Intern Ship Report of 132Kv Grid Station

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Govt. College of Technology Burewala Project Training Report 132kv Grid Station Bosan Road Multan. B-Tech (Pass) Electrical Industrial Training Program Session 2007-2009 Affiliated With

Training Supervisor Incharge B-Tech (Pass) Electrical Sig. Sig. Muhammad Tariq Khurshid Sb. Mr. Amir Gafoor Sb. Incharge Head of Department 132kv Grid Station MEPCO Tech (Pass) Electrical Bosan Road Multan. G.C.T. Burewala.

B-

Industrial Training Officer Trainee Student 3

Sig. Sig.

Mr. Ghulam Abbas Sb Muhammad Shoaib Saleem B-Tech (Pass) Electrical B-Tech (Pass) Electrical G.C.T. Burewala. University Roll# 31

Introduction The present day electrical power system is a.c. i.e. electric power

is

generated,

transmitted

and

distributed

in

the

form

of

Alternating current. The electric power is produce at the power station, which are located at favorable places, generally quite away from the consumers. It is delivered to the consumer through a large network of transmission and distribution. system,

it

may

be

desirable

At many place in the line of power and

necessary

to

change

some

characteristic ( e.g. Voltage, ac to de, frequency p.f. etc.) of electric supply.

This is accomplished by suitable apparatus called sub-station

for example, generation voltage (11kv or 6.6kv) at the power station is stepped up to high voltage (Say 220kv to 132kv) for transmission of electric power. Similarly near the consumer’s localities, the voltage may have to be stepped down to utilization level.

This job is again

accomplished by suitable apparatus called sub-station.

Definition of sub-station :-

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“The

assembly

of

apparatus

used

to

change

some

characteristics (e.g. Voltage al to de freq. p.f. etc) of electric supply is called sub-station”.

Classification of sub-station There are several ways of classifying sub-station.

However the two

most important way of classifying them are.

I) According to service requirement :According

to

service

requirement

sub-station

may

be

level

of

classified into. 1) Transformer sub-station :Those

sub-station

which

change

the

voltage

electrical supply are called TIF s/s. 2) Switching sub-station :These sub-station simply perform the switching operation of power line.

3) Power factor correction S/S :These sub-station which improve the p.f. of the system are called p.f. correction s/s. these are generally located at receiving end s/s. 4) Frequency changer S/S :Those sub-stations, which change the supply frequency, are known as frequency changer s/s. Such s/s may be required for industrial utilization. 5) Converting sub-station :-

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Those sub-station which change a.c. power into d.c. power are called converting s/s ignition is used to convert AC to dc power for traction, electroplating, electrical welding etc. 6) Industrial sub-station :Those sub-stations, which supply power to individual industrial concerns, are known as industrial sub-station.

II) According to constructional features :According to constructional features, the sub-station are classified as : 1) Outdoor Sub-Station :For voltage beyond 66KV, equipment is invariably installed outdoor.

It is because for such Voltage the clearances between

conductor

and

the

space

required

for

switches,

C.B.

and

other

equipment becomes so great that it is not economical to installed the equipment indoor. 2) Indoor Sub-station :For voltage up to 11KV, the equipment of the s/s is installed indoor

because

of

economic

consideration.

However,

when

the

atmosphere is contaminated with impurities, these sub-stations can be erected for voltage up to 66KV. 3) Under ground sub-station :In

thickly

populated

areas,

the

space

available

for

equipment and building is limited and the cost of the land is high. Under such situations, the sub-station is created underground.

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Fig. Shows a typical underground sub-station in which transformer, switch gear & other equipments are installed. The design of underground s/s requires more careful consideration 1) The size of the s/s should be as minimum as possible.

2) There should be responsible access for both equipment & personal. 3) There should be provision for emergency lighting and protection against fire. There should be good ventilation 4) Pole-mounted sub-station :This is an outdoor sub-station with equipment installed overhead on H.pole or 4-pole structure. It is the cheapest from of s/s for voltage not exceeding 11KV(or 33KV in some cases).

Electric power is

almost distributed in localities through such sub-station.

For complete

is given bellow. Fig. Shows the typical 4-pole sub-station, it is a distribution sub-station placed overhead on a pole.

