UNIT -VI

ELECTRICAL INSTALLATIONS AND

SAFTEY PROCEDURES

Syllabus

• Components of LT Switchgear: Switch Fuse Unit (SFU), MCB, ELCB, MCCB,

• Types of Wires and Cables

• Earthing , Electrical Shock and its Typical effects - first aid,

• Elementary calculations for energy consumption - simple case study,

• types of batteries-important characteristics of batteries, battery backup.

The apparatus used for switching, controlling and

protecting the electrical circuits and equipment is

known as switchgear.

The term ‘switchgear’ is a generic term

encompassing a wide range of products like circuit

breakers, switches, switch fuse units, off- load

isolators, HRC fuses, contactors, earth leakage circuit

breakers (ELCBs), etc...

Components of LT switch gear

A fuse is a short piece of wire

or thin strip which melts when

excessive current flows

through sufficient time.

whenever the current flowing

through fuse element

increases beyond its rated

capacity then short circuit or

overload occurs. This raises

the temperature and the fuse

element melts, disconnecting

the circuit is protected by it.

FUSE

It is Switched Fuse

Unit. It has one switch

unit and one fuse unit.

When we operate the

breaker, the contacts will

get close through switch

and then the supply will

passes through the fuse

unit to the output.

SWITCH FUSE UNIT (SFU)

MCB MCB is an electromechanical device which

guards an electrical circuit which automatically

switches off electrical circuit during abnormal

condition of the network means in over load

condition as well as faulty condition.

The normal current rating is ranges from 0.5-63

A with a symmetrical short circuit breaking

capacity of 3-10 KA, at a voltage level of 230 or

440V.

Characteristics of MCB

The characteristics of an MCB mainly include

the following

•Rated current is not more than 100 amperes

•Normally, trip characteristics are not adjustable

•Thermal magnetic operation

ELCB

Early earth leakage circuit breakers are voltage

detecting devices, which are now switched by

current sensing devices (RCD/RCCB).

An ECLB is one kind of safety device used for

installing an electrical device with high earth

impedance to avoid shock. There are two types of Earth Leakage Circuit

Breaker (ELCB)

Voltage Operated ELCB

Current Operated ELCB

Characteristics of ELCB

This circuit breaker connects the phase, earth wire

and neutral

The working of this circuit breaker depends on

current leakage

Molded case circuit breakers are a type of

electrical protection device that is

commonly used when load currents exceed

the capabilities of miniature circuit

breakers. They are also used in applications

of any current rating that require adjustable

trip settings, which are not available in

plug-in circuit breakers and MCBs.

The main distinctions between molded-case

and miniature circuit breaker are that the

MCCB can have current ratings of up to

2,500 amperes, and its trip settings are

normally adjustable.

MCCB

Wire is a single electrical conductor, whereas a cable is a group of wires

swathed in sheathing.

Types of wires and cables:

CABLES

• The main requirements of the insulting materials used for cable are:

1. High insulation resistance.

2. High dielectric strength.

3. Good mechanical properties i.e. tenacity and elasticity.

4. It should not be affected by chemicals around it.

5. It should be non-hygroscopic because the dielectric strength of any material goes very much down with moisture connect

TPES OF CABLES RUBBER: used for house wiring, buildings, factories and low power work.

PVC(Polyvinyl chloride): It is a thermo plastic insulating material. These are used up to 1.1kv voltages especially in concealed wiring system.

TRS(Tough rubber sheathed) or Cab type sheathed(CTS): These are used 250/ 500v circuits.

Electrical Earthing The process of transferring the immediate discharge of the

electrical energy directly to the earth by the help of the low

resistance wire is known as the electrical earthing.

Mostly galvanised iron is used for earthing.Earthing provides

simple path to the leakage current.

