ACKNOWLEDGEMENT

I would like to express our heart filled gratitude to the various people those who have helped us during the entire training period. We would especially like to extend a word of thanks to, for it was under his able guidance and leadership that I was permitted to be a part of this esteemed project.

Also we would like to thank, for he was instrumental in guiding us to the various processes in the substation and thus played a vital role in enriching our knowledge and the technical knowledge.

At last I would like to thank who helped me a lot in making this project successful.

PREFACE

Practical training sources which make an engineer perfect by imparting practical knowledge about the actual working of a company and his professional employees.

From Practical training I get the knowledge about working of 220KV G.S.S, SANGANER, JAIPUR.

I had taken my practical training at 220KV G.S.S, SANGANER, JAIPUR.

In 220 KV G.S.S. first we see the switchyard & study the working of all the equipments placed in the yard. In 220 KV G.S.S we saw the yard, control room, P.L.C.C room & battery room.

This report contains maximum technical information of 220 KV G.S.S SANGANER, JAIPUR that I was capable to attain and have tried my level best in preparing this training report.

NIRAJ KUMAR

TABLE OF CONTENTS

S.NO. CHAPTER PAGE NO.

1 INTRODUCTION 1

DESCRIPTION OF JOB 5

DETAILED ANALYSIS 7

PROTECTIVE EQUIPMENTS 18

BUS-BAR ARRANGEMENT 28

POWER LINE COMMUNICATION 30

DISTRIBUTION SYSTEM 32

BATTERIES OF BATTERY ROOM 34

CAPACITOR BANK 35

SUB-STATION 36

CONTROL ROOM 40

CONCLUSION 42

BIBLIOGRAPHY 44

INTRODUCTION

Importance of electrical energy:

The electrical energy is used in home, industries, and agriculture and even in transport. Besides its use for domestic, commercial and industrial purposes it is required for increasing defense and agricultural production. In agricultural, it is used for pumping water for irrigation and for improving the method of production and numerous other options. Electrical energy is a convenient form of energy because it can be generated centrally in bulk and transmitted economically over long distance and is almost pollution free at the consumer level further it can be adopted conveniently in the domestic, industrial and agriculture and improvement in quality of life of the people depends such upon the supply of electrical energy that the annual per capita consumption of electrical energy has emerged these days as an accepted yardstick to measure the prosperity of a nation. Some of the advanced and developed nations of North America and Europe have a very high annual per capita consumption of electrical energy; say from 8 to 13 thousand kwh, while in most of Africa, Asia and Latin America it is too low to be considered. In India had an annual per capita consumption of electrical energy of 15.5 kwh in 1950, 105 kwh in 1975, 131 kwh in 1979, 154 kwh in 1984 in 1993 and 349 kwh in 1997. the annual per capita consumption of electrical energy in some of the countries is: 16000 kWh America 13000kwh. The united states has on 6% of the world population but accounts for over 30% of electrical consumption of the world.

Electrical Energy

Superiority of Electrical Energy:

Electrical energy is considered superior to all other form of energy due to following reasons:-

1. Cheapness:

It is much cheaper than that in other forms and therefore, it is economical to use energy in this form for domestic, commercial, industrial and agricultural purposes

2. Convenient and Efficient Transmission:

The electrical energy can be transmitted convenient and efficiently from the generating stations, usually located quite away from the centers of usage, through conductors of suitable size.

3. Easy Control:

Electrically operated machines have simple and convenient starting control and operation. For example an electric motor can be started or stopped by making the switch on or off and its speed can be conveniently controlled over a wider range with simple arrangements.

4. Cleanliness:

Use of electricity does not produce smoke, fumes, dust or poisonous gases and therefore. Its use ensures cleanliness and pollution free conditions.

5. Greater Flexibility:

Electrical energy offer greater flexibility as it can be taken to any corner of the house, factor, street, hospital, farm, mine etc through solid stranded of flexible conductors.

SUBSTATION PROFILE

ABOUT 220KV SUBSTATION:

This is one of the most important substations in distribution system. This substation is located on the outskirts of JAIPUR in the signaler area. A 400kv and a 220kv supply comes from the HEERAPURA. One line also comes from KTPS. It gives power supply to SANGANER, MANSAROVAR, PRATAPNAGAR, SITAPURA INDUSTRIAL AREA, and MALPURA GATE. This substation is divided in to two main parts namely SWITCHYARD and CONTROL ROOM.

The incoming voltage is made to pass through wave trap and coupling capacitor for power line communication purpose. After this operation it appears across ABCB (air blast circuit breaker).On both side of breakers isolators are attached in order to isolate the breaker for repairing purpose. The line is then connected to 220 KV bus bars through bus couplers. At the end of this bus bar potential transformers are installed. They are being used to measure the line voltage. The supply then comes across three transformers (T1, & T2) each of voltage ratio 220/132 KV so that it can be stepped down for further transmission. Lightning arrestors are also installed on both sides of transformer in order to protect the equipment connected to the line from the high voltage of lightning during rainy seasons. We can also connect these transformers in parallel because the capacity of both transformers is same.

View of Substation

The 220 KV is fed to two bus bars through isolators. These two bus bars are connected to each other through bus-coupler. A capacitor bank is also installed to improve the power factor and it is installed at the end of the bus bar. This voltage at 33 KV is then transmitted to the nearest areas like Sanganer, Pratap Nagar, Mansarovar, Sitapura Industrial area.

Transmission in Substation

GENERATION OF ELECTRICAL ENERGY:

Electrical energy is generated by conversion of energy available in different forms from different natural sources such as kinetic energy of blowing winds, pressure head of water, chemical energy of fuels(either in solid, liquid or gaseous form) and nuclear energy of radio-active substances into electrical energy.

Conventional method of power generation:

Make use of prime-movers ( such as petrol engines, steam engines, steam turbines, gas turbines or hydraulic turbines) for driving electrical machines which convert mechanical energy into electrical energy, the electrical machines employed for generating dc are called the generators whereas those employed for generating by conventional methods are:

Thermal
Hydro
Nuclear

Power Generation Station

DESCRIPTION OF THE JOB

INTRODUCTION TO SUBSTATIONS

Substations serve as source of energy supply for the local areas of distributions in which these are located. Their main functions are to receive energy transmitted at high voltage from the generating stations, reduce the voltage to a value appropriate for local distribution and provide facilities for switching. Some substations are simply switching stations where different connections between various transmission lines are made, others are converting substations which either convert ac into dc or vice-versa or converts frequency from higher to lower or vice-versa. Substations have some additional functions. They provide points where safety devices may be installed to disconnect equipment or circuit in the event of fault. Voltage on the outgoing distribution feeders can be regulated at a substation. A substation is convenient place for installing synchronous condensers at the end of the transmission line for the purpose of improving the power factor and make measurements to check the operation of various parts of the power system. Street lighting equipment as well as switching controls for street lights can be installed in a substation.

