgear (two generator output breakers that feed a common bus?) When you say ATSs I cannot picture how they would be connected to parralel 2 gensets.:-? If the transfer gear and ATSs ore one in the same then it makes sense.
If gen #2 breaker is tripping then it is either from a fault, a shunt trip signal from the paralleling controls or the breaker inst trip unit is bad. I would not recommend "eliminating the tripping breaker" until you find out what is causing the trip.
Check if the breaker has shunt trip wires coming out of it then check the synchronizing relay to see if it is working properly. Has the system ever worked correctly? If not there may be wiring errors. AS for the code questions someone else has to answer.:grin::D
 
Two generators, one transfer switch, no paralleling gear, tripping breaker, someone giving poor installation directions.

Ask that an engineer provide you with the proper installation information so you can install this without creating such a liability for yourself.

What is the application for the generators... 700, 702?
 

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
Two generators, one transfer switch, no paralleling gear, tripping breaker, someone giving poor installation directions.

Ask that an engineer provide you with the proper installation information so you can install this without creating such a liability for yourself.

What is the application for the generators... 700, 702?[/QUOTE

Pierre
By definition. an ATS transfers power to the load from one source to another.
The mechanism is interlocked to close the contacts to one source or the other, not both. How can it parallel the 2 gens??:wink:
We need to see a 1-line diagram to help him with this problem.

Tony
 

JES2727

Senior Member
Location
NJ
First of all I am not sure what kind of a scheme you have there. :confused:You mention two ATS's and transfer gear. By transfer gear do you mean paralleling switchgear (two generator output breakers that feed a common bus?) When you say ATSs I cannot picture how they would be connected to parralel 2 gensets.:-? If the transfer gear and ATSs ore one in the same then it makes sense.
If gen #2 breaker is tripping then it is either from a fault, a shunt trip signal from the paralleling controls or the breaker inst trip unit is bad. I would not recommend "eliminating the tripping breaker" until you find out what is causing the trip.
Check if the breaker has shunt trip wires coming out of it then check the synchronizing relay to see if it is working properly. Has the system ever worked correctly? If not there may be wiring errors. AS for the code questions someone else has to answer.:grin::D
I was careless in my use of the terminology, I used the terms interchangeably. The generators are connected to paralleling switchgear (two generator output breakers that feed a common bus)
The breaker that is creating the problem does have shunt trip wires coming out of it, though I've been told they are "abandoned". This problem has arisen only recently. It was intermittent for a while but has become more troublesome now.

Two generators, one transfer switch, no paralleling gear, tripping breaker, someone giving poor installation directions.

Ask that an engineer provide you with the proper installation information so you can install this without creating such a liability for yourself.

What is the application for the generators... 700, 702?
I am unsure of the application. The generators back up a portion of a police station.
 

iwire

Moderator
Staff member
Location
Massachusetts
'Breaker keeps tripping, remove it.'



Sounds like something a homeowner would ask for and a handyman would gladly do.

For me I would need to know why the breaker is tripping and why it was in place in the original design before I would even consider eliminating it.
 
John
Now it sounds like an installation that has developed an issue. Without the diagrams, it is difficult to help. I would ask for help from an engineer or friend in the business (another EC). The application is obviously an important one.
 

JES2727

Senior Member
Location
NJ
'Breaker keeps tripping, remove it.'



Sounds like something a homeowner would ask for and a handyman would gladly do.

For me I would need to know why the breaker is tripping and why it was in place in the original design before I would even consider eliminating it.

John
Now it sounds like an installation that has developed an issue. Without the diagrams, it is difficult to help. I would ask for help from an engineer or friend in the business (another EC). The application is obviously an important one.
Thanks for the feedback.
I think you're both right. I need to find out why the breaker is tripping. However, if the problem is real and I remove the breaker, the breaker that remains (in the paralleling gear) should then behave the same way. We would then have eliminated the older breaker as the culprit and we could look deeper into the problem. That brings me back to the question about disconnecting means and overcurrent protection requirements at the generator.
 

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
Thanks for the feedback.
I think you're both right. I need to find out why the breaker is tripping. However, if the problem is real and I remove the breaker, the breaker that remains (in the paralleling gear) should then behave the same way. We would then have eliminated the older breaker as the culprit and we could look deeper into the problem. That brings me back to the question about disconnecting means and overcurrent protection requirements at the generator.

