Synchronous Motors Objectives Part 05

81 . In which range the cost of a synchronous motor can be comparable to the cost of a induction motor High HP low speed

82 . Insulation resistance test on synchronous motor can be conducted to measure stator winding to earthed frame, rotor winding to earthed shaft and phase to phase winding resistance

83 . Which of the following represent open circuit characteristics of a synchronous motor Curve A ?

84 . During short circuit test which of the following is short circuited armature terminals.

85 . The duration of sudden short circuit test on a synchronous motor is usually about one second.

86 . The maximum torque which a synchronous motor will develop at rest for any angular positions of the rotor at rated stator supply voltage and frequency is known as locked rotor torque.

87 . The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as pull in torque.

88 . The maximum sustained torque which a synchronous motor will develop at synchronous speed for 1 mm with rated frequency and rated field current is known as pull out torque.

89 . The total steady state to drive synchronous motor and the load at synchronous speed is known as synchronous torque.

90 . The space angle between the axis of the stator revolving magnetic field and the rotor pole axis both locked and running at synchronous speed is known as power angle.

91 . In synchronous machine in case the axis of field flux is in line with the armature flux, then the machine is said to be floating.

92 . If other factors remains constant, the speed of a synchronous motor in its operating (and load) range is correctly described by the speed depends on the frequency of the supply voltage and the number of its poles.

93 . The induced emf in a synchronous motor working on leading pf will be more than the supply voltage.

94 . A synchronous machine with low value of short circuit ratio has low stability limit.

95 . While starting a synchronous motor by induction motor action, very high emf is induced in the insulation of the field winding and of the slip rings. The insulation damga can be prevented by short circuit the field winding by field discharge resistance or splitting the field winding into several sections.

96 . Synchronous motors are generally of salient pole type machines.

97 . In which of the following motor the stator and rotor of magnetic fields rotate at the same speed synchronous motor.

98 . Higher the applied voltage greater will be the stator flux and greater will be the pull in torque
Consider the below data for Q 99 to 101 An industrial plant had a load of 1500 kVA at an average power factor of 06 lagging.

99 . Neglecting all losses, the kVA input to a synchronous condenser for an overall power factor of unity will be 1200kVA.

100 . A 750 kVA synchronous condenser is used to correct the lagging power factor of the plant. The total kVA of the plant is 10006.