CHAPTER 1

SOURCE OF SUPPLY

The 220/132 kV Sub-Station, Chittoor is receiving power normally from the following:-

400 KV Mahadevamangalam Sub-Station through 220 KV Mahadevamangalam -

Chittoor I & II feeders.

The 220/132 KV Sub-Station, Chittoor is transporting power normally to the following:

220 KV Kalikiri Sub-Station through 220 KV Chittoor- Kalikiri feeder.

220 KV Thiruvalam Sub-Station through 220 KV Chittoor- Thiruvalam feeder.

The 132 KV alternate supply is available through the following:

132 kV Renigunta – Tirupati – K.P.Mitta – Pakala - Chittoor feeder.

132 kV Punganoor – Palamaner - Chittoor feeder.

The 220/132 kV SS Chittoor is transmitting power to the following 132 kV Sub-Stations:-

132 kV Pakala SS through 132 KV Chittoor-Pakala feeder.

132 kV Irala SS through 132 KV Chittoor-Irala feeder.

132 KV Palamaneru, Sathipuram, Kuppam sub-stations through 132 kV Chittoor -

Palamaneru I & II feeders.

The received 220 KV Power is stepped down to 132 KV through 3 X 100 MVA [(3 x 33.33)

2 MVA] + 1 X 100 MVA of 220/132 kV Auto Power Transformers.

The 132 KV Power is stepped down to 33 kV through 2 Nos 50 MVA 132 / 33 kV Power

Transformers.

The following 220 kV equipments are individually controlled by SF 6 breakers with spring charging mechanism breakers

220 kV Mahadevamangalam - II feeder.

100 MVA 220/132 kV Auto Power Transformer- I HV Breaker.

100 MVA 220/132 kV Auto Power Transformer- II HV Breaker.

100 MVA 220/132 kV Auto Power Transformer- III HV Breaker.

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The following 220 kV equipments are individually controlled by SF 6 Pneumatic mechanism breakers.

220 KV Kalikiri feeder breaker.

220 KV Mahadeva Mangalam I feeder breaker.

220 KV Tiruvalam feeder breaker.The following 132 kV equipment are individually controlled by BHEL MOCB

132 KV Palamaneru I feeder.

The following 132 kV equipments are individually controlled by SF 6 Spring charging mechanism breakers.

100 MVA 220/132 kV Auto Power Transformer- I LV Breaker.

100 MVA 220/132 kV Auto Power Transformer II LV Breaker.

100 MVA 220/132 kV Power Transformer III LV breaker.

50 MVA 132/33 kV Power Transformer I HV breaker.

50 MVA 132/33 kV Power Transformer II HV breaker.

132 kV Pakala feeder.

132 kV Irala feeder.

132 kV Palamaneru II feeder.

132 kV, 30 MVAR capacitor bank.

The following 33 kV Equipments are individually controlled by VCB's

33 KV KR Palli feeder breaker

33 KV Venganapalli feeder breaker

33 KV Jodichinthala feeder breaker

33 KV Santhapeta feeder breaker

33 KV BNR Peta - Ramapuram feeder breaker

33 KV KG Sathram feeder breaker

33 KV Paipalli feeder breaker

33 KV Greamspet feeder breaker

33 KV,5 MVAR Capacitor Bank I breaker

33 KV,5 MVAR Capacitor Bank II breaker

33 KV,5 MVAR Capacitor Bank III breaker

33 KV,14.4 MVAR Capacitor Bank breaker

50 MVA PTR – 1 LV breaker

50 MVA PTR – II LV breaker

2

The following 33 kV Equipments are individually controlled by SF 6 with spring charging mechanism

33 kV Kothapalli - Reddigunta feeder breaker

33 kV Aragonda feeder breaker

From 33 kV Bus 10 Nos. 33 kV feeders are being fed to the following

33 KV KR Palli feeder

33 KV Venganapalli feeder

33 KV Jodichinthala feeder

33 KV Santhapeta feeder

33 KV BNR Peta - Ramapuram feeder

33 KV KG Sathram feeder

33 KV Paipalli feeder

33 KV Greamspet feeder

33 kV Kothapalli - Reddigunta feeder

33 kV Aragonda feeder

In addition to the above, there are 3 Nos. 5 MVAR Capacitor Banks & 1 No. 14.4 MVAR

capacitor banks connected to the 33 kV Bus through VCB's.

The Station auxiliary supply is taken from 33 KV/400 V, 250 kVA Station Transformer

which is connected to the 33 kV Bus. And alternate station auxiliary supply is available from

33 kV/ 4OO V, 100 kVA Station Transformer connected to the 33 kV Bus.

The Power Line Carrier Communication (PLCC) is available through CVT's and Wave Traps

of all 220 KV feeders and 132 KV feeders

The 220/132/33 kV Chittoor Sub-Station is normally receiving, power from 400

Mahadevamangalam Sub-Station and normally sending Power to 220 kV Kalikiri, 230 kV

Tiruvalam, 132 Pakala, Irala, Palamaner, Santhipuram & Kuppam sub-stations.

The Sub-Station is located in Chittoor town, Greamspet Back side of the District sub-jail in

Chittoor district.

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The single line diagram of Sub-Station is shown below:

Fig 1: Single line diagram of 220/132 kv substation

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SINGLE LINE DIAGRAM OF 220KV SS CHITTOOR

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33 kV GREAMSPET

100 KVA STATIONTRANSFORMER - 2

50 MVA PTR-150 MVA PTR-2

100 MVAPTR-1

100 MVAPTR-2

220 KV BUS PTs220KV KALIKIRI220KV TIRUVALAM220KV MAHADEVAMANGALAM-1220KV MAHADEVAMANGALAM-2

2x15 MVAR CAP.BANK

33 KV BUS PTs

Circuit BreakerCurrent Transformer

Lightning Arrester

Isolator

Earth Switch

Wave TrapSeries Reactor

132 KV Bus

220 KV Bus33 KV Bus

LEGEND

YRVT

PT

∆Y 1-Φ Auto Transformer CVT

132 KV BUS PTs

∆Y

100 MVAPTR-3

CHAPTER-2

NEED OF A SUBSTATION

SUB-STATION:

Substations are a familiar sight alongside highways and in cities. Substations take the electricity from power plants and from the transmission lines and transform it from high to lower voltage. They distribute electricity to consumers and supervise and protect the distribution network to keep it working safely and efficiently, for example by using circuitbreakers (the industrial strength equivalent of the humble fuse) to cut power in case of a problem. 

Need for substation:

Electrical power is generated at generating stations. These stations which are located far away from the different consumers. As we know that there is no storage device for electric power, hence the generated power must be conveyed to the consumer premises with less transmission and distribution losses. In order to fulfill the above conditions, we need a special apparatus system which changes the characteristics of electric supply from one to another are called sub-station.

Example: At generating station, the generating voltage 11KV (or) 6.6KV is stepped up to 400KV (or) 220KV (or) 33KV for transmission of electric power. The assembly of apparatus used for this purpose is called substation. Similarly at the consumer premises the voltage is stepped-down to consumer’s utilization level and the apparatus which is utilized for this purpose is called substation.

FUNCTIONS OF SUBSTATION:

1. To switch ON and OFF the power lines known as switching operation.

2. To transform voltage from higher to lower or vice versa known as voltage transformation operation.

3. To improve the power factor by installing synchronous condensers at the end of the line known as power factor correction operation.

