Synchronous Motors Objectives Part 07
121 . In a synchronous motor, under running conditions the angle between the induced voltage and supply voltage will be more than 1800.
122 . The rotor of a synchronous motor can only run at synchronous speed of the rotor magnetic field due to interlocking action between stator and rotor fields.
123 . An inverted V curve of synchronous motor is the variation of field current and power factor at constant load.
124 . Damper windings are provided on poles faces.
125 . Hunting of synchronous motor may be due to pulsation of power supply, reciprocating type of load and pulsating torque of driven equipment.
126 . The V curves of a synchronous motor show relationship between dc field current and ac armature current.
127 . In a synchronous motor with field under excited the power factor will be lagging.
128 . In a synchronous motor maximum value of torque angle is 90o electrical.
129 . In synchronous motor net armature voltage is vector difference of Eb and V.
130 . Increasing load in a normally excited synchronous motor the power factor becomes increasing lagging.
131 . Synchronous motor speed is controlled by varying supply voltage and frequency both.
132 . Maximum electrical power input of synchronous motor is VtEf / Xz.
133 . In a synchronous motor armature reaction at rated voltage and zero power factor leading is demagnetizing.
134 . A synchronous motor is operating with excitation adjusted for unity power factor current at constant load, on increasing the excitation power factor will lead.
135 . A synchronous motor is operated from a bus voltage of 1.0 pu at 1.0 pu pf leading current. The synchronous reactance is 0.5 p.u. The excitation emf of the motor is 1.5.
136 . A 3-phase synchronous motor connected to an infinite bus is operating at half full load with normal excitation. When the load on the synchronous motor is suddenly increased its speed will remain unchanged.
137 . A synchronous motor operating at rated voltage draw 1.0 pu current at 1.0 pu power factor. The machine parameters are: synchronous reactance 1.0 pu, armature resistance negligible. Apart from supplying this rated power, if the motor has to supply ad additional leading reactive power of 0.8 pu then the field current has to be increased by 46%