Study material for SSE/JE examination by RRB on Electrical Engineering Part I

By Global Rail Network on October 6, 2014

Last updated on October 23rd, 2014 at 03:46 am

Electrical Engineering is an important branch of engineering dealing with Electrical Voltage, Current in DC and AC state, Resistance, Inductance, Capacitance, Generation, Transmission and Utilisation of Electric Power, Electrical Drives etc. This study material is prepared to help those preparing for competition examination.

Part I consists of Fundamental of voltage and current, Resistance, Heating and magnetic effect of current, Magnetic material, Interaction of current-magnetic field-motion, DC motor, DC network theorems, Battery, Battery Charger etc.

Part II consists of AC waveform, Inductor, Transformer, Induction Motor, AC Transmission and Distribution

Fundamentals of Electricity

Electric current: Electric current is the rate of flow of charge (electron) and is also written as dQ/dt. Its unit is Ampere and symbol I. It is similar to rate of flow of water. The speed of electron in a copper conductor is just 0.58 cm/min but it is the electric field or its variation which travels at the speed of light for an electric action to perform.

Electric Potential: Electric Potential is similar to water head which makes water to flow. Electric potential is also accumulation of electric charge at one end and producing an electric field travelling at a speed of light and making the charge to flow through the conductor. Its unit is Voltage and symbol V.

Electrical Earth: Electrical Potential is measured with reference to a universal reference called earth. The earth is having very high capacitance and absorb any amount of charge without raising its potential. A leaking current is disastrous if passed through human being, and therefore, all equipment body is connected to earth. A plug is three pin terminal, of which earth is longer and thick, for the reason of easy identification, earth to connect first and should be able to carry fault current. The neutral is connected to earth at transformer end as well as utilization point.

Ohm’s Law: It is defined that the current through the conductor is directly proportional to voltage applied and constant of proportionality is called Resistance. It is written as V=IR. It is important that there is material which does not follow ohm’s law through out entire temperature range.

Electric Resistance: Flow of electron encounters resistance in its movement and loses its energy. This loss of energy is converted into heat. Unit of resistance is Ohm and symbol Ω. For conductor, a term Conductance is also used to define the property of material which is reversal of resistance (G=1/R) having unit of Siemens.

Series and Parallel combination of Resistance

When resistances are connected in series, then equivalent resistance is given by R_eq=R₁+R₂+R₃…. and when connected in parallel, it is given by 1/R_eq= 1/R₁+1/R₂+1/R₃….. Always remember, the resistance increases when connected in series and reduces when in parallel.

Specific Resistance or Resistivity of materials

It is the specific resistance of the material which is specific to the property of the material arising due to the composition of its atomic structure. It is constant for any material, ρ is the symbol and unit Ω-m and calculated by this formula R=ρ*l/A i.e. always remember that the resistance is directly proportional to the length and inversely proportional to the area of cross-section. The resistivity of material varies very largely giving scope for different applications such as conductor, resistor, insulator, semi-conductor etc.

Conductor (x10^-8 ohm-meter) : Al(2.8), Brass(6-8), Carbon(3000-7000), Copper(1.72), Gold(2.44), Iron(9.8), Silver(1.64)

Insulator (x10^-8 ohm-meter) : Bakelite(10¹⁰), Glass(10¹⁰-10¹²), Rubber(10¹⁶), Mica(10¹⁵), Sulphur (10¹⁵)

Heating Element (x10^-8 ohm-meter): Tungsten(5.5), Nichrome(108)

Semi-Conductor: Silicon, Germanium

More pages on this topic:

Effect of Current (Page 2)

DC Motor (Page 3)

DC Network Theorems (Page 4)

Storage Electric Battery (Page 5)

Basics of Capacitor (Page 6)