Blocking Scheme - Generators
Blocking Scheme - Generators
(OP)
I have a paralleling generator system in the USA at 12,470V, 5MVA (2 gens) and it parallels and terminates to the main service entrance bus. There is a bus tap on the secondary of the main utility service entrance breaker that feeds a distribution board.
Q1) If there is a fault on my distribution board on the line side of the main breaker that would cause my main utility service entrance breaker to trip (tapped the bus on the secondary of the main). That will in turn start the generators. Is it typical to wire some sort "blocking" scheme to prevent the generators from coming on the bus?
Q2) If not as soon as my utility service entrance circuit breaker opens up and the generators come online they will imediatly see the fault and trip off as well? True?
Q1) If there is a fault on my distribution board on the line side of the main breaker that would cause my main utility service entrance breaker to trip (tapped the bus on the secondary of the main). That will in turn start the generators. Is it typical to wire some sort "blocking" scheme to prevent the generators from coming on the bus?
Q2) If not as soon as my utility service entrance circuit breaker opens up and the generators come online they will imediatly see the fault and trip off as well? True?






RE: Blocking Scheme - Generators
RE: Blocking Scheme - Generators
I have seen a couple of installations such as you describe without blocking. Yes, if the main breaker trips (or is turned off manually) the generator will start. Fortunately main trips are very rare.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Blocking Scheme - Generators
I recently finished a startup of a system similar to what you described. If the main protective relay saw a "serious fault" it rolled the 86 lockout, with the main breaker's lockout rolled only one generator would start and only close to the life safety feeder. The load shed load/add system opens the other feeders on loss of the main. If the main protective relay saw a loss of phase, low voltage or frequency, it provided the signal to start both generators and allow the load shed/load add to function normally, and when it determined the utility was "OK", it would send a "Utility OK" signal to the PLC which would do a closed transition return sequence.
I have done similar systems at a number of sites, one main concern with most customers is providing proper support to the life safety circuits. Sometimes we can do as described above, in other systems we have added another smaller generator in the LV part of the system close the the life safety circuits.
So back to "it depends", but it is done on many systems, just needs a little more thought and coordination than most other types of standby systems, at least in my experience.
Hope that helps,
Mike L.