John,
The fact that you stated the tripping is intermittent is important. This means
that the wiring is correct since they do parallel properly, sometimes.
I would check the trip setting on the breaker trip unit. If the instantaneous setting is adjustable (usually 6 to 12X breaker rating) make sure it is set on or close to max to allow for inrush currents during paralleling.
If you eliminate the breaker and the breaker trip unit is defective or out of adjustment then the problem will go away. If the breaker is removed and the breaker in the paralleling gear starts tripping then you will have to look into the synchronizing circuit of the paralleling gear. Take an analog voltmeter
and connect it between gen 1 phase A breaker line side and gen 2 phase A breaker line side. Initiate the paralleling sequence and watch the voltage swing up and down. On a 480V system when the voltage drops to 90V or lower then the two sine waves are around 7 elec. degrees apart; a safe time for gen 2 breaker to close. If the close signal from the synch relay is being sent when the voltage is greater than the 90V then that's a good reason why the breaker is tripping. The relay is either out of adjustment or defective.
Another thought is to manually parallel gen 2 to gen 1. If the gear has a synchroscope or phase lights;with gen 1 breaker closed, you would close gen 2 breaker when the scope needle is just before the 12 o'clock position or when the lights go completely out. If you can manually parallel sucessfully
over and over then it's the sync circuit.
My gut feeling is that the problem is in the synchronizing circuit.
Hope this helps,:)

Tony
 

JES2727

Senior Member
Location
NJ
John,
The fact that you stated the tripping is intermittent is important. This means
that the wiring is correct since they do parallel properly, sometimes.
I would check the trip setting on the breaker trip unit. If the instantaneous setting is adjustable (usually 6 to 12X breaker rating) make sure it is set on or close to max to allow for inrush currents during paralleling.
If you eliminate the breaker and the breaker trip unit is defective or out of adjustment then the problem will go away. If the breaker is removed and the breaker in the paralleling gear starts tripping then you will have to look into the synchronizing circuit of the paralleling gear. Take an analog voltmeter
and connect it between gen 1 phase A breaker line side and gen 2 phase A breaker line side. Initiate the paralleling sequence and watch the voltage swing up and down. On a 480V system when the voltage drops to 90V or lower then the two sine waves are around 7 elec. degrees apart; a safe time for gen 2 breaker to close. If the close signal from the synch relay is being sent when the voltage is greater than the 90V then that's a good reason why the breaker is tripping. The relay is either out of adjustment or defective.
Another thought is to manually parallel gen 2 to gen 1. If the gear has a synchroscope or phase lights;with gen 1 breaker closed, you would close gen 2 breaker when the scope needle is just before the 12 o'clock position or when the lights go completely out. If you can manually parallel sucessfully
over and over then it's the sync circuit.
My gut feeling is that the problem is in the synchronizing circuit.
Hope this helps,:)

Tony
Tony,
Thanks very much for the advice. It will be useful when I return to the site.
I am now being told that the breaker trips because the gear is telling it to and ASCO addressed the problem years ago but it has now resurfaced.

Maybe I missed it but has anyone thought to actually test the breaker?
The customer wants to test the breakers in the transfer gear once the older breaker is removed. They just to get rid of this breaker because they feel it is redundant.

Thanks again to all for the help....
 

JES2727

Senior Member
Location
NJ
I'd like to revisit this issue to ask again about the code requirements.

There are some other technical people involved and they are confident that this breaker is not needed for proper operation and is a critical potential point of failure. They have asked me as the EC to remove it.
Does a remote output breaker satisfy the intent of NEC 445.18??
Also, does the remote output breaker satisfy the overcurrent protection required by 445.12?

In my opinion, the use of the word "equipped" in 445.18 means the disconnecting means is required at or on the gen, so a remote breaker doesn't cover it. I do believe, however, that the remote breaker meets the requirement for overcurrent protection.
This is just my opinion. I'd like for someone else to chime in and let me know what they think...
Thanks
 

JES2727

Senior Member
Location
NJ
Does a remote output breaker satisfy the intent of NEC 445.18??
Also, does the remote output breaker satisfy the overcurrent protection required by 445.12?

Here, I'll post the pertinent sections, so you don't even have to look it up :

445.12 Overcurrent Protection.
(A) Constant-Voltage Generators. Constant-voltage generators, except ac generator exciters, shall be protected from overloads by inherent design, circuit breakers, fuses, or other acceptable overcurrent protective means suitable for the conditions of use.


Here's the other one:

445.18 Disconnecting Means Required for Generators.
Generators shall be equipped with a disconnect by means of which the generator and all protective devices and control apparatus are able to be disconnected entirely from the circuits supplied by the generator except where both of the following conditions apply:
(1) The driving means for the generator can be readily shut down
(2) The generator is not arranged to operate in parallel with another generator or other source of voltage.


Anybody care to help me out here? Anybody??
 
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