Fig No.2 shows the schematic

connections, the transformer & other equipment are mounted on H-type pole. The 11KV line is connected to the T/F (11KV/440V) through gang isolator and fuses. The lighting arresters are installed on the H.T. Side to protect the sub-station from lighting strokes. The T/F step down voltage to 400 V, 3 phase, 4 wire supply. The voltage between any two lines is 400 V & between line & neutral is 230V.

The oil ckt breaker

installed on the L.T. side automatically isolates the mounted sub-station. T/F are generally in the event of fault generally 200KVA T/F is used.

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Functions of a Substation: 1 - Supply of required electrical power. 2 - Maximum possible coverage of the supply network. 3 - Maximum security of supply. 4 - Shortest possible fault-duration. 5 - Optimum efficiency of plants and the network. 6 - Supply of electrical power within targeted frequency limits, (49.5 Hz and 50.5 Hz). 7 - Supply of electrical power within specified voltage limits. 8 - Supply of electrical energy to the consumers at the lowest cost.

Equipment Used in a Sub-Station The equipment required for a transformer Sub-Station depends upon the type of Sub-Station, Service requirement and the degree of protection desired. TIF Sub-Station has the following major equipments.

1)

Bus - bar :When a no. of lines operating at the same voltage have to

be directly connected electrically, bus-bar are used, it is made up of copper or aluminum bars (generally of rectangular X-Section) and operate at constant voltage. Fig. Shows the arrangement of Duplicate bus-bar, generally it consist of two bus-bars a “main” bus-bar and spare bus-bar.

The

incoming and outgoing lines can be connected to either b/b. With the help of a bus-bar coupler, which consist of a ckt breaker and isolators. However, in case of repair of main bus-bar or fault accusing on it, the continuity of supply to the circuit can be maintain by transforming it to the spare bus-bar for voltage exceeding 33KV, Duplicate bus-bar is frequently used.

2)

Insulators :8

The

insulator

serves

two

purpose.

They

support

the

conductor ( or bus bar ) and confine the current to the conductor. The most commonly used material for the manufactures of insulators is porcelain. There are several type of insulator (i.e. pine type, suspension type etc.) and there used in Sub-Station will depend upon the service requirement.

3)

Isolating Switches :In Sub-Station, it is often desired to disconnect a part of the

system for general maintenance and repairs. an isolating switch or isolator.

This is accomplished by

An isolator is essentially a kniff Switch

and is design to often open a ckt under no load, in other words, isolator Switches are operate only when the line is which they are connected carry no load. For example, consider that the isolator are connected on both side of a cut breaker, if the isolators are to be opened, the C.B. must be opened first.

4)

Instrument Transformer :The line in Sub-Station operate at high voltage and carry

current of thousands of amperes.

The measuring instrument and

protective devices are designed for low voltage (generally 110V) and current (about 5A). Therefore, they will not work satisfactory if mounted directly on the power lines.

This difficulty is overcome by installing

Instrument transformer, on the power lines. instrument transformer.

i) Current Transformer :-

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There are two types of

A current transformer is essentially a step-down transformer which steps-down the current in a known ratio, the primary of this transformer consist of one or more turn of thick wire connected in series with the line, the secondary consist of thick wire connected in series with line having large number of turn of fine wire and provides for measuring instrument, and relay a current which is a constant faction of the current in the line. The current transformer (CT) is often treated as a ‘‘black box.’’ It is a transformer that is governed by the laws of electromagnetic induction: Where ε = Induced voltage β = Flux density Ac = Core cross-sectional area N = Turns f = Frequency k = Constant of proportionality

ε = k β Ac Nf

CT Connections: As previously mentioned, some dev ices are sensitive to the direction of current flow. It is often critical in three-phase schemes to maintain proper phase shifting . Residually connected CTs in three-phase ground-fault scheme sum to zero when the phases are balanced. Reversed polarity of a CT could cause a ground-fault relay to trip under a normal balanced condition. Another scheme to detect zero-sequence faults uses one CT to simultaneously monitor all leads and neutral. In differential protection schemes current-source phase and magnitude are compared. Reverse polarity of a CT could effectively double the phase current flowing into the relay, thus causing a nuisance tripping of a relay. When two CTs are driving a three-phase ammeter through a switch, a reversed CT could show 1.73 times the monitored current flowing in the unmonitored circuit.

