O & M MANUAL_ volt amp

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    A GUIDE TO INSTALLATION , COMMISSIONING, OPERATION AND

    MAINTENANCE OF OIL FILLED TRANSFORMERS

    INDEXPAGE NO.

    x INTRODUCTION 3

    1. TRANSPORT &HANDLING. 4

    1.1. GENERAL

    1.1 TRANSPORT.

    1.2 UNLOADING & HANDLING1.3 STORAGE.

    2. FITTINGS & ACCESSORIES . 6

    2.1 RATING & TERMINAL MARKING PLATE2.2 TAP CHANGING ARRANGEMENT.

    2.2.1 OFF-CIRCUIT TAP CHANGING SWITCH.

    2.2.2 OFF- CIRCUIT RATIO CHANGING LINKS.2.2.3 ON LOAD TAP CHANGER.

    2.3 EARTHING TERMINALS.2.4 LIFTING LUGS.

    2.5 VALVES.2.6 BUSHINGS.

    2.6.1 OIL COMMUNICATING TYPE BUSHINGS.

    2.6.2 CONDENSER BUSHINGS

    2.7 CABLE BOXES.2.8 BUS-DUCT TRUNKINGS.

    2.9 MARSHALLING BOX.

    2.10 BUCHHOLZ RELAY.2.11 RADIATORS.

    2.12 SILICA GEL BREATHER.

    2.13 MAGNETIC OIL LEVEL GAUGE.

    2.14 OIL TEMPERATURE INDICATOR.2.15 WINDING TEMPERATURE.

    3. INSTALLATION & COMMISSIONING. 13

    3.1 GENERAL

    3.2 INSTALLATION.3.2.1 LOCATION

    3.2.2 FOUNDATION.3.2.3 PROVISION FOR OIL DRAINING.

    3.2.4 ASSEMBLY OF DISMANTLED COMPONENTS.

    3.2.4.1 MAIN TANK

    3.2.4.2 BUSHINGS.

    3.2.4.3 CONSERVATOR & M.O.G3.2.4.4 BUCHHOLZ RELAY.

    3.2.4.5 BREATHER.3.2.4.6 RADIATORS.

    3.2.4.7 MARSHALLING BOX.3.2.4.8 CABLE BOX.

    3.2.4.9 OTHER FITTINGS.

    3.2.5 OIL SAMPLING & FILTRATION.3.2.6 AIR RELEASE.

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    INDEX

    3.3 COMMISSIONING 163.3.1 PRE-COMMISSIONING TESTS.3.3.1.1 RATIO TEST.

    3.3.1.2 VECTOR GROUP CHECK TEST.3.3.1.3 MAGNETISING CURRENT TEST.

    3.3.1.4 MAGNETIC BALANCE TEST.

    3.3.1.5 MEASUREMENT OF INSULATION RESISTANCE.

    3.3.1.6 SHORT CIRCUIT TEST.

    3.3.1.7 PARALLEL OPERATION.

    3.3.2 OTHER RELEVANT DETAILS.3.3.3 CHECK POINTS.

    3.3.4 ENERGISING.

    3.3.5 TOOLS & INSTRUMENTS.3.3.6 COMMISSIONING REPORT.

    4. OPERATION & MAINTENANCE. 274.1 OPERATION.4.2 MAINTENANCE.

    4.2.1 GENERAL.

    4.2.2 OIL.

    4.2.3 CORE & WINDING.4.2.4 O.L.T.C.

    4.2.5 CONSERVATOR & M.O.G.

    4.2.6 BREATHER.4.2.7 BUCHHOLZ RELAY.

    4.2.8 PIPE WORK.

    4.2.9 EXPLOSION VENT.

    4.2.10 GASKETS.

    4.2.11 TEMP. INDICATORS.4.2.12 BUSHINGS.

    4.2.13 EXTERNAL CONNECTIONS.

    5.0 MAINTENANCE SCHEDULE. 295.1 TROUBLE SHOOTING.

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    INTRODUCTION

    The purpose of this instruction manual is to guide the User on Installation , Commissioning,

    Operation and Maintenance of Power & Distribution Transformers manufactured by us.

    While general guidance is given in this manual, for further details reference should be made to the

    following:

    SPECIFICATION NO. TITLE

    I.S. 2026 parts I TO IV Power Transformers.

    I.S.3639 Fittings & Accessories for power Transformers.I.S. 335 New insulating Oil for Transformers & Switchgears.

    I.S. 10028- parts I to III Code of Practice for selection, Installation & maintenance of

    Transformers.

    I.S. 1866 Code of Practice for maintenance of Insulating Oil.I.S. 2099 Bushings.

    I.S.3347 Dimensions of Porcelain Transformer Bushings for use inlightly polluted atmosphere.

    I.S. 6792 Method of determination of electric strength of insulating oil.

    I.S. 8468 On- Load Tap Changers.I.S.8478 On Load Tap Changers Application Guide.

    I.S.1646 Code of Practice for fire safety of Building (General)Electrical

    Installation.I.S.3043 Code of Practice for Earthing.

    I.S 2705 Current Transformers.

    I.S. 3637 Specification for Gas-Operated Relay.I.S. 6600 Guide for loading of oil immersed transformers.

    I.s. 6272 Industrial Cooling Fans.

    - C.B.I.P.-Manual on Transformers.

    - Indian Electricity Rules.

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    1. TRANSPORT & HANDLING

    1.1 GENERAL:All our Transformers are designed, manufactured and tested with due care. Routine Tests in accordance with

    I.S. 2026/I.S. 1180 are carried out on all transformers. They will give long and trouble-free service when

    properly installed, operated and maintained. In case anything abnormal occurs during the service, reference

    should be made to us giving complete particulars as to the nature and the extent of abnormality together with

    the name-plate particulars in order to assist identification of the transformers. As efforts are being constantlymade to improve designs and services, the transformers supplied may differ in minor details from the data here

    under. Any additional information, if required, can be supplied on request.

    1.2 TRANSPORT.

    Transformers of rating 1250 KVA and above are generally dispatched with their external fittings dismantled tothe external required and weather-proof blanking plates are provided wherever necessary prior to dispatch.

