Losses in Synchronous MotorThe losses that occur in a synchronous motor can be divided into the following categories −Copper Losses or I2R LossesCopper losses or I2R losses occur in the armature winding and rotor winding of the motor. These losses occur due to the resistance of the windings.Core LossesCore losses ... Read More

The complex power input per phase of the synchronous motor is, $$\mathrm{S_{1φ}=VI^{*}_{a}\:\:\:\:\:\:...(1)}$$Taking excitation voltage (Ef) as the reference phasor, then, $$\mathrm{V=V\angle-δ=V\:cosδ-jVsinδ\:\:\:\:\:\:...(2)}$$$$\mathrm{I_{a}=I_{q}-jI_{d}}$$$$\mathrm{\therefore\:I^{*}_{a}=I_{q}+jI_{d}\:\:\:\:\:\:...(3)}$$Hence, from Eqns.(1), (2)&(3), we get, $$\mathrm{S_{1φ}=(V\:cosδ-jVsinδ)(I_{q}+jI_{d})\:\:\:\:\:\:...(4)}$$For a salient-pole synchronous motor, the quadrature-axis current and direc taxis current are given by, $$\mathrm{I_{q}=\frac{Vsinδ}{X_{q}}\:\:\:\:\:\:...(5)}$$$$\mathrm{I_{d}=\frac{E_{f}-Vcosδ}{X_{d}}\:\:\:\:\:\:...(6)}$$Substituting the values of Iq and Id in Eqn.(4), ... Read More

Let, Ef=Excitation voltageV= Terminal voltage per phase applied to the armatureIa=Armature current per phase drawn by the motor from the supplyRa= Effective armature resistance per phaseXS=Synchronous reactance per phase of armature windingCosφ= Power factorδ=Torque angleThe voltage equation of a cylindrical rotor synchronous motor is, $$\mathrm{V=E_{f}+I_{a}(R_{a}+jX_{S})\:\:\:\:\:\:...(1)}$$$$\mathrm{\Longrightarrow\:V=E_{f}+I_{a}R_{a}+jI_{a}X_{S}\:\:\:\:\:\:...(2)}$$The phasor diagrams of a 3-phase ... Read More

The excitation voltage of synchronous motor refers to the DC supply given to the rotor to produce the required magnetic flux. The excitation voltage (Ef) of a synchronous motor can be determined for different power factors using complex algebra.Let the supply voltage (V) be taken as the reference voltage. Thus, ... Read More

Consider an under-excited (i.e., Ef < V), 3-phase cylindrical rotor synchronous motor driving a mechanical load. The figure shows the per phase phasor diagram of the motor. Since the motor is under-excited, it will be operating at a lagging power factor cos φ.In practice, for a synchronous motor, XS>>Ra, then ... Read More

Hunting in Synchronous MotorHunting is the phenomenon of oscillation of the rotor about its steady state position or equilibrium state in a synchronous motor. Hence, hunting means a momentary fluctuation in the rotor speed of a synchronous motor.In a synchronous motor, when the electromagnetic torque developed is equal and opposite ... Read More

Assume that initially, the rotor of a synchronous motor is stationary. When a pair of rotating stator poles sweeps across the stationary rotor poles at synchronous speed, the stator poles will tend to rotate the rotor in one direction and then in the other direction. As a result, the rotor ... Read More

Assume that the rotor of a synchronous motor is stationary. When a pair of rotating stator poles sweeps across the stationary rotor poles at synchronous speed, the stator poles will tend to rotate the rotor in one direction and then in the other direction. As a result, the rotor experiences ... Read More

A synchronous motor is a doubly-excited system, i.e., it is connected to two electrical systems −A 3-phase supply is connected to the armature winding.A DC supply is connected to the rotor field winding.The figure shows the equivalent circuit for one phase of a three-phase synchronous motorLetV = Terminal voltage per ... Read More

In induction motors and DC motors, when the mechanical load attached to the shaft of the motor is increased, the speed of the motor decreases. The decrease in the speed reduces the back EMF so that additional current is drawn from the source to carry the increased load at a ... Read More