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(a) Over current and ground-fault protection scheme. (b) Differential protection scheme. (c) Zero sequence scheme with all three-phase leads going through the window of the CT. This connection, as well as the residual connection in Figure 7.17a, will cancel out the positive- and negative-sequence currents leaving only the zero-sequence current to the 50G device. Sometimes the ground or neutral lead will be included. The diagram on the right shows sheathed cable. It is important that one ground point go back through the window to avoid the possibility of a shorted electrical turn via the ground path.

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CT

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ii) Voltage Transformer :It is essentially a step - down transformer and step down the voltage in known ratio.

The primary of these transformer consist of a

large number of turn of fine wire connected across the line.

The

secondary way consist of a few turns and provides for measuring instruments and relay a voltage which is known fraction of the line voltage.

PTs

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5)

Metering and Indicating Instrument :There are several metering and indicating Instrument (e.g.

Ammeters, Volt-meters, energy meter etc.) installed in a Sub-Station to maintain which over the ckt quantities. The instrument transformer are invariably used with them for satisfactory operation.

6)

Miscellaneous equipment :In addition to above, there may be following equipment in a

Sub-Station. i)

Fuses.

ii)

Carrier-current equipment.

iii)

Sub-Station auxiliary supplies.

7)

Protective relay :“A protective relay is a device that detects the fault and

initiates the operation of the C.B. to isolate the defective element from the rest of the system”. The relay detects the abnormal condition in the electrical ckt by constantly measuring the electrical quantities, which are different under normal and fault condition. The electrical quantities which may change under fault condition are voltage, current, frequency and phase angle. Having detect the fault, the relay operate to close the trip ckt of C.B.

Buchholz Relays:The following protective devices are used so that, upon a fault development inside a Transformer, an alarm is set off or the Transformer is disconnected from the circuit. In the event of a fault, oil or insulations decomposes by heat, producing gas or developing an impulse oil flow. To detect these phenomena, a Buchholz relay is installed. The Buchholz relay is installed at the middle of the connection pipe 14

between the Transformer tank and the conservator. There are a 1st stage contact and a 2nd stage contact as shown in Fig. The 1st stage contact is used to detect minor faults. 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. The 2nd stage contact is used to detect major faults. 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. Buchholz Relay figure show below.

Fig Buchholz Relay

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Structure of Buchholz Relay

Attraction relays: Attraction relays can be supplied by AC or DC, and operate by the movement of a piece of metal when it is attracted by the magnetic field produced by a coil. There are two main types of relay in this class. The attracted armature relay, which is shown in fig ure 1, consists of a bar or plate of metal which pivots when it is att r acted towards the coil. The armature carries the moving part of the contact, which is closed or opened according to the design when the armature is attracted to the coil. The other type is the piston or solenoid relay, illustrated in Figure 2, in which α bar or piston is attracted axially within the field of the solenoid. In this case, the piston also carries the operating contacts. It can be shown that the force of attraction is equal to K1I2 - K2, where Κ1 depends upon the number of turns on the operating solenoid, the air gap, the effective area and the reluctance of the magnetic circuit, among other factors. K2 is the restraining force, usually produced by a spring. When the relay is balanced, the resultant force is zero and therefore Κ112 = K2, So that

I = K 2 / K1 =constant.

In order to control the value at which the relay starts to operate, the restraining tension of the spring or the resistance of the solenoid circuit can

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be varied, thus modifying the restricting force. Attraction relays effectively have no time delay and, for that reason, are widely used when instantaneous operations are required.

8) Circuit breaker :A circuit breaker is an equipment, which can open or close a ckt under normal as well as fault condition. It is so designed that it can be operated manually ( or by remote control) under normal conditions and automatically under fault condition. For the latter operation a relay wt. is used with a C.B. generally bulk oil C.B. are used for voltage upto 66 KV while for high voltage low oil & SF6 C.B. are used. For still higher voltage, air blast vacuum or SF6 cut breaker are used.

