Open-circuit saturation curve: Difference between revisions

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[[File:Synchronous machine curves.png|thumb|upright=1.5|A diagram with multiple synchronous machine curves; ''open-circuit saturation curve'' is the leftmost one]]

{{in use}}

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

[[File:Synchronous machine curves.png|thumb|A diagram with multiple synchronous machine curves; ''open-circuit saturation curve'' is leftmost]]

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 (electric machine)|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}}

The open circuit saturation curve could be used together with the [[zero power factor curve]] in Potier Triangle Method.<ref name="EEEguide">{{cite web | url=https://www.eeeguide.com/armature-reaction-in-synchronous-motor/ | title=Armature Reaction in Synchronous Motor | publisher=EEEguide – Online Electrical and Electronics Learning Site | access-date=2024-12-15 }}</ref>

== References ==

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== Sources ==

* {{cite book | last=Klempner | first=G. | last2=Kerszenbaum | first2=I. | title=Operation and Maintenance of Large Turbo-Generators | publisher=Wiley | series=IEEE Press Series on Power Engineering | year=2004 | isbn=978-0-471-61447-0 | chapter-url=https://books.google.com/books?id=DPdkLp_crLAC&pg=PA125 | chapter=Open-Circuit Saturation Characteristic | access-date=2023-07-08}}

* {{cite book | last=Boldea | first=I. | title=Synchronous Generators | publisher=CRC Press | year=2015 | isbn=978-1-4987-2355-8 | url=https://books.google.com/books?id=VB-vCgAAQBAJ&pg=PA412 | language=de | access-date=2023-07-08}}

{{Characteristics of synchronous machines}}

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[[Category:Electrical generators]]

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