FACTORS GOVERNING THE SELECTION OF SITE:

a. The site should bei. Nearer to the load centersii. The site should be away from municipal dumping grounds, burial grounds etc.,iii. The site should be away from areas where police and military rifle practices are held

b. The site should have good drinking water supplyc. The substation site should have sufficient adjacent space to accommodate the colony with the residential and non residential buildingsd. The site selected should have low cost e. The site should have transportation facilities

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f. Outdoor substations should not be located within three kilometers of any aerodromes or military training ground.g. The site selected should have center of gravity of load.

CLASSIFICATION OF SUB-STATIONS:

There are several ways of classifying sub-stations. However, the two most important ways of classifying them are according to

1. Service requirement2. Constructional feature.

1 .According to service requirement

a. Transformer substations.

b. Switching Sub-stations

c. Power factor corrections sub stations

d. Frequency changer sub-stations.

e. Converting substations.

f. Industrial substation

2. According to constructional features

a. Indoor sub-stations

b. Outdoor sub-stations

c. Underground substations

d. Pole mounted sub-stations

e. Plinth mounted sub-stations

VARIOUS EQUIPMENTS USED IN SUBSTATIONS:

1. Bus-bars2. Insulators3. Transformers4. Circuit breakers5. Protective relays6. Lighting arrestors7. Batteries ….etc

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CHAPTER-3

BUSBARS

Bus bars are defined as the conductors to which- several incoming and outgoing lines

are connected. Bus bars are made up of copper or aluminum. Commonly used bus bar dimensions:

220 K.V 29.89mm132 K.V 23.45mm33 K.V 12.27mm11 K.V. 7.77 mm

The most commonly used bus bar arrangements in substation are:1. Single bus-bar arrangement2. Single bus-bar system with sectionlisation.3. Double bus-bar arrangement.

Single Bus System:

Single Bus System is simplest and cheapest one. In this scheme all the feeders and transformer bay are connected to only one single bus as shown

Fig:2 single bus system

Advantages of single bus system:

This is very simple in design This is very cost effective scheme This is very convenient to operate

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Disadvantages of single bus system:

One but major difficulty of these type of arrangement is that, maintenance of equipment of any bay cannot be possible without interrupting the feeder or transformer connected to that bay.

The indoor 11KV switchboards have quite often single bus bar arrangement.

Single Bus System with Bus Sectionalizer:

Some advantages are realized if a single bus bar is sectionalized with circuit breaker. If there are more than one incoming and the incoming sources and outgoing feeders are evenly distributed on the sections as shown in the figure, interruption of system can be reduced to a good extent.

Fig:3 single section bus system

Advantages of single bus system with bus sectionalizer:

If any of the sources is out of system, still all loads can be fed by switching on the sectional circuit breaker or bus coupler breaker. If one section of the bus bar system is under maintenance, part load of the substation can be fed by energizing the other section of bus bar.

Disadvantages of single bus system with bus sectionalizer:

As in the case of single bus system, maintenance of equipment of any bay cannot be possible without interrupting the feeder or transformer connected to that bay.

The use of isolator for bus sectionalizing does not fulfill the purpose. The isolators have to be operated ‘off circuit’ and which is not possible without total interruption of bus bar. So investment for bus-coupler breaker is required.

Double Bus System:

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In double bus bar system two identical bus bars are used in such a way that any outgoing or incoming feeder can be taken from any of the bus.

Actually every feeder is connected to both of the buses in parallel through individual isolator as shown in the figure.

Fig:4 Double bus system

By closing any of the isolators one can put the feeder to associated bus. Both of the buses are energized and total feeders are divided into two groups, one group is fed from one bus and other from other bus. But any feeder at any time can be transferred from one bus to other. There is one bus coupler breaker which should be kept close during bus transfer operation. For transfer operation, one should first close the bus coupler circuit breaker then close the isolator associated with the bus to where the feeder would be transferred and then open the isolator associated with the bus from where feeder is transferred. Lastly after this transfer operation he or she should open the bus coupler breaker.

Advantages of Double Bus System:

Double Bus Bar Arrangement increases the flexibility of system.

Disadvantages of Double Bus System:

The arrangement does not permit breaker maintenance without interruption.

CHAPTER-4

9

INSULATORS

The conductors of transmission and distribution systems of over head lines are supported by means of insulators to avoid leakage current through the supports to the earth. A good insulator should have the following properties.1. Mechanically very strong in order to withstand due to weight of conductor and vibrating shocks due to heavy pressure of air.2. High Di-electric strength.3. High insulation resistance.4. It should not be porous.5. High ratio of rupture strength of flash over voltage.6. It must free form internal cracks etc.,7. It should not get affected due to fluids and gases of the atmosphere.

Materials used for insulators:1. Porcelain2. Glass3. Steatite and special composition materials.

TYPES OF INSULATORS:1. Pin type insulators2. Suspension type insulators3. Strain Insulators4. Shackle type insulators5. Post type insulators

Pin Insulator:Pin Insulator is earliest developed overhead insulator, but still popularly used in power network up to 33KV system. Pin type insulator can be one part, two parts or three parts type, depending upon application voltage. In 11KV system we generally use one part type insulator where whole pin insulator is one piece of properly shaped porcelain or glass. As the leakage path of insulator is through its surface, it is desirable to increase the vertical length of the insulator surface area for lengthening leakage path. In order to obtain lengthy leakage path, one, two or more rain sheds or petticoats are provided on the insulator body. In addition to that rain shed or petticoats on an insulator serve another purpose. These rain sheds or petticoats are so designed, that during raining the outer surface of the rain shed becomes wet but the inner surface remains dry and non-conductive. So there will be discontinuations of conducting path through the wet pin insulator surface.

In higher voltage like 33KV and 66KV manufacturing of one part porcelain pin insulator becomes difficult. Because in higher voltage, the thickness of the insulator become more and a quite thick single piece porcelain insulator cannot manufactured practically. In this case we use multiple part pin insulator, where a number of properly designed porcelain shells are fixed together by Portland cement to form one complete insulator unit. For 33KV tow parts and for 66KV three parts pin insulator are generally used.

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Fig:5 33KV PIN INSULATOR

Designing consideration of Electrical Insulator:

The live conductor attached to the top of the pin insulator is at a potential and bottom of the insulator fixed to supporting structure of earth potential. The insulator has to withstand the potential stresses between conductor and earth. The shortest distance between conductor and earth, surrounding the insulator body, along which electrical discharge may take place through air, is known as flash over distance.

1. When insulator is wet, its outer surface becomes almost conducting. Hence the flash over distance of insulator is decreased. The design of an electrical insulator should be such that the decrease of flash over distance is minimum when the insulator is wet. That is why the upper most petticoat of a pin insulator has umbrella type designed so that it can protect the rest lower part of the insulator from rain. The upper surface of top most petticoats is inclined as less as possible to maintain maximum flash over voltage during raining.

2. To keep the inner side of the insulator dry, the rain sheds are made in order that these rain sheds should not disturb the voltage distribution they are so designed that their subsurface at right angle to the electromagnetic lines of force.

Suspension Insulator:

In higher voltage, beyond 33KV, it becomes uneconomical to use pin insulator because size, of the insulator become more. Handling and replacing bigger size single unit insulator are quite difficult task. For overcoming these difficulties, suspension insulator was developed.

In suspension insulator numbers of insulators are connected in series to form a string and the line conductor is carried by the bottom most insulator. Each insulator of a suspension string is called disc insulator because of their disc like shape.

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Fig:6 suspension insulator

Advantages of Suspension Insulator:

1. Each suspension disc is designed for normal voltage rating 11KV(Higher voltage rating 15KV), so by using different numbers of discs, a suspension string can be made suitable for any voltage level.2. If any one of the disc insulators in a suspension string is damaged, it can be replaced much easily.3. Mechanical stresses on the suspension insulator is less since the line hanged on a flexible suspension string.  