The process of fault clearing has the following sequence: 1- Fault Occurs. As the fault occurs, the fault impedance being low, the currents increase and the relay gets actuated. The moving part of the relay move because of the increase in the operating torque. The relay takes some time to close its contacts. 2 - Relay contacts close the trip circuit of the Circuit Breaker closes and trip coil is energized. 3 - The operating mechanism starts operating for the opening operation. The Circuit Breaker contacts separate. 4 - Arc is drawn between the breaker contacts. The arc is extinguished in the Circuit Breaker by suitable techniques. The current reaches final zero as the arc is extinguished and does not restrict again. The Trip-Circuit Fig (1) below illustrates the basic connections of the Circuit Breaker control for the opening operation

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The type of the Circuit Breaker The type of the Circuit Breaker is usually identified according to the medium of arc extinction. The classification of the Circuit Breakers based on the medium of arc extinction is as follows: (1) Air break' Circuit Breaker. (Miniature Circuit Breaker). (2) Oil Circuit Breaker (tank type of bulk oil) (3) Minimum oil Circuit Breaker. (4) Air blast Circuit Breaker. (5) Vacuum Circuit Breaker. (6) Sulphur hexafluoride Circuit Breaker. (Single pressure or Double Pressure).

Type 1 – Air break Circuit Breaker 2 – Miniature CB.

Medium Air at atmospheric pressure Air at atmospheric pressure 3 – Tank Type oil CB. Dielectric oil

Voltage, Breaking Capacity (430 – 600) V– (5-15)MVA (3.6-12) KV - 500 MVA (430-600 ) V

4 – Minimum Oil CB. Dielectric oil 5 – Air Blast CB. Compressed Air

(3.6 - 145 )KV 245 KV, 35000 MVA

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(3.6 – 12) KV

6 – SF6 CB.

(20 – 40 ) bar SF6 Gas

7 – Vacuum CB. 8 – H.V.DC CB.

Vacuum Vacuum , SF6 Gas

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up to 1100 KV, 50000 MVA 12 KV, 1000 MVA 36 KV , 2000 MVA 145 KV, 7500 MVA 245 KV , 10000 MVA 36 KV, 750 MVA 500 KV DC

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21

22

Di

23

24

25

26

Fig Type 8D.2 SF6 Gas breaker Make SIEMENS. Breaker chamber Support Hydraulic storage cylinder Operating mechanism Gas tank Adapter chamber Interrupter unit

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9) Power Transformer:ANSI=IEEE defines a transformer as a static electrical device, involving no continuously moving parts, used in electric power systems to transfer power between circuits through the use of electromagnetic induction. The term power transformer is used to refer to those transformers used between the generator and the distribution circuits, and these are usually rated at 500 kVA and above. Power systems typically consist of a large number of generation locations, distribution points, and interconnections within the system or with nearby systems, such as a neighboring utility. The complexity of the system leads to a variety of transmission and distribution voltages. Power transformers must be used at each of these points where there is a transition between voltage levels. Power transformers are selected based on the application, with the emphasis toward custom design being more apparent the larger the unit. Power transformers are available for step-up operation, primarily used at the generator and referred to as generator step-up (GSU) transformers, and for step-down operation, mainly used to feed distribution circuits. Power transformers are available as single-phase or three-phase apparatus. Transformer is a vital link in a power system which has made possible the power generated at low voltages (6600 to 22000 volts) to be stepped up to extra high voltages for transmission over long distances and then transformed to low voltages for utilization at proper load centers. This flux induces an electro-motive force in the secondary winding too. When load is connected across this winding, current flows in the secondary circuit. This produces a demagnetizing effect, to counter balance this the primary winding draws more current from the supply so that

IP.NP = IS.NS

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Fig Power Transformer

CONSTRUCTION 1- Transformer Core Construction in which the iron circuit is surrounded by windings and forms a low reluctance path for the magnetic flux set up by the voltage impressed on the primary.

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The core of shell type is sh own Fig.(2), Fig.(3), Fig.(4), and Fig.(5), in which The winding is surrounded by the iron Circuit Consisting of two or more paths through which the flux divides. This arrangement affords somewhat Better protection to coils under short circuit conditions.

In actual construction there are Variations from This simple construction but these can be designed With such proportions as to give similar electrical characteristics.

Fig (2) shell type

Fig.(3) Single phase Transformer

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Fig. (5) 3- phase Transformer Shell type

Fig. (6) 3- phase Transformer core type

‘‘E’’-assembly, prior to addition of coils and insertion of top yoke.

