BEEE UNIT-1 AC & DC CIRCUITS

UNIT-3

ENERGY RESOURCES

The sources of energies are classified as follows

CONVENTIONAL ENERGY RESOURCES

Conventional energy resources are those that have been used for a long time and
are relatively well-understood. They are also known as non-renewable energy
resources because they cannot be replaced once they are used up.

The main conventional energy resources are thermal energy, nuclear energy,
hydel energy, natural gas.

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Coal: It is a type of fossil fuel which is present beneath the surface of the Earth and
was formed by decomposed organic materials due to the high compression and
temperature due to Earth’s layers. It takes millions of years to form coal which we
use. Therefore it is a non-renewable energy resource.

Natural gas and oil: These are also obtained from fossil fuels and are present
beneath the surface of the Earth and formed from decomposed organic materials.
They are in such form because of the high compression and temperature of the
Earth’s layers. Natural gas and oil also take a very long time to produce but can be
used instantly therefore these are also known as non-renewable energy
resources.

Non-commercial energy sources: The energy resources which are generally

available are free to use. Examples are fire woods, cow dung, and straw. Fire
woods are obtained from the trees and plants, dung is obtained from animal
wastes and straw is obtained from the crop plants like wheat crops, rice crops etc.

NON-CONVENTIONAL ENERGY RESOURCES

Non-conventional energy resources are those that are not as well-known or

used as conventional energy resources they are also known as renewable energy
resources because they can be replenished naturally.

The most common non-conventional energy resources are solar energy, wind
energy, tidal energy, biomass energy, hydro power energy, Geo thermal energy.

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Solar energy: The energy produced by the Sun is referred to as solar energy. It is
formed due to nuclear fission and fusion inside the Sun. This energy travels in the
form of radiation (electromagnetic waves). This energy is collected by some
photovoltaic cell panels which absorb the solar energy and convert it into
electricity that can be used for home appliances. Solar heating panels are used to
heat the water in the solar heater.

Wind: When we talk about wind energy then it means that the wind speed should
be high enough to produce a considerable amount of useful work. This kind of
wind energy is usually available near the coastal regions or near the mountains
where high wind flow is available at a constant rate. Big turbines, called wind
turbines are installed at such sites to tap this wind energy which drives these
turbines and as result, electricity is generated.

Tidal energy: We know the tides are created in the ocean due to the rotation of the
Earth and the attraction between Earth and the moon. Tides are nothing but the
rise and fall of the water level in the ocean. We can observe it easily on the shores.
The tidal energy is captured by forming narrow dams at the narrow entrances of
rivers. During high tides and low tides, the motion of the water column is used to
rotate the turbines that produce electricity.

Biomass energy: Biomass energy is extracted from biological materials where

biological materials are formed from living organisms and plants. In the biomass
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power plant, biomass is burnt into a combustor in order to produce heat which
will be further converted into mechanical energy in order to generate electricity.
Biomass can also be converted into other forms of energy like fuels used in
transportation, biodiesel or methane gas depending on the requirements.

Geothermal energy: As we know that the temperature increases as we move

inside the Earth's layers. This high temperature is the thermal energy source.
Potential sources can be hot springs and volcanoes which contain a very high
amount of heat. This kind of energy is known as geothermal energy. This energy
can be extracted and can be used to generate electricity. In Himachal Pradesh and
Ladakh, geothermal power plants are located.

Hydro energy: This energy is generally available in flowing rivers. A dam is

formed to store the water of the river at some convenient location. This stored
water contains the potential energy which can be converted into kinetic energy
by giving a narrow passage to the flow. Thus we get a water stream with high-
speed that drives large turbines to produce electricity.