    External arrangement drawings indicate various accessories, dismantled for transport, with asterisks against list

    of fittings with an appropriate note.

    All parts which are dismantled are packed either separately or in a group as appropriate. Each packing case ismarked or numbered and is included in the packing list alongwith the description of contents.

    Transformers are dispatched in one of the following modes :

    (a) Completely filled with oil.(b) With oil covering coils and top yoke (approx. 40mm below top cover). Oil for topping up, filling in

    radiators etc, is dispatched separately in sealed drums. Space above Oil level is filled with air at normal

    atmosphereic pressure.Accessories such as conservator, radiators, oil filled bushings etc., which are dispatched in different packages

    are given numbers and these numbers are indicated together with contents, in the packing list.

    1.3 UNLOADING & HANDLING :

    On receipt at site, transformers should be unloaded by means of crane or lifting devices of adequate capacity. Alllifting lugs must be used to avoid unbalanced lifting and undue stresses on lugs. Lifting lugs provided for partial

    lifting (e.g. for active part, conservator etc.) must not be used for lifting complete transformer. Parts other than

    lifting lugs must not be used for lifting. While slinging care should be taken to avoid sling touching other parts.

    (Refer Fig. 2.1)

    All other parts and case containing accessories should be unloaded by using lifting lugs. They should be handled

    in their upright position as indicated on the cases.

    Transformers should be carefully examined for transit damages. External damages could be indicative of severe

    internal damages. Following should be particularly observed:

    (a) Dents on tank wall.

    (b) Damage to protruding parts like valves, sight glass etc.(c) Oil leakage around or through welds.

    Packed components should be carefully unpacked and all parts/components received should be examined for

    transit damages.

    Rollers should be used for shifting the transformer from one place to other. Roller axles or radiators should not be

    slinged for the purpose of towing. Pulling holes provided on the tank for this purpose should only be used. .

    Transformers of higher ratings are provided with four jacking pads. (Ref. Fig. 20). Each jacking pad is designed to

    take approximately 25% of the total load. Under no circumstances, jacks should be used anywhere else other than

    these specially provided pads.

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    1.4 STORAGE:

    On receipt of the Transformer at site, it is desirable to install and commission the transformer with minimumdelay. In case, this is not possible, the silica-gel breather should be fitted. The breather incorporates an oil sealing

    device which must be filled with oil to the marked level to be effective. A periodic watch should be kept on the

    silica-gel breather to ensure that the gel is blue. The gel should be replaced or dehydrated immediately on its

    turnings pink.

    - It is advisable to check the condition of silica gel during storage atleast once a week and Break.

    Down Voltage (BDV) of oil atleast once in a month and should be maintained at a level of 50K. Itis desirable to keep on the transformer energized even at low voltage so that the oil tempertureis

    about 10 degree to 15 degree C higher than the surrounding ambient temperature

    - Even during temporary storage, it is recommended to mount rollers by jacking up thetransformers to enable free flow of air underneath.

    - The tap changer should be operated at six monthly intervals. Two or three runs from one end of

    the range to the other are considered sufficient.- Accessories like bushings, buchholz relay, dial type temperature indicator, terminal box, radiator,

    all pipe work, should be stored indoors till such time they are not required. If they are not stored

    properly, they are likely to be damaged. The conservator pipe work and radiators are dispatched

    with blanking plates and these are to be stored with their blanking plates, in position.

    If these are stored for longer period like six months or so, it is advisible to flush them with clean transformer oilbefore use.

    OIL DRUMS.If oil received in drums is not likely to be used immediately, the drums should be stored in a covered space where

    temperature variation is minimum. If it is necessary to store the drums outside, adequate protection must be provided.

    Drums should not be stored standing on end but should be placed on their sided with the bung at 45degree downwards.

    It is very important that drums are stored free from fire and explosion hazards.

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    2. FITTINGS & ACCESSORIES

    2.1 Rating & Terminal marking Plate : (R & D Plate)

    The transformer is supplied with rating and terminal marking plate made out of non-corrosive

    metal. The plate contains information concerning the rating , voltage ratio, weights, oil

    quantity vector group, etc. The plate also includes unit Sr. No. and year manufacturing.

    2.2 Tap changing arrangement:2.2.1 Off-Circuit Switch.

    The transformer is normally fitted with an off-circuit tap changing switch to obtain required voltage ratio. It can

    be hand-operated by switch handle mounted either on tank or on the tank side . The locking device is fitted tothe handle to lock in any tap position. The switch mechanism is such that it can be locked only when it locked

    in its position and not in any intermediate position.

    THE TRANSFORMERS MUST BE ISOLATED FROM ALL LIVE LINES, BEFORE OPERATING

    THE SWITCH.

    Operating the switch when transformer is energized , will damage the switch contacts due to serve arcing

    between the contracts and may damage transformer winding.

    When the switch handle is provided on the side wall, it is necessary that switch handle assembly is dismantled

    before untanking.

    2.2.2 Off-Circuit Ratio Changing links:

    Sometimes links are provided inside the transformers tank to obtain required voltage ratio. Links are required tobe loosened and fixed in new required position as given in R &D Plate. Links are accessible from the inspection

    cover. In case of conservator units, oil level has to be lowered below the inspection cover before the unbolting

    inspection cover.

    2.2.3 On Load Tap Changer:The on-load tap changer is an optional fitting. The on-load tap changes are provided with local manual control,

    local electrical control and remote electrical control. The automatic voltage regulation can also be provided as

    an optional fittings.

    The tappings are located on high voltage winding.

    For further details, please refer to the attached manual of OLTC and schematics.

    2.3 Earthing Terminals:

    The core lamination assembly is connected to core clamping frame which is in turn connected to the tank. Two

    earthing terminals are provided on the transformer tan. The earthing terminals should be connected to the

    earthing.

    2.4 Lifting Lugs:

    Two/Four lifting lugs of adequate capacity are provided on tank sides/top cover to lift fully assembledtransformer filled with oil.

    All lugs are designed for simultaneous use and must be accordingly. Two/Four lifting lugs are provided for

    untanking the core and windings of larger capacity transformers.All heavy fittings are also provided with individuals lifting lugs.

