Electrical distribution panel (very important ) 6

[Mohamed haggag]

Hi lads,
need advice here
we are building low voltage distribution panel to supply loads such as compressors, dryers, etc
the main supply will be from the utility and we use 1250A LOAD BREAK SWITCH, at the same time the same panel will be supplied from the emergency supply which will be the generator and we put 800A AS Incomer
what precautions should be in place to protect the panel from being supplied from both sources at the same time? for sure the generator breaker will be LOTO at all time unless we lose the main supply
any ideas? i will use the shunt trip coil. thanks

 

[cranky108]

I believe there are special throw over panels or switches for that, assuming you can take a dead moment between the two.
They should have an interlock, or the switches for that should be a three position with a center off. They should also be lockable in all positions.
A panel for just this could be before the main breaker.

 

[Mohamed haggag]

from the technical point of view, what is better
1- using 1250 A change over switch OR Using separate isolator and circuit breaker for each source and depending on LOTO theory?

 

[BrianPetersen]

DO NOT rely on people to follow a procedure when the consequences of failing to do so are high!

 

[Mohamed haggag]

Thanks Brian
I will use shunt trip as well besides LOTO

 

[TugboatEng]

Your backup supply is significantly less than your primary so you may also want to consider automatic load shedding. This can be as simple as undervoltage trip breakers on non-essential loads.

 

[Mohamed haggag]

All loads will be controlled manually through ON/OFF
Backup supply will be used only during emergency

 

[waross]

If you have to ask, it may not be wise to do it yourself.
I do not mean this as disrespect, I respect you for asking.
Consider an automatic transfer switch.
This will have both electrical and mechanical interlocks.
This will automatically start the generator and transfer the load to the generator in seconds.
This may send a signal to a load shedding scheme.
This will automatically transfer the loads back to the utility when the utility is available.
The transfer may be immediate, transfer may be delayed for a set time, or transfer may be inhibited until manually initiated.

It is imperative that your scheme have some type of tamper proof mechanical interlock so that it is physically impossible for both the utility breaker and the generator breaker to be closed simultaneously.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

I have the following proposals for your consideration:
Assuming that the Utility 1200 A load break switch and the Gen 800 A incomer, may be from the same or different manufacturers. A "fast changeover" from Utility to Gen is not required. The 800 A is sufficient for the "essential loads". You can switch the loads back according to the need. Therefore, load-shedding is not required.
1. Check with the manufacturers whether the breakers can install with the same say (Castel/Ronis or similar...) lock on the breakers. Attention: issue only ONE key. The key is trapped on the breaker when in closed state. Off the breaker to remove the trapped key, to close the other breaker.
2. Fabricate a simple mechanical linkage bolted onto the breaker handles, allows only one breaker to be closed. Attention: this mechanical linkage is NOT mounted on the exterior of the door, as otherwise both breaker can be switched on with the door open.
3. Electrical interlock both breakers using Under-voltage release, NOT shunt.
4. The higher outgoing load breakers suggested install with UV release. Attention: a) advantage --the Gen comes in with light load, b) disadvantage --the load would have to be switch back manually after tripped.
5. Avoid outgoing breakers with shunt or without UV/shunt. Attention: these breakers would remain closed when the Utility power failed. It is undesirable to close the Gen 800 A breaker with all the outgoing breakers closed; even though most starters would had tripped open.
Che Kuan Yau (Singapore)

 

[cranky108]

I would say, use a device made for the interconnect purpose, as the down side is a smoking heap where your generator once was. Don't try to develop this yourself. I have programmed such device for higher voltage installs, and it is concerning all the details involved.
I don't feel this is something most consumers are set up to do there selves. And I say this from both a utility and a customer perspective.
You never said the voltage level you are working with, but I can guess it is less that 600 volts, with that current level.
If you get into voltages higher than 2400 or above commercial devices are typically not available, and need to be custom installs.

 

[waross]

I don't feel this is something most consumers are set up to do there selves. And I say this from both a utility and a customer perspective.

I agree with cranky108.
While either cranky or myself would be comfortable following Mr. Che's advice, but that is for very experienced persons only.
I have seen poor and/or dangerous designs come out of professional panel building shops.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!