Are there any advantages of using a 480-208/120 transformer versus a 7200 or 12470 volt primary transformer??? We're looking at a couple of 150KVA type K and about six 200KVA 208/120v standard xfmr's. Wouldn't the 12.47KV primary xfmr deal with load changes better than the 480V xfmr? Also, we would be able to cut down on supply amperage and physical size of the package with 12.47KV vs. 480v, right? Any thoughts??

Are you wondering about the advantages of the utility supplying a high-tension (primary) service versus a 480 volt supply?

Won't the utility co. supply your x-formers? If so, they determine what size according to your load needs. You can ask for a certain secondary voltage.

Generally medium voltage (7kV or 13kV) service is better than low voltage (480V) for voltage drop, capacity and reduced conductor size.
You need to consider who will be servicing the transformer (on site personnel/electrician, a third party electrician or the utility.
Clearance and construction requirements help delineate installation differences.

This will be in a refurb of a hotel showroom where the 480 is already existing. They keep on saying that they're strapped for supply already in this area. I was thinking we should pull a 12.47KV line to a distribution to deal with the 8-10 xfmrs we will need, but they want to keep the old 480V lines... Perhaps if it was 10,000A service...

Who will supply and maintain the transformer? With deregualtion in Texas the customer would. Have you investigated the cost of going from a 480 voltage insulation rating to 12.47 kv? It seems the utility company would like to supply at the higher voltage (especially if the customer owns the transformer)because the losses on their side of the meter would be less.

How large an installation are you talking about (in additional load)?
There are big differences here.
You'd better be in the planning stages of this job?



[This message has been edited by electure (edited 04-09-2002).]

All of the equipment will be customer owned and serviced by onsite Engineering department. We're still trying to come up with load sheets because we're in the early planning stages... We know the dimming system will need 208/120 700KVA service

Is that a typo, or is the lighting dimming system need 2000 amps of capacity?

Sounds to me that you are describing the typical "Customer Owned SDS" [Separately Derived System].

The Customer is supplied with a 480Y/277 VAC 3 Phase 4 wire system of -X- KVA [or MVA].

If the load calced was higher than what can be derived from a 480 VAC service, then this would have [or should have] been supplied by a 2400 VAC system, or a 4160 VAC system.

The Utility supplied Power System will be in respect to the Calculated Load. That's where the System Voltage becomes a factor.

Scott SET.

Nope, no typo, 1200A per 3 dimmer racks... The service is not supplied by the local poco but supplied by the customer. The HV lines come into the building, get stepped down to 12.47kV on a couple of different xfmrs and then go to customer owned switchgear. Everything from there is customer owned and maintained. Just to give you an idea most buildings in this small area have their own substation and usually have 8-16 generators for emergency backup... (and employ about 10,000 employees per building)

FYI... The service for dimming just got bumped up to 1700KVA...