    2.5 Valves:

    Every transformer is provided with drain cum filter valve at bottom of the tank, and filter valve at top of the

    tank. Valves are fitted with plugs/blanking plates to stop oil coming out.

    Mainly two types of valves are provided.

    (i) Wheel Valves.

    (ii) Butterfly Valves.

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    The wheel Valves are used either with female screw threads or with flangs. These are of gun-metal/cast irontype.

    Generally, one Isolating Valve also known as shut off valve is provided for transformer upto 2000KVAbetween conservator and buchholz relay.

    The butterfly type cast-steel valves with the machnical flanges are used at points of connection between tank

    and detachable radiators.

    2.6 BUSHING:

    2.6.2 Oil Communicating type :

    Transformers windings are connected to the external circuit through terminal bushings. The bushings are

    installed on the cover or, on side walls of the transformer tank. The lower end of the bushing protrudes into thetank and at both their ends are provided with suitable fasteners to connect the line leads inside the transformers

    and external conductors outside it. Typical Bushing Assemblies are shown in Figs. 2,3,4.

    The shape and the size of the bushing depend on the voltage class, type of current. Electrical performances of

    these bushings conform to I.S. 2099 & I.S.7421. Dimensional details and associated parts generally conform to

    IS-3 upto 36KV class. Bushings of 1000 Volts are of two piece construction without arcing horns,whereas all

    other bushings are of single piece porcelain type. Assembly and dismantling of single piece type bushing is

    possible without disturbing the active part. For bushing of two piece construction, tank cover is required to beremoved for necessary access to the inner (lower) end of the bushings. These bushings are not detached at the

    time of transportation.

    2.6.2 Condenser Bushings :

    Generally, Condenser Bushings are used for 72.5KV and above. These bushings contain their own oil and aresealed to retain the same. Whenever these bushings are mounted on bushing pockets or raised truncated

    portions, air vent pipes are provided for carrying away air or gases form these pockets to Buchholz relay during

    service Typical assembly is shown in Fig.5.

    These bushings are detached from the transformers and dispatched separately. They are packed as permanufacturers instructions. The draw through type lead is coiled and kept temporarily below the bushing

    blanking plate (Ref. Fig.6). The equipment required for mounting the bushings are (i) rope sling (ii)flexible

    steel wire approx. 2mm in dia , of suitable length.

    Type procedure for mounting is as follows:(i) Open the bushing case carefully and check it for transit damage and clean the bushing thoroughly.

    (ii) Check whether the gasket on the pocket is in order. If not, clean the seat of the gasket and replace it bynew one.

    (iii) Remove the locating pin (3). The cable bolt to be used on the unit is brazed to the end of the flexible

    draw through type lead mentioned above.

    (iv) Remove the blanking plate and uncoil the draw through type lead. Tie the Flexible Steel wire to the

    head of the bolt fixed temporarily on the top of the cable bolt (2) to facilitate the threading of the mainlead through the bushing tube and at the same time preventing the lead form falling back into the tank.

    (v) Suitably raise the bushing and remove the protective cover at the oil end of the bushing. (Ref. Fig .7)

    (vi) Check that Oil Level in the bushing is appearing in the Oil Level indicating glass. In case it is notvisible, do not mount that bushing. Also do not attempt to fill oil at site as such bushing is most likely

    to fall in service.

    (vii) During the lowering operation, thread the flexible steel wire through the inside tube of the bushing andpull it. Continue the operation till the bushing rests on its flange pocket. Bolt the two flanges and

    remove the slings.

    (viii) Hold the cable bolt in position, remove the flexible wire and insert the locking pin (3) to hold the cable

    bolt downward.

    (ix) Fix the terminal cap (1) in position by screwing it on the terminal bolt.

    (x) For removing air from the central tube after oil filling, unscrew the terminal cap and press the terminalbolt downward.

    (xi) Fix upper and lower arcing horns and adjust the gap setting as per the required Insulation Co-

    ordination.

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    2.7 Cable Boxes :Cable boxes are designed for receiving and protecting cable ends. Insulating paper is most hygroscopic and all

    paper insulated cable ends must be protected by suitable insulating compound. These cable boxes are providedwith brass wiping glands and are designed with clearances inside the box suitable for compound filling. The

    cable box in such case must be filled with compound as marked as indicated in the drawling.

    Cable boxes for PVC ar XLPE cables are designed with air clearances and hence these boxes are not required to

    be filled with compound.

    Cable boxes of 3.6 KV and above are provided with detachable gland plate. Earthing terminals are also

    provided on these cables boxes for earthing the armouring of individual cables.

    When cable Boxes are provided with disconnecting chambers they permit removel of transformers for servicing

    without disturbing cable terminations.

    2.8 Bus-duct/trunkings :Some users prefer connections to load by means of busduct. Busduct is supplied by some other agency.

    However, we provide suitable flanges/trunkings around transformer bushings for receiving the busduct.

    The level of the busduct flanges from ground /rail level is indicated in the General Arrangement drawings of the

    transformer. The complete details of busduct flange is furnished by us giving complete dimensional details forthe matching flanges, bolt spacing, bushing terminal details, etc.

    2.9 Marshalling Box :The transformer is provided with certain fittings directly mounted on the transformer at various locations. These

    fittings are having electrical contract or terminals which are required to be connected to the protection schemes

    to give alarm/annunciation under abnormal conditions and if further required to disconnect the transformer frommains. In order to facilitate connections of all such devices to the protective scheme, the cables from all such

    contracts are wired upto a weather-proof terminal box. This box called marshalling box, is also used for housing

    Oil Temperature Indicator (OTI) and winding Temperature Indicator (WTI).

    The Marshalling box is made of sheet metal and is provided with a glass window for observing OTI & WTI.

    It has hinged door with locking facility to prevent unauthorized access. The capillaries from OTI & WTI come

    from the bottom of the Marshalling box through suitably recessed gland plate thus preventing ingress of dust.

    It has a detachable gland plate with glands through which cables enter and leave. It has a rain shed provided ontop to prevent rain falling directly overit. All these provisions make Marshalling Box a Weather-Proof

    enclosure.