Difference between Conventional and Non Conventional Sources of Energy

Sno Conventional Sources of Energy Non-conventional Sources of Energy

1 Derived from fossil fuels Derived from renewable sources
2 Limited availability Abundant availability
3 High carbon emissions Low or zero carbon emissions
4 Non-renewable Renewable
5 Established technology Evolving technology
6 Relatively cheaper Initially higher costs
7 Environmental impact Minimal environmental impact

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Hydro Power Plant:

Hydro Power Plant is an electricity

electricity-producing
producing plant in which the water is an
essential fuel, the potential energy is being converted into kinetic energy and
kineticc energy is further converted into mechanical and into electrical energy
with the help of a turbine and motor.

We will understand how it works in very detail. So now let’s study construction.

The main components are

• Water reservoir
• Dam
• Spillway
• Gate
• Pressure tunnel
• Surge tank
• Penstock
• Water turbine
• Draft tube
• Tail race level
• Powerhouse

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Water reservoir:
In a reservoir the water collected during the rainy season is stored behind a dam.
Continuous availability of water is a basic necessity for a hydroelectric power
plant. The level of the water surface in the reservoir is called the Headwater level.
The water head available for power generation depends on the reservoir height.

Dam:
The purpose of the dam is to store the water and to regulate the outgoing flow of
water. The dam helps to store all the incoming water. It also helps to increase the
head of the water. In order to generate a required quantity of power, it is
necessary that a sufficient head is available.

Spillway:
Excess accumulation of water cause danger to the stability of dam construction.
Also in order to avoid the overflow of water out of the dam especially during rainy
seasons spillways are provided. This prevents the rise of the water level in the
dam. Spillways are passages that allow the excess water to flow to a different
storage area away from the dam.

Gate:
A gate is used to regulate or control the flow of water from the dam.

Pressure tunnel:
It is a passage that carries water from the reservoir to the surge tank.

Surge tank:
A surge tank is a small reservoir or tank in which the water level rises or falls due
to sudden changes in pressure. There may a sudden increase of pressure in the
penstock pipe due to sudden backflow of water, as the load on the turbine is
reduced. This sudden rise of pressure in the penstock pipe is known as water
hammer effect.

Penstock:
Penstock pipe is used to bring water from the dam to the hydraulic turbine.
Penstock pipes are made up of steel or reinforced concrete. The turbine is
installed at a lower level from the dam. Penstock is provided with a gate valve at
the inlet to completely close the water supply.

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Draft tube:
Draft tube is connected to the outlet of the turbine. It converts the kinetic energy
available in the water into pressure energy in the diverging portion. Thus, it
maintains a pressure of just above the atmospheric at the end of the draft tube to
move the water into a tailrace. Water from the tailrace is released for irrigation
purposes.
Tailrace level:
Tailrace is a water path to lead the water discharged from the turbine to the river
or canal. The water held in the tailrace is called the Tailrace water level.
Power House:
The powerhouse accommodates the water turbine, generator, transformer, and
control room. As the water rushes through the turbine, it spins the turbine shaft,
which is coupled to the electric generator. The generator has a rotating
electromagnet called a rotor and a stationary part called a stator. The rotor
creates a magnetic field that produces an electric charge in the stator. The charge
is transmitted as electricity. The step-up transformer increases the voltage of the
current coming from the stator. The electricity is distributed through power lines.

Working principle

Hydroelectric power plant (Hydel plant) utilizes the potential energy of

water stored in a dam built across the river. The potential energy of the stored
water is converted into kinetic energy by first passing it through the penstock
pipe. The kinetic energy of the water is then converted into mechanical energy in
a water turbine. The turbine is coupled to the electric generator. The mechanical
energy available at the shaft of the turbine is converted into electrical energy by
means of the generator.

Classification of Hydroelectric power plant

Hydroelectric power plants are usually classified according to the available of

head of water

• High head power plants: head of water exceeds 70 meters

• Medium head power plants: water ranges from 15 to 70 meters

• Low head power plants: head is less than 15 meters

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Nuclear Power Generating Station

A generating station in which nuclear energy is converted into electrical

energy is known as a nuclear power station. In a nuclear power station, heavy
elements such as Uranium (U235) or Thorium (Th232) are subjected to nuclear
fission in a special apparatus known as a reactor. The heat energy thus released
is utilised in raising steam at high temperature and pressure. The steam runs the
steam turbine which converts steam energy into mechanical energy. The turbine
drives the alternator which converts mechanical energy into electrical energy .

