Multiple Generators Onto Single Transformers

[genhead]

A client has a temporary installation of 4 x 600kw 400v generators connected to a 400/11,000v 3MVA step-up transformer.
The generators are self-contained mobile units, each with its own circuit breaker. Each generator is cabled from the load-side of its circuit breaker to the LV terminals of the transformer, making the LV transformer terminals a common bus. There is no other 400v load, and the 11,000v feeds into an MV switchboard.
The client has been advised by somebody that additional circuit breakers must be installed at the load-end (transformer-end) of each set of generator cables, but his advisor was unable to provide any reasons why, other than "it is bad industry practice".

Can anybody please confirm if these circuit breakers are required, and why/why not.

 

[davidbeach]

What code governs? What is required in one place may not be required in an other.

 

[ScottyUK]

On the assumption - always a risky thing - that there are four generators for redundancy reasons, a 400V cable fault affecting one generator would essentially take down the whole installation if there are no breakers at the paralleling bus. If only one breaker was available / acceptable for cost reasons then I'd prefer it at the paralleling bus and include the cable within a differential zone protecting the generator.

But as David says, you may have code requirements which overrule engineering decisions.


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If we learn from our mistakes I'm getting a great education!

 

[genhead]

Scotty,

All four generators can operate in parallel. The client's concern is more about any potential protection issues (rather than loss of supply).

 

[waross]

I understood that Scotty was addressing protection issues and the possible loss of service that may follow the operation of the protection system.
But back to the original question, there may be code issues and apart from code issues, the distance and cable installation details of this particular installation would probably influence the recommendations on the second breakers.
If the transformer is very close to the generators, the second breaker may not be recommended. With a long distance from the generators to the transformer and cables subject to possible damage, the second breaker would probably be recommended. In between, "It depends".

Bill
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"Why not the best?"
Jimmy Carter