lesson 4 Three-Phase Motors
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| true/false Three-phase motors typically cost more to operate per horsepower than single-phase motors or DC motors. | show 🗑
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| If the total number of coils wound in a 3-phase stator is 24, then each phase contains ? sets of coils. | show 🗑
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| show | motor shaft
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| true/false It takes 360 electrical degrees, or one electrical cycle, to complete one revolution in a 2-pole motor. | show 🗑
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| show | 1800 rpm
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| show | Inductive reactance
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| show | direction of rotation
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| ? is the torque required to produce the rated power at full speed of the motor. | show 🗑
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| Torque is usually measured in ? . | show 🗑
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| show | watt (W)
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| show | Locked-rotor torque
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| Motor power is rated in ? or ? . | show 🗑
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| show | false
These types of loads are hard to accelerate and decelerate, even with a motor that has sufficient torque to drive the load at full speed.
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| When the speed of a motor changes, the horsepower and torque required at the new speed may be ? . | show 🗑
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| ? loads require increase in torque and horsepower with an increase in speed. | show 🗑
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| ? loads require a constant torque output at different speeds. | show 🗑
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| true/false With a variable-torque load, the horsepower varies with the square of the speed of change. | show 🗑
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| show | true power
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| show | VA or kVA
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| What is the power factor on a 480-volt, 60-horsepower, 3-phase motor with an efficiency of 85% when the full load current is 70 amperes? | show 🗑
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| true/false A low power factor indicates that the circuit is drawing more current than is required by the load; utility companies penalize customers with low power factors. | show 🗑
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| show | Motor efficiency
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| show | Flux-linkage loss
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| true/false Flux-linkage loss is energy lost by blowing air past a motor to remove heat. | show 🗑
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| show | 4.9 A
(73.8+68.5+64.4)/3=avg
73.8- avg=4.9
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| A motor operates with Phase A = 73.8 amperes, Phase B = 68.5 amperes, and Phase C = 64.4 amperes. Motors should not be operated above a 10% current unbalance. Calculate the maximum percentage phase unbalance for this motor. | show 🗑
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| true/false A motor with an 8.3% current unbalance can be operated, but with caution to avoid overheating the motor. | show 🗑
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Created by:
Athomp705