The whole arrangement can be divided into the following main stages:

(i) Nuclear reactor

(ii) Heat exchanger
(iii) Steam turbine
(iv) Alternator

Nuclear reactor: It is an apparatus in which nuclear fuel (U235) is subjected to

nuclear fission. It controls the chain reaction* that starts once the fission is done.
If the chain reaction is not controlled, the result will be an explosion due to the
fast increase in the energy released. A nuclear reactor is a cylindrical stout
pressure vessel and houses fuel rods of Uranium, moderator and control rods.

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Fig. Nuclear Power Station Schematic Diagram:

Heat exchanger:: The coolant gives up heat to the heat exchanger which is utilised
in raising the steam. After giving up heat, the coolant is again fed to the reactor.

Steam Turbine:: The steam produced in the heat exchanger is led to the steam
turbine through a valve. After doing a useful work in the turbine, the steam is
exhausted
hausted to condenser. The condenser condenses the steam which is fed to the
heat exchanger through feed water pump.

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Alternator: The steam turbine drives the alternator which converts mechanical
energy into electrical energy. The output from the alternator is delivered to the
bus-bars through trans-former, circuit breakers and isolators.

Nuclear Power Station Advantages:

(i) The amount of fuel required is quite small. Therefore, there is a considerable
saving in the cost of fuel transportation.
(ii) Nuclear power plant requires less space as compared to any other type of the
same size.
(iii) It has low running charges as a small amount of fuel is used for producing
bulk electrical energy.
(iv) This type of plant is very economical for producing bulk electric power.
(v) It can be located near the load centres because it does not require large
quantities of water and need not be near coal mines. Therefore, the cost of
primary distribution is reduced.
(vi) There are large deposits of nuclear fuels available all over the world.
Therefore, such plants can ensure continued supply of electrical energy for
thousands of years.
(vii) It ensures the reliability of operation.

Nuclear Power Station Disadvantages:

(i) The fuel used is expensive and is difficult to recover.

(ii) The capital cost on a nuclear plant is very high as compared to other types of
plants.
(iii) The erection and commissioning of the plant require greater technical know-
how.
(iv) The fission by-products are generally radioactive and may cause a dangerous
amount of radioactive pollution.

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Solar Power Generating Station

The solar energy is converted into electrical energy called as Solar Power Energy,
and this conversion process takes place by using using solar panels, charge
controller, battery and inverter.

Solar Cells

It is the energy generating unit, made up of p-type and n-type silicon

semiconductor. It’s the heart of solar power plant.

Solar Panels

It is the heart of the solar power plant. Solar panels consists a number of solar
cells. We have got around 36 solar cells in one panel. The energy produced by
each solar cell is very small, but combining the energy of 36 of them we have got
enough energy to charge a 12 volt battery.

The solar panels or photovoltaic cells are used for the conversion of (solar
energy) light into electric current (DC) using the photovoltaic effect. This system

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can be called as Solar Power System. Solar panels are inflexible modules made of
silicon or wafer-based-crystalline silicon.

Photovoltaic cells are classified into two types: poly crystalline and mono
crystalline cells. Several photovoltaic cells are interconnected to form a module
and an array of these modules is called as a solar panel.

Battery System

The battery system consists of secondary cell or rechargeable electric battery.

There are two types of batteries such as lead acid and gel-cell-deep cycle
batteries.
The battery is used to store power during the daytime, while solar panels
generate power and can be used in night times using an inverter.

Charge Controller

The charge controller is used to switch on or off the charging and load. It is mainly
used for protecting the battery from over charge and under charge conditions.

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During the daytime controller switches the battery to store power generated from
the solar panels and, during night times, it supplies power to the load through an
inverter.

