West Bengal State Electricity Transmission Company Limited (WBSETCL)

West Bengal State Electricity Transmission Company Limited (WBSETCL) was set

up in 2007 following the unbundling of the state electricity board of West Bengal. With a

share of 4 percent each in the total intrastate transformer capacity, WBSETCL is the

eleventh largest of the 23 state transmission utilities in the country. It is responsible

for power transmission across the state at the 400 kV, 220 kV, 132 kV and 66 kV

Voltage levels. The company also manages the state load dispatch center, which

monitors and controls the grid operations.

Network GrowthCompany's transformation capacity stood at about 16,350 MVA as of March 2010.

Capacity at the 220 kV and 132 kV levels constituted a roughly similar share of 40

percent of the total. WBSETCL recorded the highest compound annual growth

rate (CAGR) of 13.5% in transformer capacity during 2006-07 to 2009-10 among all

state utilities.

At the end of 2009-10, its transmission line length stood at over 11,450 ckt. km, growing

at a CAGR of 6.5% from 2005-06. About 60% of its line network is at the 132 kV level.

Across all voltage levels, its 400 kV network(constituting 14% of its network) has grown

the fastest in the past five years, with a CAGR of about 20 percent

Future PlansWBSETCL plans to add over 2,000MVA to its transformer capacity and 900 ckt. km to

its transmission line network in the current fiscal year (2010–11). A capex of over Rs 8

billion has been outlined in 2010-11 on various capacity augmentation projects. About

10 new substations would be commissioned by WBSETCL in the current fiscal(2010–

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11), which would add 2,180 MVA to its existing transformer capacity. These include a

400 kV substation at Kharagpur, two 220 kV substations at Singur and Dalkhola, and

five 132 kV substations at Chalsa, Kurseong, Khatra, Mohispota and Salt lake (this will

be GIS substation).

Besides the commissioning of new sub-stations, capacity augmentation would be

undertaken at 12 existing substations, of which five are at the 220 kV level. Over

912ckt. km of transmission line would also be added in the current fiscal through 19

ongoing transmission line projects. The estimated cost of these transmission line is Rs.

4.63 billion.

In order to reduce transmission losses further, the installation of 33 kV capacitors at

EHV substations and installation of EHV substations near the load centers are some of

the important strategies being deployed by WBSETCL

Growth Statistics[edit]

[2]

2008-09 2009-10 Growth (%)

Line length (ckt. km) 11,089.50 11,456.90 3.31

Substations (no.) 93 102 9.68

Transformation capacity (MVA) 13,951.20 16,347.70 17.18

Transmission Losses (%) 3.90 2.74 -

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ACKNOWLEDGEMENT I being a student of electrical engineering from express my sincere gratitude and heartfelt thankfulness to the WEST BENGAL STATE ELECTRICITY TRANSMISSION COMPANY LIMITED for granting us the opportunity to receive training under this esteemed organisation, from 2

nd of January 2015 to 16th January 2015, in BONGAON(Chalki power station).

We gained a lot of theoretical as well as a fabulous practical experience in this short period of time. Our special thanks extends to the Assistant Engineer of the substation, Mr. Prosenjit Sarkar. and all the employees of the substation, who were very helpful and co-operative to help us learn and understand.

Overall it was an awesome experience as we got to learn about the practical purposes of our trade.

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TRANSMISSION Electric power transmission is the bulk transfer of electrical energy from generating power plant to electrical substation located near demand centers. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. Transmission lines, when interconnected with each other, become transmission networks. These are typically referred to as “power grids” or just “the grid”.

Transmission lines mostly use high-voltage three phase alternating current (AC), although single phase. AC is sometimes used in railway electrification system. High voltage direct current (HVDC) technology is for greater efficiency in very long distances (typically greater than 400 miles, or 600 km) sub marine power cables (typically greater than 30 miles, or 50 km). HVDC links are increasingly used as isolating features to stabilize against control problems in large power distribution networks where sudden new loads or blackouts in one part of a network can otherwise result in synchronization problems that may bring the rest of the network down. Electricity is transmitted at high voltages (110 kv or above) to reduce the energy lost in long-distance transmission. Power is usually transmitted through overhead power lines. Underground power transmission has a significantly higher cost and greater operational limitations but is sometimes used in urban areas or sensitive locations. A key limitation in the distribution of electricity is that, with minor exceptions, electrical energy cannot be stored, and therefore must be generated as needed. A sophisticated system of control is therefore required to ensure electric generation very closely matches the demand. If supply and demand are not in balance, generation plants and transmission equipment can shut down which, in the worst cases, can lead to a major regional blackout. To reduce the risk of such failures, electric transmission networks are interconnected into regional, national or continental wide networks thereby providing multiple redundant. Alternate routes for power to flow should (weather or equipment) failures occur. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line ensure spare capacity is available should there be any such failure in another part of the network.

METHODS OF TRANSMISSION

OVERHEAD TRANSMISSION

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High-voltage overhead conductors are not covered by insulation. The conductor material is nearly always an aluminum alloy, made into several strands and possibly reinforced with steel strands. Copper was sometimes used for overhead transmission but aluminum is lower in weight for only marginally reduced performance and much lower in cost. Overhead conductors are a commodity supplied by several companies worldwide. Improved conductor material and shapes are regularly used to allow increased capacity and modernize transmission circuits. Conductor sizes range from 12 mm2 (36 American wire gauge) to 750 mm2 (1,590,000 circular mils area), with varying resistance and current carrying capacity. Thicker wires would lead to a relatively small increase in capacity due to the skin effect that causes most of the current to flow close to the surface of the wire. Because of this current limitation, multiple parallel cables (called bundle conductors) are used when higher capacity is needed. Bundle conductors are also used at high voltages to reduce corona discharge energy loss.

Today, transmission-level voltages are usually considered to be 110 kv and above. Lower voltages such as 66 kv and 33 kv are usually considered sub transmission voltages but are occasionally used on long lines with light loads. Voltages less than 33 kv re usually used for distribution. Voltages above 230 kv are considered high voltages are requiring different designs compared to equipment used at lower voltages.

Science overhead transmission wires depend on air for insulation, design of these lines require minimum clearances to be observed to maintain safety. Adverse weather condition of high wind and low temperatures can lead to power outages: wind speeds as low as 23 knots (43 km/h) can permit conductors to encroach operating clearances, resulting in a flashover and loss of supply. Oscillatory motion of the physical line can be termed gallop or flutter depending on the frequency and amplitude of oscillation.

UNDERGROUND TRANSMISSION :-

The design and construction of underground transmission line differ from overhead linens because of two significant technical challenges that need to be overcome. There are: 1) providing sufficient insulation so that cable can be within inches of grounded material; and 2) dissipating the heat produced during the operation of the electrical cables. Overhead lines are separated from each other and surrounded by air. Open air circulating between around the conductors cools the wires and dissipates heat very effectively. Air also provides insulation that can recover if there is a flashover. In contrast, a number of different systems, materials, and construction methods have been used during the last century in order to achieve the necessary insulation and heat dissipation required for undergrounding transmission lines. The first underground transmission line was a

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132 kv line constructed in 1927. The cable was fluid-filled and paper insulated. The fluid was necessary to dissipate the heat. For decades, reliability problems continued to be associated with constructing longer cables at higher voltages. The most significant issue was maintenance difficulties. Not until the mid-1960s did the technology advance sufficiently so that a high-voltage 345 kv line could be constructed underground. The lines though were still fluid filled. This caused significant maintenance, contamination, and infrastructure issues. In the 1990s the first solid cable transmission line was constructed more than one mile in length and greater than 230 Kv.

SUB-STATION

Introduction:A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Electric power may flow through several substations between generating plant and consumer, and its voltage may change in several steps.A substation may include step-up transformers (that increase the voltage while decreasing the current) or step-down transformers (that decrease the voltage while increasing the current) for domestic and commercial distribution. The word substation comes from the days before the distribution system became a grid.

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ELECTRICAL SUBSTATION MODEL SIDE VIEW

A:Primary power lines' side B:Secondary power lines' side1.Primary power lines 2.Ground wire 3.Overhead lines 4.Transformer for measurement of electric voltage 5.Disconnect switch 6.Circuit breaker 7.Current transformer 8.Lightning arrester 9.Main transformer 10.Control building 11.Security fence 12.Secondary power linesWhere a substation has a metallic fence, it must be properly grounded to protect people from high voltages that may occur during a fault in the network. Earth faults at a substation can cause a ground potential rise.

SELECTION AND LOCATION OF SITE FOR A SUBSTATION The following factors are considered while making site selection for a substation:-

Type of substation:-(a) 400 kv substation (b) 220 kv substation (c) 132 kv substation Availability of suitable and Sufficient Land:- Type of substation Area required

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(a). 400 kv substation 50 acres(b). 220 kv substation 25 acres (c). 132 kv substation 10 acres Communication Facility:- Suitable communication facility is desirable at a proposed substation both during and after its construction . It is better, therefore, to select the site along side on existing road to facilitate an easier and cheaper transportation. Atmospheric facility:- Atmosphere around factories, which may produce metal corroding gases, air fumes, conductive dust etc..., and nearer to sea coasts, where air may be more humid and may be salt loaden , is detrimental to the to the proper running of power system and therefore substation should not be located near factories or sea coast. Availability of Essential Amenities To The Staff:- The site should be such where staff can be provided essential amenities like school, hospital, drinking water housing etc. Drainage Facility:- The site selected for the proposed substation should have proper drainage arrangement or possibility of making effective drainage arrangement to avoid pollution of air and growth of micro-organisms detrimental to equipment and health.

