JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year ELECTRIC DRIVES AND CONTROL Previous Question Paper (July/August - 2022 - R18)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
Discuss the concept of electric drive and its advantages.
Answer
An electric drive is an electromechanical system designed to control the speed, torque, and direction of rotation of an electric motor. It consists of three main components: the power source, the power modulator (converter), and the motor-load system. The power modulator regulates the power flow from the source to the motor to achieve the desired mechanical output.
The advantages of electric drives include:
- Flexibility: They offer a wide range of control over speed, torque, and power.
- Efficiency: Electric drives are highly efficient and can be easily automated.
- Cleanliness: They produce no exhaust gases or noise pollution, making them suitable for indoor environments.
- Reliability: They have fewer moving parts compared to internal combustion engines, resulting in lower maintenance requirements.
- Regenerative Braking: Energy can be returned to the source during braking, improving overall system economy.
Give the classification of electric drives and explain them.
Answer
Electric drives are classified based on their method of operation and the type of control employed:
- Group Electric Drive: A single motor drives several machine tools through a common shaft, belts, or pulleys. It is cost-effective but lacks individual control and suffers from high transmission losses.
- Individual Electric Drive: Each machine tool is driven by its own dedicated motor. This provides independent control, higher efficiency, and better reliability compared to group drives.
- Multi-Motor Electric Drive: Multiple motors are used to actuate different parts of the same machine (e.g., in steel rolling mills or paper mills). This allows for precise coordination of speed and torque across different sections of a complex process.
Furthermore, drives can be classified by their control mode into DC Drives, which use DC motors controlled by rectifiers or choppers, and AC Drives, which use induction or synchronous motors controlled by inverters or cycloconverters.
What are the components of electric drives and discuss the role of each module in detail.
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Explain the multi quadrant operation of a motor driving a load.
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Draw the closed loop block diagram of electric drive and explain it.
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How the moment of inertia of a rotating part is determined in case of electric drive?
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Explain the concept of load equalization of an electric drive.
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Discuss the braking techniques of dc motor and explain them.
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A 220V, 21A, 1000 rpm dc shunt motor draws armature current of 21 A on full load and runs at 1000 rpm. If a resistance of 0.5 ohm is inserted in series with armature. Determine speed at full load torque.
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Explain the operation of single phase full converter fed dc motor.
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Using chopper circuit how the speed of dc motor is controlled.
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Explain the speed control of induction motor using stator variable voltage.
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Discuss the regenerative braking operation of induction motor.
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Write a short note on the following:
Losses in electric drive systems
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Energy efficient operation of drives
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Maintenance of motors.
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