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O & M OF SUB-STATIONEQUIPMENT

NARENDER KUMAR

ME MBA MIE

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SUB STATION

LOCATION WHERE A GROUP OF ELECTRICALEQUIPMENT IS CONCENTRATED FORTRANSFORMATION OF ELECTRICAL POWER

FROM ONE VOLTAGE LEVEL TO OTHER ORFROM ONE FORM TO ANOTHER LIKE AC TODC ETC.

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CLASSIFICATIONOF SUB STATIONS

LT DISTRIBUTION SUB-STATION p & p

Caters to the consumers of 440V and 230V rating,by means of 3 phase, 4 wire system.

HT / PRIMARY DISTRIBUTION SUB-STATIONCATERS TO 11 KV, 33 KV & 132 KV LOADS

TRANSMISSION SUB STATION400/220,22/132,132/33 KV PRIMARYTRANSMISSION SUB STATIONGENERATION SUB STATIONS.

INDOOR/OUTDOOR SUB STATIONS.

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OUTDOOR SUB-STATION Vs INDOOR SUB-STATIONS Minimal constructional works.

Less quantity of building materials.

Installation cost of switchgear is low.

Reduced possibility of faults due to enhanced space betweenequipments.

Minimum erection time.

Fault location easier due to enhanced visibility.

Provision for extension can be provided.

While these are positive points in favor of outdoor sub-stations, there area few negative points.

Require large area

Accumulation of dust and dirt and pollutants over insulators andcontacts.

Operational difficulties during rains.

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Selection criteriaA Number of factors are to be considered while

designing a sub-station, the most important ofwhich are : Capacity (based on load studies)

Type whether outdoor or indoor

Method of control

Number of outgoing/incoming feeders Reliability

Safety

Flexibility

Simplicity Space availability

Cost

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VARIOUS EQUIPMENT IN THESUB-STATION

1.BUS BAYS

2.LAS

3.AB SWITCHES/ISOLATORS

4.CIRCUIT BREAKERS

5.INSTRUMENT TRANSFORMERS

6.POWER TRANSFORMERS

7.AUXILIARY SUPPLIES

8.EARTHING

9.STRUCTURE

10.CONTROL PANELS, AC/DC PANELS

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11.ANNUNCIATION SYSTEM AND PANELS12.BATTERY BANK

13.BATTERY CHARGERS

14.STATION TRANSFORMERS

15.RELAYS

16.CAPACITOR BANKS

17.CONTROL ROOM

18.MARSHALLING PANEL

19.SCADA PANELS

20.LIGHTING/YARD LIGHTING

21.COMMUNICATION EQUIPMENT

22.FENCING

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BUS BAY

The location of entry and exit points of the 3 phases of a circuit into/froma Bus is called a Bus Bay.

The connection from the Bus to the Equipment is made of aluminum

stranded conductor or some cases, panther by means of a clamp, made ofAluminum alloy, designed to hold the jumper according to its size.

The term Bus is used for three conductors that acts as a junction forentry and exit of various circuits.

The conductors of the Bus are generally made of standard aluminumconductors of size Panther/Dog, or of Copper/Aluminum pipe40mm/80mm diameter.

Each 33 KV and 11 KV Bay is of dimension 4.7 meters and the length ofthe Bus depends on the number of circuits to be accommodated.

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LIGHTING ARRESTORA Protective equipment that is erected at the entry point of a line, this equipment

prevents a surge Voltage entering a sub-station and damaging the associatedequipments. Surge Voltages are created either due to lightning or switchingoperations

LINE ISOLATOR/BUS ISOLATOR

Theses are the isolating switches that can be operated electrically or manually.Mostly manual operation is the norm that is followed here. The isolators can be ofsingle break type or double break type and are designed based on the ratedcurrent to be carried.

A Bus Isolator connects the bus to the equipment by means of jumpers

and clamps.

A line isolator connects the line to the equipment by similar means.

A line isolator has and extra fitting in the form an earth switch, that

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CIRCUIT BREAKER A Circuit Breaker interrupts the flow of current in a Circuit.

Interruptions are caused either in intentionally, in order toisolate a system or the interruption is caused automaticallydue to a fault.

Quenching of an arc that is generated at the time of a Circuitopening is the primary function of a Circuit breaker.

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Circuit Breakers can be divided on the basis of the quenchingmedium that is used.

The mediums that are used are

High pressure air

SF6 gas

Transformer oil

Vacuum

In most of the 33KV Sub-stations, the vacuum type ofbreakers are used, while SF6 gas breakers are used in EHTSystem.

