Module 5

Concept of Power Transmission & Distribution

Typical Power System

Structure of Power System

Single Line Diagram

Electricity Bill

Consumption of Electrical Energy

• Electricity Bill: The amount we pay for consumption of electrical energy.
• Electrical energy consumption is given in terms of kWh.
• kWh = power consumed in kw x number of hours
• 1 Unit = 1kWh
• Number of unit consumption = number of kWh consumption

1 unit saved = 2 units generated

Power Rating of Household Appliances

Power Rating of Household Appliances

Power Rating of Household Appliances

Tariff

• The amount of money frame by the supplier for supply of electrical energy to various types of consumers is known as an electricity tariff.
• In other words the tariff is the method of charging a consumer for consuming electric power.
• Electricity tariff is the amount your electricity provider charges you for 1 unit of electricity.

• The tariff covers the total cost of producing and supplying electric energy plus a reasonable cost.
• The actual tariffs that the consumer pay depends on the consumption of the electricity.
• The consumer bill varies according to their usage.
• The industrial consumers pay more electricity bill because they use more power for long times than the domestic consumers.

• The electricity tariffs depends on the following factors:
• Type of load
• Time at which load is required
• The power factor of the load
• The amount of energy used

Types of Electricity Tariff

• Simple Tariff
• Flat Rate Tariff
• Block Rate Tariff
• Two Part Tariff
• Maximum Demand Tariff
• Power Factor Tariff
• Three Part Tariff

Two Part Tariff

• When the electrical energy is charged on the maximum demand of the consumer and the units consumed, it is called two part tariff.
• In two part tariff, the cost to be charged is divided into two parts.
• The first one is the fixed charge and the second one is the running charge.
• The fixed charge depends on the maximum demand and the second charge depends on the energy consumption by the load.

C = Ax +By

• Where C = Total cost for a period say a month

x = Maximum demand during the period

A = Cost per kW of maximum demand

y = Total energy consumed during the period

B = Cost per kWh of energy consumed

This is normally charged to industrial consumers.

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Calculation Of Electricity Bill for Domestic Consumers

• Block rate tariff
• In block rate tariff the energy consumption is divided into blocks and the and 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.

Sample Electricity Bill

Necessity Of Protective Devices

• In electrical circuits many types of faults occur which may damage the entire equipments connected to the faulty section.
• Excessive high currents can cause overheating, short circuiting.
• Excessive high voltages can cause the damage to the equipment and to the operator.
• The voltage fluctuations can cause interrupt in the operation of the device.

• The failure of insulation.
• The atmospheric lightening strokes can cause fire and damage to the buildings and structures.

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Circuit Protective Devices

• Various types of protective devices used in domestic wiring are,
• Fuse
• Miniature Circuit Breaker(MCB)
• Earth Leakage Circuit Breaker(ELCB)
• Residual Current Circuit Breaker(RCCB)
• Earthing

Fuse

• The fuse is a protecting device of simplest form.
• It consists of a small piece of metal.
• This small piece of metal used in a fuse is called fusing element.
• It is used for overload and short circuit protection in medium voltage range upto 66kV.
• The fuse is always connected in series with the circuit or the appliance to be protected.

Either copper or lead-tin alloy is generally used as a fuse wire.�Tin lead alloy fuse wires are used upto 30A�

Characteristic Of Fuse Element

• The desirable characteristics of any fuse element are ,
• Low melting point
• High Conductivity
• Free from deterioration due to oxidation
• Low cost

Fuse:

• The fuse is a device which consists of small piece of metal , which is connected in series with the circuit.
• When current through it increases beyond some predetermined value, the metal melts to interrupt the circuit current.
• This protects the circuit from excessive current.

Fuse Element

• The part of the fuse which melts when excessive current flows through it is called fuse element or fuse wire.

Rated current of fuse

• It is that maximum current which fusing element can normally carry without any undue overheating or melting.
• It depends on,
• Temperature rise of fuse contacts of fuse holder
• Fusing element material
• Deterioration of fuse due to oxidation.