    2.10 Buchholz relay :

    Buchholz Relay is a very sensitive, gas and oil operated apparatus which detects formation of gas ordevelopment of sudden pressure Inside the oil filled transformers. It is connected to protection circuit to give

    an early audible alarm of gas collection and to disconnect the transformer from supply in case of severe fault

    inside the transformer.The basic function of the relay is to initiate an electrical signal in the protection circuit when:

    (a) Gas is a accumulated in the relay, as result of incipient fault.

    (b) Surge of oil is developed on account of sudden increase in pressure inside the transformer due tosevere fault.

    (c) Oil level in the relay is reduced below the minimum level.

    Buchholz Relay operation in the following manner

    The relay comprises a housing containing two pivoted Buckets/Floats counter balanced by dead weights each

    bucket assembly carried a mercury switch. The relay is fitted in the oil connection between conservator and

    tank.Due to gas collection, the oil level inside the relay drops and the upper bucket moves down. This tilts the

    mercury switch bringing fluid mercury in such a position that it bridge the normally open (NO)contacts. Other

    probable reasons for dropping of oil level in the relay are:(a) Leakage of oil from main tank, conservator or relay itself.

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    (b) Collection of air in the relay which is trapped earlier in the tank and in the winding.The lower bucket operates similar to upper bucket when level in the relay drops further . However, important

    function of this relay is to disconnect transformer from circuit under sudden development of pressure indide thetransformer due to severe internal fault. In such cases, gas generation is rapid and displaced oil surges through

    the relay impinging on the baffle plate causing lower bucket to tilt and close the Normally Open (NO) contact

    of the mercury switch carried by it.

    Upper bucket contracts (A) are connected to audible alarm -A- circuit and lower bucket contracts -(T)- are

    connected to trip circuit.

    The relay is mounted in position with associated piping and isolating valves at works. In larger transformers ,the buchholz relay assembly is dismantled and sent separately. When Test Lever is provided, it sent in Test

    position to prevent damage in transit. On receipt at site, checks the relay for any damage to window glasses and

    mercury switches.Mount the Buchholz Relay between conservator and transformer tank cover along with piping & valves without

    straining the pipe line. Isolating valve must be fully opened after mounting is completed. To ensure successful

    operation of the relay the pipe work on either side of the relay is set inclined to horizontal by 3-5degree.

    MOUNT RELAY SUCH THAT AROW DIRECTION POINTS TOWARDS CONSERVATOR.

    After filling oil in the transformer, air trapped inside the relay is to be realized through the valve/petcock

    provided on top of buchholz collection, it must be ensured that this valve is kept open and the pipe is full of oil.When gas is collected, oil from pipe will flow outn first and then gas will come out.

    2.11 Radiators:The function of radiators is to limit the temperature of oil and winding by dissipating heat that is generated due

    to losses within the transformer while in service. The number of section per radiator and the number of radiators

    per transformer will depend upon the losses and permissible temperature rise.

    Distribution Transformers are normally provided with Radiators welded to tank. Owing to transport limination

    and possible transit damages, power transformers are normally provided with detachable radiators with radiator

    valves (Ref. Fig.18). At the time of dispatch, these radiators are detached and sent separately keeping the valves

    in position on tank flanges.

    - Each radiator consists of number of Sections made from presses CRCA Sheets forming channels

    for oil flow. These Sections are welded to Header Pipes at Top & Bottom. Detachable radiators

    are provided with M.S Flanges at Top & Bottom. Flanged radiators are fitted with Air Release

    Plug, Drain Plug, Lifting Lug, etc.- Bracing Straps, made from M.S Flat are provided on radators to prevent vibration of sections.

    Radiators are cleaned Internally to remove scales and a coat of varnish is applied. External surface is cleaned

    off all rust and one coat of Red oxide primer is applied which is followed by final painting.

    2.12 Silica Gel Breather :

    Whenever there is a change in the ambient temperature or in the load of an oil immersed transformer there is

    change in oil temp, & hence in the volume of oil. Increase in oil volume, causes the air above the oil level in the

    conservator to be pushed out and decrease causes air to be drawn in. Thus the transformer Breathes. When airis breathed in, there is possibility of moisture and dust from atmosphere to be sucked in. These contaminants

    deteriorate the insulation properties of oil. Hence Silica Gel Breather is provided which arrests moisture and

    dust from the air drawn in.

    A typical Silica Gel Breather has following main components:

    (1)A casing, (2) Silica Gel Crystals, (3) An oil seal at the lower end of casing.

    The casing has a window at the upper part for observation of the colour of the gel crystals. It has a flange

    connection at the top for connecting the breather to the breather pipe. The lower part of the casing has at itslower end an oil seal arrangement, a window for observation of oil level and an oil filling hole with gasket and

    plug.

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    Due to the chemical affinity possessed by Silica Gel Crystals, they absorb moisture from the drawn in. TheColour of silica gel is blue when dry and turns pink when it is saturated with moisture. The colour of crystal can

    be observed from outside of the casing.

    Oil seal assembly at the lower end of the casing consists of a little quantity of oil with an Inverted cup partly

    clipped in the oil and a tube fixed at the centre of the cup.

    The oil acts as a coarse filter and removes the dust from the outside air when it passes through oil.

    Silica gel breather is dispatched in a separate case.

    2.13 Magnetic Oil Gauge

    This is a dial type oil level indicating device provided on large transformers with conservator at relatively highlevel from the ground. In large transformers conventional glass oil level indicators are difficult to observe due to

    their heights and colour change/dust accumulation on the glass. Further, the low oil contacts provided on the

    magnetic oil level indicator can be used for automatic alarm when the oil level in the conservator falls to a lowlevel. This protection feature and clear visibility justify the cost of MOG on a bigger transformer

    It consists of two compartments;

    (a) The oil side compartment which is fixed on the opening in the conservator.

    (b) The pointer side compartment.