A substation is initially an assembly of the apparatus which is installed to control the transmission or distribution of the electric power. Several substations are installed in the power system to handle the power before it is being delivered to the consumers.

FOLLOWING ARE THE MAIN FUNCTION OF THE SUBSTATIONS:

To switch the power lines i.e. for the switching purpose.
To transform voltage to higher or lower level i.e. to step up or step down.
To convert the A.C. to D.C. i.e. power converting system.
To convert frequency from higher to lower i.e. to frequency control systems.
To improve the power factor by installing the capacitor bank.

TYPES OF SUBSTATIONS:

Step up sub-stations.
Primary sub-stations.
Secondary sub-stations.
Distribution sub-stations.
The bulk supply and industrial sub-stations.
Specific purpose sub-stations.

Sub-Station

ESSENTIAL EQUIPMENT FOR A SUB-STATION:

Power transformer.
Switch gear.
Current transformer and potential transformer.
Lightning arrestors.
Earthing system.
Protective equipment and control.
Isolators.
Bus bar arrangement.
Power line communication system.
Battery bank.
Capacitor bank

DETAILED ANALYSIS

POWER TRANSFORMERS:

The heart of any substation is its transformer which needs to be protected at any cost since it major part of the transmission/distribution system three installed at our substation.

Different Power Transformers

There are four transformers installed at the substation. These are two transformers of rating 100MVA, 220/66kv. These transformers are apex made. Transformers as a system consist of several elements such as core, windings, tank oil. Transformer is made and installed at the site. It is very essential to do its regular maintenance so that it keeps on working efficiency.

Some Power Transformers

Power transformer is a very costly item in the substation. It has no moving part except tap changing gear. The vital components like core, winding insulation and oil are not moving and non visible parts. The oil can be tested and topped up by adding dehydrated, clean and filtered oil. Used oil should not be used and the new oil should be of the same make and the same chemical properties.

SWITCHGEAR:

The electrical energy is almost needed in every field of our life, therefore every effort is made to protect the power system so as to maintain uninterrupted supply. For this purpose, means are provided to switch on or off generators, transmission lines, distributor and other equipment under both normal and abnormal conditions. This is achieved by switchgear, which essentially consist of switching and protecting devices such as switches, fuses circuit breakers, relay isolators etc.

The apparatus including its associated auxiliaries employed for switching controlling and protecting the electrical circuit and equipment is known as switchgear

A tumbler switch with an ordinary fuse is the simplest form of switch gear and is generally used to control and project the domestic and commercial appliances and equipment for higher rating circuits a high rupturing capacity fuse in conjunction with a switch may serve the purpose. However, such switchgear cannot be applied on power system operating at high voltage because of the following reasons:

When fuse blows, it’s some to replace it and consequently there is interruption of power

Supply

2) On high voltage system, a fuse cannot successfully interrupt large fault currents

3) When faults occurs fuse takes some time to blow. During this time the costly equipment e.g.

Generator, transformer etc, May be damaged.

Therefore in order to protect the lines, generators, transformers and other electrical equipments from damage an automatic protective device or switchgear is required. Automatic protective switchgear mainly consists of the relay and circuit breakers. Circuit breaker switchgear, which can open or close the circuit under both normal abnormal conditions. Moreover circuit breaker is rather preferred even in the instances where a fuse is adequate.

An assembly of switchgear applied to protect the power system under normal operating condition the circuit breaker connects remain closed and carries the the full-load current continuously, hi this condition, the E.M.F induced in the secondary winding of current transformer (ct) and hence the current flowing through the relay coil is insufficient to close the trip coil of the circuit breaker. When a fault occur, heavy current flows through the primary of ct. which increases the current flowing through the relay coil and closes the trip coil circuit, thus the trip coil is energized which pulls the circuit breaker contact downward and open the circuit. The arc produced in the circuit breaker during opening operation is extinguished by oil or air blast. Hence it is seen that relay detects the faults whereas circuit breaker interrupts the circuit and extinguishes the arc.

Current Transformers:

It can be used to supply information for measuring power flows and the electrical inputs for the operation of protective relays associated with the transmission and distribution circuits or for power transformers. These current transformers have the primary winding connected in series with the conductor carrying the current to be measured or controlled. The secondary winding is thus insulated from the high voltage and can then be connected to low-voltage metering circuits.

400Kv Current Transformer Metering Current Transformer

Current transformers are also used for street lighting circuits. Street lighting requires a constant current to prevent flickering lights and a current transformer is used to provide that constant current. In this case the current transformer utilizes a moving secondary coil to vary the output so that a constant current is obtained.

These instrument transformers are connected in ac power circuits to feed the current coils of indicating and metering instruments and protective relays. In high voltage installations CTs in addition to above, also isolate the indicating and metering instruments from high voltage. The current transformer basically consist of an iron core on which are wound a primary and one or two secondary winding. The primary winding is usually single turn winding and the number of turns on secondary winding depends upon the power circuit current to be measured. The ratio of primary current to the secondary current is known as transformation ratio of CT.

POTENTIAL TRANSFORMER:

The potential transformers are employed for voltages above 380 volts to feed the potential coils of indicating and metering instruments and relays. These transformers make the ordinary low voltage instruments suitable for measurement of high voltage and isolate them from high voltage. The ratio of the rated primary voltage to the rated secondary voltage is known as turn or transformation ratio. As the name indicates this type of transformers are used to test the voltage or potential in the circuit in which they are connected. This is basically are step down transformer

Potential Transformer

which steps down the voltage to be measured to a safe value, which is then displayed by the low voltage operated meters. The potential transformers are of the following types:

Hermetically Sealed Transformer:

A liquid immersed voltage transformer which is sealed and does not communicate with the atmospheric air.

Measuring Voltage Transformer:

A voltage transformer intended to supply indicating instrument, integrating meters and similar apparatus.

