Basics of Electrical Engineering

By

Ms. Nishkam DhimanAssistant Professor -EEE Deptt.

Chitkara Institute of Engg. & Technology

Wires and CablesWires & Cables are purpose built conductors.

The size & type of wire/cable must suit the power rating required for their use. The higher the power the thicker the wire/cable.

Uses of Wires

Domestic & small industry

Wiring in appliances

Uses of Cable

Small & big industries

Distribution Lines

Transmission lines

WiresVarious types of wires.1.VIR wire:It is called vulcanized insulation rubber wire. Copper &

aluminum conductor and rubber coating are used in it. Now single & double braided wires are mostly in a use. But it has lower tensile strength, chemical reaction & bad insulation so it is not used.

suitable for: low & medium voltage supply onlyold type: not readily available to purchase

2. CTS & TRS wire:

It is called crab tyre sheath wire & tuff rubber sheath wire. Hard & good rubber coating on copper wire is used in this wire. Its used in house wiring & industrial wiring.

Available in 250/440V only

3. Weather proof wire:

No weather reaction , in this types of wire. Because it has cotton breeding with water proof. But it is flammable so no in use now.

4. LC wire:

It is called lead covered wire. Lead pipe on rubber insulation & its coating on conductor. It is very good in moisture condition but less tensile strength so low uses now.

5. MICC wire :

It is called mineral insulated copper covered wire. In this type wire copper conductor coated is with magnesium oxide. And After copper coating is coated on it. In case of moisture weather PVC coating (serving) is coated on its. It is uses in mines, factory, furnace, boiler, rolling mills etc. magnesium oxide is used for avoiding moisture problems.

6. PVC wire:It is called poly vinyl chloride wire. PVC coating on copper conductor so its so many advantages as follows.

(a) High dielectric strength

(b) High tensile strength

(c) More defense against moisture

(d) High life

(e) No disturb in vibration

Available in 600, 660, 1100 Voltage, Widely used Long life Durable against water, heat, oil, UV light

Three Core WireThis is three core wire. It is pvc insulated wire.

Its used for 1-phase.

1.Blue wire for Neutral

(Returns current to power source)

2. Brown for live wire

(Provides current to appliance)

3. Yellow wire for earth

(Takes current to ground if appliance has fault)

There is color code used for wiring

&supply.

CABLE STRUCTURE

There is cable wire. Its

Use for power transmit ion.

1- core

2- pvc insulation

3- oil duct

4- metallic screen

5- rubber insulation

General construction & main parts of cableCore InsulationMetallic sheathBeddingArmouring

Metallic Sheath: A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power.

Armouring: Armoured cable is the name given to any electrical cable constructed with a layer of aluminium wire armour or steel wire armour. The armour sits below the sheath of the cable to provide protection for the conductor and insulating layers.

Bedding: Cable bedding compounds are mainly used in multi-conductor cables, filling the spaces between conductors and making the cable round.

Classification of CablesType of insulation

1. Cotton covered

2. Silk coated

3. Asbestos covered

4. Rubber coated

5. PVC coated

Type of conducting material

1. Copper

2. Aluminum

Shape

1. Flat

2. Round

Mechanical Protection

1. Unarmored

2. Armored

Voltage Rating

1. Low voltage cable.(1000V)

2. High voltage cable.(11KV)

3. Super tension cable.(upto 132kV)

4. Extra high tension.(132kV and more)

5. Ultra high voltage cables(400kV and more)

Grading of cables

 The voltage gradient is maximum at the surface of the conductor and minimum at the inner surface of the sheath (i.e., the stress decreases from conductor surface to sheath). This causes breakdown in the insulation. For avoiding this breakdown, it is advisable to have more uniform stress distribution throughout the dielectric. The process of achieving uniform distribution in dielectric stress is called the grading of cables.

S.W.G. (standard wire gauge)

Introduction

A Instrument which is use for measure Cross Area (gauge) of wire

Various uses of wire gauge• To measure Cross

area of wire• To measure gauge

Cable TerminationWhen a cable enters into an accessory its called a termination

or Cable termination is the process of connecting power cables up to the final equipment or the upstream circuit breaker.

