AC Machines 1

A single-phase induction motor is rated 5 hp, 75% power factor and 220 volts. What is the full-load current? Assume 100% efficiency.

• 22.6

• 20.5

• 16.9

• 18.5

A 1/20-HP 1,550 rpm shaded-pole motor takes 120 watts when operating at full-load . What is its efficiency?

• 39.71%

• 23.98%

• 31.08%

• 93.20%

What percent of the rated torque does a 1/20 hp 3,600 rpm shaded-pole motor develop at starting, if the average starting torque is 5.0 oz-in?

• 45.83%

• 36.00%

• 50.64%

• 40%

A ½ -hp 1,750-rpm capacitor motor develops 350 percent starting torque. What is the starting torque in pound-feet?

• 6.36

• 7.23

• 5.25

• 8.46

In performing a brake-load test upon ¼-hp capacitor start motor with its output adjusted to rated value , the following data were obtained: E = 115 volts, I = 3.8 amp, P = 310 watts, RPM = 1,725. Calculate: efficiency.

• 93.52%

• 60.16%

• 65.02%

• 83.29%

In performing a brake-load test upon ¼-hp capacitor start motor with its output adjusted to rated value , the following data were obtained: E = 115 volts, I = 3.8 amp, P = 310 watts, RPM = 1,725. Calculate power factor.

• 0.654

• 0.846

• 0.906

• 0.709

In performing a brake-load test upon ¼-hp capacitor start motor with its output adjusted to rated value , the following data were obtained: E = 115 volts, I = 3.8 amp, P = 310 watts, RPM = 1,725. Calculate torque in pound-inches.

• 9.13

• 9.86

• 8.27

• 8.93

How many poles is a motor wound that operates at 1,130 rpm from a 60-Hz source?

• 6

• 4

• 8

• 2

A 3-phase motor is rated 750 hp at 480 volts line to line, 0.85 pf lagging and 0.95 efficiency. Solve for the rated current.

• 869.64 A

• 702.23 A

• 405.43 A

• 917.32 A

A 40-hp, 3-phase , 4-pole, 230-volt , 60-Hz induction motor operating at 0.90 efficiency, 0.85 power factor and 3 percent slip, drives a water pump. Determine the current at which the motor is operating.

• 94.531 A

• 96.234 A

• 97.915 A

• 93.351 A