4. As the current carrying conductors are suspended from supporting structure by suspension string, the height of the conductor position is always less than the total height of the supporting structure. Therefore, the conductors may be safe from lightening.

Fig:7 suspension string

Disadvantages of Suspension Insulator:

1.Suspension insulator string costlier than pin and post type insulator.2. Suspension string requires more height of supporting structure than that for pin or post

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insulator to maintain same ground clearance of current conductor.3. The amplitude of free swing of conductors is larger in suspension insulator system, hence, more spacing between conductors should be provided.

Strain insulator:

When suspension string is used to sustain extraordinary tensile load of conductor it is referred as string insulator. When there is a dead end or there is a sharp corner in transmission line, the line has to sustain a great tensile load of conductor or strain. A strain insulator must have considerable mechanical strength as well as the necessary electrical insulating properties.

Fig:8 STRAIN INSULATOR

RATED SYSTEMVOLTAGE

NUMBER OF INSULATORUSED IN STRAIN TYPE TENSIONINSULATOR STRING

NUMBER OF DISC INSULATORUSED IN SUSPENSION INSULATOR

STRING

33KV 3 3

66KV 5 4

132KV 9 8

220KV 15 14

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Post Insulator:

Fig:9 Post type insulator

Post insulator is more or less similar to pin insulator but former is suitable for higher voltage application. Post insulator has higher numbers of petticoats and has greater height. This type of insulator can be mounted on supporting structure horizontally as well as vertically. The insulator is made of one piece of porcelain but has fixing clamp arrangement are in both top and bottom end.

The main differences between pin insulator and post insulator are,

PIN INSULATOR POST INSULATOR

1 It is generally used up to 33KV systemIt is suitable for lower voltage and also for higher voltage

2 It is single stag It can be single stag as well as multiple stags

3

Conductor is fixed on the top of the insulator by Binding

Conductor is fixed on the top of the insulator with help of connector clamp

4

Two insulators cannot be fixed together for higher voltage application

Two or more insulators can be fixed together one above other for higher voltage application

5

Metallic fixing arrangement provided only on bottom end of the insulator

Metallic fixing arrangement provided on both top and bottom ends of the insulator

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CHAPTER-5

TRANSFORMERS

Definition of Transformer:

A transformer is a static machine used for transforming power from one circuit to another without changing frequency. This is very basic definition of transformer.

History of Transformer:

The History of transformer commenced in the year of 1880. In the year of 1950, 400KV electrical power transformer first introduced in high voltage electrical power system. In the early 1970s unit rating as large as 1100MVA were produced and 800KV and even higher KV class transformers were manufactured in year of 1980.

Types of Transformer:

Transformers can be categorized in different ways, depending upon their purpose, use, construction etc. The types of transformer are as follows:

• Step Up Transformer & Step Down Transformer - Generally used for stepping up and down the voltage level of power in transmission and distribution power network.

• Three Phase Transformer & Single Phase Transformer - Former is generally used in three phase power system as it is cost effective than later but when size matters it is preferable to use bank of three Single Phase Transformer as it is easier to transport three single phase unit separately than one single three phase unit.

• Electrical Power Transformer, Distribution Transformer & Instrument Transformer - Transformer generally used in transmission network is normally known as Power Transformer, distribution transformer is used in distribution network and this is lower rating transformer and current transformer & potential transformer, we use for relay and protection purpose in electrical power system and in different instruments in industries are called Instrument Transformer.

• Two Winding Transformer & Auto Transformer - Former is generally used where ratio between High Voltage and Low Voltage is greater than 2. It is cost effective to use later where the ratio between High Voltage and Low Voltage is less than 2.

• Outdoor Transformer & Indoor Transformer - Transformers designed for installing at outdoor is Outdoor Transformer and Transformers designed for installing at indoor is Indoor Transformer.

Use of Power Transformer:

Generation of Electrical Power in low voltage level is very much cost effective. Hence Electrical Power are generated in low voltage level. Theoretically, this low voltage leveled power can be transmitted to the receiving end. But if the voltage level of a power is

15

increased, the electric current of the power is reduced which causes reduction in ohmic or I 2R losses in the system, reduction in cross sectional area of the conductor i.e. reduction in capital cost of the system and it also improves the voltage regulation of the system. Because of these, low leveled power must be stepped up for efficient electrical power transmission. This is done by step up transformer at the sending side of the power system network. As this high voltage power may not be distributed to the consumers directly, this must be stepped down to the desired level at the receiving end with help of step down transformer. These are the use of electrical power transformer in the Electrical Power System.

Fig:10 Power Transformer

Two winding transformers are generally used where ratio between High Voltage and Low Voltage is greater than 2. It is cost effective to use Auto transformer where the ratio between High Voltage and Low Voltage is less than 2. Again Three Phase Single Unit Transformer is more cost effective than a bank of three Single Phase Transformer unit in a three phase system. But still it is preferable to use later where power dealing is very large since such large size of Three Phase Single Unit Power Transformer may not be easily transported from manufacturer's place to work site.

Definition of Instrument Transformer:

Instrument transformers means current transformer & voltage transformer used in electrical power system for stepping down currents and voltages of the system for metering and protection purpose. Actually relays and meters used for protection and metering, are not designed for high currents and voltages.High currents or voltages of electrical power system cannot be directly fed to relays and meters. CT steps down rated system current to 1 Amp or 5 Amp similarly voltage transformer steps down system voltages to 110V. The relays and meters are generally designed for 1 Amp, 5 Amp and 110V.

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Definition of current transformer (CT):

A CT is an instrument transformer in which the secondary current is substantially proportional to primary current and differs in phase from it by ideally zero degree.

CT Accuracy Class or Current Transformer Class :

A CT is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. For metering and indication purpose, accuracy of ratio, between primary and secondary currents are essential within normal working range. Normally accuracy of current transformer required up to 125% of rated current; as because allowable system current must be below 125% of rated current. Rather it is desirable the CT core to be saturated after this limit since the unnecessary electrical stresses due to system over current can be prevented from the metering instrument connected to the secondary of the CT as secondary current does not go above a desired limit even primary current of the CT rises to a very high value than its ratings. So accuracy within working range is main criteria of a CT used for metering purpose. The degree of accuracy of a Metering CT is expressed by CT Accuracy Class or simply Current Transformer Class or CT Class.

Fig:11 current transformer

But in the case of protection, the CT may not have the accuracy level as good as metering CT although it is desired not to be saturated during high fault current passes through primary. So core of protection CT is so designed that it would not be saturated for long range of currents. If saturation of the core comes at lower level of primary current the proper reflection of primary current will not come to secondary, hence relays connected to the secondary may not function properly and protection system losses its reliability.

Potential Transformer Definition:

Potential Transformer or Voltage Transformer are used in electrical power system for stepping down the system voltage to a safe value which can be fed to low ratings meters and relays. Commercially available relays and meters used for protection and metering, are designed for low voltage. This is a simplest form of Potential Transformer Definition

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Voltage Transformer or Potential Transformer Theory:

A Voltage Transformer theory or Potential Transformer theory is just like theory of general purpose step down transformer. Primary of this transformer is connected across the phases or and ground depending upon the requirement. Just like the transformer, used for stepping down purpose, potential transformer i.e. PT has lowers turns winding at its secondary. The system voltage is applied across the terminals of primary winding of that transformer, and then proportionate secondary voltage appears across the secondary terminals of the PT.