Inverter

The inverter is used to convert the DC power into AC power , and then to provide
AC supply to the loads.
As many loads, which we use frequently, require AC power- it is necessary to
convert the DC into AC. The power stored in the battery is in DC form, this can
also be converted into AC using an inverter in the system.

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Working of Solar Power Plant

As sunlight falls over solar cells, a large number of photons strike the p-type
region of silicon. Electron and hole pair will get separated after absorbing the
energy of photon. The electron travels from p-type region to n-type region due to
the action of electric field at p-n junction. Further the diode is reversed biased to
increase this electric field. So this current starts flowing in the circuit for
individual solar cell. We combine the current of all the solar cells of a solar panel,
to get a significant output.

Solar power plants have a large number of solar panels connected to each other to
get a large voltage output. The electrical energy coming from the combined effort
of solar panels is stored in the Lithium ion batteries to be supplied at night time,
when there is no sunlight.

Advantages
The solar energy is free and renewable resource to generate electricity, but
requires collectors and some other equipment for conversion of solar energy into
electrical energy.

 Solar cells used for power generation causes no noise.

 It does not cause much pollution compared to other power generating methods
 The solar cells do not consist of any moving parts and hence requires a little
maintenance for their operation.
 It can be used in remote areas for generating and utilizing power in that
locality, where the transmission of electricity is too expensive.
 The solar power offers energy security by avoiding the general power system
in which there is a possibility of power theft.
 In general, calculators and some low-power-consuming electronic devices can
be energized using solar energy effectively.
 The solar energy can produce 50% of the power required to house by installing
the solar panels.
 In long term usage of solar energy, the solar power setup investment can be
regained at maximum levels as solar energy is free of cost.
 It is an everlasting infinite renewable energy source compared to other limited
energy sources such as nuclear energy, coal, etc., which are estimated to last for
30 or 40 years.
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Disadvantages

 The solar power energy generation entirely depends on the sunlight incident
on the solar panels and which in turn depend on the climatic conditions.
 The solar energy can be harnessed in a limited period as the sunlight is
available only during the day time and sunny days; thus, power can be
generated only in limited time period and the power has to be saved in
batteries for later usage.
 The batteries used to store solar power are very costly, huge sized and need to
be replaced from time to time.
 The efficiency of solar power system (conversion of solar energy into electrical
energy) is around 22% and for improving this, large areas are required to
capture more Sun light and produce adequate electricity.

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Wind Power Generating Station

Blades
Most turbines have three blades which are made mostly of fiberglass. When wind
flows across the blade, the air pressure on one side of the blade decreases. The
difference in air pressure across the two sides of the blade creates both lift and
drag.

Drive Hub

Turbine blades fit into the hub that is connected to the turbine's generator. The
blades and hub together form the turbine's rotor.

Nacelle
It is a chamber that contains the gearbox, brakes and a generator. However for
turbines generating up to 2MW/unit, high voltage transformer is also placed in

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nacelle itself. Also it has got direction and speed sensors mounted as back as
possible on nacelle to prevent them from the dirt coming from blades.
Gearbox
A shaft connected to the hub directly goes into the gearbox and it increases its
rpm to the required level .It is the heaviest part in the nacelle.
Brakes
Brakes are used when wind is blowing above critical level to same turbine from
damage. Brakes are mounted just behind the gearbox.
Wind vane

The wind vane measures wind direction and communicates with the yaw drive to
orient the turbine properly with respect to the wind.

The anemometer measures wind speed and transmits wind speed data to the
controller.