    These Compartments are sealed against leakage of oil by a metallic diaphragm. On the oil side compartment,

    there is a bevel gear wheel and it is positioned near the diaphragm. Movement of the float due to rise and fall of

    oil level in the conservator results into circular motion of driving magnet. A follower magnet is positioned inthe pointer side compartment neat the diaphragm. This magnet has its poles face to face to the poles of driving

    magnet from the oil side compartment coupling them magnetically. The movement of float is, therefore ,

    transferred through the diaphragm, eliminating direct oil light mechanical coupling.

    At the other end of the axis of the driven magnet an indicating pointer is fitted. The dial is calibrated to show

    the oil level in the conservator. The dial and the pointer area housed behind the front glass. The dial has three

    positions marked. The follower magnet has also a cam fitted on it which operates a mercury switch.When this

    magnet is at a position corresponding to low oil level the mercury switch close the Normally open (NO )contacts. These contacts are normally wired to give audible alarm. The contacts are brought to a terminal box at

    the lower end of the dial, for external connections.

    2.14 Oil Temperature Indicator (O.T.I) :

    - Oil Temperature indicator (O.T.I) is generally provided on all transformers except for very smallratings. The direct reading pointer arrangement in this Instrument greatly facilitates observation of

    working temp. of oil. It also helps, if need be, deciding the permissible overloads in accordance

    with I.S. 6600-1972. Guide for loading of oil immersed transformers.

    - A Typical Oil temperature indicator consist of a

    - Bourdon tube with pointer arrangement mounted in a case comprising of a reading dial and a glasscover. There is a temperature sensing bulb which communicates to the Bourdon tube through the

    armoured capillary.

    - The oil temperature indicator is provided with two pointers and associated contracts for protectionof transformers. Both the pointers are independently adjustable and can be set to desired

    temperature. Setting of these pointers at required temperature can be done from outside through

    the knob by using special keys.- The OTI is generally housed and wired upto terminal strip in the marshalling box having a glass

    window on the door for observation. The length of capillary does not influence the accuracy of

    measurement and extra length of capillary tubing must not be cut, as it would break

    communication between bulb and Bourdon tube.

    If the oil temperature increases beyond set limit due to overload or inadvertent closure of radiator valves or

    insufficient air draft, the indicating pointer touches the present alarm pointer and actuates the alarm contacts.The alarm contacts, when duly wired give an alarm. If the alarm is not attendedand threr and isolate the

    transformer from mains.

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    2.15 WINDING TEMPERTURE INDICATOR (W.T.I) :

    A Winding Temp. Indicator (WTI) is an optional fitting and is provided when ordered. It is set to read Hot SpotTemperature (HST).

    A typical WTI arrangement comprises of the following:

    (a) WTI Instrument having a temp. Sensing bulb and capillary similar to O.T.I. On addition it is provided with

    a heater coil around its operating bellow.

    (b)A current Transformer mounted on one of the transformer leads, sensing load current.

    The bulb of the instrument is placed in an oil filled pocket located on the top cover of the transformer similarTo O.T.I pocket. The Heater Coil is fed by the W.T.I.C.T.

    Thus the Temperature indicated by WTI accounts for

    (i) Temp. of Top oil and(ii) Winding Gradient (Temp. Rise of winding over surrounding oil) which is dependent on Load Current.

    And is adjusted to read HST = [ Top Oil Temp] + 1.1 x Gradient

    The heater coil is provided with an adjustable resistive shunt (Ref. Fig.24) in parallel which allow theInstrument to be adapted for a range of winding gradients.

    The adjustable shunt by-passes certain amount of current (ISH ) from the C.T . Secondary Current (ISH).

    Thus Heater Coil Current

    ISH = IS - ISHFor the particular transformer, the shunt is adjusted at factory for the applicable Winding Gradient WTI also hasAlarm &Trip contracts. For Fan cooled transformers auxiliary contracts of WTI are used for fan switching.

    2.16 REPEATER OTI & WTI INSTRUMENTSRepeater OTI & WTI instruments are Optional Fittings and are provided when ordered. They enable readings

    being taken in Control Room also. They are generally provided in the RTCC Panel, when it is a part of contract.

    They are available in one of the following types :(a) Simple Analog Repeater

    (b) 4-20 mA. D.c Analog Repeater

    (c) 4-20 mA. D.c Digital Repeater

    (d) 4-20 mA. D.c Digital Repeater Plus a signal for SCADA

    They all require the Local Instrument to be provided with a precision potentiometer.In case (b),(c) &(d), they also require Auxiliary Devices like Power Supply Unit, Resistance to Current

    Converter (RCXT) and /or Current Converter (CCXT) etc. They are housed inn UNIT BOX mounted on the

    transformer.

    Wiring Diagrams and Interconnection Diagrams necessary for the wiring of Marshalling Box, UNIT BOX and

    RTCC Panel are supplied along with transformer.

    2.17 OTI & WTI INSTRUMENTS OPERATED BY RESISTANCE TEMP. DETECTORS (RTSs)Temp. sensing can alternatively be done by Resistance Temp. Detectors (RTDs). Thus O.T.I &W.T.I.can be

    operated by RTDs. When, so ordered, they are provided accordingly. In this case also Power Supply Unit and

    RCXT Unit will be required and they are provided in the Unit Box.

    Here again Repeater Instruments are provided when ordered.

    2.18 THERMOSYPHON FILTER : Thermosyphon

    Thermosyphon Filter is a device which continuously improves the quality of oil in the transformer tank. It is

    optional fitting and is provided when ordered.It is a container having perforated trays filled with Activated Alumina. It is fitted to the transformer tank similar

    to a radiator with provision of isolating valves, air release plug, drain valve etc. Due to the convection current

    set up in oil , oil flows continuously over the exposed surface of Activated Alumina (i.e. the adsorbent material)and in the process, contaminants like moisture, organic acids etc. generated due ti ageing of insulation, get

    collected in the absorbent material and thus improve the quality of oil.

    Periodic recharging of adsorbent material is necessary.

    2.19 FLEXIBLE SEPARATORAlso known as Diaphragm Conservator or Rubber Diaphragm. It is an optional fitting and is provided when

    ordered.

    The Flexible Separator is a sealed, nonporous flexible bag of a highly resistant fabric, coated externally toresist transformer oil and internally to resist external atmosphere.

