plarmooh
Member
- Location
- Brunswick, MD
What is the allowable total transfer time for ATS to Emergency from Normal power
ATS transfer time
- Thread starter plarmooh
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Generally speaking, the upper limit is 10 seconds [700.12].
qcroanoke
Sometimes I don't know if I'm the boxer or the bag
- Location
- Roanoke, VA.
- Occupation
- Sorta retired........
That depends on what the classification is. If it is optional standby it is adjustable to whatever you want it to be.
If it is legally required emergency power it is required to be within a certain time.
I think NFPA 110 may address the time.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
701.11 Legally Required Standby Systems.
Current supply shall be such that, in the event of failure of the normal supply to, or within, the
building or group of buildings concerned, legally required standby power will be available
within the time required for the application but not to exceed 60 seconds.
The first thing to be considered is if the normal source is stable or not. What is the harm in delaying EN transfer to assure that the N souce will not fail again and is stable?
Then, there is the E souce feeding the load and now you want to transfer back to the N source. Should the and N sources not be in phase with the E source and you attempt a transfer back to the normal souce without any time delay there is a risk of a voltage spike resulting in a current spike tripping an upstream OCPD instantaneously. As such a TDN, time delay neutral, option should be considered to allow the load to settle down first and the transfer back to the N sourse.
Remember that it is common to use a generator as the emegancy source. With a normal loss of power the ATS starts the generator which must come up to speed/frequency and voltage first before the transfer is made which is a forced time delay by itself. As such what is the importance of the time it takes to transfer from the E back to the N souce?
Personally, I believe the goal should be to provide a reliable power sourse without the risk of additional power interruptions when playing around with transfer times.
Transfering between 2 POCO power can provide an opportunity to transfer if the transfer is do in phase. But, a delay between the N and E source would still exist to some degree.
- Location
- Massachusetts
The OP is not asking about E to N delay, they are asking about N to E delay.
Thasnks, You are correct.
But I be!ieve that I also addressed that also regarding assuring that the generstor is up to speed/voltager/ frequency before transfer and that the normal source is infact lost, and that is it is left up to judgement if there should be some delay to assure that the normal source my be disrupted because of a reclosure and what disruption in service that the load being surving its needs.
Upon loss of the normal source would it be appropriate to start the gernseyt(assuming that the genset is the emergency source) and transfer immediately at the time the genator is up to speed/voltage/frequency? Maybe yes maybe no.
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