Fusing Current:

• The minimum value of the current at which the fuse elements melts to interrupt the circuit current is called fusing current.
• Its value is always more than the current rating of the fuse.

Fusing Factor:

• The ratio of the minimum fusing current and the current rating of the fuse is called the fusing factor.
• The fusing factor is always greater than one.

Advantages

• It is the simplest and cheapest form of protecting device.
• It requires no maintenance.
• The operation of fuse is automatic.
• The minimum operating time is much smaller.
• Inverse time current characteristic enables it to use for the overload protection.
• Heavy currents can be interrupted without noise ,smoke, gas and flame.

Disadvantages

• The fuse is required to be replaced or rewired after its operation.
• The replacement or rewiring takes a lot of time.
• Discrimination between fuses in series cannot be obtained.
• It is not possible to provide secondary protection to fuses.

Miniature Circuit Breaker(MCB)

• A MCB is an electromechanical device which makes and breaks the circuit in normal operation and disconnects the circuit under the abnormal condition when current exceeds a preset value.
• It is a automatic switching device.
• MCB’s are rated for ac voltage of 240V for single phase, 415V for three phase or 220V dc.
• The current rating available is from 0.5A to 63A.
• It is available as Single Pole, Double Pole and Triple Pole.

Advantages

• Its operation is very fast and opens in less than 1milli second.
• The operation is automatic.
• Provides protection against overload and short circuit without noise, smoke or flame.
• It can be reset very quickly after correcting the fault, just by switching a button. No rewiring is required.
• It can not be reclosed if fault persists.
• The mechanical life is more than one lakh operating cycles.

Earthing

Earthing

• The connection of electrical machinery to the general mass of earth with a conducting material of very low resistance is called Earthing.
• Pipe Earthing
• Plate Earthing

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Necessity Of Earthing

Necessity Of Earthing

• To maintain the line voltage constant.
• To protect tall buildings and structures from atmospheric lightening strikes.
• To protect all the machines, fed from overhead lines from atmospheric lightening.
• To serve as return conductor for telephone and traction work.
• To protect the human being and animals from shock.

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Types Of Earthing

• Pipe Earthing
• Plate Earthing

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Plate Earthing

Pipe Earthing

Electric Shock

Electric Shock

• The effects of electric current passing through the human body are as follows
• 1mA causes only a faint tingle.
• 5mA causes slight shock, but may not be painful at all.
• 10 to 30mA causes painful causes leading to loss of muscular control.
• 50 to 150mA causes extremely painful shock, leading to death.

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• A sudden agitation of the nervous system of a body , due to the passage of an electric current is called an electric shock.
• The factors affecting the severity of electric shock are,
• Magnitude of current through the body.
• Path of the current through the body.
• Time for which current is passed through the body.
• Frequency of the current.
• Physical and psychological condition of the person.

First Aid Against Shock

• Do not panic
• Carry the affected person and lay him in a comfortable position and call the doctor immediately.
• Look for stoppage of breathing.
• Start giving artificial respiration if breathing is stopped.
• Never give anything to the person to drink when the person is unconscious.

• The artificial respiration should be continued for longer time.
• The burns caused due to electric flashes should be covered with the sterile dressing and then bandaged.
• Do not make crowd round and let patient get fresh air.

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Safety Precautions Against Electric Current

• Insulation of the conductor used must be proper and in good condition.
• Megger tests should be conducted and insulation must be checked.
• Earth connection should be always maintained in proper condition.
• Fuses must have current ratings.

• Before starting work with any installation switch off the supply mains and remove the fuses.
• Use rubber soled shoes while working.
• Use some wooden plank under the feet .
• Use rubber gloves while touching any terminals or removing insulation layer from a conductor.
• Make use of line tester and test lamp to check the live terminals.
• Always use insulated screw drivers, pliers, line testers etc

• Never touch two different terminals at the same time.
• Never remove the plug by pulling the wires connected to it.
• The socket should be fixed at a height beyond the reach of the children.