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    It is fitted inside the conservator such that variations in oil volume due to variations of temp. are taken up by theFlexible Bag. Oil in conservator is sealed from the outside atmosphere moisture and gases connot contaminate

    the oil inside the conservator.Fig. (a) shows the separator in inflated condition corresponding to low oil volume. When oil expands due to

    increase in temp. Atmosphere inside the separator is exhaled and the separator bag deflated as shown in Fig.

    (b).

    Oil filling in the conservator is to be done as per the procedure given in 2.20.

    2.20 OIL FILLING PROCEDURE FOR A CONSERVATOR PROVIDED WITH A FLEXIBLESEPERATOR.

    1) Set up the separator inside the conservator by suspending it from the hooks provided.

    2) Keep the 2 Nos. , SSF wheel valves at the top of the conservator open. Inflate theseparator carefully with an air pressure of not more than 2 p.s.i. A typical arrangement

    of Air inlet is shown in Fig. 27 (c).

    3) Adjust the pressure to a valve between 1.5 & 2.0 p.s.i and lock it. Observe for pressuredrop for 24 hours.

    4) If there is no pressure drop, then the separator is leak-proof 7 proceed for oil filling. If

    there is leakage contact us.

    5) Admit oil under slight pressure from the lower part of the conservator, till oil flows

    steadily from the valves mentioned in (2) above. Close the valves.6) Admit further oil. Pressure will slightly increase. Remove compressor connection from

    the Air Inlet Valve. Open this valve slightly to maintain pressure. Continue admitting

    oil slowly while maintaining pressure. Separator will deflate. Stop filling when theMOG indicates filling level. Open the Air Inlet Valve completely to equalise pressure

    inside the bag with atmospheric pressure.

    IMPORTANT WARNINGS:(1) When conservator provided with Flexible Separator is filled with oil as mentioned abov, the Valves

    mentioned above must never be opened. If opened by mistake, the air-pressure acting on the separator will

    deflate the separator.

    (2) When it is necessary to open these valves, inflate the separator with a pressure of less then 2 p.s.i. and then

    only open these valves.(3) Do not carry out any welding work on the conservator shell while separator is inside as it can damage the

    separator.

    2.21 OIL LEVEL TRANSMITTER:

    When oil level in conservator is to be remotely monitered Oil level transmitter is to be provided . It is anoptional fitting and is provided when ordered.

    Transmitter System comprises of :(i) Stainless Steel Rod which goes inside the conservator tank.

    (ii) Transducer which gives e;ectrical signal dependent on the oil level.

    (iii) Power supply / V-I Module which provided 4-20 mA signal from the transducer output.

    A typical arrangement is illustrated in Fig. 28.

    2.2.3 ON LOAD TAP CHANGER (OLTC) :

    OLTC is an optional device and is provided when ordered.

    Tappings are located on High Voltage Windings of the Transformer.One type of OLTC is fitted external to transformer main tank as shown in Fig . 22(a). In the other type,

    contracts mounted on insulated cylinder are immersed in the transformer main tank as shown in Fig. 22(b). In

    both the types. Drive Mechanism (DM) is contained in separate box.Different arrangements used to effect tap changing are shown in Fig. 23 They are :

    (a) Linear : Commonly used arrangement when no. of tap position is moderate.

    (b) Coarse/Fine : By means of a change over contract, the Coarse tap winding is included

    in or excluded from the circuit. Thus two voltage (i.e. tap positions) are obtained for

    one position of moveable arm.

    (c) Reverse/Forward : By means of a change-over contact, the tapping winding isconnected in Forward (i.e. Adding ) or Reverse(i.e. Subtracting) direction w.r.t. main

    winding. Thus two voltages (i.e. tap positions ) are obtained for one position is large.

    Arrangement (b) or (c) is used when no. of tap positions is large.

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    OLTC is generally operated electrically through a Remote Tap Control Cubicle (RTCC) LOCATED IN ControlRoom. A local electrical control is also provided in the Dm, along with a selector switch for Local or Remote

    Control. For emergency manual operation, an operating handle is provided.

    When Automatic Voltage Regulating (AVR) Relay is ordered and Voltage Transformer (V.T) wired on the

    Transformer output side (generally in users scope), the output voltage is compared in the AVR Relay with

    the settable reference voltage and difference used to give command to OLTC so as to reduce the difference.

    Thus the output voltage is automatically controlled to the preset value.

    A Line Drop Compensator (LDC) is included in the AVR when specifically ordered. R&X of the cable,

    connecting transformer to load , are to be set by means of adjustable knobs. In such a case , voltage at the end

    of the cable and not at transformer terminals, is controlled.

    Direction of Power Flow is an important consideration in OLTC. Only some types are suitable for Full Power

    Flow in terms of current and no. of operation- in the reverse direction. Other type have restrication on thecurrent and no. of operation in the reverse direction. These details are given in the plate fitted to OLTC.

    For further details, please refer to the OLTC manual and Schematic & Wiring Diagrams supplied along with the

    transformer.

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    3. INSTALLATION & COMMISSIONING

    3.1 General:

    This section illustrates procedure for installation & Commissioning of our transformers.

    A format of Commissioning Report is included at the end of this section. Result of various precommissioningtests as well as conformation of check points are to be recorded in this Report. This Report then would serve as a

    handy record for further reference.

    3.2 Installation:

    3.2.1 Location:The transformer should be kept in a well ventilated place, free from excessive dust, corrosive fumes etc.

    Adequate ventilation is necessary for tank and radiators so that they can dissipate heat. There should be

    clear space of about 1.25m on all sides of the transformers if it is enclosed in a room.

    3.2.2 Foundation:

    Foundation should be firm, horizontal and dry , where rollers are fitted, suitable ralls should be provided.

    3.2.3 Provisions for Oil Draining :

    Necessary provisions for oil draining , in the event of a fire , should be made by way of oil Soak Pits. Fire

    separation walls should be provided when necessary.