Classification OF SUB-STATIONS: On the basis of Nature of Duties 1. Step-up or Primary Substation2. Primary Grid Substation3. Step-Down or Distribution Substation On the basis of Service Rendered1. Transformer Substation

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2. Switching Substation 3. converting Substation On the basis of Operating Voltage1. High voltage Substation 2. Extra High Voltage Substation 3. Ultra High Voltage Substation On the basis of Importance 1. Grid Substation 2. Town Substation On the basis of Design 1. Indoor Substation 2. Outdoor Substation

Indoor Substation also Sub-Divided into following Categories1. Substation of The Integrated Built type2. Substation of The Composite 3. Unit Type factory Fabricated Substation and Metal Clad Switchboards

Outdoor Substation also Sub-Divided into following Categorie 1. Pole-Mounted Substation 2. Foundation Mounted Substation On the basis of working field 1. Bulk supply and industrial sub-stations 2. Mining sub-stations3. Mobile sub-stations4. Cinematograph sub-stations. The step-up sub-station are associated with the generating stations. The generation voltage is limiting to a low value and needs to be steeped up to

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the primary transmission voltage so that huge blocks of power can be carried over long distances to the load centres economically. The primary grid sub-station are created at suitable load centres along the primary transmission lines. The primary transmission voltage is steeped down to a number of suitable secondary voltages. From here secondary transmission lines are carried over to the load points. Along these secondary transmission lines secondary sub-stations are created at actual load points where the voltage is further steeped down to sub-transmission and primary distribution voltage. The Distribution sub-station are created where the sub-transmission voltage/primary distribution voltage is steeped down to supply voltage ; these sub-station feed the actual consumers through a network of distributors and service lines. The bulk supply and industrial sub-stations are generally distribution sub-stations with the difference that the sub-station is created separately for a consumer and subsequent distribution of the electric power is left to the particular consumer of large or medium supply group as may be designated by the standards laid down by the electric supply undertaking. The mining sub-station, as their name indicates, are sub-stations required for very special purpose ; they need special design consideration because of the extra precautions for safety needed in the operation of the electric supply. The mobile sub-stations are also of special purpose and designs ; they are needed primarily for temporary requirements such as for construction purposes. The cinematograph sub-stations are also specific purpose sub-stations are required to meet special requirements. Depending on the constructional features the sub-station may be further sub-divided into : 1. Outdoor type 2.Indoor type 3.Basement or Underground type 4.Pole mounting-open or kiosk type.For reason of cost and safety it is common to have Outdoor sub-stations for 33 kv and above.

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BONGAON 132/33/11 KV SUB-STATION.

Introduction:Electrical power system has generally three steps, 1. Generation 2. Transmission and 3.Distribution.The electric power is generate at the power plant. It is delivered to the consumers through a large network of transmission and distribution. At many places in the line of the power system, it may be desirable and necessary to change some characteristics (e.g. voltage, a.c to d.c, frequency, power factor etc) of electric supply. This is accomplished by suitable apparatus called sub-station.Sub-Stations are important part of power system. The wrtinuity of supply depends to a considerable extend upon to successful operation of sub- stations. It is therefore, essential to exercise utmost care while designing and building a sub- station. The following are the important points which must be kept in view while laying out a substation

1. It should be located at proper site. As far as possible, it should be located at the centre of gravity of load.2. It should be provide safe and reliable arrangement.3. It should be easily operated and maintained.BONGAON(132/33/11 KV) Sub- Station was built up under JBIC project(about 9 year ago) having 2x31.5. 132/33 kv transformer capacity power to this sub-station is feed from jeerat 400/200/132 kv sub-station through double circuit 132 kv line namely JEERAT-BONGAON feeder I & II. A separate 132 kv double circuit has also commissioned for feeding power to KRISHNAGAR 132 kv sub-station. These feeder have been designed as BONGAON-KRISHNAGAR feeder I & II.IN 132 KV SIDE, THE BAYS ARE:-

i) JEERAT-BONGAON feeder I :1nos.ii) JEERAT-BONGAON feeder II : 1nos.iii) BONGAON –KRISHNAGAR feeder I : 1nos.iv) BONGAON –KRISHNAGAR feeder II : 1nos.v) BUS-COUPLER 1nos.vi) Transformer bay : 2nos.(132 kv side of 31.5 mva transformer)IN 33 KV SIDE, Total no of BAYS ARE:-

i) Feeder bay 5 nos:-

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a)GAIGHATA 33 kv feederb)BONGAON-I 33 kv feederc)BONGAON-II 33 kv feederd)HELENCHA 33 kv feedere)GAGNAPUR 33 KV feeder ii)Transformer bay : 2 nos.(33 kv side of 31.5 MVA transformer) iii)Transformer Bus Coupler : 1 noiv)Transformer Bay : 2 nos.(33 kv side of 6.3 MVA 33/11 KV transformer)IN 11KV Side, Total no of Panels Are:-

i) Out going feeder 4 nos:- a)Gopal nagar 11 kv feeder b) Belta 11 kv feeder c) Mamudpur 11 kv feeder d) Nahata 11 kv feeder. ii) Incomming from 6.3 MVA 33/11 KVA Transformer : 2nos.iii) Bus coupler : 1 nos. The main parts of sub-station are ~A. TransformerB. Circuit BreakerC. Power Line Carrier Communication(PLCC)D. Lightning ArrestersE. Battery BankF. InsulatorG. Isolators H. Bus-barsI. Capacitor bankJ. Metering and Indicating InstrumentK. Air ConditionerL. Operating ComputerDetails descriptions of the system are describe next. The layout designed of the Sub-Station and other circuit designs are shown next

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a.TRANSFORMER

Introduction:A transformer is a static device which consists of two or more stationary electrical circuits of transferring electrical energy between then. The transfer of energy from one circuit to another takes place without a charge in frequency.

Here ∅M is flux

Arrangement of a simple transformer

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POWER TRANSFORMERA power transformer is used in a sub-station to step-up or step-down the voltage. The entire sub sequent sub-stations use step down transformer to gradually reduce the voltage of electric supply and finally delivers it at utilizations voltage. In that Bongaon 132/33/11 k v sub-station two 31.5 MVA power transformer. They are connected in parallel and two 6.3 MVA traction transformer are used.

The modern practice is to use 3-phase transformer in sub-station, although 3 single phase bank of transformer can also be used. The use of 3-phase bank of transformer i.e. 3-phase transformer permits two advantages. Firstly, only one 3-phase load tap changing mechanism can be used. Secondly, its installation is much simpler than the three single phase transformer.

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POWER TRANSFORMER (132/33 kv 31.5 MVA)

DIFFERENT PARTS OF POWER TRANSFORMER:-CONSERVATOR TANK:- Conservator is a small auxiliary oil tank(an air tight cylindrical dram) that may be mounted above the transformer and connected to the main tank by a pipe. Its function is to keep the main tank of the transformer completely filled with oil in all circumstances despite expansion or contraction of oil with the change of temperature-conservator is always partly filled with oil and absorbs the expansion and contraction of oil and keeps the main tank full oil. It also reduces the rate of oxidation of oil, partly because less oil surface is exposed to air and partly because of reduced temperature of the oil exposed to air. Normally the capacity of conservator should be approximately 10-12% of the oil volume of the main tank. BREATHER:- When the transformer becomes warm, the oil and gas expand. The gas at the top of the oil expelled out. When the transformer cools, air is into the transformer. Unless preventive measures are taken, moisture is drawn during this process, called the breathing. This moisture is readily absorbed by the oil, and the dielectric properties of oil are correspondingly reduced. The air entering the transformer is made moisture free by letting it pass through an apparatus called the breather. A breather consists of a small container connected to the vent pipe and contains a dehydrating material like silica gel crystals impregnated with cobalt chloride. The material is blue when dry and a whitish pink when damp. It sucks the moisture from the air which is taken by transformer so that dry air is taken by transformer.TAPPING:- The transformers are usually provided with few tappings so that output voltage can be varied over a small range for constant input voltage, most industrial transformers are provided with four tappings

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on the hv winding, two on each side of the ‘normal’ voltage, so that the tap changer has five position. In special cases there may be tappings on the lv winding, usually in addition to those provided on hv winding. Though the tappings can be changed while the transformer is supplying load by making some suitable arrangement but in most of the transformers the tappings are to be changed after disconnecting them from the supply mains. Buchholz Relay:- It is every sensitive gas and oil operated instrument which safely detect the formation of gas or sudden pressure inside the oil transformer. In the field of electric power distribution and transmission, a Buchholz relay is a safety device mounted on some oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a conservator. The Buchholz Relay is used as a protective device sensitive to the effects of dielectric failure inside the equipment. When gas produced in the tank due to a minor fault surfaces to accumulate in the relay chamber within a certain amount (0.3Q-0.35Q) or above, the float lowers and closes the contact, thereby actuating the alarm device. In the event of a major fault, abrupt gas production causes pressure in the tank to flow oil into the conservator. In this case, the float is lowered to close the contact, thereby causing the Circuit Breaker to trip or actuating the alarm device.RADIATOR-Radiators are used in a transformer to cool the transformer oil through natural air or forced air flowing in these radiator fins. As the transformer oil temperature goes down due to cooling it goes to the transformer tank from bottom ,cool the windings and gets heated, and then returns to the radiator for next cooling .This cycle repeats as the oil flow is also natural due difference in temperature of oil on bottom and top. In big power transformers this oil circulation is forced by oil pumps for effective cooling.The radiator has many small fins and there are 4-10 radiator banks in a transformer depending on capacity and make of the transformer.

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In BONGAON(132/33/11 kv)sub-station there are two 31.5 MVA power transformer are used, and two 6.3 MVA traction transformer are use. Two 31.5 MVA power transformer (at rating 132/33 KV) for step down from 132 KV primary voltage to 33 KV secondary voltage. The outgoing lines are Gagnapur, Helencha, Bongaon-1, Bongaon-2, and Chandpara. Two 6.3 MVA power transformer (33/11 KV) are use for step down from 33 KV primary to 11 KV secondary and the outgoing lines are Mamudpur, Gopalnagar, Belta, and NahataSPECIFICATION [31.5 MVA POWER TRANSFORMERS ]MVA 31.5 ELECTRICAL SPEC NO. ELECSPES BH8002NO LOAD HV 132 KV OGA DRG NO. MA1 08802ANO LOAD LV 33 MAKERS WO NO. BH8802AMPERES HV 137.78 MAKERES SERIAL NO BH8802/13AMPERES LV 551.10 DIAGRAM DRG NO. MA3 08802CPHASE 3 YEAR OF MFG. 2000-2001FREQUENCY 50 HZ UNTAKING MASS kg 31.150TYPE OF COOLING ONAN/ONAF TOTAL OIL kg/l 13,300/15,200RATING OF MVA 20.5/31.6 TOATL MASS kg 59,500CONNECTION SYMBOL YNd1 GUARANTEED TEMP. RISE OIL *C 50NO LOAD LOSS 19 KW MAX LOAD LOSS 102 KW MAXAUXILLARY LOSS 2 KW MAX GUARANTEED TEMP. WDG. *C 55HEAVIEST PACKAGE WITH OIL kg 49,500 HEAVIEST PACKAGE WITH OUT OIL kg 39,500

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VECTOR GROUP YNd1

SPECIFICATION [6.3MVA POWER TRANSFORMERS ] TYPES OF COOLING ONAN

MVA RATING 6.3MAKE I.M.P.LYEAR OF MFG. 2001MAIN TANK OIL QUANTITY(KILOLITRES) 3.315TOTAL WEIGHT(METTRIC TONES) 12.65T ONRATED VOLTAGR(KV) HV 33RATED VOLTAGR(KV) LV 11PHASE 3MAXIMUM VOLTAGE(KV) 34.05MINIMUM VOLTAGE(KV) 29.7NO. OF TAPS 7

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INSTRUMENT TRANSFORMERA transformer that transfers primary current, voltage, or phase values to the secondary circuit with sufficient accuracy to permit connecting an instrument to the secondary rather than the primary; used so only low currents or low voltages are brought to the instrument. An instrument transformer’s role is to provide accurate inputs to protection, control and metering systems including revenue metering. It also measuring a large current in a d.c. circuit.The main tasks of instrument transformers are:

To transform currents or voltages from a usually high value to a value easy to handle for relays and instruments. To insulate the metering circuit from the primary high voltage system.

