Components of LT switch gear
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...
• The Switched Fuse Unit 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)
Mminiature Circuit Breaker (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
• Rated current is not more than 100 amperes
• Normally, trip characteristics are not adjustable
• Thermal magnetic operation
• 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
1. Voltage Operated ELCB
2. Current Operated ELCB
Characteristics of ELCB
• This circuit breaker connects the phase, earth wire and
• The working of this circuit breaker depends on
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
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.
Wire is a single electrical conductor, whereas a cable is a group of wires
swathed in sheathing.
Types of wires and cables
• The main requirements of the insulting materials used
for cable are:
High insulation resistance.
High dielectric strength.
Good mechanical properties i.e. tenacity and
It should not be affected by chemicals around it.
It should be non-hygroscopic because the
dielectric strength of any material goes very
much down with moisture connect.
TYPES OF CABLES
RUBBER: used for house
wiring, buildings, factories
and low power work.
It is a thermo
concealed wiring system.
used 250/ 500v circuits.
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 preventsdamage 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
Types of Electrical 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
Ex. Generator, T/F, Motor etc.,
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.
Elementary calculations for energy
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
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 /
0.375 kWh per day
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
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
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
conversion of chemical
the principle of
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,
• 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
• Mostly the non electrolytes are used for the primary
• 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
• 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
Types of 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
• The electrical energy is stored in the form of chemical
• 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 )
• In emergency lighting systems
• In automobiles for starting.
• Uninterrupted power supply systems.
• Railway signalling.
• Electrical substations and the power
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
• If the discharge rate is
high, the curve is more
drooping as voltage
• The secondary cells can be alkaline cells. These are of
1. Nickel – iron cell or Edison cell
2. Nickel – cadmium or Nife cell or Junger cell
1. Nickel – iron cell or Edison cell
• Mine locomotives and mine
safety lamps Space ship
• In the railways for Lighting
and air conditioning purposes.
• 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
• Millitary aero planes, helicopters
and commercial airlines for
starting engines and provide
• In Electric Shavers.
• In the railways for Lighting and
air conditioning purposes etc.