    3.2.4 Assembly of Dismantled Components:Various components dismantled for transporation should be duly assembled.

    3.2.4.1 Main Tank:Keep the main tank in its permanent position of operation. Lock the rollers to prevent any accidental

    movement on ralls. Draw an oil sample from the bottom of the tank and test it for Break-Down Vlotage

    (BDV)Note this value in Commissioning Report.

    3.2.4.2 Bushing :

    Clean the bushing and check that there are no hair-crakcks or other damages. Test IR value of each bushing

    with a 500V Megger. It should be 100M ohms or greater. Note details of Bushings in the CommissioningReport. Mount all the bushings as described in 2.6. Ensure that the test cap is fully tightened, thus

    positively grounding the same. Adjust the Arcing Horn Gaps in accordance with the Insulation Co-

    ordination Note these values in the Commissioning Report.

    3.2.4.3 Conservator & M.O.G :

    Note details of M.O.G in the Commissioning Report. If the M.O.G is provided with a locking leaver, it

    should be removed. Mount the conservcator, When there is an OLTC its conservator is some timesprovided separately or by making a partitioned compartment in the main conservator. OLTC conservator, if

    separate, should also be mounted.

    3.2.4.4 Buchholz Relay :Note details of Buchholz Relay for the transformer and of Oil Surge Relay for the OLTC in the

    Commissioning Report. Buchholz Relay floats are tied to prevent transit damage. They should be

    released. Also if Test lever is provided, it should be in the working position. Mount the Buchholz Relayand the shut off valves as described in 2.10. similarly mount Oil Surge Relay.

    3.2.4.5 Breathers:

    Note details of Breathers, in the Commissioning Report. If OLTC is provided, it may have its ownseparate breather. Note details of these Breathers also in the Commissioning Report. Check that the

    colour of Silica Gel in Main Breather is Blue. Remove the rubber cap closing the breather pipe and fit the

    breather. Fill oil in the oil cup and remove the seal which closes the breather opening. Similarly mount the

    OLTC breather.

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    3.2.4.6 Radiators :Note the details of Radiatiors and Radiators Valves in the Commissioning Report. Mount the radiators

    as outlined below:(i) Radiators are to be assembled only one at a time.

    (ii) Oil required to fill in the radiators is sent separately in drums. Test oil sample from each drum for

    BDV. Ensure it is more than minimum specified in I.S. 1866 for New transformer.

    (iii) Fill the conservator full using an oil filter machine, if available.

    (iv) Clean one radiator externally. Remove blanking plates and clean the gaskets and radiator flanges .

    If gaskets are damaged, use spare gaskets.(v) If blanking plates are not in position and it is suspected that foreign material might have entered

    the radiators, clean them internally by flushing fresh and clean transformer oil.

    (vi) Oil might seep through the tank side radiator valves and be retained by the blanking plates. Thisoil should be collected in a clean container at the time of removing top and bottom blanking

    plates.

    (vii) Bring the radiator flanges close to the flanges on the tank. Ensure that tank gasket is in position.Fitby means of bolts, nuts, spring washers etc.

    (viii) Open the bottom radiator valve using the operating handle. Gradually unscrew the air release plug

    on the top of the radiator, until air starts escaping . Air release plug should not be removed from

    the engaging threads as it would be difficult to control oil coming out of it. Oil from main tank

    will now flow in the radiators, driving out air from air release plug. When oil comes out steadilyfrom the air release plug and no more air comes through, close the air release plug. Open the top

    radiator valve. Oil level in the conservator would now have fallen. Check that there is no oil

    leakage from the radiator itself and gasketted joints. Restore the oil level and assemble the nextradiator in the same manner.

    Assembly of radiators should be proceeded in only one direction-clockwise or anticlockwise.After filling last radiator, oil level in conservator should be restored only up to the filling mark.

    When OLTC compartment is provided in the main conservator, this compartment is to be

    Separately filled upon its filling mark.

    3.2.4.7 Marshalling Box.Marshalling box should be fitted in position. Pockets of O.T.I & W.T.I should be filled with transformer

    oil. Bulbs of O.T.I & W.T.I. should be fitted in position in their respective pockets.

    Set the Alarm & Trip contracts of O.T.I & W.T.I at required values. O.T.I settings of A=850 C &

    T = 950 C W.T.I setting of A -950 C & T= 1050 C are considered good. They can be worked out to suit localconditions.

    Note details of O.T.I & W.T.I and their settings in the Commissioning Report.

    3.2.4.8 Cable Box :

    When cable Boxes are provided they should be mounted and cable terminations done. Oil filled cable-

    boxes should be duly filled with oil. In case of Bus-Duct connections, transformer is provided with a

    flange to receive the bus-duct. Due connection and fitting should be done tio over-head line by a terminalconnector.

    3.2.4.9 Other Fittings:

    Note the details of other important fittings like fans in the Commissioning Reportand mount thesefittings.

    3.2.5 Oil Sampling & Filteration:Taking usual precautions, draw oil samples from Bottom & Top of main tank and from OLTC. Hey should

    be tested for BDV. If they meet the requirements of I.S. 1866 for new transformers, no further processing

    is required. However if they do not meet the requirements, oil needs to be filtered till the required BDV is

    obtained. Note the BDV values in the Commissioning Report.

    3.2.6 Air- Release :Release air by slowly unscrewing Air Release Plugs provided at Bushings, Bushing Pockets, Buchholz

    Relay, Main Tank Cover, Oil Surge Relay etc. From plain porcelain bushing of 11,22,& 33 KV,air can be

    release by loosening the nut pressing the rubber gasket and pressing the metal part down.

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    3.2.7 COMMISSIONING

    3.2.8 Pre-Commissioning Test :Prior to energising the transformer, several pre-commissioning tests are done .The objective of these tests is

    to conform that the transformer has not suffered damage during transit and also to check any inadvertent

    slips in the factory tests, or supply.

    3.2.8.1 Ratio Test :

    Ratio between all the three corresponding H.V. & L.V phases is to be measured on all taps. It is desirable todo this test by a Radio-meter. But if it is not available, a simple test of measuring voltages can also serve

    the purpose.