To provide possibilities of standardizing the instruments and relays to a few rated currents and voltages.CURRENT TRANSFORMER :

In electrical engineering, a current transformer (CT) is used for measurement of electric currents. When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current

VECTOR GROUP Dyn11

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accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments.

Circuit Diagram CURRENT TRANSFORMER

SL NO.

EQUIPMENT/FEEDER C.T RATIO SIDE OF C.T

1 132 KV JEERAT-BONGAON CKT-I 600-300/1A LINE SIDE2 132 KV JEERAT-BONGAON CKT-II 600-300/1A LINE SIDE3 132 KV KRISHNAGAR-BONGAON CKT-I 600-300/1A LINE SIDE4 132 KV KRISHNAGAR-BONGAON CKT-II 600-300/1A LINE SIDE5 132 KV TRANSFORMAR BUS COUPLER 800-400/1A LINE SIDE6 132 KV SIDE OF 31.5 MVA TRANSFORMER-I 300-150/1A LINE SIDE7 132 KV SIDE OF 31.5 MVA TRANSFORMER-II 300-150/1A LONE SIDE8 33 KV GAIGHATA FEEDER 400-200/1A LINE SIDE9 33 KV BONGAON –I FEEDER 400-200/1A LINE SIDE

10 33 KV BONGAON – II FEEDER 400-200/1A LINE SIDE11 33 KV HELENCHA FEEDER 400-200/1A LINE SIDE12 33 KV GAGNAPUR FEEDER 400-200/1A LINE SIDE13 33 KV TRANSFORMAR BUS COUPLER 1000-800/1A LINE SIDE

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14 33 KV SIDE OF 31.5 MVA TRANSFORMER-I 1000-800/1A LINE SIDE15 33 KV SIDE OF 31.5 MVA TRANSFORMER-II 1000-800/1A LINE SIDE16 33 KV SIDE OF 6.3 MVA TRANSFORMER-I 200-100/1A LINE SIDE17 33 KV SIDE OF 6.3 MVA TRANSFORMER-II 200-100/1A LINE SIDE18 11 KV SIDE OF 6.3 MVA TRANSFORMER-I 400-200/5A400-200/1A LINE SIDE19 11 KV SIDE OF 6.3 MVA TRANSFORMER-II 400-200/5A400-200/1A LINE SIDE20 11 KV GOPALNAGAR FEEDER 200-100/5+5A LINE SIDE21 11 KV MAMUDPUR FEEDER 200-100/5+5A LINE SIDE22 11 KV BELTA FEEDER 200-100/5+5A LINE SIDE23 11 KV NAHATA FEEDER 200-100/5+5A LINE SIDE

C.T RATIO of different feeder and transformerBongaon 132/33/11 kv sub-station

SPECIFICATION [132 KV CURRENT TRANSFORMER ]

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RATED FREQUENCY 50 Hz

ELEC SPEC 635716ELEC SPEC 635716

YEAR OF MFG. 2001

STANDARD IS.2705HIGEST SYSTEM VOLTAGE KV 145INSULATION LEVELKV/KVP 275/650 KVPSHORT TIME CURRENT KA 31.5/3SECRATED DYNAMIC CURRENT (1 DYNAMIC) 78.8 KAPRATED PRIMARY CURRENT AMPS. 300

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POTENTIAL TRANSFORMER :The instrument potential transformer (PT) steps down voltage of a circuit to a low value that can be effectively and safely used for operation of instruments such as ammeters, voltmeters, watt meters, and relays used for various protective purposes. Potential transformers (P.T.) are instrument transformers. They have a large number of primary turns and a few numbers of secondary turns. It is used to control the large value of voltage. The potential transformer works along the same principle of other transformers. It converts voltages from high to low. It will take the thousands of volts behind power transmission systems and step the voltage down to something that meters can handle. These transformers work for single and three phase systems, and are attached at a point where it is convenient to measure the voltage.The magnetic core of a potential transformer usually has a shell-type construction for better accuracy. It orders to provide adequate protection to the operator, one end of the secondary winding is usually grounded.

Circuit Diagram POTENTIAL TRANSFORMER

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ADVANTAGES OF INSTRUMENT TRANSFORMER

The errors due to stray inductance and capacitance in shunt, multipliers and their leads are eliminated. The measuring circuit is isolated from the transformer. We can use low-range and accurate A.C. instruments. The length of the connecting leads from the transformer to the instrument is of lesser importance and leads may be of small cross section area. By using a clip-on type of transformer core, the current is heavy-current conductor can be measured without breaking the circuit.

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 of the divider to the line frequency makes the overall division ratio less 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 device 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.

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

transmission network.

A CAPACITOR VOLTAGE TRANSFORMER

STATION-SERVICE TRANSFORMERStation-service transformer or Earthing transformers are used to create a neutral point in a three-phase system, which provides possibility for neutral earthing. The earthing can be through an arc-suppression reactor, a neutral earthing reactor or resistor or directly in these earth transformers. Earthing transformers are usually oil immersed and may be installed outdoor. In cases where a separate reactor is connected between the earth transformer neutral and earth, the reactor and the transformer can be incorporated in the same tank. Neutral earthing transformers are normally provided in 3-phase system, which is without neutral and earth fault protection. Neutral earthing transformer is having zig-zag (interstar) winding to achieve the required zero phase impedance. In addition an auxiliary winding can also be provided to meet the requirement of auxiliary power supply in these earthing transformers. ONAN /ONAF cooling with conventional pressed steel radiators. The range includes up to 33 KV systems and as per the site requirements.

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In this Bongaon132/33/11 kv Sub-Station two nos. of Earthing transformers or station service transformer are used( 100 KVA). This transformer is simply a well designed step down transformer. The stepped down voltage is measure with a low range A.C. voltage. It orders to provide adequate protection to the operator one end of the secondary winding is usually grounded.SPECIFICATION [STATION SERVICE TRANSFORMER ]

Vector group – ZNYN – 11

B. CIRCUIT BREAKER

A circuit breaker is defined as a mechanical device capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specific time and breaking currents under specific abnormal circuit conditions such as those of short circuit. The circuit breaker serves two basic purposesSwitching during normal operating conditions for the purpose of operation and maintenance. Switching during abnormal conditions such as short circuit and interrupting fault currents. Circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic

KVA 100 TYPE OF COOLING -- ONANVOLTAGE H.V. 33000 V FREQUENCY -- 50 HzAT NO LOAD L.V. 0.415 V VECTOR GROUP -- ZNYN ~ 11AMPERES H.V. 1.75A IMPEDANCE VOLTS – 4.70 % L.V. 139.12A QUANTITY OF OIL -- 1110 LITRESPHASE H.V. 3 WEIGHT OF OIL -- 970 Kg

L.V. 3 CORE & WINDING-- 1600 KgDIAGRAM DRG NO. Pt-242 TEMP.RISE 0*C --OIL 50 & WDG 55YEAR OF MANUFACTURE 200 TOTAL WEIGHT -- 3470 Kg

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function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.Miniature low-voltage circuit breakers use air alone to extinguish the arc.Types Of Circuit Breaker :

In larger ratings, oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil through the arc.Gas (usually sulpher hexafluoride) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the strength of the sulpher hexafluoride (SF6) to quench the stretched arc.Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched a very small amount (<2–3 mm). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 35,000 voltsAir circuit breakers may use compressed air to blow out the arc, or alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc.Circuit breakers are usually able to terminate all current very quickly: typically the arc is extinguished between 30 ms and 150 ms after the mechanism has been tripped, depending upon age and construction of the device.

In this Bongaon 132/33/11 kv sub-station two types of circuit breaker are used. SF6 circuit breaker and vacuum circuit breaker. SF6 breaker are use in 132 kv sides and vacuum breaker are used in 33 kv sides and SF6 breakers.

SULPHER HEXAFLOURIDE (SF6) CIRCUIT BREAKER

In such circuit breaker, SF6 gas is used as the arc quenching medium. The SF6 is an electro negative gas and has a strong tendency to absorb free electrons. The contacts of the breaker are opened in a high pressure flow of sf6 gas and arc is stuck between them. The conducting free electrons in the arc are rapidly captured by the gas to form relatively immobile negative ions. This loss of conducting electrons in the arc quickly builds up enough insulation strength to extinguish the

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arc. The SF6 circuit breakers have been found to be very affective for high power and high voltage service.CONSTRUCTION :

It consists of fixed and moving contacts enclosed in a chamber (called arc interruption chamber) containing SF6 gas. This chamber is connected to SF6 gas reservoir. When the contacts of breaker are opened, the value mechanism permits a high pressure SF6 gas from the reservoir to flow towards the arc interruption chamber. The fixed contact is hollow cylindrical current carrying contact fitted with an arc horn. The moving contact is also a hollow cylinder with rectangular holes in the sides. To permit the SF6 gas to let out through these holes after flowing along and across the arc. The tips of fixed contact, moving contact and arching horn are coated with copper-tungsten are resistance material. Since SF6 gas is costly, it is reconditioned and reclaimed by suitable auxiliary system after each operation of the breaker.Advantages : i) Due to the superior are quenching properties of SF6. Such circuit breakers have very short arching time. ii)Since the dielectric strength of SF6 gas is 2 to 3 times that the air, such breakers can interrupt much larger currents. The closed gas enclosure keeps the interior dry so that there is no moisture problem and there is no risk of fire in such breakers because SF6 gas is non-inflammable. iii)There are no carbon deposits so that tracking and insulation problems are eliminated.

