JNTU
JNTU B.Tech IV UTILIZATION OF ELECTRIC POWER Previous Question Paper (September 2020 - R16)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
What are electric drives? What are the main advantages and applications of electric drives?
Answer
An electric drive is an electromechanical system designed to control the speed, torque, and direction of motion of an electric motor. It typically consists of a power source, a power modulator (converter), the electric motor, a sensing unit, and a control unit.
The main advantages of electric drives include:
- High efficiency and flexible control of speed and torque.
- Capability for both motoring and regenerative braking.
- Availability in a wide range of power ratings and types (AC and DC).
- Low maintenance requirements and long operational life.
- Ability to operate in all four quadrants of the torque-speed plane.
Applications include industrial machinery such as rolling mills, paper mills, textile mills, electric traction systems, robotic arms, and domestic appliances like washing machines and fans.
What is meant by load equalization? Discuss its purpose.
Answer
Load equalization is the process of smoothing out the fluctuations in the load demand on an electric motor. In many industrial applications, such as presses, shears, or punches, the load is highly intermittent and cyclic, causing sudden peaks and troughs in power consumption.
The purpose of load equalization is to:
- Reduce the peak power demand from the supply source, which prevents voltage drops and reduces the size of the required supply equipment.
- Improve the efficiency of the motor by allowing it to operate closer to its rated capacity.
- Protect the motor and the supply system from the thermal stress and mechanical shocks associated with sudden load changes.
This is typically achieved by using a flywheel mounted on the motor shaft. During periods of low load, the flywheel stores kinetic energy by accelerating; during peak load periods, it releases this stored energy, thereby assisting the motor and reducing the peak current drawn from the supply.
How to choose a motor for electric drive application?
Answer
Sign in to view the complete answer paper.
A motor fitted with a fly wheel that supplies a load of torque 500 N-m for 33 sec. during no load period the fly wheel regains its original speed. The motor torque is required to be limited to 400 N-m. The no load speed of the motor is 800 rpm and its full load slip is 10% determine the moment of inertia of the fly wheel.
Answer
Sign in to view the complete answer paper.
Explain the different methods of Electric heating and give an example of each type.
Answer
Sign in to view the complete answer paper.
A slab of insulating material 150 cm2 in area and 1cm thick is to be heated by dielectric heating. The power required is 400 W at 30 MHz. Material has relative permittivity of 5 and p.f. of 0.05. Absolute permittivity is 8.854 × 10-12 F/m. Determine the necessary voltage.
Answer
Sign in to view the complete answer paper.
Describe with neat sketches various methods of electric resistance welding. Give its merits and demerits with respect to arc welding.
Answer
Sign in to view the complete answer paper.
Explain the difference between carbon and metallic arc welding and give their relative merits and demerits.
Answer
Sign in to view the complete answer paper.
State and explain different laws of illumination.
Answer
Sign in to view the complete answer paper.
A lamp with a reflector is mounted 12m above the centre of a circular area of 24 meters diameter. If the combination of the lamp and reflector gives a uniform Candle Power of 1000 over the circular area, determine the maximum and minimum illumination produced on the area.
Answer
Sign in to view the complete answer paper.
Make a comparison between tungsten filament lamps and fluorescent tubes.
Answer
Sign in to view the complete answer paper.
A lamp of 500 watts having MSCP of 1000 is suspended 2.7 meters above the working plane. Calculate:
- Illumination directly below the lamp at the working plane
- Lamp efficiency
- Illumination at a point 2.5 meters away on the horizontal plane from vertically below the lamp.
Answer
Sign in to view the complete answer paper.
What is electric traction? What are the motors used in electric traction? Discuss the merits of electric traction.
Answer
Sign in to view the complete answer paper.
Discuss in details the regenerating braking scheme for electric drives. Also list their advantages and applications.
Answer
Sign in to view the complete answer paper.
Explain the different factors effecting the Specific Energy consumption.
Answer
Sign in to view the complete answer paper.
A suburban train runs with an average speed of 36 kmph between two stations 1.8 km apart. The values of acceleration and retardation are 1.8 kmphps and 3.6 kmphps. Calculate the maximum speed of the train assuming trapezoidal speed-time curve.
Answer
Sign in to view the complete answer paper.