Looking for a good way to explain to the brass why operating a chiller 990HP motor is better at 4160 than 480, the bulding does have a primary rate from the POCO. I have been searching for liteature that can explin it better than me.
Then factor in the risk of all that copper in the 480V system being a juicy target for copper thieves... It would be like waving around a bag of crack on a street corner in Oakland.
I would think the in-rush on a 990HP motor would be rather large and a breaker or 3 upstream might not like that. If there is any length to the conductors/feeder you may have voltage drop issues that would cause even larger sized wire then charlie already said.
... a transformer with 480 volt secondary will also have more copper than one with a 4160 secondary of the same kVA rating, probably the same with the motor.
Agreed. But go with SI and you don't need that conversion factor.HP = HP = HP = HP, and 1HP = .746kW, nothing about that changes with voltage.
Reducing the current by a factor of ten for the same conductor size would actually reduce the losses by a factor of 100 - remember it's i2R.At 460V, 990HP means roughly 1200A FLC, vs. 990HP at 4160V = means approximately 140A FLC. You will have almost 1/10th the I2R cable losses at 4160V. I2R losses extend to the motor windings and transformer windings as well.
Neglecting differences in insulation, the transformer secondary will be the same amount of copper.
Look at it this way:
Suppose the xfm is 1000kva, 4160Y. That's three 2400V coils, 139A. Consider that each 2400V coil is made of of 5 480V coils. Parallel connect the 5 coils in each 2400V coil. Reconnect the 480V coils Delta. Transformer is good for 1000kva.
I suspect it is the same for the motors as well in that the volts per turn has to be the same
ice
..., but I kind of have the feeling there still will be less copper in the higher voltage winding than there will be in the lower voltage winding. Happens that way all the time with other parallel circuit conductors. ...
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Transformer design is out of my areas of expertice. However, I have a feeling transformers are designed to minimize costs, including copper. Happens all the time with most other commodity equipment.
Then again, when I get those feelings - its usually just indegestion. You are likely luckier than I am in that respect.
ice