Fig:12 Potential Transformer

The secondary voltage of the PT is generally 110V. In an ideal Potential Transformer or Voltage Transformer when rated burden connected across the secondary the ratio of primary and secondary voltages of transformer is equal to the turns ratio and furthermore the two terminal voltages are in precise phase opposite to each other. But in actual transformer there must be an error in the voltage ratio as well as in the phase angle between primary and secondary voltages.Capacitor Voltage Transformer:

Fig :13 Capacitor Voltage Transformer

A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay. In its most basic form the device consists of three parts: two capacitors across which the transmission line signal is split, an inductive element to tune the device to the line frequency, and a transformer to isolate and further step down the voltage for the instrumentation or protective relay. The tuning of the divider to the line frequency makes the overall division ratio less

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sensitive to changes in the burden of the connected metering or protection devices. The device has at least four terminals: a terminal for connection to the high voltage signal, a ground terminal, and two secondary terminals which connect to the instrumentation or protective relay. CVTs are typically single-phase devices used for measuring voltages in excess of one hundred kilovolts where the use of wound primary voltage transformers would be uneconomical. In practice, capacitor C1 is often constructed as a stack of smaller capacitors connected in series. This provides a large voltage drop across C1 and a relatively small voltage drop across C2.

The CVT is also useful in communication systems. CVTs in combination with wave traps are used for filtering high frequency communication signals from power frequency. This forms a carrier communication network throughout the transmission network.

CHAPTER-6

CIRCUIT BREAKERSDefinition of Circuit Breaker : Electrical Circuit Breaker is a switching device which can be operated manually as well as automatically for controlling and protection of electrical power system respectively. As the modern power system deals with huge currents, the spacial attention should be given during designing of circuit breaker to safe interruption of arc produced during the operation of circuit breaker. This was the basic definition of circuit breaker.

Working Principle of Circuit Breaker:

The circuit breaker mainly consists of fixed contacts and moving contacts. In normal "on" condition of circuit breaker, these two contacts are physically connected to each other due to applied mechanical pressure on the moving contacts. There is an arrangement stored potential energy in the operating mechanism of circuit breaker which is realized if switching signal given to the breaker. The potential energy can be stored in the circuit breaker by different ways like by deforming metal spring, by compressed air, or by hydraulic pressure. But whatever the source of potential energy, it must be released during operation. Release of potential energy makes sliding of the moving contact at extremely fast manner. All circuit

19

breaker have operating coils (tripping coils and close coil), whenever these coils are energized by switching pulse, and the plunger inside them displaced. This operating coil plunger is typically attached to the operating mechanism of circuit breaker, as a result the mechanically stored potential energy in the breaker mechanism is released in forms of kinetic energy, which makes the moving contact to move as these moving contacts mechanically attached through a gear lever arrangement with the operating mechanism. After a cycle of operation of circuit breaker the total stored energy is released and hence the potential energy again stored in the operating mechanism of circuit breaker by means of spring charging motor or air compressor or by any other means. Till now we have discussed about mechanical working principle of circuit breaker. But there are electrical characteristics of a circuit breaker which also should be considered in this discussion of operation of circuit breaker.The circuit breaker has to carry large rated or fault power. Due to this large power there is always dangerously high arcing between moving contacts and fixed contact during operation of circuit breaker. Again as we discussed earlier the arc in circuit breaker can be quenching safely if the dielectric strength between the current carrying contacts of circuit breaker increases rapidly during every current zero crossing of the alternating current. The dielectric strength of the media in between contacts can be increased in numbers of ways, like by compressing the ionized arcing media since compressing accelerates the deionization process of the media, by cooling the arcing media since cooling increase the resistance of arcing path or by replacing the ionized arcing media by fresh gasses. Hence a numbers of arc quenching processes should be involved in operation of circuit breaker.

Types of Circuit Breaker : According different criteria there are different types of circuit breaker.

According to their arc quenching media the circuit breaker can be divided as

1) Oil Circuit Breaker2) Air Circuit Breaker3) SF6 Circuit Breaker4) Vacuum Circuit Breaker

According to their services the circuit breaker can be divided as

1) Outdoor Circuit Breaker2) Indoor Breaker

According to the operating mechanism of circuit breaker they can be divided as

1) Spring operated Circuit Breaker2) Pneumatic Circuit Breaker3) Hydraulic Circuit Breaker

According to the voltage level of installation types of circuit breaker are referred as

1) High Voltage Circuit Breaker2) Medium Voltage Circuit Breaker

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3) Low Voltage Circuit Breaker

CHAPTER-7

RELAYS

 Definition of protective relay:

A relay is automatic device which senses an abnormal condition of electrical circuit and closes its contacts. These contacts in turns close and complete the circuit breaker trip coil circuit hence make the circuit breaker tripped for disconnecting the faulty portion of the electrical circuit from rest of the healthy circuit.

Now let’s have a discussion on some terms related to protective relay

Pickup level of actuating signal: The value of actuating quantity (voltage or current) which is on threshold above which the relay initiates to be operated.If the value of actuating quantity is increased, the electromagnetic effect of the relay coil is increased and above a certain level of actuating quantity the moving mechanism of the relay just starts to move.

Reset level: The value of current or voltage below which a relay opens its contacts and comes in original position.

Operating Time of Relay: Just after exceeding pickup level of actuating quantity the moving mechanism (for example rotating disc) of relay starts moving and it ultimately close the relay

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contacts at the end of its journey. The time which elapses between the instant when actuating quantity exceeds the pickup value to the instant when the relay contacts close.

Reset time of Relay: The time which elapses between the instant when the actuating quantity becomes less than the reset value to the instant when the relay contacts returns to its normal position.

Reach of relay: A distance relay operates whenever the distance seen by the relay is less than the pre-specified impedance. The actuating impedance in the relay is the function of distance in a distance protection relay. This impedance or corresponding distance is called reach of the relay.

Power system protection relays can be categorized into different types of relays.

Types of Relays:

Types of protection relays are mainly based on their characteristic, logic, on actuating parameter and operation mechanism.

Based on operation mechanism protection relay can be categorized as Electro Magnetic relay, Static relay and Mechanical relay. Actually relay is nothing but a combination of one or more open or closed contacts. These all or some specific contacts the relay change their state when actuating parameters are applied to the relay. That means open contacts become closed and closed contacts become open. In electromagnetic relay these closing and opening of relay contacts are done by electromagnetic action of a solenoid.

In mechanical relay these closing and opening of relay contacts are done by mechanical displacement of different gear level system.

In static relay it is mainly done by semiconductor switches like thyristor. In digital relay on and off state can be referred as 1 and 0 state.

Based on Characteristic the protection relay can be categorized as

1. Definite time Relays

2. Inverse time Relays with definite minimum time (IDMT) 

3. Instantaneous Relays

4. IDMT

5. Stepped Characteristic

6. Programmed Switches

7. Voltage restraint over current relay

Based on of logic the protection relay can be categorized as

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1. Differential

2. Unbalance

3. Neutral Displacement

4. Directional

5. Restricted Earth Fault

6. Over Fluxing

7. Distance Schemes

8. Bus bar Protection

9. Reverse Power Relays

10.Loss of excitation

11.Negative Phase Sequence Relays etc.