Disadvantage : i)SF6 breakers are costly due to high cost of SF6.Since SF6 gas has to be reconditioned after every operation of the breaker , additional equipment is required for this purpose. ii)SF6 is to some extent suffocating. In case of leakage in the breaker tank, this gas, being heavier than air settles in the surroundings and may lead to suffocation of the operating personnel.SPECIFICATION (SF6 CIRCUIT BRAKER( 33 KV ))

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TYPE 30 - SF6P - 25 A RATED FREQUENCY 50 Hz

RATED VOLTAGE 33 KV RATED MAKING CURRENT 62.5 Kap RATED NORMAL CURRENT 1250 A RATED SHORT TIME CU 25 KV , 3 SEC

RATED SHORT CIRCUIT BREAKING CURRENT 25KA FIRST POLE TO CLEAR FACTOR 1.5 RATED OPERATION SEQ. 0 - 0.3 SEC - CO - 3 MIN - CO RATED LIGHTNING IMPULSE WITHSTAND VOLTAGE 170 KVp

GAS WT. 1.7 Kg TOTAL WT. 750 Kg GAS PRESSURE (NORMAL) 5 Kg / CM^2 - G (AT 20 * C) GAS PRESSURE ( LOCK OUT ) 4 Kg / CM^2 - G (AT 20 * C) GAS PRESSURE ( ALARM ) 4.5 Kg / CM^2 - G (AT 20 * C) RATED COIL VOLTAGE CLOSING 220 VDC , TRIPPING 220 VDC MOTOR VOLTAGE 230 VAC AUX. CURRENT 230 A at 50 Hz RATED POWER FREQUENCY WITH STAND VOLTAGE 80 KV (R.M.S.)

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SPECIFICATION ( SF 6 CIRCUIT BRAKER (132 KV )) OPERATING MECHANISM OPENING HYDRAULIC PRESSURECLOSING HYDRAULIC PRESSURE

OPERATING MECHANISM OPENING 5OCLOSING 100NO.OF TRIP COILS TRIP CKT VOLTAGES

PRESURE(QUINCHING)(KG/CM2) PRESSURE(OPERATING)(KG/CM2) TESTING TEMP.20*C

NORMAL 7.5 bar NORMAL 340 barALARM 6.7bar ALARM 272 + 3 barLOCK OUT 6.5bar LOCK OUT >353&<273 bar

Vacuum circuit breaker:

Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the

2 COMMON FOR 3 POLES220 VOLTS

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contact material), so the arc quenches when it is stretched a very small amount (<2–3 mm). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 35,000 voltsAdvantages :

High breakdown strength for short gaps. Half-cycle interruption of power currents. Small and compact size of the interrupting unit and mechanism.

Disadvantage : Seals ware not capable of withstanding the stresses of high short-circuit currents. Electrode material gave out large amounts of gases at large and vacuum was destroyed.Current dropping resulted in severe surge voltage. At times the surfaces of the contacts produced strong welds in vacuum with normal contact pressure at normal current.SPECIFICATION (VACUM CIRCUIT BRAKER )

SYM BREAKING CAPACITY 20 KASHORT TIME CURRIENT 20 KADURATION 3SCMAKING CAPACITY 50 KPAP.F WITHSTAND 75 KVIMPULSE 170 KVPSHUNT TRIP COIL 220 VDCSPRING REL COIL 220 VDCTOTAL WIGHT 900 KGSPEC IS 13118/IEC 56C. POWER LINE CARRIER COMMUNICATION (P.L.C.C)INTRODUCTION:

TYPE PVN 36 RATED FREQUENCY 50 Hz OPERATION SEQENCY 0 - 0.3 SEC - CO - 3 MIN - CO RATED NORMAL CURRENT 1250 A RATED SHORT TIME CU 25 KV , 3 SEC

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Communication between various stations is essential for power system to maintain a co-ordination between various units and to obtain an optimised working condition. Power line carrier communication has found to be most economical and reliable method of communication for medium and long distance in a power network.GENERAL REQUIREMENTS OF POWER LINE CARRIER COMMUNICATION

Transmission of speech and data for system operation, monitoring and control. Tele-metering of measured and Tele-indication of status of switching equipment like circuit breakers etc. Transmission of carrier protection signals. Transmission of operational data for generation of reports.

Management information system of monitoring of project implementation, system hazards, power station status, equipment failure and rectification report etc... PLCC COMMUNICATION

Operating principle:

In power line carrier communication, the carrier signal is transmitted through r and b phase. This Bongaon 132/33/11 kv sub-station the carrier transmitted to the b phase. The carrier frequency used in this communication. Range from 50 kHz to 500 kHz. The carrier signal is modulated by speech signal

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and sent over power line. In this communication system amplitude modulation is not use due to its broad bandwidth requirements. The carrier signal used for the communication is not entering in power equipment in the power station. For this purpose a line trap and wave trap which is nothing but a inductance produce negligible impedance to RF carrier power frequency coupling capacitor is also connected with parallel with line trap, that it can be pass high frequency to flow through P.L.C.C.VARIOUS COMPONENTS:

LINE TRAP OR WAVE TRAP :

As discussed earlier the function of a line trap is to present high blocking impedance for the carrier frequency, while introducing negligible impedance at the power frequency. Web traps fall into two main categorise, Turned and unturned. The tuned type of line trap is essentially a parallel l-c network with variations in the tuning circuit. This sub-station(Bongaon 132/22/11 kv) here four wave trap are used. Two wave traps are connected to the incoming line KRISHNAGAR and others two wave trap are connected another incoming line JEERAT.

Coupling capacitor :

The function of the coupling capacitors is to present a high blocking impudence for the power frequency and low negligible impendence at the carrier frequency.

PROTECTIVE DEVICES :A three elements protective device is used as outdoor equipment to protect the communication system from dangerous over voltages. It usually consists of- I. ORAINAGE COIL.II. LIGHTNING ARRESTER.III. EARTHING SWITCHES. LINE MATCHING UNIT (L.M.U) :It is a unit, which is present in line current to match impedance and thus transfer maximum power to the carrier set. LINE MATCHING UNIT

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consists of the drainage coil, lightning arrester, matching transformer and earth switching. CO-AXIAL CABLE :The H.F. cable shall have a dielectric strength about 2 KW against ground. Cables are partly of single-centre-conductor type; the wire serving for carrier energy transmission and the cable heat as return path. CARRIER SET :

Its basic version the signal channel multipurpose set (ETBA) is fully equipped for duplex transmission of a speech channel, with two and four wire inputs and outputs, an AF hybrid and the input and the relay output for the associated calling and dialing signals. Current power line carrier communication devices use old technologies and are slow and simple. It can be seen that for reliable performance in a hostile communication environment, a PLCC system must use frequency-hopping communication technology to avoid superimposed charging noise, and efficient error correction method to errors encountered. The method used for coupling signal to the power line must be able to operate in a number of unpredictable channel impedance. Lastly, the modulation technique of choice is frequency shift being reliable in an environment of unpredictable phase shift.

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CIRCUIT DIAGRAM OF BONGAON SUB STATIONS. PLCC CONNECTION(CIRCUIT TO CIRCUIT)

D. LIGHTNING ARRESTERSA lightning arrester is a device used on electrical power systems to protect the insulation on the system from the damaging effect of lightning. The typical lightning arrester also known as surge arrester has a high voltage terminal and a ground terminal. When a lightning surge or switching surge travels down the power system to the arrester, the current from the surge is diverted around the protected insulation in most cases to earth. Lightning arresters are protective devices for limiting surge voltages due to lightning strikes or equipment faults or other events, to prevent damage to equipment and disruption of service. Lightning arresters are installed on many different pieces of equipments such as power poles and towers, power transformers, circuit breakers, bus structures, and steel superstructures in substations.

LIGHTENING ARRESTER

ACTIONS OF A LIGHTNING ARRESTER:-

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Under normal operation, the lightning arrester is off the line i.e. it conducts no current to earth or the gap is non-conducting. On the occurrence of overvoltage, the air insulation across the gap breaks down and an arc is formed, providing a low resistance path for the surge to the ground. In this way, the excess charge on the line due to the surge is harmlessly conducted through the arrester to the ground instead of being sent back over the line.SPECIFICATION (132 KV LIGHTNING ARRESTER)

MODEL NO. ZLAX2KC YEAR OF MFG. 2000SR .NO 10297 RATED VOLTAGE 120 KV

SYSTEM VOLTAGE 132 KV MCOV 102NOM. DISCH. CURRENT 10 KAP LD CLASS 3

PR.RELIF CURRENT 40 KA APPR. WEIGHT 12O kg

SPECIFICATION (33 KV LIGHTNING ARRESTER)MODEL NO. ZLAX2KC YEAR OF MFG. 2000

SR .NO 10446 RATED VOLTAGE 42KVSYSTEM VOLTAGE 33 KV MCOV 36 KV

NOM. DISCH. CURRENT 10 KAP LD CLASS 2PR.RELIF CURRENT 40 KA APPR. WEIGHT 40 kg

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E. BATTERY BANK & BATTERY CHARGERIntroduction:- Battery bank and battery charger system plays an important role in sub-station controlling and metering the circuits and communication system. From an auxiliary transformer AC power of three phase is taken and with the help of a rectifier ac voltage is connected into step down dc voltage this power is used to charged the battery. Battery bank is “Heart of the sub-station”.There are two methods of charging a Battery –

1. FLOAT METHOD,2. BOOST METHOD.1. FLOAT CHARGING METHOD : In this method all the cells are charged together. The auto/manual selector switch is set to auto i.e.. the voltage and current are selected automatically.2. BOOST CHARGING METHOD : In this method is used when quick charging of battery is needed. In this charging method some selected cells are charged together. The auto/manual switch is set to manual i.e., the voltage and current are set manually.