Generator
It converts the energy of fast rotating shaft into electrical energy, and finally the
high voltage transformer converts it to high voltage to be ready to go in
transmission lines.
Tower
It‘s the cylindrical structure on which nacelle is mounted. For a turbine
generating up to 400-600 watts of power its height may vary from 25m to 45m.
However the diameter of this cylinder reduces as we go up the tower. The
transmission cable from generator comes down inside this tower to the high
voltage transformer. Tower also has a ladder inside it with wooden platforms at
different heights. The platform connected to the nacelle is called the yaw
platform.
Yaw Platform
It is a steel platform at the top of the tower and helps the nacelle to yaw in the
direction of the wind. It has also got brakes in some high end wind turbines to
maintain the direction of the nacelle

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Working of Wind Power Plant

Blades of the wind turbine work as an airfoil of different cross-sections all along
the length. When air moves over this airfoil it generates a lift force thus making
the blade to rotate at its axis. The generator is also connected to the rotor shaft
starts rotating and produces electricity.

Now, we all know that the wind speed keeps on changing with time so we get a
fluctuation in power. To overcome this, threshold velocity is decided at which
turbine will start rotating, below that brakes are used to prevent the blades from
rotating. And for high wind velocity brakes are applied to prevent turbine from
damage.

Motors and sensors are used to rotate the blades about their axis so that they can
adjust according to the varying direction of wind and to extract maximum power
out of wind. Blades are also rotated to stop the turbine from rotating, means they
are oriented in such a way that no lift will be generated even with the blowing
wind.

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POWER RATINGS OF HOUSE HOLD APPLIANCES

S.No HOUSE HOLD APPLIANCES WATTAGE

1 Lamps
a) Incandescent 60W, 100W
b) fluorescent 36W, 40W
c) CFL
1)650-850 lumens 13- 18W
2)1000-1400 lumens 18-22W
d) LED
1)650-850 lumens 7-10W
2)1000-1400 lumens 12-13W

2 Water Heater 1000-2000W

3 Electric Iron 1200W
4 Fans 60-80W
5 Refrigerator 700W
6 Air & Water Cooler 125-230W
7 Television set (LED)
a) 30 inches 50W
b) 42 inches 80W
c) 50 inches 100W
8 Air Conditioners
a) 1.0 ton 1 KW
b) 1.5 ton 1.5 KW
c) 2.0 ton 2 KW
9 Water Pumps
a) Well pumps 1000W
b) Sump pumps 800W
10 Computer (desktop PC) 80-200W
11 Printers 100-200W
12 Washing Machines 1150W
13 Vacuum cleaner 450W
14 Electric shaver 15W
15 Hair dryer 1250W
16 Laptops 60-250W
17 Rice Cooker 450-1500W

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Unit of electrical energy

DEFINITION

The kilowatt-hour is a standard unit of electricity production and consumption.

By definition, noting that 1 kilowatt = 1000 watts:

One kilowatt-hour is the electrical energy consumed by an electrical appliance of

power 1kW when it is used for one hour 1h.

1kWh=1kilowatt×1hour

The unit of electrical energy consumed is 1 kWh.

TRAIFF

The amount of money frame by the supplier for the supply of electrical energy to
various types of consumers in known as an electricity tariff. In other words, the
tariff is the methods of charging a consumer for consuming electric power. The
tariff covers the total cost of producing and supplying electric energy plus a
reasonable cost.

The actual tariffs that the customer pay depends on the consumption of the
electricity. The consumer bill varies according to their requirements. The
industrial consumers pay more tariffs because they use more power for long
times than the domestic consumers.

The electricity tariff depends on the following factors:

 Flat Demand Rate tariff

 Block meter Rate tariff
 Two-part tariff
 Power factor tariff
 Peak load tariff
 Three-part tariff

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Two-Part Tariff

A Two-Part Tariff is a Pricing Method where a Consumer is charged an Initial

Fixed Payment to Access a Service or Product, Followed by a Variable Fee Based
on Usage or Quantity Consumed.

In such type of tariff, the total bill is divided into two parts. The first one is the
fixed charge and the second is the running charge. The fixed charge is because of
the maximum demand and the second charge depends on the energy
consumption by the load.

The factor A and B may be constant and vary according to some sliding.

