Circle diagram constant air-gap induction motor images shown here, where, The circle diagram is drawn using the data obtained from no load and either short circuit or, in case of machines, blocked rotor tests by fitting a half-circle in points O and A. Beyond the error inherent in the constant air-gap assumption, the circle diagram introduces errors due to rotor reactance and rotor resistance variations caused by magnetic saturation and rotor frequency over the range from no-load to operating speed. Steinmetz equivalent circuit Circle diagram First conceived by A. Heyland in 1894 and B.A. Behrend in 1895, the circle diagram is the
Dividing a circle into areas of regions can also be determined in a non-inductive way, using the formula for the Euler characteristic of a connected planar graph (viewed here as a graph embedded in the 2-sphere S). A planar graph determines a cell decomposition of the plane with "F" faces (2-dimensional cells), "E" edges (1-dimensional cells) and "V" vertices (0-dimensional cells). As the graph is connected, the Euler relation for the 2-dimensional sphere S holds. View the diagram (the circle together with all the chords) above as a planar graph. If the general formulas for "V" and "E" can both be found, the formula for