The air break circuit breakers and oil circuit breakers arebeing phased out gradually owing to increasing repair andmaintenance costs.

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The circuit breakers can also be divided based on the mechanism itadopts.

The operating mechanism is an absolute necessity and anintegral part of a breaker, in view of the speed that is required toopen or close the contacts in a breaker.

The breakers can be divided again based on the operatingmechanism Pneumatic type where compressed air under high pressure is used to

operate the contacts. The pressures used vary from design to design andwill be between 13 to 15 atmospheres.

Hydraulic breakers in which a hydraulic liquid by trade nameAeroShellisused. This liquid is maintained at a pressure of 300 psi in order to operatethe contacts.

A spring charge mechanism in which the stored energy of a spring is usedto activate the moving contacts.

While all the three types of mechanisms are used in EHT sub-stations, only spring charge mechanism is used in 33/11 KV sub-stations.

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CURRENT TRANSFORMERS

Current Transformers are equipments designed to transform thecurrent from a high value (Primary Current) to low value(Secondary current).

The standards of low value that are in use are 1 Amp and5 Amps called the secondary current.

The need for secondary current is to help in measurement ofprimary current which is made possible by the linearrelationship between the primary and secondary circuits.

One other function of a CT is to help protecting the system andequipments from high fault currents by isolating the faultysection.

CTs are rated for different current ratings and aremanufactured as per specifications.

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A Single CT can be used for connecting to any one of3 different rated Currents and is calledAvailable Ratio.

The single rated current to which it is connected is called

Connected RatioorAdoptedRatio.

The purpose of this available ratio is to help alter the primaryconnection from one rated current to another one, withoutthe need for changing the CT or disconnecting the Cables,there by reducing the time to undertake the change.

A CT has one primary coil and a number of secondary coilsdesigned as per specifications and purpose.

The CTs are always connected in series

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POTENTIAL TRANSFORMER : (P.T.)

A PTs role is same as that of a C.T.

It measures Voltage in a system

In addition to measurement, the P.T. secondary Voltage is also made use of, for distance protection in EHT Systems.

P.T. supply is also utilized for measuring energy consumed or sent, thatfacilities billing and energy audit,

The secondary Voltage in a potential transformer in Vogue is 110V, phase tophase, irrespective of the primary voltage, like 400 KV, 220KV, 132KV, 33KV& 11KV.

The P.T.s are generally connected in parallel.

For industrial consumers P.Tsand CTsare combined together to form a singleunit. This helps in sealing of the unit in order to avoid tampering

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POWER TRANSFORMER

Power transformers are equipments that transform the powerat a given voltage to another

Power transformers consist of two windings primary andsecondary and are designed on the basis of specificrequirements and purpose.

The windings are placed in an insulating medium, i.e., thetransformer oil filled in a tank for the purpose.

The purpose of oil is to insulate and cool the windings, sincethe windings of undergo a temperature rise while in service. The transformers are provided with OLTCs (on load tap

changes) which are operated to raise of lower the voltages asper requirement.

The capacity of a transformer is measured in terms ofKVA/MVA, and every transformer can only take loadcommensurate with its capacity.

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When load grows beyond the capacity of a single transformer,additional transformer of similar capacity is provided, thecharacteristics of the additional transformer should be similar tothat of the existing transformer to facilitate parallel operation.

The transformer is a costliest equipment in a sub-station andhence a number of protective devices such as Temp, Alarm,Bucholtz, and differential protection in addition to the overloadand earth fault relays.

These relays are set to isolate the transformer in the event ofan abnormal fault condition, which may harm the equipment ifnot isolated.

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The transformers upto 8.0 MVA capacity are provided with a groupcontrol breaker on HV side and individual breakers on LV side. In afew cases, group control breakers on HV side is dispensed with andinstead, a HG fuse is used on the HV side.

The life of a transformer depends on its conditions of operationover loaded transformers, transformers operating under hightemperatures tend to loose their life span.

Frequent faults on lines exerts additional pressures on the windingof the transformers. Both electrical and mechanical forces comeinto play.

The quality of the oil in a transformer also contributes to the life oa transformer.

Transformer oil is hence tested once in 6 months for its BreakDown Voltage (BDV), which is a measure of the insulation value ofthe oil.