Bongaon 132/33/11 KV Sub-Station’s Battery Bank & Battery Charger:-

I visited BONGAON 132/33/11 kv sub-station and here a battery bank. Battery bank is “Heart of the sub-station”. Here 15 nos. of cells each are 2v total 15*2=30v battery are employed for the 11 kv control, protection and indication. The capacity of this Battery Bank is 75 AH and this type is YKP-7.Another side 24 nos. of cell each are 2 V total 24*2=48v Battery Bank are used for Power Line Carrier Communication (P.L.C.C) equipments. This Battery Bank capacity 100 AH and the type YKP-9.

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Other side 110 nos. of cell each 2v having total 110*2=220 v. it is used for 132/33 kv system control, protection, indication and annunciation. Capacity of this Battery Bank 200AH and type is YKP-17.All cell’s specific gravity are from 1200 to 1180. 220V DC supply has been effected through Battery. The caldyne battery charger is provide with separate Float and Boost charger. Normally float charger is parallel with battery will eater total D.C load of the system. If battery is drained for a considerable time. It is advisable to change the battery on boost from Battery charger. Incoming D.C has been brought to D.C distributer main D. C is distributed to different locations. From D.C distributer main D.C has been terminated at terminals of Bus- Coupler panel(control switch) from terminals through fuse, bus wire has been formed to feed control and annunciation sets.

Diagram (charger + battery bank):-

When AC supply available at charger : When AC supply not available at charger :

CHARGING AND DISCHARGING METHOD DIAGRAM

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SPECIFICATION (220 V FOLAT & BOOST CHARGER)

CHARGING PROCESS ( REVERSE OF DISCHARGING )

2PbSO4 + H2O PbO2 + Pb + 2H2SO4

CHARGING PROCESS ( REVERSE OF CHARGING )

PbO2 + Pb + 2H2SO4 2PbSO4 + H2O

AC INPUT SUPPLY

400 VOLTS + 10%3 PHASE 4 WIRE 50 HZ

OUT PUT FLOAT 242 VOLTS 25 AMPS. D.C CONTINOUS480 mA TRICKLE CHARGING CURRRENT

BATTERY BANK 110 NOS. LEAD ACID CELL OF200 AH. CAPACITY

OUTPUT BOOST STRING RATE 28 AMPSFINISHING RATE 14 AMPS

MAX.OPERATING TEMP.

50*C

TYPE FCBSL. NO 677/8

YEAR 2001

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SPECIFICATION (30 V FOLAT & BOOST CHARGER)

D.C is distributed through fuse

In each 132KV panels, D.C is distributed through fuse as below:-i) C.B. Remote close & local operation - Fuse FS 2, FS 3ii) Remote and Protection trip through TC 1 - F use FS 4, FS 5iii) Remote and Protection trip through TCII - Fuse FS 6, FS 7iv) Indication circuit - Fuse FS 8,FS 9

AC INPUT SUPPLY

240 VOLTS + 10%1 PHASE 2 WIRE 50 HZ

OUT PUT FLOAT 32.25 VOLTS 6AMPS. D.C CONTINOUS180 mA TRICKLE CHARGING CURRRENT

BATTERY BANK 15 NOS. LEAD ACID CELL OF75 AH. CAPACITY

OUTPUT BOOST 36 VOLTS 10 AMPS

MAX.OPERATING TEMP.

50*C

TYPE FCBSL. NO 677/8

YEAR 2001

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v) Isolator Control - Fuse FS 10,FS 11vi) Syn. Scheme socket circuit - Fuse FS 18, FS 19vii) D.C Emergency Circuit - Fuse FS 14,FS 15viii) Protection Relay Circuit - Fuse FS 16,FS 17 In each 33KV panels, D.C is distributed through fuse as below:-

i) Local closing & Remote & Protection trip - Fuse FS 2, FS 3Through TC 1 & TC 2ii) C.B Remote close operation - Fuse FS4iii) Indication Circuit - Fuse FS 8, FS 9iv) D.C Emergency circuit - Fuse FS 14, FS 15v) Protection Relay Circuit - Fuse FS 16, FS 17

F. CAPACITOR BANKA capacitor bank is a grouping of several identical capacitors interconnected in parallel or in series with one another. These groups of capacitors are typically used to correct or counteract undesirable characteristics, such as power factor lag or phase shifts inherent in alternating (AC) electrical power supplies. Capacitor banks may also be used in direct current (DC) power supplies to increase stored energy and improve the ripple current capacity of

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the power supply. While the primary power requirement of the industry and community is that of reactive Power. The reactive power invariably associated with the active power consumption of various system components and nature of loads to be controlled and compensated to a level where the primary object of economic supply of good quality active power is achieved without over burdening the sources. Depending upon specific effects of reactive power at a given point in the system, different configurations are advised. Mainly two types of compensations are involved inductive and capacitive. In the country with power shortage, inductive compensation is restricted to trunk transmission system. Mainly in case of minimize the heavy valve load the capacitor bank is needed.

Capacitor banks control the level of voltage supplied by minimizing voltage drops and absorbing energy from a line spike. The banks also provide Volt / VAR Control by switching in capacitor banks to compensate for VAR losses when large inductive loads occur, such as when air conditioners, furnaces, dryers, and/or industrial equipment start.Capacitor Bank of Bongon 132/33/11 kv sub-station :- 33kv,10MVAR Capacitor BankAdvantages of Capacitor Bank :

1. Increased voltage drop resulting in poor regulation.2. Undesirable losses rendering the line efficiency to go down to a value less than the designed3. Unnecessary utilization of thermal capabilities and burdening of lines , transformers and cables due to higher currents4. Save much power factor. And save huge amount of financial lose.5. There are large amount of harmonics introduced in the system due to pulsating loads and saturating system components which cause distortion in wave forms detrimental to certain consumer equipments.

SPECIFICATION [CAPACITOR BANK]

SERIAL NO. SR-149 TYPE NO. 09NO V. 30

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RATED OUTPUT 13260 KVAR RATED VOLTAGE 38KVCONNECTION 3-PHASE R.FREQUENCY 50 HzU.TEMP.CAT 50*C NO. OF PHASES THREEINS LEVEL 70/170 KV TOTAL WEIGHT (APPROX) 3120 KGS.DIELECTRIC P.P. IMPREGNANT N.P.C.BCAPACITOR BANK OUT DOOR DISCHARGE TIME 50V-600 SEC.

STANDARD IS: 13925 (PART 1): 1998 CUSTOMER – WBSETCL

g. BUS BARS . Introduction:An aluminum or copper conductor supported by insulators that interconnects the loads and the sources of electric power in an electric power system. A typical

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application is the interconnection of the incoming and outgoing transmission lines and transformers at an electrical substation. Bus-bars also interconnect the generator and the main transformers in a power plant. In an industrial plant such as an aluminum smelter, large bus-bars supply several tens of thousands of amperes to the electrolytic process. See also Electric power sub-station.TYPES:The major types are (1) rigid bus-bars, used at low, medium, and high voltage; (2) strain bus-bars, used mainly for high voltage; (3) insulated-phase bus-bars, used at medium voltage; and (4) sulphur hexafluoride (SF6)-insulated bus-bars, used in medium- and high-voltage systems.

In sub-station there are use ~ 132 KV transfer bus, 132 KV main bus, 33 KV main bus and 33 KV sub bus, 11 KV main bus and neutral bus.Common arrangement of bus-bars:1.Single Bus-bar 2.Single Bus-bar with Bus Sectionalizer 3.Double Bus-bar 4.Double Breaker Scheme 5.Breaker and half scheme 6.Main and Transfer Bus-bar 7.Double Bus-bar with Bypass Isolators and 8.Mesh Scheme

In this BONGAON 132/33/11 kv sub-station are used Main and Transfer Bus-bars.

h. INSULATOR.

An insulator, also called a dielectric, is a material that resists the flow of electric charge. In insulating materials valence electrons are tightly bonded to their atoms. These materials are used in electrical equipment as insulators or insulation. Their

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function is to support or separate electrical conductors without allowing current through themselves. The term also refers to insulating supports that attach electric power transmission wires to utility poles or pylons.

InsulatorSome materials such as glass, paper or Teflon are very good electrical insulators. Even though they may have lower bulk resistivity, a much larger class of materials are still "good enough" to insulate electrical wiring and cables. Examples include rubber-like polymers and most plastics. Such materials can serve as practical and safe insulators for low to moderate voltages (hundreds, or even thousands, of volts).

I. ISOLATER.

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In electrical engineering, a dis connector or isolator switch is used to make sure that an electrical circuit can be completely de-energised for service or maintenance. Such switches are often found in electrical distribution and industrial applications where machinery must have its source of driving power removed for adjustment or repair. High-voltage isolation switches are used in electrical substations to allow isolation of apparatus such as circuit breakers and transformers and transmission lines, for maintenance. Often the isolation switch is not intended for normal control of the circuit and is only used for isolation. In some designs the isolator switch has the additional ability to earth the isolated circuit thereby providing additional safety. Such an arrangement would apply to circuits which inter-connect power distribution systems where both end of the circuit need to be isolated. An isolator is an off-load device intended to be opened only after current has been interrupted by some other control device. Safety regulations of the utility must prevent any attempt to open the dis connector while it supplies a circuit.

In that sub-station(BONGAON 132/33/11 k v sub-station) Single make single break, Double make double break, isolators are used.132 kv side single make single break and 33 kv side double make double break isolator are used. Double make double break isolator are Mechanically operated and single make single break isolator are operated by electrically and mechanically.

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SPECIFICATION [ ISOLATOR 33 KV SIDE ] TYPE :RATED VOLTAGE: SYSTEM FREQUENCY:RATED CURRENT: PHASE :RATED S.T.C : WEIGHT OF ISOLATOR:

RATED INUSULATOR LEVEL:-EARTH AND BETWEEN POLES: ACROSS ISOLATING DISTANCE:

ONE MINUTE POWER FREQUENCY WITHSTAND VOLTAGE:-EARTH AND BETWEEN POLES: ACROSS ISOLATING DISTANCE:

CENTER RATING DOUBLE BREAK ISOLATOR(Manually operated )50 HZ3270.5 kg (APPROX)

170 KVp195 KVp

170 KVp195 KVp

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J. METERING & INDICATING INSTRUMENTS

There are several metering and indicating instrument (e.g. Ammeters, Voltmeters, Energy meter etc.) installed in a sub-station to maintain watch over the circuit quantities. The instrument transformers are invariably used with them for satisfactory operation.

