Diesel stand-by Generator Circuit breaker

[Mila2015]

We are planning to install a 2MW, 4.16KV stand-by generator to feed existing MV switchgear. Are there any special requirements for the Generator Breaker? IEEE C37.013 talks about DC components of fault current up to 75% (due to high X/R ratio), but the standard indicates it applies to "all ac high-voltage generator circuit breakers rated on a symmetrical current basis that are installed between the generator and the
transformer terminals". This generator will be feeding a MV SWGR directly, not a step-up transformer this standard refers to. Any thoughts?

 

[crshears]

To my view, this question would be a better fit in the Electric Motors & Generators Forum...but don't bother re-posting it now.

Will the switching always be performed "break before make?" The nature of the load will dictate this...and the AHJ will definitely have stipulations either way...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Mila2015]

crshears, you are correct regarding the forum...sorry about that!

The generator may need to be synced with the electrical system, so I don't believe it's always "break before make". All other breakers in the SWGR assembly are normal feeder breakers feeding MV motor loads, and distribution XFMRs.

 

[waross]

cr A standby generator is generally protected by a circuit breaker that is not part of the ATS.
The best and cheapest answer is to let the set manufacturer select, supply and install the breaker.
Spec: "The set will be constructed in accordance with all applicable codes and standards including, but not limited to...."

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

 

[waross]

The most difficult duty of the breaker will be clearing back fed faults into a faulted generator, when in parallel mode.
The high impedance of the generator limits the fault current supplied by the generator to much less than grid fault levels.

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

 

[Mila2015]

waross, that is correct. The ETAP model show fault from system around 33kA, while generator is supplying additional 3kA. The Breaker's interrupting rating is 50kA. The longer DC contribution will be from the generator side I believe, so I'm sure if the 75% IEEE C37.013 is applicable in this situation?

 

[cuky2000]

See if this Link can help.

 

[Mila2015]

cuky2000, thanks for the link. This addresses the IEEE standard I mentioned above, which specifically applies to Generators connected directly to step-up XFMR as I mentioned. Are there any examples of systems involving stand-by generators feeding MV switchgear? Why would that differ from other breakers in the same lineup exposed to the same level of fault levels?