Protective Voltage Transformer:

A voltage transformer intended to supply protective relays and similar apparatus.

Dual Purpose Voltage Transformer:

A voltage transformer intended to serve the dual purposes of the measuring and protection.

LIGHTINING ARRESTOR

An external cause due to which over-voltages occur on the power system in lightning. In the high voltage system, much damage is caused by the lightning in spite of taking all types of protective measures.

Lightning causes an increase in voltages which may be nearly double of that of the normal operating voltage of the system. Therefore, the common practice is to design the insulation of the system to withstand such high voltages for a reasonable length of time and provide protective devices for the voltages having value more than this high voltage. These devices are known as over-voltage protection devices. The common devices used for the protection of power system against over-voltage are:

Ground wires
Earthing screens
Lightning arrestors.

The ground wire or earthing screens used for the protection of overhead lines and power station and substation not only provides an adequate protection against lightning but also reduces the overvoltage’s induced electrostatically, but such shielding is inadequate in providing protection against traveling waves which may reach the terminals of the equipment and cause damage to it. The damages that may be caused by traveling waves are:

The high peak or crest voltage of the surge may cause flashover in the internal winding

Thereby spoil the winding insulation.

The steep wave front of the surge may cause internal flashover between interterm of the

Transformer.

The high peak voltage of the surge may cause external flashover, between the terminals of the electrical equipment which may result in damage to insulators
The step wave front resulting into resonance and high voltage may cause internal or external flashover of the oscillation in the electrical apparatus.

Thus it is absolutely necessary to provide some protective device at the power stations or substation to prevent transformers and other equipment from being subjected to traveling surges reaching there. The most common devices used for protection of equipment at the substation against traveling surges are lightning arrestors or surge diverters. A surge diverter is a device that is connected between line and earth i.e. in parallel with the equipment to be protected at the substation.

The line lead of the lightning arrestor should be firmly connected with the phase wire. The earth connection should be light and the earth resistance of earth wire should be less than 10Q. Damage if located should be rectified.

Line in rural areas:

During conducting survey of distribution lines In voltage, the map of village is taken and following are marked on the and following are marked on the map

The nearest HT lines from which the tapping will be taken.
Load
Layout of line

Line in urban area:

The power lines should be plotted on map of the city after consultation with the municipal authorities.

Agricultural area:

The transformer should be installed in the center of load so as to reduce the length of lines and voltage drop.

Survey of H.T. lines(11kv to 33kv)

Point to be considered

1) The H.T. lines should be run along if possible. This will help in Construction and maintenance

Of lines.

2) The number of angle pole should be minimum.

3) An intersection of highway and railway tracks and telephone lines

Should be avoided.

Repairing and jointing of conductor:

Whenever an ACSR conductor is damaged i.e. its strands break but whole conductor is not broken, it should be repaired by pulling sleeve over the damaged part of conductor.

Jumper:

It is short length of conductor used to connect the line pole to the conductor on the line conductor on the other side of the terminal pole is known as jumper is made of same material and

Current carrying capacity as that of line conductor.

Guarding:

A guarding is provided for safety of life. The guarding for 11kv lines providing at road crossing. Canal crossing, railway crossing telephone lines generally cardie guard is provided and directly connected to the earth wire. If a line conductor breaks it will fall on the guard thus blowing the fuse. Guard is made of same material as used for earth wire 8.5 WG guards should be uniformly spaced.

Faults:

Most of the faults on the power system lead to a short-circuit condition. When such a condition occurs a heavy current called short-circuit current flows through the lines causing considerable damage to the equipments and interruption of service to consumers. There are various type of faults which may occur in the system during transmission and distribution of electric power.

Types of fault in overhead lines:

The most common fault that occur in the overhead lines is the short circuit fault. The main reason of this is insulation failure due to over voltage caused by lightning and due to broken conductors

The following are the various faults which can occurs in the 3-phase overhead transmission lines.

1) Single phase to ground: This may occur when one of the Conductors of transmission line

Breaks and falls on the ground.

Phase to phase: If one of the conductor of the 3-phase line breaks and fall on the other

Conductor, it forms a phase to phase fault.

3) Two phases to ground: If two conductor of 3-phase transmission line break and fall on the ground fault.

4) Phase to phase and third phase to ground: This is combination of Fault shown at number 1 and 2 i.e. if one conductor breaks and Fall on the second and if third break and fall on the ground.

5) AH the three phases shorted: This may occur if two conductor of Transmission line fail on the third conductor.

6) All the three phases to ground: In this type of fault all the three Conductor break and fall on the ground or fall on any other which Is further grounded.

Location of faults in overhead transmission lines:

Overhead lines are generally subjected to various troubles, lightning snow and ice being perhaps the most prevalent. Lightning will induced a high voltage in a line irrespective of the working voltage of the circuit. It causes less trouble on extremely high tension lines than on those work at lower pressures. This is because of the heavier insulation of the former. For location of faults, overhead lines are patrolled regularly by skilled linemen whose job is to notice even the smallest visible defect. This work is added by binoculars. In addition, the linemen keeps an eye for anything which might lead to trouble such as growth of trees building work going on in the neighboring place of the line the erection of radio and television aerials. The comparatively few interruption of current shows the general reliability of equipment and do credit to those whose duty is to maintain supply.

Types of faults in underground cables:

1) Breakdown of cable insulation:

When the insulation of the cables gets damaged the current starts rowing from the core to earth or to the cable or to the cable sheath and such faults arc known as ground or earth faults.

2) Short circuit fault:

When the insulation between two cables or between two core to another core of a multi-core cable directly without passing through the load. Such faults are known as short Circuit faults in case of short circuit faults the protection system will switch off the line.

3) Open circuit fault:

When the conductor of the cable is broken or a Joint is pulled out and there is no current in the cable, such faults are known as open circuit faults. If a faults occur on my section of A power system network is likely that the immediate effect will be to interrupt the supply to a section of the consumers. It may be possible to restore the supply by using the alternative routes in the network but by doing so the circuits involved become overloaded, resulting in these too become faulty which do arise be located and repaired as quickly as possible and various techniques have been adopted for this purpose. Different methods are in use for underground cables.

Lightning arresters:

The line lead of the lightning arrester should be firmly connected with the phase wire. The earth connection should be light and the earth resistance of earth wire should be less than 10Q. Damages if located should be rectified.