K.AIR CONDITIONERIt is used in control room to protect the equipments from heat. It controls the desirable’s air temperature of substation control room which leads to temperature control of the equipment also.

L. OPERATING COMPUTER

There are two computers in that substation, one in control room other in office room. They are used to store various data of sub-station like load voltage fluctuations, monthly data, power consumption, load curve data etc.

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PROTECTIVE – RELAYIntroduction:

A protective relay is a device that detects the fault and initiates the operation of the circuit breaker to isolate the defective element from the rest of the system.

A Basic RELAY circuit

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Some Important Relay And Their Functions :

Buchholz Alarm Relay : In the field of electric power distribution and transmission, a Buchholz relay is a safety device mounted on some oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a conservator. The Buchholz Relay is used as a protective device sensitive to the effects of dielectric failure inside the equipment. When gas produced in the tank due to a minor fault surfaces to accumulate in the relay chamber within a certain amount (0.3Q-0.35Q) or above, the float lowers and closes the contact, thereby actuating the alarm device. Buchholz Trip Relay : In the event of a major fault, abrupt gas production causes pressure in the tank to flow oil into the conservator. In this case, the float is lowered to close the contact, thereby causing the Circuit Breaker to trip or actuating the alarm device. Over Current Relay : This relay provides protection mainly against phase to phase fault and over loading current. Pressure Release Valve (PRV) : It provides the protection against undesirable high pressure. If the pressure within the transformer tanks increases over a certain level then pressure is release through PRV. Winding Temperature Alarm : When the winding of the transformer increases more than the preselected value, then this relay provides an alarm. Winding Temperature Trip : When winding temperature of the transformer crosses a certain value then this relay trip the circuit.

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Oil Temperature Alarm : This relay gives an alarm if the temperature of the transformer increases above a certain value. Low Oil Alarm : If the level of the oil with in the main tank of the transformer decreases below a certain level then this relay provides an alarm.

Differential Relay : Generation trip E/F – HV , Bias Trip OC-LV(R) ,H/S Trip OC-LV(Y) , Differential(R) O/C-LV(B) , Differential(Y) EE-1 , Differential(B) W/O Trip, O/C-HV(R) BU Trip O/C-HV(Y) BU Alarm O/C-HV(B) W/O Alarm. Master Trip Relay : This relay ‘s functions is correlated with all other transformer relays. It operates when any other transformer relay operates.

Design and theory of these protective devices is an important part of the education of an electrical engineer who specializes in power systems. Today these devices are nearly entirely replaced with microprocessor-based digital protective relays (numerical relays) that emulate their electromechanical ancestors with great precision and convenience in application. By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays. However, due to their very long life span, tens of thousands of these “silent sentinels” are still protecting transmission lines and electrical apparatus all over the world.

There are many types of relay-

Directional Over Current Relay Auxiliary Relay High Impedance Differential Relay Directional Earth Fault Relay

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Numerical RelayAUXIALIARY, NUMERICAL AND PROTECTIVE RELAYS

IMTDL OVER-CURRENT RELAY Frequency: 50 Hz In: 1 Amp M2: 0.5Multiple of Setting 2 5 10 20Time Setting(50 Hz) 10.0 4.3 3.0 2.2

Time Setting(60 Hz) 8.5 3.52 2.45 1.81SENSESTIVE EARTH FAULT RELAY TYPE CTUM

CTUM 15ZG001A

N0130213130132019 Vx 24-250V USE Rext 2700 Ω FOR 220-250 V ONLY

Features of REL relay:-Basic protection functionally of this relay is line distance, which comprises:a) Simultaneous measurement of phase to phase and phase to earth impedance for ease type of fault and ease distancezone.b) Five Zone of operation- Z1,Z2 &Z3 are for three Zones protection.Z4 for operation Soft Z5 is for reverse direction.Scheme communication logic with current reversal and weak and in feed logic.c) Power swing Detection.Additional protection functionality such as:

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i) Phase over current, residual current and voltage functions.ii) Breaker failure protection.iii) Fuse failure and current transformer circuit supervision.iv) Single or multi pole tripping.Control:-

i) Command controlii) Auto recessing and synchronies

Monitoring:-

i) Event Recorder.ii) Disturbance Recorderiii) Fault locator.Through many functions can be used in the relay, have only Distance protection function has been used with: i) Fuse Failure supervision.ii) Loss of voltage supervision.iii) Power swing Detector.iv) Switch auto fault protection (SOTF)v) Broken conductor protection.No other back up protection is used as separate O/C & E/F protection have been provided.Any disturbance will be recorded and maximum no. of recording is 10. New disturbance will be recorded automaticallyerasing the first one .Any disturbance record can be called from memory and different information can be viewed.

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Protection Relay In Bongaon 132/33/11 kv Sub -Station :-

SL.NO RELAY LOCATION OF RELAY PROTECTION

1 2TJM10X3,IDMT 11 KV FEEDER PANELS O/C & E/F PROTECTION2 2TJM12,67A & 2TJM12,67C 132 KV FEEDER PANEL OVER CURRENT3 2TJM12,67N 132 KV FEEDER PANEL EARTH FAULT4 REL 511 132 KV FEEDER PANEL & T.B.C PANEL DISTANCE5 2TJM1051A,51B,51C 132 KV SIDE 31.5 MVA TRAN. PANEL33 KV SIDE 31.5 MVA TRAN. PANEL && BOTH 132 KV & 33 KV TRANSFORMER BUS COUPLER PANEL

BACK UP OVER CURRENT6 RADSB 132 KN TRANSFORMER PANEL DIFFERENTIAL

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7 RADHD,64REF 132 KV SIDE 31.5 MVA TRAN.PANEL33 KV SIDE 31.5 MVA TRAN. PANEL & 6.3 MVA TRANSFORMER PANELRESTRICTED EARTH FAULT

8 2TJMH104 50/51 A 33 KV FEEDER PANEL 6.3 MVA TRANSFORMER PANEL OVER CURRENT9 CTUM15,50N 33 KV FEEDER PANEL,33 KV TRANSFORMER BUS COUPLER PANEL SENSITIVE E/F

10 RXIG22,50 33 KV SIDE 31.5 MVA TRAN.PANEL SYSTEM EARTH FAULT11 RXFK2H 33 KV TRANSFORMER BUS COUPLER PANEL UNDER FREQUENCY

Relay Flags In Bongaon 132/33/11 kv Sub -Station :-

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SL NO.

REALY FLAG

LOCATION OF RELAY MEANING

1 30A IN ALL PANELS C.B oil Pr. low general lockout2 30B IN ALL PANELS SF6pressure low/general lockout 3 30C IN ALL PANELS Oil/SF6/N2 Pr. low/general lockout4 30D IN ALL PANELS Loss of N2 warning5 30E IN ALL PANELS Motor o/l relay operated6 30F IN ALL PANELS Motor M.C.B tripped7 74B TR. PANELS(33 KV) Earthing Tr. Buchholz Trip8 86L IN ALL PANELS Master Trip Relay9 95/86L IN ALL PANELS Supervise healthiness of 86 relay10 80A IN ALL PANELS Protection D.C failed 11 195 IN ALL PANELS TC1 unhealthy12 295 IN ALL PANELS TC2 unhealthy13 74A TR.PANELS(132 KV) Buchhloz trip14 74B IN ALL PANELS Buchhloz Alram 15 74C IN ALL PANELS Diverted tank oil surge relay trip 16 74D IN ALL PANELS PRV trip17 74E IN ALL PANELS H.V wdg. temp. trip18 74F IN ALL PANELS H.V WDG. Temp. Alarm19 74G IN ALL PANELS Oil temp. Trip20 74H IN ALL PANELS Oil temp. Alarm21 74J IN ALL PANELS MOG alarm22 74L IN ALL PANELS L.V WDG. Temp. Trip23 74M IN ALL PANELS L.V WDG. Temp. Alarm24 74A TR. PANELS(33 KV) Earthing Tr.Buchholz Trip25 74C TR. PANELS(33 KV) Earthing Tr.WDG. Temp. Trip26 74D TR. PANELS(33 KV) Earthing Tr.WDG. Temp. Alarm27 74E TR. PANELS(33 KV) Earthing Tr. Oil Temp. Trip 28 74F TR. PANELS(33 KV) Earthing Tr. Oil temp. Alarm 29 74G TR. PANELS(33 KV) Earthing Tr. Oil level low Alarm

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OPERATION GUIDESwitching operation is a transmission sub-station is done is a very cautions way as any mal-operation may cause power interruption of a very large area. Operation is normally of two types. They are as following: PRE-ARRANGED SHUTDOWN : It means operation of various switching equipment for a pre-decided maintenance, inspection or testing program for which a clearance from STATE LOAD DISPATCH CENTER (SLDC) is required before taking the shut-down. SLDC gives clearance of all pre-arranged and emergency shut down for generating and transmission substation all over WEST BENGAL. Pre arranged shut down may be of different types. In BONGAON 132 KV sub-station it may be characterised into the following sections.1. Shut down of a 33 KV line bay or equipment bay.2. 33 KV Bus-section shut down.3. Shut down of Power Transformer (132/33 ,31.5 MVA transformer 1 and transformer 2)4. Shut down of 132 KV line.5. 132 KV bus section shut down. EMERGENCY OPERATION : In any emergency situation like - 1. Tripping of 132 KV /33 KV line, 2. Tripping of 31.5 MVA transformers.

Switching operations are done in a fast but precise manner, in order to ensure safe operation at the same time. In emergency situation all these operations are carried out as per the adviser of SLDC. A few special point need to be kept in mind

When two 132/33 KV Transformers are running in parallel, both the earthing transformers should be kept connected to bus with Earthing Tr. Protection selector switch in Both modes. If the transformers are required to be run individually with bus section, then the switch should be kept in individual mode. In case of failure of feeder to trip on earth fault ,132 KV and 33KV Breakers of both the transformers will trip. In such case , recording relay indication, switch off all 33 KV feeders & open the faulty feeder isolator. And then Energies the transformer one after another and then load the transformer gradually. Inform SLDC and maintenance wing. In each, the transformer trips on 64R-LV, both 132 KV and 33 KV side breaker will trip. Do not energies the transformer and inform Testing wing.