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Windings: The windings consist of the current-carrying conductors wound around the sections of the core, and these must be properly insulated, supported, and cooled to withstand operational and test conditions. The terms winding and coil are used interchangeably in this discussion. Copper and aluminum are the primary materials used as conductors in power-transformer windings. While aluminum is lighter and generally less expensive than copper, a larger cross section of aluminum conductor must be used to carry a current with similar performance as copper. Copper has higher mechanical strength and is used almost exclusively in all but the smaller size ranges, where aluminum conductors may be perfectly acceptable. In cases where extreme forces are encountered, materials such as silver-bearing copper can be used for even greater strength. The conductors used in power transformers are t y pically stranded with a rectangular cross section, although some transformers at the lowest ratings may use sheet or foil conductors. Multiple strands can be wound in parallel and joined together at the ends of the winding, in which case it is necessary to transpose the strands at various points throughout the winding to prevent circulating currents around the loop(s) created by joining the strands at the ends. Individual strands may be subjected to differences in the flux field due to their respective positions within the winding , which create differences in voltages between the strands and drive circulating currents through the conductor loops. Proper transposition of the strands cancels out these voltage differences and eliminates or greatly reduces the circulating currents. A variation of this technique, involving many rectangular conductor strands combined into a cable, is called continuously transposed cable (CTC), as shown in Figure

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Continuously transposed cable (CTC).

Concentric arrangement, outer coil being lowered onto core leg over top of inner coil.

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A variety of different types of windings have been used in power transformers through the years. Coils can be wound in an upright, vertical orientation, as is necessary with larger, heavier coils; or they can be wound horizontally and placed upright upon completion. As mentioned previously, the type of winding depends on the transformer rating as well as the core construction. Several of the more common winding types are discussed here..

Pancake Windings Several types of windings are commonly referred to as ‘‘pancake’’ windings due to the arrangement of conductors into discs. However, the term most often refers to a coil type that is used almost exclusively in shell-form transformers. The conductors are wound around a rectangular form, with the widest face of the conductor oriented either horizontally or vertically. Figure 2.12 illustrates how these coils are typically wound. This type of winding lends itself to the interleaved arrangement previously discussed.

Pancake winding during winding process.

Layer (Barrel) Windings: Layer (barrel) windings are among the simplest of win dings in that the insulated conductors are wound directly next to each other around the cylinder and spacers. Several layers can be wound on top of one another, with the layers separated by solid insulation, ducts, or a combination. Several strands can be wound in parallel if the current magnitude so dictates. Variations of this win ding are often used for applications such as tap windings used in load-tap-changing (LTC) transformers and for tertiary windings used for, among other things, third-harmonic suppression. Figure shows a layer winding during assembly that will be used as a regulating winding in an LTC transformer.

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Stacked pancake windings.

Layer windings (single layer with two strands wound in parallel).

Helical Windings: Helical windings are also referred to as screw or spiral windings, with each term accurately characterizing the coil’s construction. A helical winding consists of a few to more than 100 insulated strands wound in parallel continuously along the length of the cylinder, with spacers inserted between adjacent turns or discs and suitable transpositions included to minimize circulating currents between parallel strands. The manner of construction is such that the coil resembles a corkscrew. Figure 2.15 shows a helical winding during the winding process. Helical windings are used for the higher-current applications frequently encountered in the lower-voltage classes.

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Helical winding during assembly.

Tank: The tank has two main parts: a –The tank is manufactured by forming and welding steel plate to be used as a container for holding the core and coil assembly together with insulating oil. The base and the shroud, over which a cover is sometimes bolted. These parts are manufactured in steel plates assembled together via weld beads. The tank is provided internally with devices usually made of wood for fixing the magnetic circuit and the windings. In addition, the tank is designed to withstand a total vacuum during the treatment process. Sealing between the base and shroud is provided by weld beads. The other openings are sealed with oil-resistant synthetic rubber joints, whose compression is limited by steel stops. Finally the tank is designed to withstand the application of the internal overpressure specified, without permanent deformation.

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Fig Power Transformer 30 MVA 132 / 11 KV

Conservator: The tank is equipped with an expansion reservoir (conservator) which allows for the expansion of the oil during operation. The conservator is designed to hold a total vacuum and may be equipped with a rubber membrane preventing direct contact between the oil and the air.

