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3-phase A-connected induction motor has a rated current and a full-load slip of 4 %. Answer the following questions: (a) Under direct starting conditions, calculate the percentage of the starting torque compared to rated torque. (b) If an autotransformer is used to reduce the starting current of the motor to 250 % of rated value, calculate the transformation ratio of the transformer, and the corresponding percentage value of the new starting torque. ho motor is to be started using Y-A starting method, calculate the new nt and the corresponding starting torque.

3-phase A-connected induction motor has a rated current and a full-load slip of 4 %. Answer the following questions: (a) Under direct starting conditions, calculate the percentage of the starting torque compared to rated torque. (b) If an autotransformer is used to reduce the starting current of the motor to 250 % of rated value, calculate the transformation ratio of the transformer, and the corresponding percentage value of the new starting torque. ho motor is to be started using Y-A starting method, calculate the new nt and the corresponding starting torque.

Introductory Circuit Analysis (13th Edition)
Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
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3-phase A-connected induction motor has a direct starting current of 800 % of rated current and a full-load slip of 4 %. Answer the following questions: (a) Under direct starting conditions, calculate the percentage of the starting torque compared to rated torque. (b) If an autotransformer is used to reduce the starting current of the motor to 250 % of rated value, calculate the transformation ratio of the transformer, and the corresponding percentage value of the new starting torque. (c) If the motor is to be started using Y-A starting method, calculate the new percentage of the starting current and the corresponding starting torque. laging (6) A 4 MW, 0.707 industrial plant is supplied from a 6 MVA three-phase power transformer. A 1.0 MW, 11 kV, 0.8 leading power factor, 88 % efficient, 3-phase synchronous motor is to be installed in the plant. Answer the following questions: Case (a) What is the new overall power factor of the plant. (b) Is the 6 MVA transformer over-loaded after connecting the synchronous motor. (c) If yes find the over-loading percentage. (7) A 500 V, A-connected, three-phase synchronous motor has an EMF of 600 V. The motor synchronous impedance is (0.4+j5) 02/ph, and the rotational losses are neglected. Calculate the maximum power output that can be delivered, the corresponding line current, the input power factor and efficiency of the motor. (8) A 3300 V, A-connected synchronous motor has a synchronous reactance of 18 0/ph. It operates at a 0.707 leading power factor when drawing 800 kW from the mains. Answer the following questions: (a) Calculate the motor EMF and torque angle. (b) If the field current in increased by 20 % while the load power is unchanged calculate the new value of the line current and the corresponding input power factor.
Transcribed Image Text:3-phase A-connected induction motor has a direct starting current of 800 % of rated current and a full-load slip of 4 %. Answer the following questions: (a) Under direct starting conditions, calculate the percentage of the starting torque compared to rated torque. (b) If an autotransformer is used to reduce the starting current of the motor to 250 % of rated value, calculate the transformation ratio of the transformer, and the corresponding percentage value of the new starting torque. (c) If the motor is to be started using Y-A starting method, calculate the new percentage of the starting current and the corresponding starting torque. laging (6) A 4 MW, 0.707 industrial plant is supplied from a 6 MVA three-phase power transformer. A 1.0 MW, 11 kV, 0.8 leading power factor, 88 % efficient, 3-phase synchronous motor is to be installed in the plant. Answer the following questions: Case (a) What is the new overall power factor of the plant. (b) Is the 6 MVA transformer over-loaded after connecting the synchronous motor. (c) If yes find the over-loading percentage. (7) A 500 V, A-connected, three-phase synchronous motor has an EMF of 600 V. The motor synchronous impedance is (0.4+j5) 02/ph, and the rotational losses are neglected. Calculate the maximum power output that can be delivered, the corresponding line current, the input power factor and efficiency of the motor. (8) A 3300 V, A-connected synchronous motor has a synchronous reactance of 18 0/ph. It operates at a 0.707 leading power factor when drawing 800 kW from the mains. Answer the following questions: (a) Calculate the motor EMF and torque angle. (b) If the field current in increased by 20 % while the load power is unchanged calculate the new value of the line current and the corresponding input power factor.
Expert Solution
Step 1

Given -

For three phase induction motor-

Direct starting current to rated current = 800%

Slip value, SFL = 4%

 

 

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