Definition Of Salient Electrical Terms

1. Electricity: Electricity is a form of energy, which is invisible but it can be felt by some of its effects, such as lighting effects, heating effects, magnetic effects, chemical effects, etc.

2. Voltage: It is the electrical pressure which makes the electric current (electrons) to flow in the circuit. The unit by which voltage is measured is called Volt.

In A.C., we have single phase supply 230V and three phase supply 400V. Normally single phase supply is given for lighting loads and three phase supply for power intensified loads.

Low medium, High and Extra High Voltage:
Upto 250 Volts, it is called low voltage.
Upto 650 Volts, it is called medium voltage.
Upto 33,000 Volts, it is called high voltage (HV).
Voltage exceeding 33,000 Volts is called extra high voltage (EHV)

3. Current: Flow of electrons in any conductors is called Current. the unit by which the current is measured is called Ampere. There are two types of Electric current. viz., Direct and Alternating Current.
Direct Current: It is unidirectional current which changes its magnitude but not the direction.
Alternating Current: It is the current which changes its magnitude and direction periodically.

4.Resistance: It is the property of a substance which does not allow the electricity to pass through it. The unit used to measure the resistance is called Ohm.

5. Watt: It is the unit used for measuring electric power. The product of Volt, ampere and the power factor is watt.
Kilowatt Hour: The unit used to measure electrical energy is called Kilowatt Hour. This is the product of the electric power used in kilowatts and the No. of hours of power was utilized. The consumption bill sent to L.T. consumers is based on kilowatt hour (KW Hr.)

6. Short Circuit: When positive and negative or phase and neutral wires meet each other (bare conductor) without any resistance, then it is called short circuit. High current will flow due to this and cables will be over heated.
Short Circuit leading to overheating of cables will result in meeting of the cables with fuse blowing out causing strain to the Board's equipments.

7. Fuse: Fuse is the weakest point if an electrical circuit that may cut the circuit when an abnormal current flows. It is therefore very essential that fuse wire is provided for safety of machines and persons.
Lead or Tinned Copper is used for fuse wires.
If no fuse is provided in an electrical circuit, in the event if short circuit, high current will flow in the circuit, which will heat the cables and there will be danger or fire.

8. Earth: A solid wire coming from an electrode driven 2.5 to 3 meters deep into the ground is called earth.
Earthing is done to save human life from danger of electric shock and death by blowing the fuse of the apparatus which become leaky (faulty).
A good earthing gives very low resistances to the flow of whole current of a circuit.
Double earth is necessary for all three phase machines for the following reasons:
(a) To give low resistance.
(b) If one earth is out of order, the second will do the work.

9. Capacitor: It is a static device consisting of two metallic plates insulating by a dielectric medium. This dielectric medium can be air, paper or polypropylene
The capacity of a capacitor is expressed in terms of KVAR.

10. Generator: This is an appliance which converts mechanical energy into electrical energy. The mechanical energy is produced by a prime mover, like, diesel engine, steam turbine, etc.
D.C. generators are called Dynamos and AC generators termed Alternators.

11. Transformer: This is a static machine which converts high voltage into low voltage and vice versa, without change in supply frequency.

12. Frequency: The rate at which the no. of cycles are performed in one second is termed as frequency. The standard frequency for AC supply in India is 50 cycles/sec.