POWER FACTOR

(a) It shall be obligatory for the consumer to maintain the desired average power factor of 0.9 for his load or any other value that the Commission may specify in its Tariff order during any billing period.

(b) The Licensee may disconnect the supply temporarily if power factor is below 0.75 unless otherwise specified in the tariff order, during any billing period as per details given in clause 4.36.

(c) Licensee may charge a penalty and / or give an incentive for high/low power factor as per the tariff order of the Commission

The electric energy is almost generated, transmitted and distributed in the form of alternating current. Therefore the question of power factor immediately comes into picture. Most of the load i.e. 3-phase induction motors are inductive in nature and hence have low lagging power factor. The low power is highly objectionable as it causes an increase in current resulting in more losses. In order to ensure more favorable conditions for a supply it is most important to have power factor as close to unity as possible.

Concept of power factor:

Power factor may be defined as cosine of angle between voltage and current.
The ratio of resistance to impedance
P.F. = R/z = resistance/impedance

The ratio of real power to apparent power Real power/apparent power=V1cos/V1= cos. The term cos is called power factor.

Advantages:

The term cos is called power factor. Its value can never be more than one. To obtain maximum power, the power factor in a circuit is made high as possible i.e. current is brought in phase with the applied voltage so that cos is nearly equal to unity. The leading and lagging power factor depends upon the phase of current vector with respect to voltage vector in case current lags the voltage, the power factor is lagging if it leads the voltage the power factor is leading thus current “I” lags the voltage “v”.

Advantages of Power Factor

let current I be resolved in two components so that I cos@ the horizontal component is in phase with voltage and I sin@ lagging the voltage by 90 degree let all the three sides of triangle shown in fig be multiplied by voltage “v” the triangle so obtained is shown in fig.

All the three angle of the triangle still remain unchanged VI cos@ in the phase component of voltage is called real power and is denoted by “p”.

VIsin@ lagging voltage V by 90 degree is called the reactive power and is represented by VAR.

VI is called apparent power and is represented by “VA”

Thus power factor cosc@

= VI cos@/ VI –Real power/apparent power/

Thus if the power factor is made to unity @ should be made zero. This can be achieved if reactive power is made zero by supplying equal amount of leading reactive power so that resultant of leading and lagging components of reactive power becomes zero.

Disadvantages of low power factor

For fixed power and voltage P and V are fixed load current and is inversely proportional to the power factor. Lower the p.f. higher the current and results in following disadvantages.

a) Large KVA rating of equipment: the electrical machinery e.g.

Alternator transformer is always rated in KVA. KVA rating of equipment is inversely

Proportional to power factor for given amount of power KVA rating will be more for p.f. and

Vice versa.

b) Greater conductor size: To transmit fixed amount of power at fixed voltage the conductor will

Have to carry more current at low p.f therefore large size of conductor is required.

c) Large copper losses: At low power factor conductor have to carry large current therefore

IxIxR loses are increased. This result in power efficiency.

Causes of low power factor:

1) A transformer draws a magnetizing current which remain constant at loads. This magnetizing current makes the total current lag with Respect to EMF at normal loads this magnetizing current is quite Small as compared to load current and therefore does not effect. The power factor much but at light loads.

ECONOMICS OF POWER FACTOR IMPROVEMENT:

When the power factor is to be improved power factor improvement plant is required to be installed which involves some expenditure. Improvement of power factor results in reduction of maximum demand which in turn reduce the maximum demand charges annually but extra expenditure is to be increased every year in the form of interest and depreciation on account of investment made over the power factor improvement equipment. If the yearly interest and depreciation on power factor improvement plant is more than the annual saving on account of maximum demand charge it is uneconomical to install power factor improvement plant but on the contrary if the annual saving in account of maximum demand charge as a result of power factor improvement is more that the yearly interest and depreciation on power factor improvement plant it is advisable to install the power factor improvement plant as it is economical. The most economical power factor shall be when this net annual saving is maximum.

EARTHING

The process of connecting metallic bodies of all the electrical apparatus and equipments to the huge mass of earth by wire having negligible resistance is called earthing. When a body is earthed, it is basically connected to the huge mass spindle of the disk carries the moving contact which close the trip, circuit under fault condition. Under normal condition, the currents at the two ends of the feeder are equal so that the secondary current in both sets of CTs are equal. Consequently, the emfs induced in the secondary winding c and c’ are equal and opposite and no current flows through the closed circuited secondary. However when fault occurs on the feeder say at point f the voltage induced in C and CI will no longer remain equal therefore current flows through this winding and torque is developed in the disc hence the disc of both the relays rotate and close the trip circuit.

Earthing :

Connecting of an electrical equipment or apparatus to the earth with the help of connecting wire of negligible resistance is known as earthing or grounding. There are four main purpose of earthing:

To avoid electric shock to human body.

To avoid risk or fire due to earth leakage current through unwanted path.

To maintain the potential of any part of a system at a definite value with respect to earth.

To make sure that in the event of fault the apparatus should normally be dead and cannot reach a dangerous potential with respect to earth.

Significance of Earthing:

In an installation if a metallic part of an electrical apparatus comes

In direct contact with a bare or live wire the metal being good conductor of electricity, is charged. If any person comes in contact with this charged metallic part, he will get a sever shock. But if the metallic parts of the equipment are earthed the charged will be transferred to earth immediately when the metal part comes in direct contact with a live wire. The charge is earthed through the earth wire because that is the path of least resistance for the current. Therefore from safety point of view against electric shock the electricity will flow directly to earth and circuit’s fuse blow off. But in case of improper earthing or if fuse wire of improper rating is used, then the user will experience a severe electric shock.

PROTECTIVE EQUIPMENTS

Switch, Isolators and circuit breakers:

Switch:

It makes and breaks the circuit under full load or normal load condition but it cannot be operated under fault condition it is generally operated manually.

Circuit Breaker:

It makes and breaks the circuit under no load full load or fault conditions. It can be operated manually under normal conditions and automatically under abnormal conditions.

Typical Circuit Breaker Panel

Classification of circuit breaker On the basis of the medium used for arc extinction, the circuit breaker is classified as:

Oil circuit breaker in which transformer oil is used for arc extinction.
Air blast circuit breaker in which blast of air is utilized for extinguishing the arc.

