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SKM Result - Negative Voltage Drop

SKM Result - Negative Voltage Drop

SKM Result - Negative Voltage Drop

(OP)
We are running a low voltage (<600v) drop study in SKM and are coming up with a few values with a negative voltage drop. Curious as to why the results might be coming up with a negative % voltage drop result on some of the buses and feeders and the negative % results means.

Thanks.
b

RE: SKM Result - Negative Voltage Drop

Closely bundled and long cables on lightly loaded feeders?

On long sections of transmission lines, if they are lightly loaded or open ended, the voltage swings up from the Ferranti effect.

Depending on how strong your grounding is, imbalanced load can cause overvoltages on some of your phases.

RE: SKM Result - Negative Voltage Drop

(OP)
This is for 480v, 60hZ three phase feeders within a building 200'-300' long. The feeders are lightly loaded.

RE: SKM Result - Negative Voltage Drop

Calculate the surge impedance loading of your cables and compare that with your load.

RE: SKM Result - Negative Voltage Drop

Maybe you in-service some capacitors in your system.

RE: SKM Result - Negative Voltage Drop

Power factor correction at the end of the feeders?
The cable capacitance on an unloaded or very lightly loaded cable?
Single phase loading will cause a voltage drop on the neutral which will be a voltage rise on the unloaded phases.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: SKM Result - Negative Voltage Drop

What load are you simulating and what is its power factor?

RE: SKM Result - Negative Voltage Drop

All of the above responses are valid.
Are you referring to the branch voltdrop or bus volt drop ?
PTW reports bus voltdrop in percentage with respect to the nominal voltage.
eg. If the bus nominal voltage is 415V and the bus loadflow volts are 425V, then the reported LF VD% is +2.4%.

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