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14 Cards in this Set
- Front
- Back
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State two advantages that across the line starting has over reduced voltage starting for AC motors |
Simple control Low component cost Maximum starting torque Minimum acceleration time for the motor |
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State two disadvantages that reduced voltage starting has over across the line for AC motors |
Reduced inrush current on starting Reduced torque on starting Less disturbance (Line drop) to the power system |
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List three methods of reduced voltage starting |
Auto transformer starters Wye Delta starters Solid state starters Part winding starters Primary impedance starters |
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What is the difference between a reduced voltage starter with an open transition and a reduced voltage starter with a closed transition? |
For open transition: Momentary loss of voltage (power) to the motor as the control transfers from the starting to running stage. Closed transition: No interruption of voltage (constant power) |
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If an AC motor will not start under load with rated voltage, will you be able to start it with reduced voltage? Explain. |
No, voltage is directly proportionate to torque. If it won't start with full voltage, it definitely won't with reduced voltage |
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Why is it sometimes necessary to provide larger than normal contactors for some motors? |
Frequent (repetitive) operation under large starting in rush conditions will greatly shorten the life of the contacts. |
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What type of motor duty is required for a service that must operate for definite specified alternate intervals of load and rest? |
Intermittent duty |
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What is the most important consideration in determining whether or not a motor may be started directly across the line? |
Permissable voltage fluctuations ( disturbance) to the power distribution system. Or else the popo will come after you |
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What type of starter is the primary resistance starter? |
Closed transition. |
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State two situations where it may be necessary to use starting reactors rather than resistors? |
For high voltage/ high current motors Where heating or physical construction of the resistors create a problem. |
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Describe how several steps can be added to the starting stage of the primary resistance starter. |
By adding additional resistors in series, each with an accelerating contactor |
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What standard taps are available on motor starting autotransformers? |
50% 65% 80% |
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Auto transformer starters are sometimes referred to as _______ starters. |
Compensator |
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Autotransformers used for starting motors are generally intended for intermittent duty. 1) What does this mean 2) What protection is usually provided for the auto transformer |
1) cycles on and off 2) Thermal ( high limit switches) equipped with heat sensors |