Based on actuating parameter the protection relay can be categorized as

1. Current Relays2. Voltage Relays3. Frequency Relays4. Power Relays etc.

Based on application the protection relay can be categorized as

1. Primary Relay2. Backup Relay

Primary relay or primary protection relay is the first line of power system protection whereas Backup relay is operated only when primary relay fails to be operated during fault. Hence backup relay is slower in action than primary relay. Any relay may fail to be operated due to any of the following reasons,

1) The protective relay itself is defective2) DC Trip voltage supply to the relay is unavailable3) Trip lead from relay panel to circuit breaker is disconnected4) Trip coil in the circuit breaker is disconnected or defective5) Current or voltage signals from CT or PT respectively is unavailable

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As because backup relay operates only when primary relay fails, backup protection relay should not have anything common with primary protection relay.

Some examples of Mechanical Relay are

1. Thermal (a) OT Trip (Oil Temperature Trip)(b) WT Trip (Winding Temperature Trip)(C) Bearing Temp Trip etc.

2. Float Type (a) Buchholz (b) OSR(c) PRV (d) Water level Controls etc.

3. Pressure Switches.

4. Mechanical Interlocks.

5. Pole discrepancy Relay.

List Different protective relays are used for different power system equipment protection:

Now let’s have a look on which different protective relays are used in different power system equipment protection schemes

CHAPTER-8

ISOLATORS

Definition of Isolator:

Fig:17 Isolator

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Circuit breaker always trip the circuit but open contacts of breaker cannot be visible physically from outside of the breaker and that is why it is recommended not to touch any electrical circuit just by switching off the circuit breaker. So for better safety there must be some arrangement so that one can see open condition of the section of the circuit before touching it. Isolator is a mechanical switch which isolates a part of circuit from system as when required. Electrical isolators separate a part of the system from rest for safe maintenance works.

So definition of isolator can be rewritten as Isolator is a manually operated mechanical switch which separates a part of the electrical power system normally at off load condition.

Types of Electrical Isolators:

There are different types of isolators available depending upon system requirement such as 

Double Break Isolator

Single Break Isolator

Pantograph type Isolator

Depending upon the position in power system, the isolators can be categorized as 

Bus side isolator – the isolator is directly connected with main bus

Line side isolator – the isolator is situated at line side of any feeder

Transfer bus side isolator – the isolator is directly connected with transfer bus

Constructional features of Double Break Isolators:

Lets have a discussion on constructional features of Double Break Isolators. These have three stacks of post insulators as shown in the figure. The central post insulator carries a tubular or flat male contact which can be rotated horizontally with rotation of central post insulator. This rod type contact is also called moving contact. The female type contacts are fixed on the top of the other post insulators which fitted at both sides of the central post insulator. The female contacts are generally in the form of spring loaded figure contacts. The rotational movement of male contact causes to come itself into female contacts and isolators becomes closed. The rotation of male contact in opposite direction make to it out from female contacts and isolators becomes open.Rotation of the central post insulator is done by a driving lever mechanism at the base of the post insulator and it connected to operating handle (in case of hand operation) or motor (in case of motorized operation) of the isolator through a mechanical tie rod.

Constructional features of Single Break Isolators:

The contact arm is divided into two parts one carries male contact and other female contact. The contact arm moves due to rotation of the post insulator upon which the contact arms are

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fitted. Rotation of both post insulators stacks in opposite to each other causes to close the isolator by closing the contact arm. Counter rotation of both post insulators stacks open the contact arm and isolator becomes in off condition. This motorized form of this type of isolators is generally used but emergency hand driven mechanism is also provided.

Fig:18 Single break isolators

Earthing Switches:

Earthing switches are mounted on the base of mainly line side isolator. Earthing switches are normally vertically break switches. Earthing arms (contact arm of earthing switch) are normally aligned horizontally at off condition. During switching on operation, these earthing arms rotate and move to vertical position and make contact with earth female contacts fitted at the top of the post insulator stack of isolator at its outgoing side. The earthing arms are so interlocked with main isolator moving contacts that it can be closed only when the main

contacts of isolator are in open position. Similarly the main isolator contacts can be closed only when the earthing arms are in open position.

Operation of Electrical Isolator:

As no arc quenching technique is provided in isolator it must be operated when there is no chance current flowing through the circuit. No live circuit should be closed or open by isolator operation. A complete live closed circuit must not be opened by isolator operation and also a live circuit must not be closed and completed by isolator operation to avoid huge arcing in between isolator contacts. That is why isolators must be open after circuit breaker is open and these must be closed before circuit breaker is closed. Isolator can be operated by hand locally as well as by motorized mechanism from remote position. Motorized operation arrangement costs more compared to hand operation; hence decision must be taken before choosing an isolator for system whether hand operated or motor operated economically optimum for the system. For voltages up to 145KV system hand operated isolators are used whereas for higher voltage systems like 245 KV or 420 KV and above motorized isolators are used.

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CHAPTER-9

LIGHTNING ARRESTORS

CAUSES OF OVER VOLTAGES:

Internal causes

External causes

Internal causes

Switching surge

Insulation failure

Arcing ground

Resonance

Switching surge: The over voltages produced on the power system due to switching are

known as switching surge.

Insulation failure: The most common case of insulation failure in a power system is the

grounding of conductors (i.e. insulation failure between line and earth) which may cause

overvoltage in the system.

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Arcing ground: The phenomenon of intermittent arc taking place in line to ground fault

of a 3phase system with consequent production of transients is known as arcing ground.

Resonance: It occurs in an electrical system when inductive reactance of the circuit

becomes equal to capacitive reactance. under resonance , the impedance of the circuit is

equal to resistance of the circuit and the p.f is unity.

Types of lightning strokes

Direct stroke

Indirect stroke

(1) Direct stroke

In direct stroke, the lightning discharge is directly from the cloud to the subject

equipment. From the line, the current path may be over the insulator down the pole to the

ground.

(2) Indirect stroke

Indirect stroke results from the electro statically induced charges on the conductors due to

the presence of charge clouds.

Harmful effects of lightning

The traveling waves produced due to lightning will shatter the insulators.

If the traveling waves hit the windings of a transformer or generator it may cause

considerable damage

PROTECTION AGAINST LIGHTNING :

Surge arresters are devices that help prevent damage to apparatus due to high voltages.

The arrester provides a low-impedance path to ground for the current from a lightning

strike or transient voltage and then restores to a normal operating conditions.

A surge arrester may be compared to a relief valve on a boiler or hot water heater. It will

release high pressure until a normal operating condition is reached. When the pressure is

returned to normal, the safety valve is ready for the next operation.

When a high voltage (greater than the normal line voltage) exists on the line, the arrester

immediately furnishes a path to ground and thus limits and drains off the excess voltage.

The arrester must provide this relief and then prevent any further flow of current to

ground. The arrester has two functions; it must provide a point in the circuit at which an

over-voltage pulse can pass to ground and second, to prevent any follow-up current from

flowing to ground.

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fig19- 132 KV Lightning Arrester

TYPES OF LIGHTNING ARRESTORS:

1. Rod gap lightning arrestor2. Horn gap lightning arrestor3. Multi-gap lightning arrestor4. Expulsion type lightning arrestor5. Electrolytic type lightning arrestor6. Valve type or thyrite type lightning arrestor7. Lead oxide type lightning arrestor8. Pellet type lead-peroxide lightning arrestor9. Impulse protective lightning arrestor

CHAPTER-10

CONTROL ROOM

The room in which all the protecting and functional equipments such as ckt breakers, relays, C.TS., Potential transformers etc., are installed is known as "CONTROL ROOM". It is essential to control different types of equipment installed at different places in the substation. Which is easy in the efficient with the help of protective relays.

It consists of number of control panels, relay alarms, measuring meters are placed at the bottom. Essential meters are placed at the top. The following are different types of control panels according to their use and design.1. Cubical with extended control disk.2. Cubically with separate control disk.3. Cubical type.4. Duplex type.

