N+N power supply to a building

[psc2262]

We have a project where the deisgn criteria specified is: Emergency Power utilising Direct Coupled Generator and Rotary UPS – N+N system required.

Our design is a 1000 kVA substation for normal power supply (which meets the total power requirement) from the utility grid and a 1000 kVA Rotary UPS with Diesel generator. In normal situation the power supply is from the grid through the rotary UPS and when the normal supply fails there is a no break transfer to the rotary UPS and power is supplied by the diesel generator. Could this be called a N+N system?

A single line diagram is attached for clarity.

 

[Art]

We have a project where the deisgn criteria specified is: Emergency Power utilising Direct Coupled Generator and Rotary UPS – N+N system required.Our design is a 1000 kVA substation for normal power supply (which meets the total power requirement) from the utility grid and a 1000 kVA Rotary UPS with Diesel generator. In normal situation the power supply is from the grid through the rotary UPS and when the normal supply fails there is a no break transfer to the rotary UPS and power is supplied by the diesel generator. Could this be called a N+N system?

A single line diagram is attached for clarity.

first, that single line looks like a mil (defence) installation...should it be posted?

second, to be a '2N' or N+N as you put it, you would need another identical rotary UPS

I would not even classify it as a N+1 (1+1), if you loose the UPS you can feed it by by-passing with ATS's, but you have no UPS back-up if you lose your utility power...you're down until the genset winds up...

N+1 (5+1) would be say 6 each 220kva units, so if you lost 1, you would still have 1100kva to carry the entire load...

 

[Wolverine]

Just curious - what's the ride-through time of the R-UPS? Basically, what is it's purpose? Is it a buffer for short term outages of a few seconds until the utility returns, or is it capable of carrying the load long enough for the Diesels to fire up? In either case, it seems to be more of a power conditioner than a backup since I'm guessing only the gens can carry the full load continuous (I'm going to assume they're fully rated for load?). I have heard of rapid start gens though, so maybe only a few seconds of UPS are needed.

Hey Art, check out the note to the right of the main supply bus. Perhaps there is a plan for a second R-UPS. Does that also imply a second genset? Or back to my last question, is the one genset fully rated and this is just a second load bus? Interesting.

I haven't done this kind of work in a while, and then only rarely, but I'll say I'm never quite comfortable with N designations. Does the customer want backup, redundant backup, or backup with redundant backup to the backup? How many N's is that?

One more question: does the utility require any sort of reverse power protection?

 

[Art]

Just curious - what's the ride-through time of the R-UPS? Basically, what is it's purpose? Is it a buffer for short term outages of a few seconds until the utility returns, or is it capable of carrying the load long enough for the Diesels to fire up? In either case, it seems to be more of a power conditioner than a backup since I'm guessing only the gens can carry the full load continuous (I'm going to assume they're fully rated for load?). I have heard of rapid start gens though, so maybe only a few seconds of UPS are needed.
Hey Art, check out the note to the right of the main supply bus. Perhaps there is a plan for a second R-UPS. Does that also imply a second genset? Or back to my last question, is the one genset fully rated and this is just a second load bus? Interesting.

I haven't done this kind of work in a while, and then only rarely, but I'll say I'm never quite comfortable with N designations. Does the customer want backup, redundant backup, or backup with redundant backup to the backup? How many N's is that?

One more question: does the utility require any sort of reverse power protection?

they used to be the standard method...I saw many of them in the 80's...usually they carry over for a few seconds, obviously depending on the size of the flywheel

the ones I saw had batteries/inverters as the emergency power...they would power the rotary UPS until the genset wound up...

sometimes the batteries/inverter would actually carry the load until the genset could fire up...

good eye, yep bet your right, looks like a second R-UPS is planned, then it would be 2N, as long as it carries the full common load...and not another bus

the xfer switches provide utility isolation...as long as they are all coordinated properly...becasue as you observed the M could become a G under some circumstances

the 'Day 1' cable is probably emergency power the driver the r-ups until the genset stabilizes

 

[psc2262]

To clarify some of the queries, the Rotary UPS is designed to provide uninterrupted power supply with the stored energy in the flywheel used to ride through the 15 seconds period during which the diesel generator will start and support the full load. The diesel generator set is an integral part of the Rotary UPS and is rated for prime power (unlimited continuous operation as per ISO 8528).Ten percent overload capability is also available in accordance with ISO 3046, AS 2789, DIN 6271 and BS 5514.

Yes there will be directional relays to prevent power feedback to the grid.

The Rotary UPS and the utility are each capable of supporting the full load independently. That is the reason why I asked if it would be considered to be a N+N configuration. As per definition if I need 1 MVA supply to support the full load and there is a 1 MVA addtonal supply through the Rotary UPS then it should be called a N+N configuration.

Your feedback/ comments would be most appreciated.

 

[Art]

To clarify some of the queries, the Rotary UPS is designed to provide uninterrupted power supply with the stored energy in the flywheel used to ride through the 15 seconds period during which the diesel generator will start and support the full load. The diesel generator set is an integral part of the Rotary UPS and is rated for prime power (unlimited continuous operation as per ISO 8528).Ten percent overload capability is also available in accordance with ISO 3046, AS 2789, DIN 6271 and BS 5514.
Yes there will be directional relays to prevent power feedback to the grid.

The Rotary UPS and the utility are each capable of supporting the full load independently. That is the reason why I asked if it would be considered to be a N+N configuration. As per definition if I need 1 MVA supply to support the full load and there is a 1 MVA addtonal supply through the Rotary UPS then it should be called a N+N configuration.

Your feedback/ comments would be most appreciated.

no, it's not a N+N (2N)

if you lose the UPS, you have no back-up...no redundency

a single compnent failure results in loss of back-up power...

you need another UPS or 6 smaller ones of 200KVA each (N+1 or in this case 5+1)