Open-circuit saturation curve: Difference between revisions

Revision as of 04:10, 8 July 2023

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[[File:Synchronous machine curves.png|thumb|A diagram with multiple synchronous machine curves:; ''open-circuit saturation curve,'' short-circut curve, zero poweris factorleftmost]]

The '''open-circuit saturation curve''' (also open-circut characteristic, OCC) of a [[synchronous generator]] is a plot of the output voltage as a function of the [[excitation current]] or field.{{sfn | Klempner | Kerszenbaum | 2004 | p=125}}

At the low field, the [[magnetic permeability|permeable]] iron in the [[magnetic circuit]] of the generator is not [[magnetic saturation|saturated]], therefore the [[reluctance]] almost entirely depends on the fixed contribution of the air gap, so the part of the curve that starts at the [[Origin (mathematics)|point of origin]] is a linear "air-gap line" (output voltage is proportional to the excitation current). As the iron saturates with higher excitation and thus higher [[magnetic flux]], the reluctance increases, and the OCC deflects down from the air-gap line.{{sfn | Klempner | Kerszenbaum | 2004 | p=125}}

The curve is obtained by rotating the generator at the rated [[RPM]] with the output terminals disconnected and the output voltage typically going to at least 120% of the rated for the device. The hydraulic units sometimes have to be tested at lower RPM with the resulting voltage scaled up to accommodate the differences in frequency. Since the test goes above the rated voltage, the [[step-up transformer]] is typically also disconnected to avoid damaging it.{{sfn | Boldea | 2015 | p=412}}

== References ==