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A. BATTERIES

D.C. supply mainly used for emergency purpose and also for relays testing. Generally lead-acid cells are used for D.C. supply.

BATTERY:

It is the combination of cells either in series or in parallel. Normally they are connected in series. These consists of +ve and +ve plates. +ve plates are made up of lead-peroxide (Pbo) and +ve plates are made up of Sponge Lead (Pb). Type of Electrolyte used is diluted Hydro sulphuric Acid (H2SO4).

In series connection of batteries, current is constant and batteries are having from Lower Ampere-hour capacities to Higher Ampere-hour capacities. Batteries are charged on constant current charging in olden days but, now normally charged is constant potential charging.

Normally batteries always works in float voltage i.e., 2.25 V/Cell. When batteries are fully discharged condition boost voltage (2.3V) is used. In maintenance wide batteries, we have to replace H2SO4 acid and distilled water.

APPLICATIONS OF BATTERIES IN SUB-STATIONS:

1. Telecommunication i.e., power line carrier communication 2. Lighting system3. Switch gear operation4. Control system i.e., relays etc5. Micro Wave repeater stations and other applications

IDENTIFICATION OF FULLY CHARGED BATTERIES:

1. It gives hydrogen at Cathode and Oxygen at Anode2. The colour of +ve and –ve plates are brown and in clear gray respectively 3. Specific gravity is 1.285 gm/cum

IDENTIFICAITON OF FULLY DISCHARGED:

1. Specific gravity is 1.12 gm/cum

Normally in float position 2.2 V/Cell, a total voltage of 242V.In boost position 2.3V/Cell at a total voltage of 253V. The output voltage must never exceed 245V

Suppose if the float fails, Boost-charge is used at that time only 106 cells are used.

B. SERIES REACTOR

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A bar stranded Copper Coil of large size and wound and for high self-inductance and very low resistance is known as “REACTOR’.

NEED OF REACTORS:

Where a short circuit occurs at a point in a generation and transmission scheme, a heavy sort CKT current flows through it. To limit that current flowing to a safe value, thus protecting the plant. For this purpose reactors are used.

TYPES OF REACTORS ACCORDING TO CONSTRUCTION:

1. Dry type air cored Reactors or Unshielded Reactors2. Oil immersed Air cored or Magnetically shielded Reactors Dry type reactors are used upto 33K.V. only. They are generally cooled by Natural of forced Air cooling. For high voltages, the Oil immersed Reactors are used, they are self-cooled by Oil or fan cooled. The object of the shielding is used to avoid considerable losses and heating under normal loads.

ADVANTAGES OF MAGNETICALLY SHIELDED REACTORS:

1. High factor of safety against flash over2. Smaller in size because of Easy cooling3. High thermal capacity4. No magnetic field outside the tank to cause heating or magnetic forces in adjacent

reactors or metal structures during short circuit.

LOCATIONS OF REACTORS:

Reactors scheme in power system can be divided into four types.

1. Generator Reactor scheme2. Feeder Reactor scheme3. Bus bar Reactor

a). Ring system b). Tie bar system.

C. CAPACITOR BANKS:

Shunt capacitor banks are used to improve the quality of the electrical supply and the efficient operation of the power system. Studies show that a flat voltage profile on the system can significantly reduce line losses. Shunt capacitor banks are relatively inexpensive and can be easily installed anywhere on the network.

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Shunt capacitor banks are installed for a variety of reasons in industrial,distribution and transmission systems.A common thread to all installations is the question of what,if any series reactor should be installed with the capacitor bank.Series capacitors are used with capacitor banks for two main reasons:

To dampen the effect of transients during capacitor switching,and to Control the natural frequencyof the capacitor bank and system impedance to avoid

resonance or to sink harmonic current.

Capacitor switching transients: When a capacitor bank is energized,the bank and the network are subject to transient

voltage and current.The severity of the effect is determined by the size of the capacitor and the network impedance.

The worst case occurs when a capacitor bank is energized close to a bank that is already connected. The inrush into the newly connected bank is determined by the size of the capacitor bank and the inductance between the two banks.

The larger the banks and the smaller the inductance between banks, the higher will be the inrush current.

The frequency of the inrush current is determined by the ratio of capacitor bank reactance and the impedance between the banks.The smaller the impedance,the higher will be the frequency.

Fig:20 Capacitor bank

If the only impedance between the two banks is that in the bus bar and cabling between the banks, a very large, high frequency inrush current will flow between the banks. Large and high frequency inrush current can damage capacitors, circuit breakers and contactors. All connected equipment, and even remote substations are subject to voltage transients and may result in sporadic equipment malfunction or failure. To avoid this problem , it is common practice to insert inrush limiting reactors in series with the capacitor banks.

The protection of shunt capacitor bank includes: a) protection against internal bank faults and faults that occur inside the capacitor unit; and, b) protection of the bankagainst system disturbances.

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Shunt capacitor banks (SCB) are mainly installed to provide capacitive reactive compensation, power factor correction. The use of SCBs has increased because they are relatively inexpensive, easy and quick to install and can be deployed virtually anywhere in the network. Its installation has other beneficial effects on the system such as: improvement of the voltage at the load, better voltage regulation (if they were adequately designed), reduction of losses and reduction or postponement of investments in transmission.The main disadvantage of SCB is that its reactive power output is proportional to the square of the voltage and consequently when the voltage is low and the system need them most, they are the least efficient.

THE CAPACITOR UNIT AND BANK CONFIGURATIONS

The Capacitor Unit

The capacitor unit, Fig. 1, is the building block of a shunt capacitor bank. The capacitor unit is made up of individual capacitor elements, arranged in parallel/ series connected groups, within a steel enclosure. The internal discharge device is a resistor that reduces the unit residual voltage to 50V or less in 5 min. Capacitor units are available in a variety of voltage ratings (240 V to 24940V) and sizes (2.5 kvar to about 1000 kvar).

Fig:21 The capacitor unit

Capacitor unit capabilities:

Relay protection of shunt capacitor banks requires some knowledge of the capabilities andlimitations of the capacitor unit and associated electrical equipment including: individual capacitor unit, bank switching devices, fuses, voltage and current sensing devices.Capacitors are intended to be operated at or below their rated voltage and frequency as they are very sensitive to these values; the reactive power generated by a capacitor is proportional

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to both of them (kVar ≈ 2π f V 2). The IEEE Std 18-1992 and Std 1036-1992 specify the standard ratings of the capacitors designed for shunt connection to ac systems and also provide application guidelines.These standards stipulate that:a) Capacitor units should be capable of continuous operation up to 110% of rated terminalrms voltage and a crest voltage not exceeding 1.2 x √2 of rated rms voltage, includingharmonics but excluding transients. The capacitor should also be able to carry 135% ofnominal current.b) Capacitors units should not give less than 100% nor more than 115% of rated reactivepower at rated sinusoidal voltage and frequency.c) Capacitor units should be suitable for continuous operation at up to 135%of ratedreactive power caused by the combined effects of:• Voltage in excess of the nameplate rating at fundamental frequency, but not over110% of rated rms voltage.• Harmonic voltages superimposed on the fundamental frequency.• Reactive power manufacturing tolerance of up to 115% of rated reactive power.

