Main-Tie-Tie-Main Switchboards

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mbrooke

mbrooke

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Ok, say you have a main-tie-tie-main normal power switchboard setup and a main-tie-tie-main emergency switchboard setup. The gear is in separate rooms. My question is, are interlocks required? If so how do you interlock the two ties/mains? Do you need lights or gauges on the source/bus side of the tie?
 
Typically you would have 3 Kirk Key interlocks installed on M1, M2 and T1. They would all be keyed the same and only 2 keys available to the operator. The 3rd key is stored in the plant safe.
The 2 keys are inserted in M1 & M2 and closed, T1 is normally opened. The breaker can only be closed by inserting the key and turning it to release the breaker trip lever. If M1 side looses power, the M1 key is removed, breaker trips and key is inserted in T1 to close T1. All load is now fed from M2 side. Same procedure if M2 side looses power.
The purpose of this design is to prevent operation of the two supply transformers in parallel (phased properly, of course.)
Phase lights or gauges would be nice but not necessary.
 
ATSman said:
Typically you would have 3 Kirk Key interlocks installed on M1, M2 and T1. They would all be keyed the same and only 2 keys available to the operator. The 3rd key is stored in the plant safe.
The 2 keys are inserted in M1 & M2 and closed, T1 is normally opened. The breaker can only be closed by inserting the key and turning it to release the breaker trip lever. If M1 side looses power, the M1 key is removed, breaker trips and key is inserted in T1 to close T1. All load is now fed from M2 side. Same procedure if M2 side looses power.
The purpose of this design is to prevent operation of the two supply transformers in parallel (phased properly, of course.)
Phase lights or gauges would be nice but not necessary.
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I tried to edit but my time ran out.
Sorry, I just noticed that you have M-T-T-M. The configuration and theory wound be the same. Just add a 4th interlock to T2. M1, M2, and T1 would be normally closed with T2 normally open.
 
ATSman said:
I tried to edit but my time ran out.
Sorry, I just noticed that you have M-T-T-M. The configuration and theory wound be the same. Just add a 4th interlock to T2. M1, M2, and T1 would be normally closed with T2 normally open.
Click to expand...

Ok. The gear is in separate rooms, hence the two ties and conduit through fire stops linking the gear together. Same would apply?
 
You did not say that the two switchboards were tied together.
Is this an automatic transfer scheme where on loss of normal power the logic takes over and switches breakers to feed the load from the emergency switchboard? If so then mechanical interlocking will not work. Electrical interlocking would have to be employed to prevent the wrong breaker from closing during the breaker switching.
The scheme I described is for manual operation by an operator in a power failure.
 
ATSman said:
You did not say that the two switchboards were tied together.
Is this an automatic transfer scheme where on loss of normal power the logic takes over and switches breakers to feed the load from the emergency switchboard? If so then mechanical interlocking will not work. Electrical interlocking would have to be employed to prevent the wrong breaker from closing during the breaker switching.
The scheme I described is for manual operation by an operator in a power failure.
Click to expand...

No, not automatic. Manual. Both for the main power and emergency power. Its simple as possible. Basically 2 fully replicated systems only tied together via breaker, conduit and wire at the switch boards.



Question- do you know the code section that requires interlocking?
 
Single Line

Single Line

It would help if you sent us a 1-Line diagram of the complete distribution system so
we can address your application. Are there 2 gens feeding the emergency board?
Don't know about the code but it sure sounds like it should be required by some entity.
I am curious how this passed any inspections since without interlocking it becomes a life safety issue with
people's necks on the line. :eek:
 
ATSman said:
It would help if you sent us a 1-Line diagram of the complete distribution system so
we can address your application. Are there 2 gens feeding the emergency board?
Don't know about the code but it sure sounds like it should be required by some entity.
I am curious how this passed any inspections since without interlocking it becomes a life safety issue with
people's necks on the line. :eek:
Click to expand...

Generator 1 feeds E Board 1, Generator 2 feeds E board 2. Board 1 and Board 2 are linked via conduit. Same applied for the main feed but separate switch-gear.
 
From your link, here is a dual tie. In my case normal bus 1 and normal bus 2 instead of normal bus and emergency bus for the main power, and backup bus 1 and backup bus 2 instead of normal bus and emergency bus for backup power. 4 sets of gear in total in the building. For the sake of the argument we can discuss either one, preferably the emergency setup.
 

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mbrooke said:
From your link, here is a dual tie. In my case normal bus 1 and normal bus 2 instead of normal bus and emergency bus for the main power, and backup bus 1 and backup bus 2 instead of normal bus and emergency bus for backup power. 4 sets of gear in total in the building. For the sake of the argument we can discuss either one, preferably the emergency setup.
Click to expand...

Is there a reason you are keeping your as-built 1-Line a secret?
Liability issue?
 
There’s a problem with Kirk, Castell or Fortress keys, there’s always a way around them. We only had one panel with Kirk keys and in the 20 years I know of it was used once, that was by me.

Castell and Fortress, I have master keys
 
The code required part for transfer control is either because it is a 700, 701, or 702 source, which you would look to 70X.5 section for Transfer equipment for that requirement, or it is a 705 type system (which yours is not) which would be grid tied, which does not need the transfer equipment.

Transfer equipment is either automatic or manual. The key interlock or controller based electrically operated breakers would be the transfer equipment method unless you applied ATSs.
 
ron said:
The code required part for transfer control is either because it is a 700, 701, or 702 source, which you would look to 70X.5 section for Transfer equipment for that requirement, or it is a 705 type system (which yours is not) which would be grid tied, which does not need the transfer equipment.

Transfer equipment is either automatic or manual. The key interlock or controller based electrically operated breakers would be the transfer equipment method unless you applied ATSs.
Click to expand...

But as 700, 701, and 702 stands, this is for loss of normal power and transferring to emergency rather than switching outside of that scope.
 
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