MODULE 6 EE 100 Basics of Electrical Engineering Page 1 of 19 MODULE 6 TARIFF, WIRING AND LIGHTING SYSTEMS In this module, we will be learning about the different types of tariff schemes, basic concept of wiring, devices used in wiring and protection and various types of light and its working. The following topics will be discussed. Different Types of Tariffs Classification of Consumers. Conduit Wiring Service Mains Switch Board Distribution Board Fuses and Other Protective Devices Earthing and Methods Different Types of Lamps
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MODULE 6 EE 100 Basics of Electrical Engineering
Page 1 of 19
MODULE 6
TARIFF, WIRING AND LIGHTING SYSTEMS
In this module, we will be learning about the different types of tariff schemes, basic concept
of wiring, devices used in wiring and protection and various types of light and its working.
The following topics will be discussed.
Different Types of Tariffs
Classification of Consumers.
Conduit Wiring
Service Mains
Switch Board
Distribution Board
Fuses and Other Protective Devices
Earthing and Methods
Different Types of Lamps
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1. TARIFF
The rate at which electrical energy is supplied to a consumer is known as tariff. Although
tariff should include the total cost of producing and supplying electrical energy plus the
profit, yet it cannot be the same for all types of consumers..
A tariff should include the following items :
Recovery of cost of producing electrical energy at the power station.
Recovery of cost on the capital investment in transmission and distribution
systems.
Recovery of cost of operation and maintenance of supply of electrical energy e.g.,
metering equipment, billing etc.
A suitable profit on the capital investment.
1.1 Desirable Characteristics of a Tariff
A tariff must have the following desirable characteristics :
Proper return : The tariff should be such that it ensures the proper return from
each consumer..
Fairness : The tariff must be fair so that different types of consumers are satisfied with the
rate of charge of electrical energy. Thus a big consumer should be charged at a lower
rate than a small consumer. Similarly, a consumer whose load conditions do not deviate
much from the ideal (i.e., non variable) should be charged at a lower rate than the one
whose load conditions change appreciably from the ideal.
Simplicity : The tariff should be simple so that an ordinary consumer can easily understand
it. A complicated tariff may cause an opposition from the public which is generally
distrustful of supply companies.
Reasonable profit : The profit element in the tariff should be reasonable.
Attractive : The tariff should be attractive so that a large number of consumers are
encouraged to use electrical energy.
1.2 Types of Tariff
There are several types of tariff. However, the following are the commonly used types
of tariff :
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a) Simple tariff. When there is a fixed rate per unit of energy consumed, it is called a
simple tariff or uniform rate tariff. In this type of tariff, the price charged per unit is constant
i.e., it does not vary with increase or decrease in number of units consumed.
Disadvantages
There is no discrimination between different types of consumers since
every consumer has to pay equitably for the fixed charges.
The cost per unit delivered is high.
It does not encourage the use of electricity.
b) Flat rate tariff. When different types of consumers are charged at different uniform per
unit rates, it is called a flat rate tariff. In this type of tariff, the consumers are grouped into
different classes and each class of consumers is charged at a different uniform rate. The
advantage of such a tariff is that it is more fair to different types of consumers and is
quite simple in calculations.
Disadvantages
Since the flat rate tariff varies according to the way the supply is used, separate
meters are required for lighting load, power load etc. This makes the application
of such a tariff expensive and complicated.
A particular class of consumers is charged at the same rate irrespective of the
magnitude of energy consumed. However, a big consumer should be charged at a
lower rate as in his case the fixed charges per unit are reduced.
c) Block rate tariff. Here energy consumption id divide into blocks.The price per unit is
fixed in each block. The price per unit in the first block is the highest and it is progressively
reduced for the succeeding blocks of energy. This type of tariff is being used for majority
of residential and small commercial consumers.
d) Two-part tariff. In two-part tariff, the total charge to be made from the consumer is
split into two components viz., fixed charges and running charges. The fixed charges
depend upon the electrical load (maximum demand) of the consumer while the running
charges depend upon the number of units consumed by the consumer. Thus, the consumer is
charged at a certain amount per kW of maximum demand plus a certain amount per kWh of
energy consumed i.e.,
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Total charges = Rs (b × kW + c × kWh)
where,
b = charge per kW of maximum demand
c = charge per kWh of energy consumed
This type of tariff is mostly applicable to industrial consumers who have appreciable
maximum demand.
Advantages
It is easily understood by the consumers.
It recovers the fixed charges which depend upon the maximum demand of the
consumer but are independent of the units consumed.
Disadvantages
The consumer has to pay the fixed charges irrespective of the fact whether he has
consumed or not consumed the electrical energy.