Advantages:
(i) It is easily understood by the consumers.
(ii) It recovers the fixed charges which depend upon the maximum demand of the
consumer but are independent of the units consumed.
Disadvantages:
(i) The consumer has to pay the fixed charges irrespective of the fact whether he
has consumed or not consumed the electrical energy.
(ii) There is always error in assessing the maximum demand of the consumer.

Electricity bills

Electricity bills are an essential part of our monthly expenses. In India, electricity
tariffs are regulated by the State Electricity Regulatory Commissions, and the
billing process is fairly straightforward.

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What is the formula to calculate electricity bills in India?

To calculate your electricity bill, follow these steps:

Watts = (amps) x (volts)

Kilowatt-hours = (watts) x (usage) / 1000.

Cost = (kilowatt-hours) x (electricity rate)

 Subtract the current meter reading from the previous month’s reading to
find the energy consumption.
Ex: Let’s take the previous meter reading to be 1500 kWh and current meter reading at 1750
kWh
Step 1: Current reading – Previous reading = 1750 kWh – 1500 kWh = 250 kWh
In this example, the energy consumption between the two meter readings is 250 kilowatt-
hours.
 Multiply the units consumed by the per-unit charges based on the
applicable slabs (e.g., Rs. 4.22 for 1-100 units, Rs. 5.02 for 101-200 units).
 Add the fixed charge and energy duty (e.g., Rs. 40 fixed charge and Rs. 0.15
per unit) to the energy charges.
 The sum of the energy charges, fixed charge, and energy duty gives you the
total bill amount.

Question: Calculate the electricity bill amount for a month of 31 days, if the
following devices are used as specified:
a) 3 bulbs of 30 watts for 5 hours
b) 4 tube lights of 50 watts for 8 hours
c) 1 fridge of 300 watts for 24 hours
Given the rate of electricity is Rs. 2 up to 100 units, Rs.3 for 101 to 200 units and
Rs. 5 for 201 and above units.

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Solution
The energy consumed by the bulbs,
As we know Energy = power × time
3 bulbs × 30 watts × 5 hours × 31 days = 13950 Wh
The energy consumed by the tubes,
4 tubes × 50 watts × 8 hours × 31 days = 49600 Wh
The energy consumed by the fridge,
1 fridge × 300 watts × 24 hours × 31 days = 223200 Wh
Therefore, the total energy consumption is given by,
13950+49600+223200 = 286750 Wh
= 286750/1000= 286.75 KWh
We need to convert it into units, where 1 unit = 1 kWh
So, electricity bill up to 100 units = 100 units × 2 rs = Rs. 200
Electricity bill for 101 to 200 units = 100 units × 3 rs = Rs. 300
Electricity bill for remaining units = 286.75 – 200 = 86.75 units × 5 rs
= Rs. 433.75
Total Electricity Bill = 200+300+433.75 = Rs. 933.75

Question: Calculate the electricity bill amount for a month of 30 days, if the
following devices are used as specified:
(i). 2 Bulbs of 40 W for 6 h/day
(ii). 2 Tube lights of 50 W for 8 h/day
(iii). 1 TV of 120 W for 6 h/day, given the cost of electricity is Rs. 2.5/unit.

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Solution:
Total energy consumed,
E=2×(40/1000)×6×30+2×(50/1000)×8×30+1×(120/1000)×6×30
E=60 kWh=60 unit [∵1 kWh=1 unit]
Given, the cost of electricity is Rs. 2.5/unit.
So, total cost will be, Rs. 60×2.5=Rs. 150

Question: An electric bulb of 40 W glows for 10 hours a day. What is the amount
to be paid in the month of 30 days if 1 unit of electricity cost Rs. 2.50?

Solution:
Power = 40 W
Time =10h×30 days=300 hrs
Units of energy =Power × Time=40 W× 300 hr
=12000 Whr=(12000/1000) kWhr=12 units
Cost for one unit of electricity = Rs. 2.50
Cost for 12 units of electricity =12×2.50=Rs. 30

Question: Five 100 W bulbs are used for 10 hr every day for 30 days. If the rate of
electricity is Rs. 4.00/unit, find the cost of electricity.