Sulphur hexa fluoride circuit breakers in which sulphur hexa fluoride (SF6) gas is used for arc excitation.

Sf6 Circuit Breaker High Voltage Sf6

Water circuit breakers in which water is used for arc extinction.

Oil Circuit Breaker:

In this circuit breaker, the current carrying arc is immersed in transformer oil. When contacts are separated, arc is struck between them. The heat of the arc dissociates the oil and gases viz. hydrogen etc is evolved. The hydrogen gas bubbles surround the arc and cool it down which help in deionization of the medium between the contacts and extinguishing the arc. Moreover, gases set up turbulence in the oil and force it into the arc space when the current is zero which further helps in extinguishing the arc. The major advantages of coil as an arc quenching medium are given below:

Oil Circuit Breaker

Advantages

It absorbs the arc energy in decomposing the oil into gases.
The gases evolved provide good cooling effect.
It has ability to flow into the arc space after the current zero.
It acts as an insulator between the live contact and earthed tank.
The surrounding oil in close proximity to the arc provides cooling effect.

Disadvantages

It is easily inflammable.
It may from an explosive mixture with air.
It requires more maintenance.

Types of oil circuit breakers:

1) Bulk Oil Circuit Breaker:

In this circuit breaker oil serves two purposes:

a) It extinguishes the arc when contact is separated.

b) It acts as an insulator between the live contact and earthed tank. For this reason,

depending upon the dielectric strength of oil, a particular clearance is required between

the live contact and earthed tank. Therefore, bulk of oil is required.

In the bulk oil circuit breakers the oil moves into the arc space after the current zero may be affected

By the pressure due to the natural head of the oil above the contacts.
By the pressure generated by the action of a.c current itself.
By the pressure exerted by the external means.

Accordingly the oil circuit breaker is called;

Plain break oil circuit breakers
Self generated pressure oil circuit breaker.
Externally generated pressure oil circuit breaker.

2) Minimum Oil Circuit Breakers:

In these circuit breakers, a small quantity of oil used which only serves to extinguish the arc. The live parts are insulated by porcelain or organic insulating materials.

Air Blast Circuit Breaker:

In this circuit breaker compressed air (18 to 20 kg/cm*cm) is employed for arc extinction. When contacts are separated, the arc is struck; simultaneously the blast valve is opened. The air blast cools the arc and sweep away the ionized medium between the contacts and prevent the restriking of the arc. Thus the extinguished and current is interrupted.

These circuit breakers are finding their best application in system. Operating at 132 kv and above (up to 400 kv) with breaking capacity of 7000 MVA and above. However, this type of circuit breakers has also designed to cover the voltage range 11kv to 132 kv. The following are the advantages and disadvantages of air blast circuit breaker over the oil breaker

Advantages:

There is no risk of fire and explosion.
Due to short arc duration, burning of contacts is lees.
They require less maintenance.
The arc extinguished very quickly, since the ionized medium between the contact is removed rapidly by air blast.
The arc is extinguishes quickly through long distance, therefore, They are smaller in size
They provide facility of high speed reclosure.

Disadvantages

Compressor plant requires for compressed air.
Air leak at the pipe line fittings.
They are very sensitive to restriking voltage.
Since air is poor dielectric medium as compared to oil, therefore, it has relatively inferior arc extinguishing properties.

Type of air blast circuit breakers

Accordingly to the direction of air blast with respect to the direction of arc struct between the contacts, air blast circuit breaker are classified into:

Cross-Blast Circuit Breakers: In which air-blast cuts across the Arc.
Axial-Blast Air Circuit Breakers: In which air-blast acts along the Arc.

1) Cross-Blast Circuit Breakers:

In cross blast air circuit breakers the fixed contact is located, at the base of chute between two insulating blocks. The fixed contacts has a number of spring loaded fingers, the arcing portion of one of the fingers is being coated with silver tungsten alloy. The moving contact consist of flat copper silver faced blade, the arcing tip also being of silver tungsten alloy.

When a fault occurs an arc is struck between the fixed and moving contacts. Simultaneously a high pressure cross-blast forces the arc on the splitter plates of the chute. The splitter plates cause lengthening and cooling of arc. Thus the arc is extinguished quickly since the blast pressure is independent of the fault current; therefore, the efficiency at low fant currents is eliminated.

2) Axial–Blast Air Circuit Breakers:

Axial-blast air circuit breakers the arcing portion of the fixed and moving contacts is coated with silver tungsten alloy. The moving contact is connected to a piston and shaft of the contact is guided by guide springs. Opening the lower air valve closes the circuit.

RELAYS:

The protective relay is an electrical device interposed between the main circuit and the circuit breaker in such a manner that any abnormality in the circuit acts on the relay, which in turn, if the abnormality is of a dangerous character, causes the breaker to open and so to isolate the faulty elements. The protective relay ensures the safety of the circuit equipment from any damage which might otherwise caused by the fault.

All the relays have three essential fundamental elements:

Sensing element, sometimes also called the measuring element, responds to the change in the actuating quantity

Comparing element serves to compare the action of the actuating quantity on the relay with a pre-selected relay setting.

Control element on a pickup of the relay, accomplishes a sudden change in the control quantity such as closing of the operative current circuit.

The connection is divided into 3 main circuits consisting of:

1) Primary winding of the CT (current transformer) connected in

Series with the main circuit to be protected.

2) Secondary winding of the CT and the relay operating winding.

3) The tripping circuit.

Under normal operating condition, the voltage induced in the secondary winding of the CT is small and, therefore, current flowing in the relay operating coil is insufficient in magnitude to close the relay contacts. This keeps the trip oil of the circuit breaker inactive. Consequently, the circuit breaker contacts remain closed and it carries the normal load current. When some fault occurs, large current flows through the primary of CT. this increases the voltage induced in the secondary and hence the current flows through the relay operating coil. The relay contacts are closed and the trip coil of the breaker gets energized to open the breaker contacts

FUNDAMENTAL REQUIREMENTS OF RELAY

The main protective relay is to disconnect the faults sections of power system through circuit breaker, before damaging the costly equipment , in order to perform this function satisfactorily. It should have the following important features:

Selectivity
Sensitivity
Reliability
Quickness.