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The dehydrating breather: The dehydrating breather is provided at the entrance of the conservator of oil immersed equipment such as Transformers and reactors. The conservator governs the breathing action of the oil system on forming to the temperature change of the equipment, and the dehydrating breather removes the moisture and dust in the air inhaled and prevents the deterioration of the Transformer oil due to moisture absorption. Construction and Operation See Fig.. The dehydrating breather uses silica - gel as the desiccating Agent and is provided with an oil pot at the bottom to filtrate the inhaled air. The specifications of the dehydrating breather are shown in Table (1) and the operation of the component parts in Table (2).

Fig. Dehydrating breather

Bushing: Having manufactured various types of bushings ranging from 6kV-class to 800kV-class, Toshiba has accumulated many years of splendid actual results in their operation. Plain-type Bushing Applicable to 24 kV-classes or below, this type of bushing is available in a standard series up to 25,000A rated current. Consisting of a single porcelain tube through which passes a central conductor, this bushing is of simplified

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construction and small mounting dimensions; especially, this type proves to be advantageous when used as an opening of equipment to be placed in a bus duct Fig.

Fig. 24 KV Bushing Oil-impregnated, Paper-insulated Condenser Bushing

Fig. 800 KV bushing

Temperature Measuring Device: Liquid Temperature Indicator (like BM SERIES Type) is used to measure oil temperature as a standard practice. With its temperature detector installed on the tank cover and with its indicating part installed at any position easy to observe on the front of the Transformer, the dial temperature detector is used to measure maximum oil temperature. The indicating part, provided with an alarm contact and a maximum temperature pointer, is of airtight construction with moisture absorbent contained therein; thus, there is no possibility of the glass interior collecting moisture whereby it would be difficult to observe the indicator Fig. (30&31). Further, during remote measurement and recording of the oil temperatures, on request a search coil can be installed which is fine copper wire wound on a bobbin used to measure temperature through changes in its resistance. Winding Temperature Indicator Relay (BM SERIES). The winding temperature indicator relay is a conventional oil temperature indicator supplemented with an electrical heating element. The relay measures the temperature of the hottest part of the Transformer winding. If specified, the relay can be fitted with a precision potentiometer with the same characteristics as the search coil for remote indication.

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Fig. (29) Construction of Winding Temperature Indicator Relay

Fig (30) Oil Temperature Indicator

Fig. (31) Winding Temperature Indicator

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The temperature sensing system is filled with a liquid, which changes in volume with varying temperature. The sensing bulb placed in a thermometer well in the Transformer tank cover senses the maximum oil temperature. The heating elements with a matching resistance is fed with current from the Transformer associated with the loaded winding of the Transformer and compensate the indicator so that a temperature increase of the heating element is thereby proportional to a temperature increase of the windingover-the maximum- oil temperature. Therefore, the measuring bellows react to both the temperature increase of the winding-over-the-maximum-oil temperature and maximum oil temperature. In this way the instrument indicates the temperature in the hottest part of the Transformer winding. The matching resistance of the heating element is preset at the factory.

Pressure Relief Device: When the gauge pressure in the tank reaches abnormally To 0.35-0.7 kg/cm.sq. The pressure relief device starts automatically to discharge the oil. When the pressure in the tank has dropped beyond the limit through discharging, the device is automatically reset to prevent more oil than required from being discharged.

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Fig. (32) Pressure Relief Device

PARALLEL OPERATION OF THREE-PHASE TRANSFORMERS: Ideal parallel operation between Transformers occurs when (1) there are no circulating currents on open circuit, and (2) the load division between the Transformers is proportional to their kVA ratings. These requirements necessitate that any - two or more three phase Transformers, which are desired to be operated in parallel, should possess: 1) The same no load ratio of transformation; 2) The same percentage impedance; 3) The same resistance to reactance ratio; 4) The same polarity; 5) The same phase rotation; 6) The same inherent phase-angle displacement between primary and secondary terminals. The above conditions are characteristic of all three phase Transformers whether two winding or three winding. With three winding Transformers, however, the following additional requirement must also be satisfied before the Transformers can be designed suitable for parallel operation. 7) The same power ratio between the corresponding windings. The first four conditions need no explanation being the same as in single phase Transformers. The fifth condition of phase rotation is also a simple requirement. It assumes that the standard direction of phase rotation is anti-clockwise. In case of any difference in the phase rotation it can be set right by simply interchanging two leads either on primary or secondary. It is the intention here to discuss the last two i.e., sixth and seventh conditions in detail.

