Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech IV UTILIZATION OF ELECTRICAL ENERGY Previous Question Paper (February/March - 2022 - R18)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
State the advantages of electrically produced heat by means of arc furnaces. Distinguish between the direct and indirect type of arc furnaces. State their field of application.
Answer
Electric heating, particularly through arc furnaces, offers significant advantages over conventional fuel-fired furnaces due to precise control and high thermal efficiency. The primary advantages include:
- High Temperature Capability: Arc furnaces can achieve extremely high temperatures, often exceeding 3000°C, which is essential for melting refractory metals and high-grade steel.
- Precise Temperature Control: The heat input can be regulated accurately by adjusting the arc length or current, ensuring consistent metallurgical quality.
- Cleanliness and Atmosphere Control: Since there is no combustion of fuel, there is no contamination from flue gases, allowing for the maintenance of a neutral or reducing atmosphere.
- Uniform Heating: The heat is generated directly within the charge or in close proximity, leading to uniform distribution and reduced thermal gradients.
- Efficiency: Electric arc furnaces exhibit high thermal efficiency as the heat is concentrated in the melting zone with minimal losses to the surrounding environment.
The distinction between direct and indirect arc furnaces is based on the path of the electric arc relative to the charge:
| Feature | Direct Arc Furnace | Indirect Arc Furnace |
|---|---|---|
| Arc Path | The arc is struck between the electrodes and the charge itself. | The arc is struck between two electrodes, and heat is transferred to the charge via radiation. |
| Current Flow | Current passes directly through the charge. | Current does not pass through the charge. |
| Heat Transfer | Heat is produced by the arc and the resistance of the charge. | Heat is transferred primarily by radiation from the arc to the charge. |
Fields of Application:
- Direct Arc Furnaces: Primarily used in the steel industry for melting and refining high-quality alloy steels and for the production of ferro-alloys. They are preferred for large-scale industrial melting where the charge is conductive.
- Indirect Arc Furnaces: Primarily used for melting non-ferrous metals such as copper, bronze, and brass. They are also employed in laboratories or small-scale foundries where precise temperature control is required without the risk of carbon pickup from the electrodes affecting the melt.
Answer the following:
What are the factors to be considered for inductor design in induction heating?
Answer
- Coupling Efficiency: The inductor must be designed to maximize the magnetic flux linkage with the workpiece. A smaller air gap between the coil and the load increases coupling efficiency, though it must be balanced with electrical insulation requirements.
- Frequency Selection: The operating frequency determines the depth of penetration (skin effect). Higher frequencies are used for surface heating of small parts, while lower frequencies are required for deep heating or large workpieces.
- Coil Geometry: The shape of the inductor must conform to the shape of the workpiece to ensure uniform heating patterns. Complex shapes require multi-turn or custom-contoured coils.
- Electrical Impedance Matching: The inductor's impedance must be matched to the power supply output to ensure maximum power transfer. This often involves the use of impedance-matching transformers or capacitor banks.
- Cooling Requirements: Since high currents flow through the coil, significant heat is generated within the inductor itself. Water-cooled copper tubing is typically used to prevent coil deformation and failure.
- Material and Insulation: The coil material (usually high-conductivity copper) and the insulation material must withstand the high electromagnetic fields and thermal environment without breaking down.
Explain the principle of dielectric heating. Also write the applications of Dielectric heating.
Answer
Sign in to view the complete answer paper.
Answer the following:
Explain in detail about the working principle of resistance and arc welding.
Answer
Sign in to view the complete answer paper.
With a neat diagram, explain the working of metallic Arc welding.
Answer
Sign in to view the complete answer paper.
Explain in detail about the following with respect to Welding:
- Spot welding
- Seam welding
- Butt welding
- Projection welding
Answer
Sign in to view the complete answer paper.
Answer the following:
Explain with a neat diagram the principle of operation of a sodium vapour lamp and mention its use.
Answer
Sign in to view the complete answer paper.
A lamp with a reflector is mounted 12 m 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.
Answer the following:
Define inverse square law and cosine cube law of illumination.
Answer
Sign in to view the complete answer paper.
A lamp giving 300 C.P in all directions below horizontal is suspended 2m above the centre of a square table of 1m side. Calculate the maximum and minimum illumination on the surface of the table.
Answer
Sign in to view the complete answer paper.
Answer the following:
An electric train has a maximum speed of 60 kmph. The scheduled speed including the station stop of 30 seconds is 40 kmph. If the acceleration is 1.5 kmphps, find the value of retardation when the average distance between the stops is 3 km.
Answer
Sign in to view the complete answer paper.
Sketch the typical speed-time curves for mainline service and suburban service with electric traction.
Answer
Sign in to view the complete answer paper.
Answer the following:
With the help of neat diagram, explain the method to obtain unidirectional polarity in train lighting.
Answer
Sign in to view the complete answer paper.
Draw and explain the sequence of operation of Double Battery Parallel Block System in Train lighting.
Answer
Sign in to view the complete answer paper.