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9.13 Three-Phase Asynchronous Motor Starting
9.13 Three-Phase Asynchronous Motor Starting
练习题
When a three-phase asynchronous motor starts directly across the line, what is the typical relationship between the starting current and the rated current?
A. Starting current is approximately 0.5 to 1 times the rated current
B. Starting current is approximately 2 to 3 times the rated current
C. Starting current is approximately 5 to 7 times the rated current
D. Starting current is approximately equal to the rated current
At the instant of starting a three-phase asynchronous motor, which of the following conditions is true?
A. , , mechanical power is maximum
B. , , mechanical power is zero
C. , , mechanical power is zero
D. , , mechanical power is maximum
Which of the following are common methods used to reduce the starting current of a three-phase asynchronous motor? (Select all that apply)
A. Star-delta (Y-Δ) starting
B. Direct-on-line (DOL) starting
C. Autotransformer starting
D. Soft starter with variable frequency
E. Increasing the supply voltage
During the startup phase of a three-phase asynchronous motor, the rotor only dissipates power as losses since the shaft remains stationary and no mechanical power is delivered.
If the resisting torque at startup exceeds the motor's starting torque, the motor will still be able to start but will run at a lower speed.
When using star-delta starting, the starting torque is reduced to one-third of the torque produced during direct-on-line starting.
During the startup of a three-phase asynchronous motor, the slip value is ___ (as a decimal).
The motor can only achieve operating speed when the motor torque equals the ___ torque.
Explain why a three-phase asynchronous motor draws significantly higher current during starting compared to normal running conditions.
Describe what happens during motor startup when the motor torque exceeds the resisting torque, and how the motor reaches its stable operating point.
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