ELECTRO-MAGNETIC ATTRACTION RELAYS

These are the simplest type of relays and include plunger (or solenoid), hinged armature, rotating armature (or balanced beam) and moving iron polarized relays. All these relays operate on the same principle i.e. in such relays the operation is obtained by virtue of an armature being attracted to the poles of an electromagnet or a plunger being drawn into a solenoid. The electromagnet force being exerted on the moving element is proportional to the square of the current flowing through the coil.

In an electromagnetic attraction relays, the flux developing the electromagnetic force is splitted into two fluxes acting simultaneously but differing in time phase, so that the resulting deflecting force is always positive and constant. This can be easily achieved either by providing two winding on the electromagnet having a phase shifting network or by putting shading rings on the poles of the electromagnet .the sensitivity of the hinged armature relays can be increased for dc operation by the addition of a permanent magnet. This is known as a polarized moving iron relay.

Attraction armature relays can be designed to respond over and under current , over-under voltage for both dc and ac operations. They are employed as measuring or auxiliary relays.

PROTECTION OF TRANSFORMER

BUCHHOLZ RELAY

Buchholz relay is a gas actuated relay. It is practically universally used on all oil immersed transformers having rating more than 500 kVA. Such relay can only be fitted to the transformer equipped with conservator tanks as it is installed in between the conservation and main tank i.e. in the pipe connecting the two. It is employed in conjunction with the same form of electricity operated protective gear because it provides protection only against transformer internal faults and does not respond to external bushing or cable connection faults.

Working Principle:

Whenever a fault occur inside the transformer, the oil of the tank gets overheated and gases are generated. The generation of the gases may be slow or violent depending upon whether a fault is minor or incipient one or heavy short-circuit. Most short-circuits are developed either by impulse breakdown between adjacent turns at the end turns of the winding or as a very poor initial contact which will immediately heat to arcing formation. The heat generated by the high local current causes the transformer oil to decompose and produce gas which can be used to detect the winding faults. Buchholz relay operate on this principle.

Construction:

It consist of two hinged floats in a metallic chamber located in the pipe connection between the conservator and the transformer tank. One of the floats is near the top of the chamber and actuates the mercury switch connected to the external alarm circuit. The other float is opposite the orifice of the pipe to the transformer and actuates the mercury switch connected to the tripping circuit.

Fuse:

A fuse is short piece of metal, inserted in series with the circuit which melts when excessive current flows through it and thus breaks the circuit.

The material used for the fuse element should posses the following properties:

Low melting point
High conductivity
Free from oxidation

The common material for fuse element are copper, in-lead alloy(63% and lead 37%) silver, aluminum etc.

A fuse is connected in series with the circuit to be protected and carries the load current series with the circuit to be protected and carries the load current without over heating under normal conditions. However, when abnormal condition occurs, an excessive current flows through it. The raises the temperature which melts the fuse elements and open the circuits. This protects the machines or apparatus from damage which can be caused by the excessive currents.

Time current characteristics:

The time requires to blow out the depends upon the magnitude of excessive current smaller is the time taken by the fuse to blow out. Hence a fuse has inverse time current characteristics which is desirable for a protective devices:

Advantages:

1) It is the cheapest from of protection.

2) It requires no maintenance.

3) It interrupts heavy currents without noise or smoke.

4) The smaller size of fuse element imposes a current limiting effect under short circuit.

5) The minimum time of operation can be made much smaller than with circuit breaker.

6) The inverse time breaker characteristics make it suitable for over current protection.

Disadvantages:

1) Considerable time is lost in re-wiring or replacing fuses after every operation.

2) On short-circuit determination between fuses in series can only be obtained if there is considerable difference in the relative sizes of the fuse concerned.

Types of fuses

There are basically two main categories of fuses:

Low voltage fuses
High voltage fuses

Some High Voltage Fuse

Low voltage fuses:

These fuses can be further subdivided into two classes namely

Semi-closed rewirable fuse
High rupturing capacity cartridge fuse

Low Voltage Fuse

Insulators:

These are used to connect to conductors without any leakage of current. These are basically employed to completely insulate any object in the substation from the supply or any leakage current.

Various types of insulators:

Pin type
Suspension type
Strain type
Spool type or shackle type

Suspension Type Insulators

Pin Type Insulators:

These insulator are moulded with a central threaded hole so that the insulator is supported from thread insulators are grooved on the side or top to support the wires. Medium voltage pin insulator have grooves on both top sides. High voltage pin insulators are stronger in construction and they consist of two or three pieces of porcelain cemented together. These pieces from what we call petti-coats that are designed to shed rain and sleet easily. The conductor is placed in the groove at the top of the insulator and is then attached to insulator by typing it down with the binding wire which is usually of the same material as the conductor.

Pin Type Insulators

Advantages:

1) It is cheaper than the suspension insulator.

2) Pin type insulator is placed on top of the pole to achieve more

Conductor clearance above the ground. Pin insulator raises the

Conductor above the cross arms while the suspension insulator suspends insulator suspends it

below the cross arm.

ISOLATORS:

It is only operated under no load condition. Its main purpose is to isolate the portion of the circuit from the other. These are generally placed on both sides of circuit breakers in order to make repairs and maintenance on the circuit breaker without any danger.

Mcb Isolators Battery Isolaters For Alternaters

BUS BAR ARRANGMENT

MAIN BUS-BAR

Bus-bar term is used for a main bar or conductor carrying current to which many connections may be made. Bus-bar are merely convenient means of connecting switches and other equipment into various arrangements. The usual arrangement of connections in most of the sub-stations permits working on almost any piece of equipment without interruption to incoming or outgoing feeders. The aluminium used for bus –bar should have conductivity, good mechanical properties, high softening temperature etc.

BUS BAR ARRANGEMENT AND LAYOUT

Before the rating of all the equipment in a sub-station are chosen and there location in the sub-station decides, it is necessary to draw a single line diagram are called key diagram. This indicate the proposed bus bar arrangement and relative position of all the equipment to be installed.

These are various numerations of the bus bars arrangement. The choice of a particular arrangement depends upon the various factors i.e. system voltage, reliability of supply and cost etc.

VARIOUS ARRANGEMENTS OF BUS-BAR

1). SINGLE BUS-BAR:

This arrangement is simplest and cheapest, it suffers however from two major defects.

Maintenance without interruption of supply is not possible.
Extension of the sub- station without a shut down is not possible.

The equipments connections are simple and hence easy to operate.

