(SEM VII) THEORY EXAMINATION 2022-23 UTILIZATION OF ELECTRICAL ENERGY & ELECTRIC TRACTION

SECTION A (2 Marks Each)

(a) D.C. Arc Heating

D.C. arc heating is a method of heating in which heat is produced by an electric arc formed between electrodes supplied with direct current. It is mainly used in electric arc furnaces for metal melting.

(b) Heating Method Not Dependent on Frequency

Resistance heating is not dependent on the frequency of supply because heat produced depends on current and resistance.

(c) TIG and MIG Welding

TIG (Tungsten Inert Gas) welding uses a non-consumable tungsten electrode, while MIG (Metal Inert Gas) welding uses a consumable metal electrode with shielding gas.

(d) Faraday’s First Law of Electrolysis

The mass of substance deposited at an electrode is directly proportional to the quantity of electricity passed through the electrolyte.

(e) Basic Nature of Light

Light has dual nature, behaving both as a wave and as a particle (photon).

(f) Laws of Illumination

The two laws are Inverse Square Law and Lambert’s Cosine Law.

(g) Speed-Time Curve of Traction System

It shows variation of speed with time and consists of acceleration period, free-running period, coasting, and braking.

(h) Adhesive Weight

Adhesive weight is the portion of locomotive weight available for traction to prevent slipping of wheels.

(i) Traction Systems

Steam traction, diesel electric traction, electric traction, and battery traction.

(j) Diesel Electric Traction

Advantages: no overhead lines, flexible operation.
Disadvantages: higher fuel cost, pollution, lower efficiency.

SECTION B (10 Marks Each – Attempt Any Three)

(a) Ajax Wyatt Furnace

Ajax Wyatt furnace is an induction furnace used for melting metals. It works on the principle of electromagnetic induction where alternating current produces eddy currents in metal, generating heat. It is used in foundries for melting steel and non-ferrous metals.

(b) Electric Resistance Welding

Resistance welding methods include spot welding, seam welding, butt welding, and projection welding. Heat is produced due to resistance at the joint.
Merits over arc welding: high speed, no filler metal, uniform weld.
Demerits: high initial cost, limited thickness.

(c) Illumination Problem

Height of lamp = 10 m
Radius of area = 10 m
Candle power = 800

Maximum illumination (at centre):
Emax = I / h² = 800 / 10² = 8 lux

Minimum illumination (at edge):
Distance = √(10² + 10²) = 14.14 m
Emin = I / d² = 800 / (14.14)² ≈ 4 lux

(d) Systems of Track Electrification

DC system (600 V – 3000 V), single-phase AC system, three-phase AC system, and composite system are used for track electrification.

(e) Suitability of Series Motor for Traction

DC series motors provide high starting torque, variable speed, and good acceleration, making them suitable for traction duties. Speed-torque characteristics favor heavy loads.

SECTION C (10 Marks Each)

Q3

(a) Induction Heating

Induction heating works on electromagnetic induction. Methods include core-type and coreless induction heating.
Applications include metal melting, surface hardening, forging, and welding.

(b) Numerical – Efficiency of Induction Furnace

Heat required:
To raise temperature = m c ΔT = 1.8 × 0.88 × (660 − 150) = 807.84 kJ
Latent heat = 1.8 × 32 = 57.6 kJ
Total heat = 865.44 kJ = 0.24 kWh

Input energy = 4.8 × (10/60) = 0.8 kWh
Efficiency = (0.24 / 0.8) × 100 = 30%

Q4

(a) Arc Welding

Arc welding works by producing heat through an electric arc.
Carbon arc uses carbon electrode, metallic arc uses metal electrode.
DC welding gives stable arc, AC welding is cheaper.

(b) Electro-Deposition

Electro-deposition is the process of depositing metal on a surface using electrolysis. Factors affecting quality include current density, temperature, electrolyte concentration, and voltage.

Q5

(a) Fluorescent Tube

It works on gas discharge principle. Main parts include choke, starter, electrodes, and tube coating. It gives higher efficiency and longer life than incandescent lamps.

(b) Air Conditioning

Air conditioning controls temperature, humidity, purity, and air movement. It depends on heat load, occupancy, climate, and building design.

Q6

(a) Functions of Tractive Effort

Tractive effort is used to overcome train resistance, acceleration, gradient resistance, and braking.

(b) Numerical – Acceleration

Given:
Schedule speed = 30 kmph
Distance = 1 km
Stop time = 20 s
Max speed = 1.25 × 30 = 37.5 kmph

Acceleration required = approximately 1.5 kmphps

Q7

(a) Metadyne Control

Metadyne control uses a rotating amplifier to control traction motor voltage.
Merits: smooth control, high torque.
Demerits: bulky, high maintenance.

(b) Reversal of Traction Motor

Direction is reversed by reversing field or armature current.
Thyristor control advantages include smooth control and high efficiency; disadvantages include harmonics and high cost.