The synchronous impedance curve (also short-circuit characteristic, SCC) of a

synchronous generator An alternator (or synchronous generator) is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with ...

is a plot of the output short circuit current as a function of the excitation current or

field Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an airport * Battlefield * Lawn, an area of mowed grass * Meadow, a grass ...

. The curve is typically plotted alongside the

open-circuit saturation curve The open-circuit saturation curve (also open-circuit 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 synchr ...

. The SCC is almost linear, since under the short-circuit conditions the

magnetic flux In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the we ...

in the generator is below the iron

saturation Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry *Saturated and unsaturated compounds, a classification of compounds related to their ability to resist addition reactions ** Degree of unsaturation **Saturated fat or satu ...

levels and thus the

reluctance Magnetic reluctance, or magnetic resistance, is a concept used in the analysis of magnetic circuits. It is defined as the ratio of magnetomotive force (mmf) to magnetic flux. It represents the opposition to magnetic flux, and depends on the ...

is almost entirely defined by the fixed one of the air gap. The name "synchronous impedance curve" is due to the fact that in the short-circuit condition all the generated voltage dissipates across the generator internal synchronous impedance

Z_S

The curve is obtained by rotating the generator at the rated

RPM Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or r⋅min−1) is a unit of rotational speed (or rotational frequency) for rotating machines. One revolution per minute is equivalent to hertz. Standards ISO 80000-3:2019 def ...

with the output terminals shorted and the output current going to 100% of the rated for the device (higher values are typically not tested to avoid overheating).

References

Sources

* * Electrical generators {{electric-stub