Busbar Arrangment

2) DOUBLE BUS-BAR:

This scheme allows the use of two identical bus bars so that:

Each load may be fed from either bus.
The load circuit may be divided into two separate groups.
Either bus –bar may be taken for maintenance and cleaning purpose.

This arrangement is frequently used where the load and continuity of supply justify the additional cost. In such a scheme a bus coupler is generslly provided as to enable ‘on load’ change of bus –bar over to another. Also the normal bus isolators cannot be used for breaking load current.

3) MESH SCHEME:

This scheme is also known as ring bus, the most important features of this scheme are; provides a double feed to each circuit opening of one breaker under maintenance or otherwise does not affect the supply.

It permits breaker maintenance.
It is cheaper than double bus scheme.
So long, as the mesh is closed any breaker is taken out of commission for maintenance. If however a circuit trips under these circumstances supply to a number of cuts may be lost, so the mesh scheme is limited to four or six circuits.

BUS BAR MATERIAL

The bus bar material is mainly Copper, Aluminum Tubes, ACSR (Aluminum conductor steel reinforced).

POWER LINE COMMUNICATION:

The main purpose of power line communication is to transmit speech or to convey message from one substation to the other through transmission lines at higher frequencies. However power line communication serves also other purpose like tele-metering, tele-printing, tele-control, tele-indication and tele-protection. All these signals are being communicated in carrier frequency range 35 KHz to 500KHz. Thus by PLC system, the various electrical quantities are measured, message conveyed can be printed on the paper and protective devices can be operated very quickly in mili-seconds.

Principle of operation of PLC:

In power line communication a speech signal is modulated with the carrier frequency ranging from 35 kHz to 500 kHz before modulation the speech band is limited to 300 to 2400 Hz whereas 2.4 to 4.0 kHz frequency band is used for tele-metering tele-printing tele-indication and tele-protection. The modulation signal is filters and amplified the it is transmitted over the power lines through line matching unit protective devices and coupling capacitor. At receiving end the HF carrier signal is protected from the HV power frequency with the help of line trap and coupling capacitor through line matching unit carrier frequency signal is sent to the power line communication terminal. Where the speech signal is separated from the carrier frequency and is sent to subscriber.

Equipment used in power line communication:

The following are the main equipment used in the power line carrier communication:

Wave Trap:

Wave trap contains main coils lightning arrestor and a tuning device. All are connected in parallel; the main coil has an inductance of 0.2 mH to 2.0 mH. This inductance offer high impedance to the high frequency carrier signals and block them here.

Coupling Capacitor:

The coupling capacitor used for power line carrier communication has capacitance ranging from 2200 pF to 1000 pF. It allows a low impedance path to high frequency carrier signals and allows them to enter the line matching unit however it offers a high impedance path to low frequency signals or wave and block it.

Coupling Capacitor

Line matching unit:

The carrier signal received from the high voltage transmission line through coupling capacitor is given to the line matching unit 2 form here the signal is transferred to power line communication terminal. On other hand the carrier signal generated in a high frequency cubicle is transmitted via terminal 6 through a line matching unit 2.

Power line carrier communication terminal:

It is just a cabinate which contain number of electronic circuit.

Power Line Carrier Power Line Communication

Switching equipment:

The signal is fed to the switching system where it is used for any one operation i.e. tele-metering, tele-printing, tele-control .300Hz to 2.4Hz band is used for tele-voice whereas 2.4 kHz to 4 kHz band is used for remaining operations.

Switching Equipment

DISTRIBUTION SYSTEM

Introduction:

Distribution of electrical power is an important part of power system. The important requirement of a distribution system is that the power should be distributed to various consumers economical and efficiently. Distribution system which can be subdivided into three distinct parts.

Feeders
Distributors
Service mains

Distribution system:

The arrangement of conveying electric power from bulk power source to the various consumers is called distribution system. Distribution itself is of two types:

High voltage of primary distribution
Low voltage or secondary distribution

Power Distribution Transformer

High voltage distribution which is carried out at voltage of the order of 33kv, 66kv or 11kv supplies power to those consumers who take bulk power and have their own step down substation like factory owners, institutions etc. low voltage distribution which is carried at 400/230 volts supplies power to small factories or residential buildings which do not have step down transformer. 400 volts is available between line and neutral.

Important terms

Feeder:

A feeder is a conductor which connects substation to area where the power is to be distributed these are the conductors which carry large current to the feeding points in the substation and SA and SC are the feeders. A and C are the feeding points. Generally no tapping are taken from the feeder so that the current throughout it remains the same.

Distributor:

Distributor is a conductor from which tapping are taken for supply to the consumers or it is the conductor which carries current to the service mains from the feeding points. The current loading of a distributor varies along its length. Distributor is designed from the point of view of the voltage drop in it because the voltage drop in the distributor is solely dependent on the loading done on it by the consumer. There is a limit for the variation of voltage at any point of distributors.

Service mains:

A service main is generally a small cable which connects the distributor to the consumer terminals classification of distribution system. The distributor system may be classified in the following ways:

1) According to nature of construction: According to the nature of construction the distribution system may be classified as:

i) Over head distribution system

ii) Underground distribution system

Overhead system is cheaper than underground system. However underground system is used in thickly populated area where

overhead system may not be practicable.

2) According to nature of current: According to the nature of current

the distribution system may be classified as:

D.C distribution system
A.C distribution system

A.C. distribution is universally adopted due to many advantages of A.C. power over D.C. power

3) According to nature of wire: According to the number of wires.

Distribution system may be classified as:

2-wire d.c sytem
3-wire d.c system
Single phase, 2-wire a.c. system
3-phase, 3-wire, a.c system
3-phase, 4-wire a.c. system

BATTERIES OR BATTERY ROOM

In electric power stations and large-capacity substations, the operating and automatic control circuit, the protective relay systems, as well as emergency lighting circuits, are supplied by station batteries. The latter constitute independent sources of operative dc power and guaranty operation of the above mentioned circuits irrespective of any fault which has occurred in the station or substation, even of complete disappearance of the ac supply in the installation. Station batteries are assembled of a certain number of cells depending on the operating voltage of the respective dc circuits. Storage batteries are of two type viz lead acid and alkaline batteries. Lead-acid batteries are most commonly used in power stations and substations because of their higher cell voltage and low cost.