Transformer oil is subjected to filtration in case of low BDV valuesor once in a year. In addition to these test the transformer oil is also subjected to

various other tests such as tan delta test, DGA test and acidity test

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AUXILLIARY SUPPLY

A Sub-station requires supplies such as 440V & 230V AC supplyand 230V, 48V or 24V DC supply depending upon the DC

Voltage rating of auxiliaries to meet other types of loads whichoperates under these voltages.

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A.C. SUPPLY

AC Supply in a sub-station is used for spring charge motors,

OLTC motors, lighting circuits, charger supply etc.,.

AC auxiliary supply is availed from a distribution transformerof 11 KV/440 V rating of adequate capacity.

The AC supply is distributed to various loads by means of a

AC Distribution board which is provided with a number ofoutlets with independent fuse controls.

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D.C.SUPPLY DC Supply is required basically to isolate the faulty feeders from the

healthy system. This process is carried out by tripping the breaker

of a faulty circuit. The tripping is carried out by means of a DCSupply, which is fed to the tripping coil in a breaker.

DC supply is generally obtained from a charger unit, which convertsAC supply to DC supply.

In addition to the charger unit, a back up source of DC supply is aset of batteries which feed the DC loads as end when AC supplyfails for some reason or the other.

Maintenance of the uninterrupted DC supply is crucial for a sub-station since a fault can occur at any movement and loss of DC

supply would be a LUXURY

1

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1.structure2.insulators3.control panels4.battery and batter charger

5.ac/dc panels6.annunciation panels7.station transformers8.capacitor banks9.relays.

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OPERATIONOperation in a sub-station involves : Supervision of equipments and their critical operating recommendations. Measurement of electrical parameters. Inspection and reporting. Circuit isolation activities.

Reclosing functions for breakers after fault clearance. Load transfer coordination. Communication with feeding sub-station. Load control Voltage control Batteryl voltage and specific gravity measurements and general check-up. Issue of line clears.

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MAINTENANCE : A sub-station performance lies in its effective maintenance activities. Effective maintenance in turn results in minimum interruption to the

consumers, and a low down time always results in increased revenue for theutility.

One should aim at Maintaining the utility system equipment as close to brandnew condition as possible.

Complete all preventive and predictive maintenance work regularly onscheduled basis without exceeding the point of the diminishing returns oninvestmentfor the labor, tools & materials.

Maintenance activities are of two types Preventive maintenance (PM)

Preventive maintenance is the scheduled inspection or servicing of equipmentat specific times frames as advised by the manufacturer, in order to retain thefunctional capabilities of the unit that is serviced.

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CORRECTIVE MAINTENANCE : CM or Break down maintenance as is popularly called, is the

unscheduled repair of a failed equipment to restore its

functional capabilities. CM is generally found to be timeconsuming and uneconomical in terms of operating cost. CMis generally resorted to only when the equipment fails eithertotally or partially.

The goal hence, shall be to develop a maintenance plan thatwill offer reliability in function and at the same time fulfills thebudgetary goals.

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CORRECTIVE OR BREAK DOWN MAINTENANCE

Consists of the actions taken to restore a failed system tooperational status.

The cost of corrective maintenance is substantially higher andmay result in short term/long term interruptions.

The C.M. needs to be performed at unpredicted intervals

since there is no advance intimation of a system componentfailure.

The Three steps in which it is carried out are : - Diagnosis of the problem

Repair & replacement of faulty component. Rectification for a successful repair by checking its operation

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GENERAL OBJECTIVES OF UTILITY MAINTENANCE : Reduce utility and energy costs.

Control inventory and assets

Extend life of the equipment.

Increase productivity. Improve maintenance responsiveness.

Improve facility appearance.

Reduce facility and personal liability risks.

Anticipate scheduled maintenance.

ELEMENTS OF A UTILITY MAINTENANCE PLAN :

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S O U CThe Plan Should, at the minimum, target the following goals :

Assess and minimise risks. Ensure operational reliability.

Identify equipment included in the programme. Ensure testing, inspection and maintenance of critical components. Provide utility system plans and layouts to personnel operating the

system. Investigate utility failures and identify necessary corrective actions. Provide training and education to all personnel responsible for operation

and maintenance of the system. Develop performance standards for personnel, equipment operation,

maintenance and repair. Develop emergency procedures detailing the initial response to utility

failures.

The e a e q ite a fe mode n technologies a ailable to

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There are quite a few modern technologies available todevelop maintenance program to meet individualrequirements such as :

Infra red thermography Ultra sonic and vibration detection

Breaker Diagnostic maintenance

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THANK YOU