Earthing is an important component of electrical

systems because of the following reasons:

•It keeps people safe by preventing electric shocks

•It prevents damage to electrical appliances and devices by

preventing excessive current from running through the circuit

•It prevents the risk of fire that could otherwise be caused by

current leakage

Types of Electrical Earthing:

•Neutral Earthing:

In neutral earthing, the neutral of the system is directly connected to earth by the help of the GI wire. The neutral earthing is also called the system earthing. Ex. Generator, T/F, Motor etc., •Equipment Earthing:

Such type of earthing is provided to the electrical equipment. The non-current carrying part of the equipment like their metallic frame is connected to the earth by the help of the conducting wire.

Electric shock

An electric shock happens when an electric current passes

through your body. This can burn both internal and external

tissue and cause organ damage.

First Aid:

If you receive an electric shock

•Let go of the electric source as soon as you can.

•If you can, call 911 or local emergency services. If you can’t, ask for someone

else around you to call.

•If the shock feels minor ,See a doctor as soon as you can, even if you don’t have

any noticeable symptoms. Remember, some internal injuries are hard to detect at

first.

In the meantime, cover any burns with sterile gauze(శుభ్రమైన గాజుగుడ్డ). Don’t

use adhesive bandages or anything else that might stick to the burn.

If someone else has been shocked •Don’t touch someone who has been shocked if they’re still in contact with the

source of electricity.

•Turn off the flow of electricity if possible.

•Stay at least 20 feet away if they’ve been shocked by high-voltage power lines

that are still on.

Elementary calculations for energy consumption

STEP I : Calculate Watts Per Day

In this step, simply multiply your device’s wattage by the number of hours you use it in a day. This will give you the number of watt-hours consumed each day.

For example, say you use a 125-watt television for three hours per day. By multiplying the watts (125) by the hours used (3), we find that the television is consuming 375 watt-hours per day.

125 watts X 3 hours =

375 watt-hours per day

Cont., STEP II : Convert Watt-Hours to Kilowatts

Electricity is measured in kilowatt-hours on your bill, not watt-hours. One kilowatt is equal to 1,000 watts.

so to calculate how many kWh a device uses, divide the watt-hours from the previous step by 1,000. Using our previous example, this means you would divide 375 watt-hours by 1,000, resulting in 0.375 kWh.

375 watt-hours per day / 1000 =

0.375 kWh per day

Cont., STEP III : Find Your Usage Over a Month

Now that you know the kWh used per day, multiply that by 30 to find your approximate usage for the month.

So, if your daily usage is 0.375 kWh, your monthly usage would be 11.25 kWh.

375 watt-hours per day X 30 days =

11.25 kWh per month

Cont., STEP IV : Figure Out the Cost

For the final step, refer to your last electric bill to see how much you pay per kWh, i.e. Tariff. Let’s say, according to your bill, your electric rate is 3 rupees per kWh.

Multiply your electric rate (₹3) by your monthly usage (33.75) to find out how much your TV is costing you in a month (₹33.75).

11.25 kWh per month X ₹5 per kWh =

₹33.75 per month

What about devices that use more electricity?

• For refrigerator, for instance, runs 24 hours a day. Most

refrigerators consume anywhere between 300 to 780 watts of electricity. Let’s say your model only uses 300 watts.

300 watts X 24 hours = 7,200 watt-hours per day

7,200 watt-hours per day / 1000 = 7.2 kWh per day

7.2 kWh per day X 30 days = 216 kWh per month

216 kWh per month x ₹3 per kWh = 648 per month

Cells and Batteries

• A device which is used as a source of e.m.f. and

which works on the principle of conversion of chemical energy into electrical energy is called a cell.

• But practically the voltage of a single cell is not sufficient to use in any practical application.

• Hence various cells are connected in series or parallel to obtain the required voltage level.

• The combination of various cells, to obtain the desired voltage level is called a battery.

Types of Cells

• There are two types of cells, Primary Cells: • The chemical action in these cells is not reversible and

hence the entire cell is required to be replaced by a new one if the cell is down.

