THEORY EXAMINATION (SEM–VIII) 2016-17 UTILIZATION OF ELECTRICAL ENERGY & TRACTION

SECTION A – Basic Concepts of Electrical Energy Utilization and Traction

Section A includes short questions that test basic concepts related to electric heating, welding, illumination, and electric traction systems. 

Question (a): What are the Advantages of Electric Heating?

Answer:
Electric heating has several advantages over conventional heating methods such as coal or gas heating.

It is a clean method because it does not produce smoke or harmful gases.

It provides precise temperature control which is important in industrial processes.

Electric heating is highly efficient since most electrical energy converts directly into heat energy.

It allows uniform heating and is easy to control automatically.

Due to these advantages, electric heating is widely used in domestic appliances and industrial furnaces.

Question (b): Write Stefan’s Law of Heat Radiation

Answer:
Stefan’s Law states that the total radiant heat energy emitted by a black body is proportional to the fourth power of its absolute temperature.

Mathematically:

E=σT4E = \sigma T^4E=σT4

Where:
E = Energy radiated per unit area
σ = Stefan-Boltzmann constant
T = Absolute temperature in Kelvin

This law is important in understanding heat transfer by radiation.

Question (c): Why Alternating Current is Suitable for Resistance Welding?

Answer:
Alternating current is preferred for resistance welding because it provides controlled heating at the welding joint.

AC welding systems are simpler and cheaper compared to DC systems. The alternating current also allows the heat generation to be easily regulated, preventing overheating of the material.

Additionally, AC systems reduce electrode wear and allow efficient welding operations.

Question (d): What is Meant by Welding Electrode?

Answer:
A welding electrode is a conductor through which electric current flows during the welding process.

Electrodes can be classified into two types:

Consumable electrodes – which melt and become part of the weld.

Non-consumable electrodes – which conduct current but do not melt.

Electrodes help create an electric arc that produces the heat required for welding.

Question (e): Calculate MSCP

Given:
Total luminous flux = 1000 lumens

The formula for mean spherical candle power (MSCP) is:

MSCP=Total luminous flux4πMSCP = \frac{\text{Total luminous flux}}{4\pi}MSCP=4πTotal luminous flux​ MSCP=10004πMSCP = \frac{1000}{4\pi}MSCP=4π1000​ MSCP=100012.57MSCP = \frac{1000}{12.57}MSCP=12.571000​ MSCP≈79.6 candle powerMSCP ≈ 79.6 \text{ candle power}MSCP≈79.6 candle power

Therefore, the MSCP of the lamp is approximately 79.6 candle power.

Question (f): What is Flood Lighting?

Answer:
Flood lighting is a method of illumination in which large areas are illuminated using high-intensity light sources.

Flood lighting is used for:

Stadium lighting

Building illumination

Monuments and advertising displays

Outdoor events

The aim of flood lighting is to provide uniform and powerful illumination over large areas.

Question (g): Why Single Phase System is Preferred for Main Line Railway Service?

Answer:
Single-phase systems are preferred for mainline railway electrification because they allow efficient transmission of electrical power over long distances.

Advantages include:

Lower transmission losses

Simpler overhead equipment

Reduced installation cost

Efficient power supply for heavy traction loads

Single-phase systems are widely used in high-speed railway networks.

Question (h): What is Meant by Speed-Time Curve?

Answer:
A speed-time curve represents the variation of train speed with respect to time during a journey between two stations.

It is used in electric traction studies to analyze the performance of trains.

The curve typically includes four phases:

Acceleration

Free running

Coasting

Braking

Speed-time curves help calculate energy consumption and journey time.

Question (i): Why DC Series Motor is Suitable for Traction?

Answer:
DC series motors are ideally suited for traction applications because they provide high starting torque.

High starting torque is required to start heavy trains from rest.

Other advantages include:

Smooth acceleration

Simple speed control

Ability to handle heavy loads

Because of these characteristics, DC series motors have historically been used in electric locomotives.

Question (j): Why Traction Motors Have One-Hour Rating and Continuous Rating?

Answer:
Traction motors operate under varying load conditions.

One-hour rating refers to the maximum load the motor can carry safely for one hour without overheating.

Continuous rating refers to the load that the motor can carry continuously without exceeding temperature limits.

These ratings help ensure reliable motor operation in traction systems.

SECTION B – Intermediate Concepts of Electrical Energy Utilization

Section B questions involve deeper understanding of electrolysis, illumination, air conditioning, and traction performance. 

Question: Principle of Electro Deposition

Electro deposition is the process of depositing a metal layer on a surface using electrolysis.

When electric current passes through an electrolyte containing metal ions, the metal ions move toward the cathode and deposit on the surface.

Electro deposition is widely used in:

Electroplating

Corrosion protection

Decorative metal finishing

Question: Speed-Time Curve of a Train

The speed-time curve illustrates how the speed of a train changes during a journey.

It includes:

Acceleration period – train speed increases.

Constant speed period – train runs at steady speed.

Coasting period – power supply is cut off and speed decreases gradually.

Braking period – train slows down to stop.

Mainline services have longer constant-speed periods, while suburban services have frequent stops and shorter running periods.

Question: Laws of Illumination and Good Lighting Conditions

The two important laws of illumination are:

Inverse Square Law

Illumination decreases with the square of the distance from the light source.

Cosine Law

Illumination depends on the cosine of the angle between light direction and surface normal.

Good lighting requires:

Adequate brightness

Uniform illumination

Absence of glare

Proper color rendering

Comfortable lighting environment

Question: Working of Window Air Conditioner

A window air conditioner works based on the vapor compression refrigeration cycle.

Main components include:

Compressor

Condenser

Expansion valve

Evaporator

The refrigerant absorbs heat from the room in the evaporator and releases it outside through the condenser, thus cooling the room.

SECTION C – Advanced Concepts of Electric Traction

Section C questions require deeper understanding of traction systems and electrical supply systems. 

Question: Features of Electric Supply System Affecting Drive

Electric supply systems influence the performance of electric drives in traction systems.

Important factors include:

Voltage level

Frequency stability

Power supply reliability

Efficiency of transmission system

Proper design of supply systems ensures smooth operation of traction motors.

Question: Diesel Engine Driven DC Generating System

In this system, a diesel engine drives a DC generator that supplies power to DC traction motors.

The diesel engine converts chemical energy into mechanical energy, which rotates the generator.

The generator produces DC electrical energy, which powers the traction motors connected to the wheels.

Advantages include:

Independence from overhead electric supply

Reliable operation in remote areas

Suitable for long-distance railways

Conclusion

Utilization of electrical energy and traction systems are essential for efficient operation of transportation systems and industrial processes. Concepts such as electric heating, welding, electrolysis, illumination, and traction motors demonstrate the practical applications of electrical engineering in everyday life.

Understanding these concepts helps engineers design efficient power systems and improve modern transportation technologies.