What is voltage imbalance. Is it one phase has more voltage then the other?
- Thread starter zappy
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gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
100124-1827 EST
Why pick on 1%? Suppose I have a 120-0-120 supply and one single phase load of 200 A, a real big heater, can not split it. I am likely to have 5% or more difference, maybe 10% because the power company does not put in a very large transformer.
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Why pick on 1%? Suppose I have a 120-0-120 supply and one single phase load of 200 A, a real big heater, can not split it. I am likely to have 5% or more difference, maybe 10% because the power company does not put in a very large transformer.
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mivey
Senior Member
For poly phase systems:
% unbalance = 100 * maximum deviation from average voltage / average voltage.
According to ANSI C84.1:
Supply systems should be at 3% or less at the meter under no-load conditions. 98% of systems surveyed are within 3% and 66% of the systems surveyed were with 1% unbalance.
That said, when you get to the 0.5-1% range, you might expect to have to derate the equipment. Your class notes were probably referring to what you need to do to avoid derating the equipment.
Add: In the formula, use line-line voltages.
% unbalance = 100 * maximum deviation from average voltage / average voltage.
According to ANSI C84.1:
Supply systems should be at 3% or less at the meter under no-load conditions. 98% of systems surveyed are within 3% and 66% of the systems surveyed were with 1% unbalance.
That said, when you get to the 0.5-1% range, you might expect to have to derate the equipment. Your class notes were probably referring to what you need to do to avoid derating the equipment.
Add: In the formula, use line-line voltages.
quogueelectric
Senior Member
- Location
- new york
For example if a service would be delivered on the fringe edge of pocos distribution they may have 600 homes tapped off the primary phase A 200 homes tapped off the primary phase B and 1000 homes tapped off the primary phase C. This because of poorly distributed load can cause a substantial voltage difference on the voltages measured to ground on A,B,and C phase .
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