71. The power developed by a synchronous motor for constant supply voltage and constant excitation will be maximum when load angle δ is
- 90°
- 0°
- slightly less than 90°
- slightly more than 90°
72. A synchronous motor will deliver maximum power when
- load angle is equal to internal angle θ
- input power factor is unity
- load angle is 45°
- load angle is 0°
73. Armature reaction in a synchronous motor at rated voltage and zero power factor(lead) is
- magnetizing
- cross-magnetizing
- both magnetizing and cross-magnetizing
- demagnetizing
74. In the V-curve of a synchronous motor, the parameter of x and y coordinates are respectively
- armature current and field current
- power factor and field current
- armature current and torque
- torque and field current
75. An inverted V-curve of a synchronous motor shows the variation of
- power factor and dc excitation at constant load
- supply voltage and field current at constant excitation
- power factor and supply voltage during hunting
- supply voltage and excitation current at constant load
76. Synchronous capacitor is
- an ordinary static capacitor bank
- an overexcited synchronous motor driving mechanical load
- an overexcited synchronous motor without mechanical load
- none of the above
77. An induction motor and synchronous motor are connected to a common feeder line. To operate the feeder line at unity pf, the synchronous motor should be
- underexcited
- overexcited
- normally excited
- disconnected from the common terminals
78. Synchronous condensers, when operated at power factor ranging from lagging through unity to leading for voltage control, are called the
- voltage boosters
- synchronous reactors
- mechanical synchronizers
- none of the above
79. The power factor of a synchronous motor
- improves with increase in excitation and may even become leading at higher excitation
- decreases with increase in excitation
- is independent of excitation
- increases with loading for a given excitation
80. A pony motor is basically a
- small induction motor
- DC series motor
- DC shunt motor
- double winding AC/DC motor