Solution:
For each bulb, power, P=100 W=100/1000 = 0.1 kW
So, total energy used by five bulbs,
E=5×0.1×10×30=150 kWh=150 unit
So, cost of electricity =150×4=Rs. 600

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EQUIPMENT SAFTEY MEASURES

Fuse:

A fuse is a small electrical safety device that protects an electric circuit from
excessive electric current. Fuses are designed to allow current through the circuit,
but in the event that the current exceeds some maximum value it will burn out
the wire, so that there is no longer a circuit.

The following diagram shows the symbols of an electrical fuse used:

The construction of a fuse is simple and typically consists of:

 Fuse Element: It is a metallic wire that melts when subjected to excessive

amount of current.
 Fuse Body: The fuse element is enclosed by the fuse body.
 Fuse Caps or Terminals: These are end metallic terminals of a fuse that
connects the wire.

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Electric fuse works on the principle of the heating effect of electric current. It is
placed in series with the device. A fuse consists of a piece of wire made of a metal
or an alloy of an appropriate melting point, for example aluminium, copper, iron,
lead etc. If a current larger than the specified value flows through the circuit, the
temperature of the fuse wire increases. This melts the fuse wire and breaks the
circuit.

Merits and Demerits of Fuse:

Merits

1. Fuse is cheapest type of protection in an electrical circuit

2. Fuse needs zero maintenance

3. Operation of fuse is simple and no complexity is involved

4. Fuse has the ability to interrupt enormous short circuit current without
producing noise, flame, gas or smoke

6. It affords current limiting effect under short-circuit conditions

Demerits

1. During short circuit or overload once fuse blows off replacing of fuse takes
time. During this period the circuit lost power

2. When fuses are connected in series it is difficult to discriminate the fuse unless
the fuse has significant size difference

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MCB

A miniature circuit breaker (MCB) iiss an Electrical Switch that automatically

switches off the electrical circuit during an abnormal condition of the network
means an overload condition as well as a faulty condition. MCB is much more
sensitive to over current than a fuse.

Working Principle of MCB

Whenever continuous over current flows through MCB, the bimetallic strip is
heated and deflects by bending. This deflection of the bi
bi-metallic
metallic strip releases a
mechanical latch.

As this mechanical latch is attached to the operating mechanism, it causes

ca to open
the miniature circuit breaker contacts, and the MCB turns off thereby stopping the
current to flow in the circuit. To restart the flow of current the MCB must be
manually turned ON. This mechanism protects from faults arising due to over
current
nt or overload and short circuits.

But during short circuit conditions, the current rises suddenly, causing
electromechanical displacement of the plunger associated with a tripping coil or
solenoid. The plunger strikes the trip lever causing the immediate release of the
latch mechanism consequently opening the circuit breaker contacts. This was a
simple explanation of a miniature circuit breakers working principle.

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There are two main types of trip mechanisms.

A bi-metal provides protection against overload current and an electromagnet

provides protection against electric short-circuit current.

Merits

1. Handling of an MCB is safer.

2. Restoration of power supply quickly is possible with MCBs.

3. During abnormal conditions such as overload and fault conditions,

automatically switches off the electrical circuit.

4. Power restoration can be done quickly.

5. It is easier to identify when they have tripped.

Demerits

1. Slow tripping

2. Aging and wear

3. Vulnerability to heat

4. They are more expensive than fused switches.

5. Cannot protect against earth faults.

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PERSONAL SAFETY MEASURES:

ELECTRIC SHOCK:

An electric shock occurs when a person comes into contact with an electrical
energy source. Electrical energy flows through a portion of the body, causing a
shock. Exposure to electrical energy may result in no injury at all or may result in
devastating damage or death. Burns are the most common injury from electric
shock.
Electric Shock Symptoms
A person who has had an electric shock may have very little external evidence of
injury or may have obvious severe burns. The person could even be in cardiac
arrest.