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Under frequency relay has been provided in 33 KV Bus-coupler panel for tripping of all 33KV feeders. When it will be required to keep the total U/F tripping out , switch off UFS at Bus-coupler panel. If any feeder requires to be undisturbed in U/F tripping, individual switch situated inside each panel should be kept off. Under frequency tipping will be controlled as per direction of S.L.D.C. In case of any tripping of line and equipment the following operations occurs sequentially

1. Accept the bell in the control panel of the faulty line of the transformer.2. Note down the relays appeared.3. Inform to the engineer-in-charge and SLDC (in case of 132 KV line and transformer).4. Try to reset the relay, flags and bell, facia.5. In case of 33 KV feeder line may be charged after taking current from the receiving end and to be informed to engineer-in-charge. In case of 33 KV capacitor bank tripped with unbalanced relay protection should never be charged again and to be declared break down after first tripping. If the 33 KV line does not hold, the receiving sub-station should be informed immediately and the relay should be accepted and rested. The feeder may be charged for seriousness of the fault or tripping. In case the 33 KV line does not hold even after the second charging , the line must be declared break down and to be informed to the receiving sub-station through message and to be informed to the engineer-in-charge and cannot be recharged without any clearance message from the receiving end.6. In case of any tripping relays of transformer panel are to be accepted and the 33 KV feeder tripping as per load rejection scheme, may be charged or remain unchanged depending on the load condition of the other transformers. The incident has to be informed immediately to the engineer-in-charge , SLDC , control testing dept. and should not be charged without permission of engineer-in-charge , SLDC and control testing department (if required).7. In case of 132 KV line tripping the relays and facia of 132 KV line panel and the 33 KV feeder tripped in load rejection scheme are to be accepted and to be

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informed in load rejection scheme may be switched on depending on the load condition of the order line circuit. After taking permission from SLDC the line may be charged by the sending end transmission sub-station and consequently by BONGAON (receiving and sub-station) and the same to be informed immediately to engineer-in-charge as advisor. If the line does not hold the same also to be informed to the engineer-in-charge immediately.

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PROTECTIONLOAD REJECTION SCHEME :

33 KV load rejection schemes at BONGAON are done in two following ways : Incoming Trip : For BONGAON 132/33 KV sub-station there are two incoming lines. They are a. JEERAT, b. KRISHNAGAR. If any of the incoming line be tripped then the whole load has to be carried out by the remaining incoming line. If the current through that line exceeds 375 A then some selected feeders of 33 KV side will be tripped. In incoming line CR panel there is an auxiliary relay. By this relay dc voltage appears across the tripping circuit of the selected 33 KV feeders. As a result those 33 KV feeder gets tripped and total load of the sub-station is reduced to be less than 375 A or at a lower value as far as possible.Transformer Trip :

In case of transformer trip , if any of the transformer be tripped then all the selected feeders of 33 KV side are tripped , this tripping does not depend upon the amount of current carried by other transformers. By auxiliary contact of trip relay of the faulty transformer tripping of the feeders of 33 KV side occurs.GENERAL PROTECTION OF 33 KV FEEDERS:In general there are four types of protection for 33 KV feeders. They are as follows –

I. Over Current Protection.II. Earth Fault Protection.III. Protection by Master Trip Relay.IV. DC Fail Protection.OVER CURRENT PROTECTION : There is an over current relay in the feeder. When over current flows through the feeder circuit, then it trips the circuit.

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EARTH FAULT PROTECTION :

The Substation earthing system which is provided for the following purpose:- (a) Safety of Operational and Maintenance staff. (b) Discharge of Electrical charges to Ground. (c) Grounding of Overhead Shielding wires. (d) Electromagnetic Interference.PROTECTION BY MASTER TRIP RELAY :

Master trip relay operates by protection relay. When any fault occurs then the no circuit of protection relay become NC circuit and protection relay operates. By this protection relay master trip relay operates and trip the circuit. 86 R is the master trip relay.DC FAIL PROTECTION :

Almost all the tripping and closing circuits are energized by DC voltage. So supervision of that DC system ensures healthiness of the tripping and closing circuits. An AC voltage is used for the relay auxiliary contacts and the system DC is used for the relay coil. When the DC supply fails, the relay coil gets disenergized and the auxiliary contacts are closed to give supply to DC fail bell.

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ALARM ANNUNCIATION AND ACTION TO BE TAKEN BY

OPERATING PERSONEL :-

A) 132 KV Line Feeder:-

SL.No

Annunciation Action to be taken

1 Distance Protection Accept alarm. Normalize the discrepancy of control switch. Observe the display window. Distance summary will be automatically scrolled. Two latest disturbances (disturb summary 1,which is the latest and Disturb summary 2, Which is the second latest and disturb summary 3, which is the third latest) are presented with#Date and Time# Selected indication#Pre fault and post fault values,#Nature of faultRecord all information and press C button to put the window in idle mode. Rest 86 relay by pressing PB/86L. Yellow and Red LED's of REL 511 will also reset. Reset all other relays, if any. Reset annunciation. Contact SLDC. Getting their clearance close the breaker. IF it trips again, repeat the above and take action as per instruction of SLDC.2 O/C & E/F Protection Accept alarm .normalize discrepancy switch. Note relay indication. Also note whether there is any message scrolling in REL 511 window. Reset 86 relay. Reset annunciation. Take for charging on clearance from SLDC.3 CB SF6/Oil Pr.Low/N2General Lock out

Accept alarm. Check which of the relays 30A,B or C has operated. Go to switchyard to check whether SF6 pressure is below 6.5 Bar, If Oil pressure is below 253 Bar and N2 Pressure is above 345 Bar, this alarm may come. See whether pump motor starts. After some time reset 30 A,B,C relays and annunciation. If the relays do not reset, divert

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the feeder through Bus-coupler and inform Maintenance wing for further checking.4 CB /oil Presser Lowwarning closing lockout

Accept alarm. Check the switchyard and whether pump is running to up oil pressure which has fallen to 273 Bar. Try to reset after some time. If it is not reset divert the feeder through Bus-coupler. Inform Maintenance wing.5 CB Loss of SF6warning Accept alarm. Check whether SF6 pressure has fallen below 6.7 bar. If it is so, divert the feeder through bus-coupler. Inform Maintenance wing.6 CB Loss of N2 warning Accept alarm. Check whether 30D relays has operated. After some time reset the relay ,if the relay not reset check hydraulic oil pressure .If oil pressure increase above 350 bar, divert the feeder through bus-coupler. Inform Maintenance wing.7 C.B /motor O/L/MCBTrip

Accept alarm. Check whether 30 E,F relay operated. An attempt may be made to reset MCB/over load push and to run the motor. If MCB again trip or O/L, operates, do not run the motor again and inform maintenance wing.8 Distance protectionfuse fail

Accept alarm. Check the display in REL 511.Note the display message. Check up P.T fuse (fuse FS 21, FS 22, & FS 23 IN RELAY. Replace the damaged fuse. Reset annunciation and display.9 Back of ProtectionMCB trip

Accept alarm. Check whether MCB 2A in. Relay panel has tripped. Close the MCB once. IF the trip again, Inform Testing wing. The feeder need not be switched off or diverted through Bus-Coupler as main protection is healthy.10 Protection D.C supplyfail

Accept alarm. Check up whether 80 A relay has reset. Check the fuse FS 16 and FS 17 and replace. Reset 80A relay and annunciation.11 Distance protectionRelay trouble

Accept alarm. Inform SLDC and divert the feeder through Bus coupler with protection selection switch (PSS) in Feeder Position. Inform Testing Wing.12 TC1/TC2 unhealthy Accept alarm. Check whether 195 or 295 relay have reset depending on whether TC1 or TC2 is unhealthy. Divert the feeder through Bud-Coupler Keeping TTS in Transformer position Inform Maintenance Wing.13 Trip relay Coil Accept alarm. Check whether 95/86L relay has reset.

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Unhealthy Inform SLDC and divert the feeder through Bus-Coupler Keeping PSS in Feeder position. Inform maintenance wing.14 TTS position wrong Accept alarm. Check whether i) Feeder is fed through normal breaker and TTS is in Transformer position. ii) Feeder is fed through Bus-Coupler breaker and TTS is in Normal Position. Inform maintenance wing. iii) Feeder is fed through normal breaker but transfer bus is closed.Change the position of TSS or isolator and reset alarm. closing lock out15 Power Swing Blockoperated

Accept alarm. Note whether any tripping took place. If not, note the time and record of the incident .Reset annunciation.16 Distance protectionLose of voltage

Accept alarm. Check all the fuse in PT circuit FS 21, FS 22AND FS 23. Reset annunciation and display.17 Broken Conductorprotection operated

Accept alarm. Record the massage from display of REF 511.Check whether load current is available in all 3-phase. Cross check from other and also inform SLDC and taken action as per their instruction.

B) 132 KV Transformer Panel:-

SL.No

Annunciation

Action to be taken

1 Distance protection OperatedAccept alarm. Record the relay indication. Reset relays and annunciation. Do not energies the Transformer. Inform Testing Wing, SLDC and all concerned.

2 H.V O/C Protection operatedAccept alarm. Note relay indications and annunciation. Check up. Whether it has tripped on over load. It is so, energies and load the transformer .If tripping is due to fault, Inform Testing wing & SLDC.