• The primary cells can produce only a limited amount of energy.

• Mostly the non electrolytes are used for the primary cells. • The various examples of primary cells are

i. Dry Cell (zinc-carbon) ii. Mercury cell iii. Zinc chloride cell iv. Lithium cell v. alkaline cells

Dry Cell (zinc-carbon)

•The zinc container is lined with paper to avoid direct reaction of zinc with carbon. •The container is sealed with an insulator called pitch. •The tin plates are used at top and bottom which are positive and negative terminals of the cell. •Applications are Used in torch lights, Electronic apparatus and toys, wall clocks etc.

Mercury cell

Applications These cells are preferred for providing power to small devices like Electronic calculators, Audio devices, Cameras etc.,

Types of Cells

Secondary Cells: • The chemical action in this cells is reversible. • Thus if cell is down, it can be charged to regain its

original state, by using one of the charging methods.

• The electrical energy is stored in the form of chemical energy.

• secondary cells are also called storage cells, accumulators or rechargeable cells.

• The various types of secondary cells are i. Lead-acid cell. ii. Alkaline cell (Nickel-cadmium )

Lead-acid cell

Applications

1. In emergency lighting systems

2. In automobiles for starting.

3. Uninterrupted power supply systems.

4. Railway signalling.

5. Electrical substations and the power

stations.

Characteristics of Lead-acid cell

• During charging of the

lead acid cell, the voltage

increases from 1.8V to

2.5V-2.7V, when cell is

completely charged.

• If the discharge rate is

high, the curve is more

drooping as voltage

decreases faster.

Alkaline cells

• The secondary cells can be alkaline cells. These are of two types

1.Nickel – iron cell or Edison cell

2. Nickel – cadmium or Nife cell or

Junger cell

1.Nickel – iron cell or Edison cell

Applications 1. Mine locomotives and mine safety lamps 2. Space ship 3. In the railways for Lighting and air conditioning purposes. 4. To supply power to tractors, submarines, aeroplanes etc.

Electrical Characteristics of Nickel Iron cell

•The Characteristics will show the variations in the terminal voltage of cell against the charging or discharging hours. •When fully charged its voltage is about 1.4V and during discharging it reduces to 1.1 to 1V. During charging, the average charging voltage is 1.7 to 1.75 V.

Nickel – cadmium cell

Applications

1.Millitary aero planes , helicopters and commercial airlines for starting engines and provide emergency supply. 2. In Electric Shavers. 3. In the railways for Lighting and air conditioning purposes etc.

Battery Charging

• The main methods of battery charging are

1. Constant current method

2. Constant voltage method

3. Rectifier method

Battery Charging – Constant Current Method

• When the supply is high voltage but battery to be charged is of low voltage, then this method is used.

• The number of batteries are connected in series across the available D.C. voltage.

• The constant current is maintained through the batteries with the help of variable resistor connected in series.

Battery Charging – Constant Voltage Method

• In this method constant voltage is applied across the cells, connecting batteries in parallel.

• The charging current varies according to the state of the charge of each battery.

• The battery is first connected, a high charging current will flows meanwhile the terminal voltage of the battery increases, the charging current reduces automatically.

• At the end of full charge, the voltage of the battery is equal to the voltage across the busbars and no current flows.

Battery Charging – Rectifier method • When battery is required to be charged from A.C supply,

this method is used. • The rectifier converts A.C to D.C supply generally bridge

rectifier is used for this purpose. • The step down transformer lowers the A.C supply voltage

as per the requirement.

Battery Backup

• A battery backup device is an electronic device that supplies secondary power in the absence of main power, such as during a power outage.

• The battery backup will supply power when it detects an outage.

• Battery backup devices can also protect electronic hardware from power spikes, dirty electricity and power outages.

• Battery backup devices in all sizes and power capacities available but this will affect the size and capacities required.