lesson 4 Three-Phase Motors
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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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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| show | 8
each phase must have the same number of coils, so the total number of coils must be divisible by the number 3.
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| The ? is a cylindrical bar used to carry the revolving rotor and to transfer power from the motor to the load. | show 🗑
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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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| The synchronous speed of a 60-hertz, 4-pole motor is ? . | show 🗑
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| show | Inductive reactance
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| The ? of 3-phase motors can be reversed by interchanging any two of the 3-phase power lines to the motor. | show 🗑
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| show | Full-load torque
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| show | pound-feet (lb-ft)
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| A(n) ? is the base unit of electrical power. | show 🗑
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| show | Locked-rotor torque
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| Motor power is rated in ? or ? . | show 🗑
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| true/false High-inertia loads are always easy to accelerate and decelerate with a motor that has sufficient torque to drive the load at full speed. | show 🗑
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| show | higher, lower, or the same
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| ? loads require increase in torque and horsepower with an increase in speed. | show 🗑
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| show | Constant-torque
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| show | false
horsepower varies with the cube of the speed change
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| show | true power
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| Apparent power is measured in ? or ? . | show 🗑
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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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| ? is calculated by dividing output power by input power. | show 🗑
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| ? is the loss of flux in the air gap between the stator and rotor because the air gap has increased reluctance compared to the cores. | show 🗑
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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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| A motor operates with the following phase currents: Phase A = 73.8 amperes, Phase B = 68.5 amperes, and Phase C = 64.4 amperes. What is the maximum current difference from the average? (Round the FINAL answer to one decimal place.) | show 🗑
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| show | 6.64%
4.9/73.8 X 100= 6.64
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| show | true
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Created by:
Athomp705