Using a 480 240y/139 transformer for 240 lights

Status
Not open for further replies.
B

BenS

Member
Before I started my current job, the powers-that-be decided to revamp a floating dock's lighting system. The current system is 240V provided by a 480 240/120 transformer via a submerged cable. They ordered a 30kva 480d-240y/139 transformer, which is to be installed on the dock instead of onshore. A new submerged cable (4/4) will supply the 480 to the dock.
They seemed very surprised when I told them 120 wouldn't be available with this transformer. Further, I really don't think this is the appropriate transformer for single phase lighting. I was of the understanding that this type if transformer is rarely used, and then only for specific types of motors. I also am not certain how to go about grounding this system.
 
You just ground XO like you would on a 208/120 wye system. I see no reason why you can't use this for 240 volt lighting, but as you said, you can't use it to supply 120. The most common use of this transformer is as a drive (VFD or other) isolation transformer.
 
Like Don said, there is no problem using this for 240V lighting. These transformers offer a convenient grounding point, so they are starting to be used instead of 240V delta units to supply industrial heaters as well as drives.

However all of your 2-pole circuit breakers need to be rated for 240V only, you may not use the common/normal 120/240 ones.
 
Okay, Thanks.
Now,
Power is generated from a 480v 3 phase 250Kw generator, we are not tied to the grid at all. It is already fairly unbalanced, anywhere from 20-50 amps difference between legs. Since I will have 240V 3 phase running single phase loads, should I attempt to balance the generator by using the banks of lights? Or should I try to balance loads on the transformer the best I can? They will be on 24x7, so this will be a constant load. The lights are going to come in somewhere around 15KVa. Efficiency is not top priority since we are using hydro 99% of the time.

Simply by doing this conversion we are taking a step in the right direction by getting the 480-240/120 transformer out of the circuit, but it was only a 7KVa to begin with so not too big a deal. Speaking of which... I am very tempted to use the old 7Kva transformer to provide the 120 service which will be needed. The other option would be a 240/120 step down transformer. Loads will be limited to infrequent use of power tools, battery chargers and a few incandescent lights so I can go quite small, maybe 1kva or less. Which sounds like the better option?
Thanks a lot,
Ben
 
It depends on how your lighting reacts to un-regulated voltages, but I would go for balancing the generator rather than balancing the transformer.

Re-use the 7kVA. It may be possible to reconfigure its primary to be 240V, in which case you can run it off of your 240Y/139 unit as if it were a light.
 
Status
Not open for further replies.
Top