Emergency power supply requirement

[krisys]

I have a system where the emergency diesel generator (EDG) is located in the main substation which is about 200 mtrs away from the new electrical room. The 415V main emergency switchboard (SWBD) at the main substation has one normal incomer and the EDG incomer. During the normal operation the normal incomer will supply power and during the blackout or normal incomer fails the EDG will start and restore voltage to the 415V emergency switchboard (SWBD). This is an industry standard arrangement in the main substation.

One of my emergency load in the new electrical room is supplied from the main emergency Distribution Board (DB) through three (3) intermediate emergency Distribution Board (DBs).

Up to the final load point, there are total eleven (11) circuit breakers in series. So many no. of breakers in series would reduce the system security drastically. Additionally, the relay coordination will be extremely difficult from the source to the load point.

I want to know whether there is any standard which specifies the maximum no. of circuit breakers permitted in the emergency supply circuit. Any reference is available?

Any thought/input is most welcome.

 

[Mbrooke]

None that I know of personally, but I do know with the correct relays and enough money you can coordinate anything. FWIW, fuses coordinate better then breakers.

 

[krisys]

Mbrooke (Electrical)
Thanks for your quick input.

If you have to coordinate all these breakers, imagine how many layers of curves. How can you give sufficient grading between some many devices. Please remember that all these relay/fuses are in the same voltage level.

 

[Mbrooke]

I will be honest, unless I want the first breakers holding a fault for some time I will either reach for fuses or "interlocking" (communicating) protection. The more time current curves are stacked on top of one anther the longer the trip time which I can imagine will not fair well for a short circuit sensitive source.


I can't remember off the top of my head at the moment, but I believe Eaton offered some type of solution for this.

 

[waross]

If there is a fault between the EDG and the Emergency Load of Interest it is expected that a breaker will clear it. If the branch circuit breaker does not clear the fault it will be cleared by an upstream breaker. Whichever breaker clears, regardless of coordination, the Emergency Load of Interest will be without power.
What is of more concern is all the other loads and breakers. If a fault on any branch circuit is cleared by a main breaker rather than the branch circuit breaker, you may lose power on your Emergency Load of Interest.
For a critical circuit, the coordination of all other circuits fed from the same main is more important than the coordination of the Load of Interest.
That said, if this Emergency Load is very critical, have you considered a new feeder from the source?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[krisys]

waross (Electrical)
Thanks for the input.

In our set up, it is very difficult to initiate any re-configuration and introduce anything new, unless there is some documentary evidence which suggests that. So in order to make the case strong, I need some good reference of codes.

My location is in the offshore oil platform in the middle east region. So mostly we refer IEC standards. However, API and NFPA are also referred, if the requirement is stringent.

I am still searching in some IEEE books like, IEEE 493 (Gold, Reliable Power systems) and IEEE Std 446 (IEEE Orange Book) - emergency and standby power.

I would appreciate if anyone provides me some lead.