Bank Configurations

The use of fuses for protecting the capacitor units and it location (inside the capacitor unit oneach element or outside the unit) is an important subject in the design of SCBs. They also affect the failure mode of the capacitor unit and influence the design of the bank protection. Depending on the application any of the following configurations are suitable for shunt capacitor banks:

a) Externally Fused

An individual fuse, externally mounted between the capacitor unit and the capacitor bank fuse bus, typically protects each capacitor unit. The capacitor unit can be designed for a relatively high voltage because the external fuse is capable of interrupting a high-voltage fault. Use of capacitors with the highest possible voltage rating will result in a capacitive bank with the fewest number of series groups.A failure of a capacitor element welds the foils together and short circuits the other capacitorelements connected in parallel in the same group. The remaining capacitor elements in the unit remain in service with a higher voltage across them than before the failure and an increased in capacitor unit current. If a second element fails the process repeats itself resulting in an even higher voltage for the remaining elements. Successive failures within the same unit will make the fuse to operate, disconnecting the capacitor unit and indicating the failed one.

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Fig:22 Externally fused shunt capacitor bank and capacitor unit

Externally fused SCBs are configured using one or more series groups of parallel-connectedcapacitor units per phase (Fig. 23). The available unbalance signal level decreases as the number of series groups of capacitors is increased or as the number of capacitor units in parallel per series group is increased. However, the kiloVar rating of the individual capacitor unit may need to be smaller because a minimum number of parallel units are required to allow the bank to remain in service with one fuse or unit out.

b) Internally Fused

Each capacitor element is fused inside the capacitor unit. The fuse is a simple piece of wireenough to limit the current and encapsulated in a wrapper able to withstand the heat produced by the arc. Upon a capacitor element failure, the fuse removes the affected element only. The other elements, connected in parallel in the same group, remain in service but with a slightly higher voltage across them.Fig. illustrates a typical capacitor bank utilizing internally fused capacitor units. In general,banks employing internally fused capacitor units are configured with fewer capacitor units inparallel and more series groups of units than are used in banks employing externally fusedcapacitor units. The capacitor units are normally large because a complete unit is not expected to fail.

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Fig 23 – Internally fused shunt capacitor bank and capacitor unit

c) Fuse less Shunt Capacitor Banks

The capacitor units for fuse less capacitor banks are identical to those for externally fuseddescribed above. To form a bank, capacitor units are connected in series strings between phase and neutral, shown in Fig.

The protection is based on the capacitor elements (within the unit) failing in a shorted mode,short- circuiting the group. When the capacitor element fails it welds and the capacitor unitremains in service. The voltage across the failed capacitor element is then shared among all the remaining capacitor element groups in the series. For example, is there are 6 capacitor units in series and each unit has 8 element groups in series there is a total of 48 element groups in series. If one capacitor element fails, the element is shortened and the voltage on the remaining elements is 48/47 or about a 2% increase in the voltage. The capacitor bank continues in service; however, successive failures of elements will lead to the removal of the bank.

The fuse less design is not usually applied for system voltages less than about 34.5 kV. Thereason is that there shall be more than 10 elements in series so that the bank does not have tobe removed from service for the failure of one element because the voltage across the remaining elements would increase by a factor of about E (E – 1), where E is the number of elements in the string.

The discharge energy is small because no capacitor units are connected directly in parallel.Another advantage of fuse less banks is that the unbalance protection does not have to bedelayed to coordinate with the fuses.

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Fig 24 – Fuseless shunt capacitor bank and series string

d) Un fused Shunt Capacitor Banks

Contrary to the fuse less configuration, where the units are connected in series, the un fused shunt capacitor bank uses a series/parallel connection of the capacitor units. The un fused approach would normally be used on banks below 34.5 kV, where series strings of capacitor units are not practical, or on higher voltage banks with modest parallel energy. This design does not require as many capacitor units in parallel as an externally fused bank.

CHAPTER-11

POWER LINE CARRIER COMMUNICATION

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Fig:25 -Power Line Carrier Communication

Different communication technologies are being used for the transmission of information from one end to another depending on the feasibility and needs. Some include Ethernet cables, fiber optics, wireless transmission, satellite transmission, etc. A vast amount of information travels through the entire earth every day and it creates an essential need for a transmission medium that is not only fast but economically reasonable as well. One of the technologies that fit in the above stated criteria is PLCC.

PLCC, Power Line Carrier Communication, is an approach to utilize the existing power lines for the transmission of information. In today’s world every house and building has properly installed electricity lines. By using the existing AC power lines as a medium to transfer the information, it becomes easy to connect the houses with a high speed network access point without installing new wirings. 

This technology has been in wide use since 1950 and was mainly used by the grid stations to transmit information at high speed. Now a days this technology is finding wide use in building/home automation as it avoids the need of extra wiring. The data collected from different sensors is transmitted on these power lines thereby also reducing the maintenance cost of the additional wiring. In some countries this technology is also used to provide Internet connection.

History

The idea of using an existing medium to send the communication signals is as old as the telegraph itself. But it had not been possible until the recent decades. The first significant step in the field was when two patents were issued to American Telephone and Telegraph Company in the name of 'Carrier Transmission over Power Circuits' in 1920. After four years later in 1924 two other patents were filed for the systems transmitting and receiving communication signals over three phase power lines. 

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Harsh characteristics of the power cables were the key problem in further development. Researchers were involved to overcome the unpredictable characteristics of the power lines. Since the early 1980, spread spectrum power line communication was the main focus of the research. This technology is now developed far better than that initial improvement and is promising a reliable utilization in home automation and security systems. Applications of PLCC :

PLCC technology can be deployed into different types of applications in order to provide economic networking solutions. Hence merging with other technologies it proves useful in different areas. These are few key areas where PLC communications are utilized:

1. Transmission & Distribution Network: PLCC was first adopted in the electrical transmission and distribution system to transmit information at a fast rate.

2. Home control and Automation: PLCC technology is used in home control and automation. This technology can reduce the resources as well as efforts for activities like power management, energy conservation, etc.

3. Entertainment: PLCC is used to distribute the multimedia content throughout the home.

4. Telecommunication: Data transmission for different types of communications like telephonic communication, audio, video communication can be made with the use of PLCC technology.

5. Security Systems: In monitoring houses or businesses through surveillance cameras, PLCC technology is far useful.

CHAPTER-12

EARTHING

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A connection to be the general mass of the earth by means of an earth electrode. An object is said to be earthed when it is electrically connected to an earth Electrode.

The Earthing practice is adopted at such stations should be in such a manner as to provided for the following purpose.1. Safely to personnel.2. Minimum damage to equipment as a result of flow of heavy fault currents.3. To provide earth connections for the Earthed Neutral system.4. To provide discharge path for lighting arrestors, gap etc.,Generally two types of Earthing systems are mostly used. Those are1. Pipe Earthing.2. Plate EarthingEvery type of earthing should satisfy the following conditions as per the rural Electrification Corporation Limited.1. Voltage drop between nominal earth part's which any one is liable to be in simultaneous contact shall not exceed 55 V.2. Earthing Conductors shall not be set in concrete.3. Preferably Earthing conductors should not be run in metal conduits.

4. The Earth resistance of the system shall not exceed the limits specified below.

Power Stations : 0.5 ohmsMajor sub-stations : 1.0 ohmsOther sub-stations : 2.0 ohmsDistribution transformer sub-station : 5.0 ohmsTower, poles etc. : Less than 25 ohms

In substations grid system of earthing is generally used. The grid comprises a number of meshes. These are bounded to the general mass of earth by a number of low resistance earth electrodes. -The size of Electrode 4 x 5m buried horizontally. Each conductor shall be made of copper and have a cross-sectional area of not less than 1.3 sq cms. Conductors forming earth grid shall be laid in the ground at a depth of not less lhan 30 cm below.Earthing practice can be broadly divided into the following two types.1. Equipment earthing.2. System Earthing or Grounding of power system neutrals.