 Burns are usually most severe at the points of contact with the electrical
source and the ground. The hands, heels, and head are common points of
contact.
 In addition to burns, other injuries are forceful muscular contraction. A
spine injury may happen. The person also may have internal injuries,
especially if they are having any shortness of breath, chest pain, or
abdominal pain.
 Pain in a hand or foot or a deformity of a part of the body may indicate a
possible broken bone resulting from the electric shock.
 In children, the typical electrical mouth burn from biting an electric cord
appears as a burn on the lip. The area has a red or dark, charred
appearance.

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SAFETY PRECAUTIONS:

Here are some electric shock safety precautions to follow at home:

 Never work on electrical equipment with wet hands. Water conducts

electricity, so if you touch an electrical wire with wet hands, you could
receive a shock.
 Always turn off the power before working on electrical equipment. This
includes changing light bulbs, repairing appliances, and even plugging in
new appliances.
 Inspect electrical cords and plugs regularly for damage. If a cord is frayed or
a plug is cracked, do not use it. Replace it immediately.
 Use ground fault circuit interrupters (GFCIs) in wet areas, such as
bathrooms and kitchens. GFCIs can help prevent electrical shocks by
detecting small ground faults and shutting off the power.
 Keep electrical cords away from water and other liquids. Water can make
electrical cords more conductive, increasing the risk of a shock.
 Do not overload electrical outlets. Overloading an outlet can cause it to
overheat and start a fire.
 Be careful when using extension cords. Extension cords should only be used
for temporary purposes. Do not overload them and do not use them in wet
areas.
 Teach children about electrical safety. Children should be taught to never
touch electrical cords or outlets, and to always ask an adult for help when
using electrical appliances.

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EARTHING AND ITS TYPES:

Earthing is defined as “the process in which the instantaneous discharge of the

electrical energy takes place by transferring charges directly to the earth through
low resistance wire.”

How is Earthing Done?

To ensure safety, earthing can be done by connecting the electrical appliance to

earthing systems or electrodes placed near the soil or below the ground level.
When the overload current is passed through the equipment or when the fault
occurs in the system due to the current, the fault current from the equipment
flows through the earthing system. The earth mat conductors aid in raising the
voltage value equal to the resistance of the earth mat multiplied by a ground fault
and helps guard the equipment against overload current or fault current.

In homes, there shall be three types of wires, live, neutral, and earth. Live
and neutral carry electric current from the power station and the earth is
connected to the buried metal plate. Electric appliances like refrigerators, iron
boxes, and TV are connected to the earth wire while operating. Hence, these

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devices are protected from the surge or faulty electrical supply. Local earthing is
done near the electrical meter of the house.

Types of Earthing

There are three types of earthing, they are:

 Pipe earthing
 Plate earthing
 Strip earthing

Pipe earthing is the best and most efficient way of earthing and is also easily
affordable. Pipe earthing uses 38mm diameter and 2 meters length pipe vertically
embedded in the ground to work as earth electrodes.

In plate earthing, an earthing plate made of copper or G.I. is buried into the
ground at a depth more than 3 meters from the ground level. This earthing plate
is embedded in an alternative layer of coke and salts.

Strip earthing is used in transmission processes. Strip electrodes of cross section

not less than 25mm X 1.6mm of copper or 25 mm X 4mm of G.I. or steel are buried
in horizontal trenches of a minimum depth of 0.5m.

Advantages of Earthing

1. Earthing is the safe and the best method of offering safety. We know that
the earth’s potential is zero and is treated as Neutral. Since low equipment
is connected to earth using low resistance wire, balancing is achieved.
2. Metal can be used in electrical installations without looking for its
conductivity, proper earthing ensures that metal does not transfer current.
3. A sudden surge in voltage or overload does not harm the device and person
if proper earthing measures are done.

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