How many secondary connections to one primary transformer?

[wehaveplans]

Hi everyone!

We are designing a very purpose built data center for a customer who does not need a secondary PUD feed or UPS battery backup systems. This is a long term storage (LTS) back up site. Our capacity plans for a 4.4mVa data center; backup servers are extremely dense and require a ton of potential energy. There will be 8 aisle of server racks in which we are planning on installing one busway systems per two rows of server racks, a total of 4 busway systems. We are planning on sourcing a European 13.2kV/415Y 5000 kVa transformer since we have PDU's that feed each phase to neutral resulting in 240v single phase without any secondary transformers. Each of our busway systems are 18 meters in length and are sized at 1200 amps (415v 4W L-N).

We are planning on having fusible disconnects that directly feed into the busway system. Do we need a distribution panel feeding the disconnects, or can we hook four fusible disconnects directly into the transformer in this configuration? The transformer is outside of the building 8 to 10 meters away from where the fusible disconnects will be located. 16 feed wires will be significantly cheaper in T&M than massive switchboard or distribution panels.

Thanks in advance for the help and let me know if I didn't include any information.

 

[Tony S]

With just one transformer you’re putting all your eggs in one basket. Personally I’d be looking at four 1500kVA units.

 

[steve66]

Hi everyone!

We are designing a very purpose built data center for a customer who does not need a secondary PUD feed or UPS battery backup systems. This is a long term storage (LTS) back up site. Our capacity plans for a 4.4mVa data center; backup servers are extremely dense and require a ton of potential energy. There will be 8 aisle of server racks in which we are planning on installing one busway systems per two rows of server racks, a total of 4 busway systems. We are planning on sourcing a European 13.2kV/415Y 5000 kVa transformer since we have PDU's that feed each phase to neutral resulting in 240v single phase without any secondary transformers. Each of our busway systems are 18 meters in length and are sized at 1200 amps (415v 4W L-N).

We are planning on having fusible disconnects that directly feed into the busway system. Do we need a distribution panel feeding the disconnects, or can we hook four fusible disconnects directly into the transformer in this configuration? The transformer is outside of the building 8 to 10 meters away from where the fusible disconnects will be located. 16 feed wires will be significantly cheaper in T&M than massive switchboard or distribution panels.

Thanks in advance for the help and let me know if I didn't include any information.

You probably could. I's suggest reviewing the rules in 240.21 for outdoor taps. You also need to comply with the rules for not more than 6 service disconnects, but it sounds like you will only have 4.

 

[wehaveplans]

With just one transformer you’re putting all your eggs in one basket. Personally I’d be looking at four 1500kVA units.

That's a very good idea as it would provide additional redundancies. In that configuration, we would most likely want to install a disconnect before the transformer so we wouldn't have to take the whole system offline for servicing one unit. Do you know what type of disconnect we should use? Preferably it would be able to mount on the transformer and provide over current protection. (at least I think, I only work with LV).

 

[JFletcher]

Does any of your gear require a neutral? If so, it may not like 240V on one side, but need 120-0-120. Not all 230/240VAC inputs are the same...

 

[Tony S]

That's a very good idea as it would provide additional redundancies. In that configuration, we would most likely want to install a disconnect before the transformer so we wouldn't have to take the whole system offline for servicing one unit. Do you know what type of disconnect we should use? Preferably it would be able to mount on the transformer and provide over current protection. (at least I think, I only work with LV).

Have a read through this

 

[steve66]

That's a very good idea as it would provide additional redundancies. In that configuration, we would most likely want to install a disconnect before the transformer so we wouldn't have to take the whole system offline for servicing one unit. Do you know what type of disconnect we should use? Preferably it would be able to mount on the transformer and provide over current protection. (at least I think, I only work with LV).

Its a site for long term storage, and doesn't need any backup power, and first cost is important enough to use individual disconnects instead of a switchboard.

But now you are looking at multiple transformers and a HV switchboard on the line side for the off chance the transformer dies or needs serviced?

Just saying....

 

[wehaveplans]

Its a site for long term storage, and doesn't need any backup power, and first cost is important enough to use individual disconnects instead of a switchboard.

But now you are looking at multiple transformers and a HV switchboard on the line side for the off chance the transformer dies or needs serviced?

Just saying....

We have a client who's facility has three 13.2kV/208Y transformers with 15kV load break switches in front of each of the transformers. If we were to use four 1500 kVa units, what issue would we run into with a similar configuration? We do need to service the gear once a year and ideally we would like to do it in sections.

 

[Tony S]

How much does reliability cost and how much is your client willing to pay?

I’ve installed plants with 100% back up, it’s a bloody expensive road to go down.

Limited back up is doable at reasonable cost. I don’t know about American standards for power transformer construction, UK transformers are rated for cyclic overload at 125% summer 150% winter. If you need to take a transformer out of service the LV load could be shifted to another unit for several hours.

 

[wehaveplans]

How much does reliability cost and how much is your client willing to pay?

I’ve installed plants with 100% back up, it’s a bloody expensive road to go down.

Limited back up is doable at reasonable cost. I don’t know about American standards for power transformer construction, UK transformers are rated for cyclic overload at 125% summer 150% winter. If you need to take a transformer out of service the LV load could be shifted to another unit for several hours.

The reason I have so many questions on what can be done is we actually do not need any reliability. Our facility is a very interesting case. The client performs data transfer once or twice a week. Due to this, we can build the facility to allow for complete power outages. A simple control server will be on two UPS battery back ups in case we lose the utility feed during a data transfer. This would simply save what is currently in the queue and communicate back saying there was an interruption.


"Data Center" would be the wrong term to tell an engineer since it's a completely different model. What we are looking for the most inexpensive way to take power from the utility and feed it to the racks, while following the NEC. Sourcing a 415v transformer seems to be a bit of an issue now.