Compensate for Load Voltage Drop with a Transformer
Compensate for Load Voltage Drop with a Transformer
(OP)
I have a situation where I have a 277 Vac, 20 A load about 750 ft from the source. Due to the voltage drop I would like to us a 480/277 transformer at the source and bump the secondary voltage to approximately 285 Vac to compensate for the voltage drop.
Two problems I have is; that I will need to purchase components (Lighting Panel and Circuit Breakers) rated for the higher voltage and finding an appropriate transformer. If I adjust the primary taps on the transformer I will exceed the rating of the secondary because the source is 480 V. If I use a Buck-Boost Transformer it will have to be at the load, which is not acceptable. Please correct me if I’m wrong.
I would appreciate any information or assistance.
Brandon
Two problems I have is; that I will need to purchase components (Lighting Panel and Circuit Breakers) rated for the higher voltage and finding an appropriate transformer. If I adjust the primary taps on the transformer I will exceed the rating of the secondary because the source is 480 V. If I use a Buck-Boost Transformer it will have to be at the load, which is not acceptable. Please correct me if I’m wrong.
I would appreciate any information or assistance.
Brandon






RE: Compensate for Load Voltage Drop with a Transformer
Hopes this helps,
Sense
RE: Compensate for Load Voltage Drop with a Transformer
Sometime I get confused when denoting the voltage. For 480/277 source the primary voltage is 480 and the secondary 277. Please adive.
Thanks again
Brandon
RE: Compensate for Load Voltage Drop with a Transformer
RE: Compensate for Load Voltage Drop with a Transformer
RE: Compensate for Load Voltage Drop with a Transformer
as for the rating of breaker, cables etc. goes, most devices are rated up to 600V, if you check its compelete listing.
But above all 285 is barely 2.9% change is well within tolerance and average deviation of utitly voltages of -15% to +10%..for which all electrical devices are expected to fucntion..so I would not worry about device ratings. In fact this range would be covered by tranformer taps.
If you already have 480Y/277 supply, you can use buck-boost tranfromer at the "Supply" end too.
RE: Compensate for Load Voltage Drop with a Transformer
Also, a 2 winding dry transformer has an impedance of around 5.4% which means that an extra transformer will be murder on inductive loads, particularly when motors start. Also, each transformer introduces no load and full load resistive losses. You would also need power factor correction capacitors that are hooked up to both current and voltage sensors so that the power factor can be made capacitive on the secondary of a 2 winding transformer so that the inductance of the transformer acts a a voltage booster; however, the capacitors will cause a severe voltage swell if a load suddenly drops out.
What would be more economical is to go to www.sefcor.com and buy some aluminum alloy weldment lugs that you can tungsten-inert-gas weld to the ends of aluminum conductors. For what copper costs you can put in twice as much aluminum cross section and get better voltage drop. For this distance fatter wires would be the best bet for controlling voltage drop.
If First Energy had used welded lugs for all wire terminations and splices on the Chamberlin-Harding 345 KV line the 14 August 2003 blackout would never have happened. The only way that line could have sagged into trees at 44% of rated current ( 20% of maximum theoretiucal heating ) is if 1/3 or 1/2 of the wire strands were conducting.
RE: Compensate for Load Voltage Drop with a Transformer
RE: Compensate for Load Voltage Drop with a Transformer
I believe I'm providing the confusion. I don't think I used the proper notions to describe the situation and I didn't understand the complete system.
To clarify I have a 277 Light Panel in an electrical room. Due to the voltage drop the lighting panel would not be an option without using either extremely large copper wire (aluminum is not an option) or a buck-boost transformer per circuit either at the load 750ft away or in the electrical room near the panel.
I thought that there was a 480 to 277V transformer supplying the light panel, which is stupid. A 277 Vac panel is powered from a 480V 3phase Y supply. 277 line to neutral and 480 line to line. The correct notion should have been 4160 - 480/277. Correct?
One Alternative would be to use a 3 phase 480V buck-boost transformer to supply a 480/277V Light Panel at a voltage of 493/285V. I will still need to use large cable but not quite as large as without the buck-boost.
I apologize for the earlier confusion. I am new to this arena of engineering and still learning. Again thank you for your assistance and patience.
Brandon
RE: Compensate for Load Voltage Drop with a Transformer
Sense
RE: Compensate for Load Voltage Drop with a Transformer
I would agree with Sense that if your lighting load is only 20A, the best solution is to use larger conductor. You will also lower losses this way which would partially offset the extra conductor cost.
If you have multiple fixtures, you could run 3-phase and serve about 1/3 of the fixtures from each phase. This would greatly reduce the voltage drop. The current would be about 1/3 and the impedance about 1/2 for the same size wire.