Cable Sizing for Generators: 125% Rule vs. PF
Cable Sizing for Generators: 125% Rule vs. PF
(OP)
This should be a quick one:
For Medium Voltage applications, lets say I have a 2.6MW generator and I need to size the cable for this.
I normally go 2.6MW / 0.8PF to give me 3.25MVA (worst case PF, they typically run at 1PF).
And then go 3.25MVA / root3 / 4.16kV = 451A.
And then on top of that I add the 125% factor to give me 563A for minimum cable ampacity.
My colleagues say, that since you are already including a safety buffer in the 0.8PF, you don't need to add the 125% additional safety factor anymore....
I disagree, b/c the PF during operation can range anywhere between 0.8 to 1.0. So you can't rely on that for cable ampacity calcs.....
Thoughts?
For Medium Voltage applications, lets say I have a 2.6MW generator and I need to size the cable for this.
I normally go 2.6MW / 0.8PF to give me 3.25MVA (worst case PF, they typically run at 1PF).
And then go 3.25MVA / root3 / 4.16kV = 451A.
And then on top of that I add the 125% factor to give me 563A for minimum cable ampacity.
My colleagues say, that since you are already including a safety buffer in the 0.8PF, you don't need to add the 125% additional safety factor anymore....
I disagree, b/c the PF during operation can range anywhere between 0.8 to 1.0. So you can't rely on that for cable ampacity calcs.....
Thoughts?





RE: Cable Sizing for Generators: 125% Rule vs. PF
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Cable Sizing for Generators: 125% Rule vs. PF
The maximum allowable current is at .8 PF
This is not a safety factor. It is the maximum possible load.
Then add 125% safety factor as you do.
You are correct.
In North America the code requires 125% of rated current. That is current at 0.8 PF X 125%.
Bill
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"Why not the best?"
Jimmy Carter
RE: Cable Sizing for Generators: 125% Rule vs. PF