Bus-Bar Schemes used in a sub station :Bus-Bar Isolator:

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1 2 3 4 5 6 7

– – – – – – –

Bus-Bar Isolator. (Disconnector Switch) Maintenance Earth Switches. CT's For Transformer protection. Circuit Breaker. CT's for Bus-Bar protection and metering. Maintenance Earth Switches. Transformer Isolator.

Maintenance Earth Switches. (Transformer E.S) Drawing

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1 – Bus-Bar Isolator. (Disconnector Switch) 2 – Maintenance Earth Switches.

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3 – CT's For Bus-Bar protection and metering. 4 – Circuit Breaker. 5 – Maintenance Earth Switches.

Bus Section:

1 2 3 4 6 7

– – – – – –

Bus-Bar Isolator. (Disconnector Switch) Maintenance Earth Switches. CT's For Bus-Bar protection and metering. Circuit Breaker. Maintenance Earth Switches. Bus-Bar Isolator.

Bus coupler:

Battery: 45

A battery is a device that converts the chemical energy contained in its active materials directly into electric energy by means of an electrochemical oxidationreduction (redox) reaction. In the case of a rechargeable system, the battery is recharged by a reversal of the process. This type of reaction involves the transfer of electrons from one material to another through an electric circuit. In a no electrochemical redox reaction, such as rusting or burning, the transfer of electrons occurs directly and only heat is involved. As the battery electrochemically converts chemical energy into electric energy, it is not subject, as are combustion or heat engines, to the limitations of the Carnot cycle dictated by the second law of thermodynamics. Batteries, therefore, are capable of having higher energy conversion efficiencies.

Electrochemical operation of a cell (discharge). The discharge reaction can be written, assuming a metal as the anode material and a cathode material such as chlorine (Cl2), as follows: Negative electrode: anodic reaction (oxidation, loss of electrons) Zn → Zn2_ _ 2e Positive electrode: cathodic reaction (reduction, gain of electrons) Cl _ 2e → 2Cl_ 2 Overall reaction (discharge): Zn _ Cl → Zn2_ _ 2Cl_(ZnCl ) 2

Charge: During the recharge of a rechargeable or storage cell, the current flow is reversed and oxidation takes place at the positive electrode and reduction at the negative electrode, as shown in Fig. 1.2. As the anode is, by definition, the electrode at which oxidation occurs and the

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cathode the one where reduction takes place, the positive electrode is now the anode and the negative the cathode. In the example of the Zn/Cl2 cell, the reaction on charge can be written as follows: Negative electrode: cathodic reaction (reduction, gain of electrons) Zn2_ _ 2e → Zn Positive electrode: anodic reaction (oxidation, loss of electrons) 2Cl_ → Cl _ 2e 2 Overall reaction (charge): Zn2_ _ 2Cl_ → Zn _ Cl2

Charging of battery batteries joint

Ban dale of

Battery Room

Batteries Room: Batteries are very important part of the grid. It works as a standby storage device, that provides D.C power to the grid’s dc supply equipment in case of failure of A.C supply. Different protection devices i.e relays, circuit breakers and other control equipment of relay room, 11KV control room, 132KV control room and yard operates on 110 D.C volt supply

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that is normally supplied by a rectifier. In case of failure of A.C power batteries works as a standby source of 110 D.C supply. No. of cells installed = 55 2 Volt/cell, 150 AH Total Output Voltage = 110 Volt. Made by EXIDE Pakistan LTd. Energized on 13-01-1992 Recommended Float Voltage = 202 Volt/cell at 25 C Recommended Boost Voltage = 2.4 Volt/cell Minimum 2.8 Volt/cell Maximum Total Float Voltage = 121 Volt

Skills Learnt:To understand the purpose of Grid Station, Breakers, Relays, Switching, Transformer, CT, PT, Batteries as well as many more things which used at the 132KV Grid Station Bosan Road Multan.

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Training Supervisor Trainee Student Sig. Sig. Muhammad Tariq Khurshid Sb. Muhammad Shoaib Saleem Incharge B-Tech (Pass) Electrical 132kv Grid Station MEPCO University Roll# 31 Bosan Road Multan.

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Imp 55

La 56

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Li 58

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