Question 13:Ī radial-flow centrifugal cooling water pump is being powered by a 480 VAC induction motor. ![]() Which one of the following is the primary reason for limiting the number of motor starts in a given time period?Ī) Minimizes the pitting of contacts in the motor breaker.ī) Prevents overheating of the motor windings.Ĭ) Minimizes axial stresses on the motor bearings.ĭ) Prevents excessive torsional stresses on the motor shaft. How will the fan motor current change if its discharge damper is fully opened?Ī) The motor current will decrease in accordance with the centrifugal pump laws.ī) The motor current will decrease, but not in accordance with the centrifugal pump laws.Ĭ) The motor current will increase in accordance with the centrifugal pump laws.ĭ) The motor current will increase, but not in accordance with the centrifugal pump laws Question 12: The fan is operating at 90 percent of the rated flow rate with its discharge damper partially closed. Question 11:Īn axial flow ventilation fan is being driven by an AC motor. The frequency of starts for large AC motors should be limited to prevent excessiveĪ) arcing and degradation of motor breaker contacts.ĭ) torsional stresses on the motor shaft. Question 9:Ī diesel generator (DG) is supplying an electrical bus that is connected to an infinite power grid.Īssuming DG terminal voltage and bus frequency do not change, if the DG governor setpoint is increased from 60 Hz to 60.1 Hz, DG KVAR will be _ and DG amps will be _. The starting current in a typical AC induction motor is usually much higher than the full-load running current becauseĪ) starting torque is higher than full-load running torque.ī) rotor current during start is too low to generate significant counter electromotive force in the stator.Ĭ) starting torque is lower than full-load running torque.ĭ) rotor speed during start is too low to generate significant counter electromotive force in the stator. What is the current rating for the motor? Which one of the following describes how and why pump motor current will change if the pump shaft seizes?Ī) Decreases due to decreased pump flow rate.ī) Increases due to decreased counter electromotive force.Ĭ) Increases due to decreased pump flow rate.ĭ) Decreases due to increased counter electromotive force. ![]() Question 6:Ī cooling water pump is being driven by an AC induction motor. Which one of the following will result from the prolonged operation of an AC induction motor with excessively high stator temperatures?Ī) Decreased electrical resistance to ground due to breakdown of winding insulation.ī) Increased electrical current demand due to reduced counter electromotive force.Ĭ) Increased electrical resistance to ground due to breakdown of winding insulation.ĭ) Decreased electrical current demand due to reduced counter electromotive force. ![]() The number of starts for an electric motor in a given period of time should be limited because overheating of the _ can occur due to the _ counter electromotive force produced at low rotor speeds.ĭ) commutator and/or slip rings high Question 5: What is the approximate MW load on the main generator? The main generator is supplying 300 MVAR to the power grid with a 0.85 power factor. Which one of the following describes a possible cause for the ammeter response?Ī) The pump was started with a fully open discharge valve.ī) The pump shaft separated from the motor shaft upon start.Ĭ) The pump was started with a fully closed discharge valve.ĭ) The pump shaft seized upon start and did not rotate. When a motor-driven centrifugal pump was started, the motor ammeter reading immediately increased to, and stabilized at, many times the normal operating value. Which one of the following will occur if the motor is continuously operated at rated load with an ambient temperature of 50☌?Ī) Accelerated breakdown of the motor winding insulation, leading to an open circuit within the motor windings.ī) Accelerated embrittlement of the motor windings, leading to a short circuit within the motor windings.Ĭ) Accelerated breakdown of the motor winding insulation, leading to a short circuit within the motor windings.ĭ) Accelerated embrittlement of the motor windings, leading to an open circuit within the motor windings. Question 1:Ī large AC motor has a maximum ambient temperature rating of 40☌. Click on the below start button to get complete 100+ questions with answers. ![]() Motors and Generatorsįind the sample 25 questions from the motors and generators quiz. We provide you the latest 100 multiple choice questions and answers on motors and generators for electrical and instrumentation engineers.
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