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Nominal voltage of equipment

Nominal voltage of equipment

Nominal voltage of equipment

(OP)
The voltage at power equipment terminals usually declines with drawn current causing voltage regulation. With that in mind, I get confused of the relation between transformer %impedance and associated range of tap changer to compensate the regulation?

On other hand, how much current that can be drawn from an equipment (assuming the thermal capability is available) before its terminal voltage falls beyond the operational range? (-10%) can that current be a basis for nominal equipment rating other than thermal capability?

a bit messed up!

RE: Nominal voltage of equipment

I am far from an expert on this subject, but there is a curve (power transfer curve?) (forget the name darnit) that when when the load increases beyond a certain point it cause the voltage to dip at the load end, that dip in voltage then cause automatic voltage regulators tap up (boost) which draws more current, causes more voltage drop and then boost even more. Eventually this run away condition leads to voltage collapse. As a result each feeder has a limit on how much current it can stably be loaded to. The idea is to make sure you do not go past the parabola-often with some safety factor approaching that peak.

RE: Nominal voltage of equipment

Don't confuse regulation with %impedance.
Regulation describes the voltage drop at full load current and a specified power factor.
%Impedance describes the EMF driving current through a short circuit. In this case, the power factor is determined by the X/R ratio of the transformer. That is a much lower power factor than is specified for regulation.
The %regulation is always less than the %impedance. That is, less voltage drop under load than calculations using %impedance will show.

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

RE: Nominal voltage of equipment

(OP)
@Mbrooke, welcome to P-V nose curve.



a narrow +/-10% range is where the operation takes place.

the curve shows that you can never transfer power more than short circuit MVA, which is logical, but the SC MVA is a huge figure with the fault current multiplied by nominal pre-fault voltage, which can never happen as well!.

RE: Nominal voltage of equipment

Yes, thats the curve I was thinking of! :)

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