Battery Room

CAPACITOR BANK

A capacitor bank is built up of a number of capacitors units connected in series and in parallel. The units of series capacitor are designed, manufactured and tested with due to regard for the specific service conditions, such as high over-voltage and capacitor discharge currents.

A capacitor unit consists of a number of capacitor elements in a container. The units are equipped with fuses, which may be either external ones for each unit or internal individual element fuses, The capacitor units are mounted in simple frames, called the racks, placed on supporting insulators and stacked in top of each other.

The cosine of angle between voltage and current in an ac system is called power factor. The electrical energy is distributed in the form of alternating current in ac power induction motors, furnaces, arc lamps are nature and operate at low lagging power factor. For economical reasons it is preferred to keep power factor of the power system as close to unity as possible.

Power capacitors have generally two functions i.e. to improve the voltage conditions and reduce the system losses. These are achieved by improving the power factor. Maximum benefits are derived when the demand for the reactive power is met at consumer’s premises. Yet even when consumers load have been compensated to the desired extent large quantity of reactive compensation is needed at grid sub-station to control voltage variations in the transmission system from minimum load conditions to maximum load conditions and also to reduce the transmission losses.

SUBSTATION

A substation may be defined as an assembly of apparatus which is installed in control transmission and distribution of electric power. Substation took place when it became possible to generate high voltage for transmission to load centres which were far away from generating stations. The substation from the most important part of power system. The electric power is generated at the power stations handled at several substation and then delivered to the consumers of electricity.

Function of a substation:

A substation may be required to perform one or more of the following functions:

To switch on and off the power lines, this operation is known as switching operation.
To raises or lower the voltage the operation is known as voltage transformation operation.
To convert ac into dc or vice-versa, this operation is known as power converting operation.
To convert frequency from higher to lower or vice-versa the operation is known as frequency operating operation.
To improve the power factor by installing synchronous condensers at the end of the line the operation is known as power factor correction operation.

Out of these operations probably the voltage transformation is most important of a substation.

TYPES OF SUBSTATION:

There are many ways of classification of substation as under:

1) According to system of supply

a) D.C. Substation.

600volts Dc Sub-Station

b) A.C. Substation.

Ac Sub-Station

2) According to design

a) Indoor type.

b) Outdoor type.

230/115 KV OUT DOOR

SUBSTATION

3) According to the equipment in substation

a) Motor converter.

b) Rotary converter.

c) Mercury arc rectifier.

d) Metal rectifier.

e) Transformer.

4) According to the system of operation

a) Manual.

b) Automatic.

The entire substation working on A.C. has transformers. These may be outdoor indoor or pole mounted type. The operation may be automatic or manual.

Pole Mounted Transformer

Types of substation according to design:

According to design there are two types of sub-stations,

1) Indoor substation

2) Outdoor Substation

Indoor substation:

In such substations the apparatus is installed within the substation building and hence the name indoor substation. Such substation are usually for a voltage up to 11 kv but can be erected for 33kv or 66kv when the surrounding atmosphere is contaminated with such impurities which may damage the equipment.

Outdoor Substation:

In this type the apparatus of the substation is installed in open and hence the name Outdoor Substation can be designed to handle low medium and extra high voltages.

CONTROL ROOM

The control room ( or the operating room) is the nerve centre of a power station. The various controls performed from here are voltage adjustment, load control, emergency tripping of turbines etc. and the equipments and instruments housed in a control room are synchronizing equipment, voltage regulators, relays, ammeters, voltmeters, wattmeters, kWh meters, kVARh meters, temperature gauges, water level indicators and other appliances, as well as a mimic diagram and suitable indicating equipments to show the open or closed position of circuit breakers, isolators etc.

CONTROL PANNEL

The location of control room in relation to other sections of the power stations is also very important. It should be located away from the sources of noise and it should be near switch house so as to save multi-core cables used for interconnection. Of course, if there is any fire in the switch house, the control room should remains unaffected. Also there should be access from the control room to the turbine houses. The control room should be neat and clean, well lighted and free from draughts. There should be no glare and the color scheme should be soothing to eyes. The instruments should have scales clearly marked and property calibrated and all the apparatus and circuits should be labeled so that they are clearly visible.

Nuclear Power Plant

Control Room

CONCLUSION

SUBSTATION:

The substation plays a very important role in the distribution system as it steps down the transmitted voltage for further distribution from 33kv to 11kv.

POWER TRANSFORMER:

It is used to step down the transmitted voltage from 33kv to 11kv for further distribution. Power transformer of 2mva, 33/11kv rating is used at this substation.

INSTRUMENT TRANSFORMER:

There are two types of instrument transformer which are as follows:

a) Current Transformer:

It is used for measuring high ampere current in transmission line. By using CT 200 ampere

Current can be measured in simple ammeter located in control room.

b) Potential Transformer:

The potential transformer are employed to feed the potential coils of indicating and metering

Instruments and relays located in control room.

CIRCIUT BREAKER:

It makes and breaks the circuit under no-load, full-load or fault conditions. It can be operated manually under normal conditions and automatically under abnormal conditions.

RELAYS:

The protective relay is an electrical device interposed between the main circuit and the circuit breaker in such a manner any abnormality in the circuit acts on the relay, which in turn, if the abnormality is of a dangerous character, causes the breaker to open and so to isolate the faulty element. The protective relays ensure the safety of the circuit equipment from any damage which might otherwise cause by the fault.

LIGHTNING ARRESTORS:

The line lead of the lightning arrestors should be firmly connected with the phase wire. The earth connections should be light and the earth resistance of earth wire should be less than 10Q. Damages if located should be rectified.

BATTERIES OR BATTERY BANK:

In electric power stations and large capacity substations, the operating and automatic control circuit, the protective relay systems, as well as emergency lighting circuits are supplied by station batteries.

CAPACITOR BANK:

A capacitor bank is built up of a number of capacitors units connected in series and in parallel. The units for series capacitors are designed, manufactured and tested with due regard for the specific service conditions, such as high over-voltages and capacitor discharge current.

EARTHING:

The process of connecting metallic bodies of all the electrical apparatus and equipment to the huge mass of earth by a wire having negligible resistance is called earthing

BIBLIOGRAPHY

The reference of the books and author I have referred to complete my training report are as follows:

A Course in Power System By J.B.GUPTA
Electrical Technology By B.L.THERAJA
Electrical Machinery By P.S. BHIMBRA
Basic Electrical Engineering By S.K.SAHDEV
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