There is always error in assessing the maximum demand of the consumer.
e) Maximum demand tariff. It is similar to two-part tariff with the only difference that
the maximum demand is actually measured by installing maximum demand meter in the
premises of the consumer.
f) Power factor tariff. The tariff in which power factor of the consumer’s load is taken into
consideration is known as power factor tariff. In an AC system, power factor plays an
important role. A low power factor increases the rating of station equipment and line losses.
Therefore, a consumer having low power factor must be penalised.
g) Three-part tariff. This type of tariff is generally applied to big consumers. When the
total charge to be made from the consumer is split into three parts viz., fixed charge, semi-
fixed charge and running charge, it is known as a three-part tariff. i.e.,
Total charge = Rs (a + b × kW + c × kWh)
Where,
a = fixed charge made during each billing period.
b = charge per kW of maximum demand,
c = charge per kWh of energy consumed.
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1.3 Classification of Consumers
The consumers are classified into following categories.
Domestic consumer : Small consumer with single phase supply. e.g.: houses.
Commercial consumer : Mainly shops and small offices.
Industrial consumer : Big factories and industries with three phase supply.
Public utility : Street lights and public amenities.
Public institutions : schools, colleges, hospitals etc.
The consumers are also classified as
Low tension (LT) consumer : Consumers who are supplied with 230V single phase or
415V three phase supply.
High Tension (HT) consumer : Consumers who are supplied with 11kV or 22kV
sypply.
Extra High Tension (EHT) consumer : Consumers who are supplied with 33kV and
above.
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2. WIRING
A network of wire connecting various accessories for distribution of electrical energy from
supplier meter board to the numerous electrical energy consuming devices such as lamps,
fans and other domestic appliances through controlling and safety devices is known as wiring
system. There are different types of wiring
1. Cleat wiring.
2. Wooden casing and capping wiring.
3. CTS or TRS wiring
4. Lead sheathed wiring
5. Conduit wiring
2.1 Conduit Wiring
Out of the above different types, we will be learning about conduit wiring in detail. There are
two types of conduit wiring
(i) Open type
(ii) Concealed type.
In open type conduit wiring steel tubes known as conduits are installed on the surface of the
walls by means of saddles or pipe hooks.
In concealed type the conduits are buried inside the walls of building. The wire are then
drawn into the conduits. PVC conduits are commonly used for residential building. The
concealed type conduit wiring is preferred for residential and public buildings. The conduit
used for this purpose is of two types namely
(1) Light gauge
(2) Heavy gauge.
Heavy gauge conduits are used for all medium voltage (250 V to 600 V) circuits and in places
where good mechanical protection and absolute protection from moisture is desired.
Conduit wiring are used in places where
considerable dust is present,
damp situations
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in workshops for lighting and motor wiring
residential and public buildings where the appearance is the prime thing
2.2 Service Mains
These are the service wires drawn from the electric post to home and other buildings. A
service wire has two separate and insulated conductors inside it. For a single phase supply
only once service wire will be drawn. For a three phase supply 2 service wire will be drawn.
2.3 Meter Board.
These are installed on the consumer premises. The service wire from the post terminated at
meter board. In the meter board, there will be an energy meter for measuring the electricity, a
main switch and a fuse for protection.
2.4 Distribution Board.
These are installed inside the consumer building. It can be either concealed or open type. The
connection from the meter board terminates at the distribution board. From distribution board,
the electricity is distributed to different floor and room. Each room/floor is provided with a
separate circuit. Each circuit from the distribution board is protected with MCB’s
2.5 Main Switch
The main switch is used to protect the circuit against excessive current. It is also known as
switch fuse unit. Switch fuse unit is made of iron, so known as iron clad switch. It may be
double pole for controlling single phase two wire circuits or triple pole for controlling three
phase, 3-wire circuits or triple pole with neutral link for controlling 3-phase, 4-wire circuits.
The respective switches are known as double pole iron clad (DPIC), triple pole iron clad
(TPIC) and triple pole with neutral link iron clad (TPNIC) switches.
2.6 Fuse
Fuse is a protective device. It is a thin wire having low melting point. Under normal working
condition the current flowing through the circuit is within safe limits. When a fault occurs,
the current exceeds the limiting value, the fuse wire gets heated, melts and breaks the circuit.
So fuse protects the machine or apparatus from being damaged due to excessive current.
Larger the current, the more rapidly the fuse will blow.
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The materials used for fuse wires must be of low ohmic loss and high conductivity. The
materials commonly used for this purpose are tin, lead, copper, zinc, aluminum and alloy of
tin and lead. An alloy of tin and lead (37% lead and 64% tin) is used for small current rating