3 HV-CB SF6 /OIL/N2 Pr.Low General Lockout4Accept alarm. Check which of the relays 30A,B or C has operated. Go toswitchyard to check whether SF6 pressure is below 6.5 Bar, If Oil pressure is below 253 Bar and N2 Pressure is above 345 Bar, this alarm may come. See whether pump motor starts. After some time reset 30 A,B,C relays and annunciation. If the relays do not reset, divert the feeder through Bus-coupler and

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inform Maintenance wing for further checking4 CB /oil Presser Lowwarning closing lock out

Accept alarm. Check the switchyard and whether pump is running to up oilpressure which has fallen to 273 Bar. Try to reset after some time. If it is not reset divert the feeder through Bus-coupler. Inform Maintenance wing.5 REF Protection Trip Accept alarm. Note Relay indication. Reset relays and annunciation. Do notenergize the transformer. Inform testing Wing & CLD and all concerned.6 CB Loss of SF6 warning Accept alarm. Check whether SF6 pressure has fallen below 6.7 bar. If it is so, divert the feeder through bus-coupler. Inform Maintenance wing.7 CB Loss of N2 warning Accept alarm. Check whether 30D relays has operated. After some time reset the relay, if the relay not reset check hydraulic oil pressure .If oil pressure increase above 350 bar, divert the feeder through bus-coupler. Inform Maintenance wing.8 C.B /motor O/L/MCB Trip Accept alarm. Check whether 30 E,F relay operated. An attempt may be made to reset MCB/over load push and to run the motor. If MCB again trip or O/L, operates, do not run the motor again and inform maintenance wing.9 Transformer Trouble Trip Accept alarm. Check and note the relay indication. If alarm is due to operation of 74E,G,L check the switchyard. Record physical temperature from wdg. And oil thermometers. Check whether fans are running. After temperature falls by 10. -15.energies and load the Transformer after resetting relays and annunciation. In case of operation of 74 A,C,D. do not energize the transformer. Inform Testing Wing and SLDC and all concerned.10 Transformer Trouble Alarm Accept alarm. Check and note the relay indication. If alarm is due to operation of 74 B, J do not charge the transformer. Inform Testing & SLDC. If it is due to operation of &74 F,H,M relays, inspect the temp. indicator, Check whether fans are running. After temp. falls by 10. C, energies and load the transformer after resetting relay and annunciation. Reduce load, If required. 15 Differential Relay Loss of Voltage 2 O/C & E/F Protection Operated 3 CB SF6/Oil Pr. Low/N2 General Lock out 4 CB /oil Presser Low warning closing lock out11 Protection D.C Supply fail Accept alarm. Check up Whether 80 A relay has reset. Check the fuse FS 16 and FS17 and replace. Reset 80 A and

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annunciation.12 TC1/TC2 unhealthy Accept alarm. Check whether 195 or 295 relay have reset depending on whether TC1 or TC2 is unhealthy. Divert the feeder through Bus-Coupler Keeping TTS in Transformer position Inform Maintenance Wing.13 Trip relay Coil Unhealthy Accept alarm. Check whether 95/86L relay has reset. Inform SLDC and divert the feeder through Bus-Coupler Keeping PSS in Feeder position. Inform maintenance wing.14 TTS position wrong Accept alarm. Check whether i) Feeder is fed through normal breaker and TTS is in Transformer position. ii) Feeder is fed through Bus-Coupler breaker and TTS is in Normal Position.Inform maintenance wing. iii) Feeder is fed through normal breaker but transfer bus is closed. Change the position of TSS or isolator and reset alarm.15 Differential Relay Loss ofVoltage

Accept alarm. Check up Whether 80 A relay has reset. Check the fuse FS 16 and FS17 and replace. Reset 80 A and annunciation. If fuse are in order, Inform Testing Wing.

C)132KV Transfer Bus Coupler Panel:-

SL.No

Annunciation Action to be taken

1 Distance protection OperatedAccept alarm. Normalize the discrepancy of control switch. Observe the display window. Distance summary will be automatically scrolled.

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Two latestdisturbances (disturb summary 1,which is the latest and Disturb summary 2, Which is the second latest and disturb summary 3, which is the third latest) are presented with#Date and Time# Selected indication#Pre fault and post fault values,#Nature of faultRecord all information and press C button to put the window in idle mode. Rest 86 relay by pressing PB/86L. Yellow and Red LED's of REL 511 will also reset. Reset all other relays, if any. Reset annunciation. Contact SLDC. Getting their clearance close the breaker. IF it trips again, repeat the above and take action as per instruction of SLDC.2 O/C & E/F Protectionoperated

Accept alarm .normalize discrepancy switch. Note relay indication. Also note whether there is any message scrolling in REL 511 window. Reset 86 relay. Reset annunciation. Take for charging on clearance from SLDC.3 CB SF6/Oil Pr. Low/N2General Lock out

Accept alarm. Check which of the relays 30A,B or C has operated. Go to switchyard to check whether SF6 pressure is below 6.5 Bar, If Oil pressure is below 253 Bar and N2Pressure is above 345 Bar, this alarm may come. See whether pump motor starts. After some time reset 30 A,B,C relays and annunciation. If the relays do not reset, divert the feeder through Bus-coupler and inform Maintenance wing for further checking. If annunciation is not reset after some time, Inform CLD for isolation of CB.4 CB /oil Presser Low warningclosing lock out

Check the switchyard and whether pump is running to up oil pressure which has fallen to 273 Bar. Try to reset after some time. If it is not reset divert the feeder through Bus-coupler. Inform Maintenance wing. If annunciation is not reset after some time, Inform CLD for isolation of CB.5 CB Loss of SF6 warning Accept alarm. Check whether SF6 pressure has fallen below 6.7 bar. If it is so, divert the feeder through bus-coupler. Inform Maintenance wing6 CB Loss of N2 Accept alarm. Check whether 30D relays has

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warning operated. After some time reset the relay, if the relay not reset check hydraulic oil pressure .If oil pressure increase above 350 bar divert the feeder through bus-coupler. Inform Maintenance wing.7 Main A.C supply fail Accept alarm. Check whether 80 A,C relay has reset. Check Fuse FS31 and FS37 and replace fuse. Reset relay and annunciation.8 C.B Motor O/L/MCB Trip Accept alarm. Check whether 30 E,F relay operated. An attempt may be made to reset MCB/over load push and to run the motor. If MCB again trip or O/L, operates, do notrun the motor again and inform maintenance wing.9 Distance protection fuse fail

Accept alarm. Check the display in REL 511.Note the display message. Checkup P.T fuse (fuse FS 21, FS 22, & FS 23 IN RELAY. Replace the damaged fuse.Reset annunciation and display.10 Back of Protection MCB trip

Accept alarm. Check whether MCB 2A in. Relay panel has tripped. Close the MCB once. IF the trip again, Inform Testing wing. The feeder need not be switched off or diverted through Bus-Coupler as main protection is healthy.11 Protection D.C Supply fail Accept alarm. Check up Whether 80 A relay has reset. Check the fuse FS 16 and FS17 and replace. Reset 80 A and annunciation.12 TC1/TC2 Unhealthy Accept alarm. Press PB05 to confirm which of the trip circuit is defective. Also check whether corresponding 195 or 295 ha operated. If TC1 is defective, check fuse FS4 and FS5 and replace IF TC2 is defective , FS6 and FS7 may be checked. In case of failure of one TC. Do not switch off the breaker, Inform Maintenance wing.13 Distance protection Relaytrouble

Accept alarm. Inform SLDC and divert the feeder through Bus coupler with protection selection switch (PSS) in Feeder Position. Inform Testing Wing.14 Trip relay Coil Unhealthy Accept alarm. Check whether 95/86L relay has reset. If the annunciation and 95/86L relay do not reset, Inform SLDC .and If any feeder or Transformer use the protection of Bus-Coupler. With the concern of SLDC, switch off thebreaker. Inform Testing Wing.

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15 PSS Position is Wrong Accept alarm. Check Whether i) PSS is in TR Position but any one Transformer bus isolator of any feederis closed. ii) PSS is in FR position but one of the Transformer bus isolators of Transformer is closed. Change the position of switch or isolator and annunciation.16 Power Swing Block Operated Accept alarm, Note Whether any tripping took place. If not, note the time and record of the incident. Reset annunciation.17 Distance protection Lose of voltage

Accept alarm. Check all the fuse in PT circuit FS 21, FS 22 and FS 23. Replace fuse. Reset annunciation and display.18 Broken Conductor protection operated

Accept alarm. Record the massage from display of REF 511.Check whether load current is available in all 3-phase. Cross check from other and also inform SLDC and taken action as per their instruction.19 Earth fault protection Accept alarm. Check whether any Tr. Supervision relay has operated. Check the switch yard and physically check the concerned Transformer Which is on Bus- Coupler. Check any other 132 KV Feeder has tripped during the incident. Ifeverything is normal, the Transformer may be energies and loaded after resetting relay and annunciation.

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Safety

Safety Precautions to be observed during Switching Operations:- Safety precautions are:-

i) Persons performing switching operations on high voltage apparatus shall do so while using rubber glovesor standing on insulated stools, platforms or rubber mats.ii) When low or medium voltage fuse which are not in series with circuit breakers are to be operated, the person shall use rubber gloves, insulted platforms or rubber mats. Where there is a possibility of arcing inthe switching operation, the operator shall use goggles or eye shields and keep his body as far as possible from the switch.iii) When replacing a low voltage fuse which is in series with the switch, the switch shall first be opened.iv) Where isolators are in use with circuit breakers, the breakers shall always be opened before opening the isolators, and conversely when the circuit is being closed, the circuit breakers shall be closed last.

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v) Any abnormality in the condition or operation of any switch shall be reported to the maintenance wing.vi) Where there is interlock system to guard against irregular sequence of operation in switching, the failure of interlock shall not be taken as an excuse for incorrect operation.

CONCLUSION

The Industrial Training at WBSETCL has been a practical experience for all of us from BONGAON Tr.(O&M) Sub-Division. We have been extremely fortunate to have got a scope to learn the various intricate details of Power Transmission from the Engineers and Officers of WBSETCL, Bongaon(132/33/11 kv sub-station). It was a firsthand experience for all of us to see the various transmission methods that are employed at a transmission sub-station. We got to understand how power from various generating station is transmitted to a transmission sub-station and the several processes that are undergone before transmitting the power to a distribution sub-station. While consuming a power we hardly cares about the fact that is the effort of a million tireless people that we get to enjoy power at home.We actually realize that power transmission is not an easy task and that it comes after a lot of hard work and loss of innumerable energy. We also got to see transformers and understand its functioning from very close quarters. We saw the functioning of circuit breakers, isolators and capacitor banks all that we had been only reading in textbooks. It was an enlightening experience to interact with the engineers who had help us to enrich our knowledge.During our visit I got a clear idea on how a sub-station works. I understood the functions of different electrical equipments like C.B, C.T , C.V.T , P.T , Bus–Bar , Lightning Arrester , Isolator , Insulator , Capacitor Bank and got some idea how a Sub-Station tackles problem like various faults multi functioning of various equipments , maintenance of different units and got a good exposure of the SWITCHYARD and its layout which help me to understand Power System analysis , its transmission and distribution aspects.

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We also learnt about PLCC and the various modes of communication that are employed in power plants and other sub-stations. In all we had an overall understanding and knowledge of the functions of a transmission sub-stations. We as student fell proud to have been associated with the WBSETCL and hope to strengthen our relationship in the near future.We sincerely thank all the staff of WBSETCL, BONGAON (132/33/11 k v sub –station) for making our training a truly enriching and enjoyable.

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