First conceived by A.heyland in 1894 and B.A. Behrend in 1895, the circle diagram is the graphical representation of the performance of the

electrical machine In electrical engineering, electric machine is a general term for machines using electromagnetic forces, such as electric motors, electric generators, and others. They are electromechanical energy converters: an electric motor converts electricity ...

drawn in terms of the locus of the machine's input voltage and current. The circle diagram can be drawn for

alternator An alternator 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 a stationary armature.Go ...

synchronous motor A synchronous electric motor is an AC electric motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integral number of AC cycles. Sync ...

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

induction motor An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. An induction mot ...

s. The Heyland diagram is an approximate representation of circle diagram applied to induction motors, which assumes that stator input voltage, rotor resistance and rotor reactance are constant and stator resistance and core loss are zero. Another common circle diagram form is as described in the two constant air-gap induction motor images shown here, where, * R_s, X_s: Stator resistance and leakage reactance * R_r^', X_r^', s: Rotor resistance and leakage reactance referred to the stator and rotor slip * R_c, X_m, : Core and mechanical losses, magnetization reactance * V_s, Impressed stator voltage * I₀ = OO^', I_BL = OA, I₁ =OV: No load current, blocked rotor current, operating current * Φ₀, Φ_BL : No load angle, blocked rotor angle * P_max, s_Pmax, PF_max, T_max, s_Tmax: Maximum output power & related slip, maximum power factor, maximum torque & related slip * η₁, s₁, PF₁, Φ₁,: Efficiency, slip, power factor, PF angle at operating current * AB: Represents rotor power input, which divided by synchronous speed equals starting torque. The circle diagram is drawn using the data obtained from no load and either

short-circuit A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the 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.

References

{{Electric transformers Electromechanical engineering Electric motors Synchronous machines Electric transformers

See also

References