Building Generator power distribution questions and how they relate to Canadian/Ontario ESA/CSA code 1

[CanuckEngineer]

Hello All,

I have some questions regarding Emergency Generator distribution systems and how they relate specifically to Canadian/Ontario ESA/CSA codes since this particular installation has been built in Ontario.

First the overview: What we have is a Main-Tie-Main 600V-2500A distribution switchboard. This SWBD provides power for the entire site. This SWBD also acts as the emergency generator paralleling SWBD, there are embedded paralleling generator breakers within the SWBD. The main SOP is that after a utility power failure, the Main breakers open, the qty:3 diesel generators come up to speed and voltage, they parallel and close to the dead bus. The Tie breaker closes.

1. My first question, is that the Main breakers have manual operator push buttons located on them. Currently there is no electrical interlocks wired to these buttons to prevent the Main breakers from being accidentally closed to an unsynched generator bus. The contractor has placed padlocks on them currently to prevent this from happening. However I do not think it is sufficient. Is there any applicable code in CSA 22.2 that states there has to be some form of electrical protection on this breaker?

2. My second questions, we have a three generator system installed, however the engineer has only designed the system with a failure of one generator system via a load shedding system. Basically if one generator fails, loads are dropped and the other two generators take up the remaining load of the building. The engineer however has not designed for a two generator failure situation. Basically right now we have if a two generators fail, the one remaining generator will be overloaded and drop off. My questions is that is there some specific code reference which dictates that load shedding must be implemented all the way down to a one generator running system?

3. My third questions is: The engineer has placed the fire pump breaker upstream of the main breaker, which I understand is per code. The problem is that during a utility fail situation there is a Fire Pump ATS which transfers between the Utility feed to a single generator feed only for the fire pump. Basically if that one generator fails, let's call it G1, then the fire pump is lost however there are still two other running generators in the building. My questions is there any specific code references which dictate that if there is a multiple generator set installation that there has to be some form of redundancy for the Fire Pump distribution?

Much thanks.

 

[rcw retired EE]

Based on my work in Ontario, I do not recall seeing any code reference to the items that you mention. While each of the modifications you suggest might be good or better design, the original designs are not against CEC or Ontario code, unless the local inspector decides they are. There may be special considerations if this is a hospital.

Code is a minimum. Just because it meets code, doesn't mean it will work, or that it is safe or that it is what the client paid for.

Also, just because there is a better way of doing something doesn't mean that is what the client specifed or paid to have done. Designing for second, third or fourth contingencies is not usually part of a basic design. Your example 2 covers three contingencies: 1.loss of normal power, 2. loss of one generator, 3. loss of second generator.

 

[CanuckEngineer]

Thanks RC.

You make good points, primarily about if it meets code it is not necessarily safe and about three levels of contingency.

 

[davidbeach]

As you start adding contingencies the number of possible responses rises rapidly. At some point you are much better off with capable personnel on site to determine the necessary response when too much sh!t is clogging the ventilator.

As for your first question, the close button on the breaker is a mechanical close and can't be interlocked. Lock is the best you can do.

 

[rcw retired EE]

On one job in Toronto, the back up generator connected to one side of the Main-Tie-Main normal power switchgear with a sophisticated PLC system operating all breakers for power loss or paralleling. It also had the manual close button problem. We purchased blanking plates to cover the Manual Close PB's on all synchronizing breakers.

Another issue was the switchgear also fed the fire pump form one of the load busses. Per Ontario Code, fire pump feeders cannot have ground fault protection and must be able to carry full locked rotor current. To comply, we had to defeat ground fault on the entire switchgear, Mains, Tie and Feeder breakers and raise the short time trips which caused arc flash issues. The electric fire pump was backed up by a diesel fire pump, so this excessive caution was unnecessary. It took several sessions with the inspector before we were able to go back to more reasonable protection settings.

Moral of the story- simple is better.