AC Machines Loaded

In a 3 phase IM

• The developed torque is approx. directly proportional to slip in normal running range and inversely proportional to it low-speed range
• The developed torque is approx. directly proportional to slip in normal running range as well as low-speed range
• The developed torque is approx. inversely proportional to slip in normal running range and inversely proportional to it low-speed range
• The developed torque is approx. inversely proportional to slip in normal running range and directly proportional to it low-speed range

A dual voltage single phase ac motor can be operated on either

• 230 V or 400 V
• 30 or 400V
• 115 or 230 V
• 160 V or 320 V

An IM always operates on lagging power factor. This is due to

• Stator Reactance
• Rotor Leakage reactance
• the large reactive lagging magnetizing current essential to produce the magnetic flux
• all of the above

An 8 pole single phase IM is running at 690 RPM. What is its slip with respect to forward and backward fields, respectively

• 0.08, 2.0
• 0.08, 1.92
• 1.92, 0.08
• 2.0, 0.08

For High starting torque, the most suitable 3 phase IM is ___________ IM

• Slip ring
• Squirrel Cage
• Double Cage
• Deep Bar squirrel cage

The PF at which single phase IM usually operate is

• 0.7 Lag
• 0.8 lag
• 0.7 Lead
• unity

If a 3 phase IM is started when one of the phase is not available, then the motor

• will hum but not start
• will continue to operate satisfactorily on load below 57.7% of rated load if brought up to speed by some external means
• will operate under reduced load but usually with considerable vibrations in case of wound rotor motor is brought up to speed by some external means
• start and operate at lower speed
• all except d

A 3-Phase IM when started picks up speed but runs stably at about half the normal speed. This is because of

• Unbalance in the supply voltages
• non-sinusoidal nature of the supply voltage
• Stator ckt asymmetry
• Rotor Ckt Symmetry

Capacitor in a single phase IM is used for

• Improving the PF
• Improving the starting torque
• starting the motor
• reducing the harmonics

The starting torque of an IM varies as

• f
• 1/f^2
• 1/f
• f^2