Fig26- Eathing pit

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CHAPTER-13

SAFETY RULES OF EHT SUBSTATION

Safety Requirements in construction of Transmission Lines & Substations:

Safety shall form an integral, part of work processes to ensure safety for employees including employees of contractors and sub-contractors as well as visitors.

Provisions relating to Transco:- A sound and scientific management system should be set up which shall include:a) Formulation of a written statement of policy in respect of safety and health of employees. b) Defining and documenting responsibilities for all levels of functionaries to carry out safety related activities including responsibilities of the contractors.c) Preparing detailed Safety Manual complying with statutory requirements, manufactures' recommendations, BIS and any other relevant standards and codes.d) Establishing procedures to identify hazards that could give rise to the potential of injury health impairment or death and measures to control impact of such hazards.e) Providing adequate human, physical and financial resources to implement the safety management system. !f) Providing safe working environment and evolving framework for occupational safety and health.g) Providing and maintaining medical facilities. ; h) Providing adequate training to all employees to make them aware of safety related issues.i) Establishing system for accident reporting, analysis, investigation and.Implementation of recommendations. j) Establishing system for proper communication, documentation and record of management in relation to occupational safety and health, k) Filing periodic and other returns to the statutory bodies as required various Acts; and Rules within stipulated time. 1) Formulating emergency management plan for quickly and effectively dealing with probable emergencies that stipulated time. m) Establishing methodology for internal and external audit of safety management system. n) Establishing system for periodic monitoring and review of safety system by Management. o)Overseeing the safety performance of the contractors.

Detailed site specific safety manuals should be prepared. However common safety j manuals may be prepared for similar installations. Safety Manuals be prepared for construction of Transmission Lines and Substations and for Operation & Maintenance of Lines & Substations.

Provisions relating to Contractor:

Transco shall incorporate requisite safety provisions in the contract document which are required to be compiled by the contractor's personnel during execution of contract to facilitate safe working during execution of works.

Contractor shall observe safety requirements as laid down in the contract as well as comply with statutory requirements as provided in the existing Acts/ Rules. In case of sub-

41

contracts, it shall be the responsibility of main contractor that all safety requirements are followed by the employees/staff of the sub-contractors.One of the employees of the contractor shall act as safety coordinator, who will liaison with safety officer on matters relating to safety.

Contractor shall be responsible for non-compliance of any of the safety measures, implications, injuries, fatalities and compensation arising out of such situations or incidents. In case of any accident, contractor shall immediately submit a statement of such accidents to the department and the safety officer concerned for the project showing the details of accident, any injury/casualties, extent of property damage and remedial action taken to prevent recurrence. The contractor shall submit a statement of various accidents to the department at the end of each month within a week.

Reporting of accidents:

i) Notice of any accident, resulting in death of any person or in such bodily injury which is likely to cause death or prevents the injured person from working for a period of 48 hours of more, shall be sent to the statutory authorities within the prescribed time as per the Factories Act and Rules or the Building and other Construction workers (Regulation of Employment and Conditions of Service) Act and Rules as applicable.ii) Cases of outage of a substation or a transmission line 132KV above due to any accident related to any equipment (e.g. fire, explosion, emission of hazardous chemicals, collapse of transmission tower, flooding of sub-station area) shall be reported to the Authority within 24 hours, whether or not any death or disablement is caused to any person.

Emergency Management Plan:

i. An on site emergency management plan shall be formulated for a) each substation and b) group of transmission lines for quickly and effectively dealing with probable emergencies like fore, explosion, gas leakages, landslides, floods etc. and reducing response time.

ii. Provisions to be made for the onsite emergency management plans shall conform to the following:

a. Major fire in cable galleryMajor fire in transformer yard

iii. Onsite emergency management plan for the substations and lines should be prepared by the department before commissioning. In case of existing substations and lines the plan may be prepared within 90 days. However in case of construction of Substations and lines, emergency action plan shall be prepared, before commencement of construction activity, to handle emergencies like fire, explosion, collapse of lifting appliances and transport equipment, collapse of building or structures, gas leakages, landslides, floods etc.

iv. Department should ensure that a mock drill of the onsite emergency management plan is conducted at least once every six months.

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Medical facilities:

Medical facilities shall be provided to arrange immediate relief to accident victims. A fully equipped first-aid box shall be made available at the plant or at the site. A few persons (say 5) should be trained in first-aid procedures amongst whom at least one shall always be available during the working period. Arrangements for procuring ambulance van for transportation of persons involved in serious accident or sickness to the hospital' shall be made at short notice.

Training and Awareness:

Regular training programmes should be conducted for all employees covering general safety awareness, first-aid, emergency procedures including shock treatment, use of personal protective equipment, safety pre-cautions while handling electro-mechanical equipment, use of different types of firefighting equipment, response in the event of emergencies including fire, floods, landslides, earthquakes etc., site specific hazards and relevant safety acts, rules and regulations.

Safety Manual for construction of Substations and lines:

A safety Manual shall be prepared with the following contents:

Safety policy, Safety organization, Responsibilities of contractor, responsibilities of employees, Reporting of accidents, Enquiry of accident, dangerous occurrence, 1 occupational health and medical facilities, emergency management plan, location of safety equipment and emergency facilities in the substation, safety inspections/audits, Safety training, awareness and promotion, Personal protection equipment, communication facilities, Fire prevention and protection, emergency escape routes.

Safe working environment:

Illumination and emergency lighting, Noise pollution, Harmful gases and dust pollution, Thermal radiation, Ventilation, confined spaces.

Safety In handling oils, Safety in painting works, Safety in transportation, earth moving equipment and other construction equipment/machinery, Safety in use of electricity.Safety in handling electrical equipment such as: Earthing of equipment, working on ! bus-bars, transformers, circuit breakers, insulators etc, Working on lines during ! installation of insulators, stringing of conductors, jumpering and fixing of spacers/vibration dampers, DHV/HV static capacitor banks, opening or splicing de-energized conductors or overhead ground wires, storage batteries, testing of : MV/HV/EHV equipment, SF6 gas filled equipment.

Housekeeping, Safety in material handling, safety in use of lifting machines and tackles, Safety while lifting heavy equipment, fencing of rotating machinery, Safety during demolition and excavation Safety while working in any rainy and foggy environment, safety during blasting, Safety. A Safety manual for O&M of Substations and Lines shall be prepared with the following contents.

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i) Procedure for obtaining permission to work for carrying out O&M of equipment, ii) Safety in O&M of various electro-mechanical equipment as

per recommendations of manufacturesiii) Safety of structures/buildings iv) Safety in work shop and garages

Safe working clearance Guarding of live apparatus Operation on live apparatus General provision relating to maintenance Working in areas containing exposed live HV/EHE conductors Demarcation of work areas Working on remotely controlled and automatically controlled equipment Working on equipment containing or operated by compressed air.

v) Safe handling, collection and disposal of hazardous waste vi) Safety in substations/Switchyard/Switch boards

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REFERENCES :

[1]C.L.Wadhwa, Electrical Power Systems, 3rd edition, New Age International (P) Limited, Publishers, 2005.

[2]B.L.Soni, Gupta, Bhatnagar, Chakrabarthy, A Text Book on Power System Engineering, Dhanpat Rai & Co, 2007.

[3]T.S.Madhava Rao, Power System Protection: Static Relays, 2nd edition, Tata McGraw-Hill inc., US2004.

[4] http://en.wikipedia.org/wiki/Electrical_substation.

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