Thimble or terminals must be used at termination points, where thimble is the termination point which can be connected to the source or load.

These must be as mechanically & electrically strong as the conductor or device which it is used.

Cable SafetyWeather ProofRust proofFree from wear and tearArmouredGood insulation

DIFFERENT TYPES OF JOINTSBritannia Joint Straight JointTee JointWestern Union Joint

1. Britannia Joint : The Britannia joint is a form of electrical joint used for bare overhead wires where great tensile strength is required. The two wires are each tinned, and then each have a short shoulder bent in them, and are then bound together with tinned wire before the whole is soldered.

2. Straight JointThe braiding is cut back to a distance of about 6 inches,

and a shoulder is neatly formed with a sharp knife. The rubber insulation is also cut back and neatly tapered to a conical form about 1 1/2 inch in length. The copper wires are separated for a length of about 2 inches from the end, and carefully cleaned with emery cloth. The remainder of the exposed copper wires are twisted tightly together, and the central strand is cut out as close as possible to the point where the strands commence to separate.

3. T JointWhen a tee joint is to be made in single wires, about 2

inches of the main cable and 2 inches of the branch cable are bared, the insulating material being treated as before described. The wires are cleaned, and about 1 inch of the branch is wound round the main cable, and soldered to it at the extreme end.

4. Western Union Joints The wires are crossed positioned to make a long twist or bend in each wire. One end of the wire is wrapped and then the other end four or five times around the straight portion of each wire The ends of the wires are pressed down as close as possible to the straight portion of the wire.

5. Married JointThe married joint is an electrical joint used

for joining multi-strand cables. The wires are unstranded, then interlaced with the wires of the other cable, and then married (twisted) together before finally being soldered.

Signs and SymbolsIntroduction:

In electrical, so many signs & symbols are used for drawing electrical circuits also use for short identification.

Different types of sign & symbols used in Electrical Engineering.

1) A.C. = ~

2) D.C. = ־3) Power = w

4) Voltage = v

5) Current = I

6) Resistance = R

7) Inductor = L

Ohm’s LawFor a fixed metal conductor, the temperature & other conditions remaining constant the current (I) through it is proportional to the potential difference (V) between its ends

Equation ,

I=V/R

I=current , V=voltage and R=resistance

Applications of Ohm’s Law

By using Ohm's law, you are able to find the resistance of a circuit, knowing only the voltage and the current in the circuit.In any equation, if all the variables (parameters) are known except one, that unknown can be found. 

Concept of Electric CircuitAn electric circuit is formed by interconnecting

components having different electric properties. A collection of devices such as resistors and sources in

which terminals are connected together by connecting wires is called an electric circuit. These wires converge in nodes, and the devices are called branches of the circuit.

Components of electric circuit

1. Resistance

2. Voltage or Current Sources

3. Wires

Series and Parallel Circuits

Series circuitsA series circuit is a circuit in which resistors are arranged in a

chain, so the current has only one path to take. The current is the same through each resistor. The total resistance of the circuit is found by simply adding up the resistance values of the individual resistors:

equivalent resistance of resistors in series : R = R1 + R2 + R3 + ...

Parallel circuitsA parallel circuit is a circuit in which the resistors are arranged with

their heads connected together, and their tails connected together. The current in a parallel circuit breaks up, with some flowing along each parallel branch and re-combining when the branches meet again. The voltage across each resistor in parallel is the same.

The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the resistance values, and then taking the reciprocal of the total:

equivalent resistance of resistors in parallel: 1 / R = 1 / R1 + 1 / R2 + 1 / R3 +...

Mixed CircuitsResistor circuits that combine series and parallel resistors

networks together are generally known as Resistor Combination or mixed resistor circuits. The method of calculating the circuits equivalent resistance is the same as that for any individual series or parallel circuit and hopefully we now know that resistors in series carry exactly the same current and that resistors in parallel have exactly the same voltage across them.