    Referring to R &D plate, find out which terminals of H.V & L.V. correspond to one phase e.g for a vector

    Group of Dyn-11, H.V. Terminals 1U, IV, & L.V. terminals 2U, 2N correspond to U phase. Apply single

    phase, 415V or 240V, AC.;50Hz to H.V. side and measure voltage on the L.V. side. Measure these voltageson all taps and note them in Commissioning Report. Repeat for the other two phases. These observation

    should indicate a consistent trend of variation in line with the details given in R & D plates. Numerical

    values should approximately check with the voltage ratio.

    3.2.8.2 Vector Group Check Test :

    Connect terminal 1U, 2U together. Apply 3 Phase , 415V, 50Hz, AC. to H.V. terminals 1U, 1V, 1W.Measure voltages between terminals 1V-2V, 1V-W (for suitable other voltage if required). Check that the

    measured voltages confirm the relative position of H.V. & L.V. vector group. For vector group Dyn-11, the

    method is illustrated below.

    H.V. &L.V. vectors are shown independently positioned for Dyn-11. For the condition 1U & 2U connected

    together, L.V. Vectors are redrawn as shown. With this configuration, Voltages 1V-2V 7 1V-2W will be equalwhile 1W-2V will be greater than 1W-2W.

    This method can be extended to any other Vector Group. Note the observations in the Commissioning Report.

    3.2.8.3 Magnetising Current Test :

    Apply 415 volts, 2 phase, AC. to the H.V terminals, keeping the L.V. terminals open and tapping switch inthe normal position. Measure the 3 line currents, if possible simultaneously, otherwise one after the other.

    Because the 3phase of the magnetic current of the core are not similar, the 3 line currents will be

    approximately equal & v phase current around 805 of either of them. If H.V. is delta connected, V & Wphase currents will be approximately equal and U phase current around 110%.

    In case of Power Transformers, such a test is done, some times, alongwith routine tests at the manufacturesworks. When done at site and results compared with the factory test confirms that there are no transit

    damages to the core and windings.

    Note the observations in the Commissioning Report.

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    3.2.8.4 Magnetic Balance Test:

    This is a simple test to detect shorted turns ion a winding. Its principle is that shorted turns opposeestablishment of flux in that limb because of the current that circukates through the shorted turns.

    As indicated in 3.3.2 apply single phase, 415 or 240V. AC to such H.V. line terminals which would

    energies U phase (outer limb) Use an averaging instrument like a Multimeter. Measure the voltage induced

    in the V phase (Centre limb and W phase (other outer limb). Measure also the current drawn by the

    energised phase. In case the H .V. Voltage is 66KV and above the current drawn may be very small. In thatcase L.V. would , generally, be 11KV or more. This test can , then, be carried out on L.V . Side. Centre

    limb being nearer ti the energized limb, more flux passes through it and less flux in the outer limb. /the

    division is around 70-30% & hence the measured voltages will be having approx this proposition. Next,energise W phase and measure the other two voltages as before. Results should be similar to previous ones.

    Then energise V phase (Centre limb0. As both the outer limbs are symmetrically located w.r.t centre limb,

    flux will divide equally between them. Hence the voltages measured on outer phases will be approx. equal .Also , for reasons explained earlier, Currents drawn when outer phases are excited the healthiness of the

    windings.

    In case one of the phases has shorted turns, it will draw a comparatively large current when it is energized.

    When other phases are energized, flux and hence voltage in the shorted phase eill be significantly reduced.

    Hence all three observations will indicate the shorted phase. Note the observations in the CommissioningReport.

    When the Magnetic Balance Tes5t indicates a shorted phase, commissioning cannot be undertaken contact

    us immediately giving detailed test results.

    3.2.8.5 Measurement of Insulation Resistance:

    Measure Insulation Resistance (IR) between windings and between windings and earth with a 2500/1000v

    Megger, preferably motor driven, otherwise hand-driven. Before measuring I.R, thoroughly clean all the

    bushings with clean cotton cloth. If required using Carbon Tetrachloride. Also, there should be no external

    connections to the transformer terminals. check and adjust, if required, the infinity setting of the Megger.

    Lead wires from the Megger to the transformer should run independently and be permanently clamped.They should not have any joints. It is known that the I.R reading continues to increase initially and for

    comparison purpose, reading is to be taken at 1 minute of energizing, It is also known that I.R value

    dependent on temperature. Hence temperature at the time of measurement should be noted. Compare the

    I.R values measured, with the Factory results keeping in view the temperature at the time of measurement.

    Note the observation in Commissioning Report. Also measure and note the I.R. values of the powerCables.

    3.2.8.6 Short-Circuit Test :

    For the H.V side voltage and the % impendence, it would be possible to calculate the current which would

    flow in the H.V. side, with 415V applied to it, while keeping L.V. side shorted. If the 415V source can feed

    that current, a short-circuit test can be carried out.

    This test would confirm proper contract engagement at all tap positions. Apply 3Ph.415V, 50Hz to H.V.

    side, keeping L.V. side shorted. Measure the 3 line currents at all tap positions. If the switch is anOFF-CIRCUIT switch, supply has to be disconnected before changing tap. Note the observations in the

    Commissioning Report. Note also details of OLTC, if any.

    A Consistent trend indicates healthiness. If short-circuit test is not possible due to limitation of source.carry out one tap changing operation over the entire range increasing as well as decreasing. Check the other

    modes of OLTC operation and note in Commissioning Report.

    3.2.8.7 Parallel Operation:

    Sometimes the transformer to be commissioned is required to run in parallel with an existing transformer.

    In is case, the following conditions must be fulfilled by the incoming transformer:(1) Its voltage ratio is same as the existing transformer on all tappings.

    (2) Its % Impedance is within -1% of value of existing transformer.

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    NOTE : Due to difference in % impedances, when one transformer reaches its rated load, the other would

    share less than its rated load. As a result, the combination can supply load less than the sum of the twoKVAs.

    (3) Rated KVAs of the two transformers to be connected in parallel should not

    doffer by more than 1:3 as otherwise only marginal increase will be obtained in

    the capacity o f the combination.

    (4) Vector group is compatible. if the vector group of the two are such that

    terminals to be paralleled have a phase different then they cannot be connectedin parallel. Hence only certain Vector Groups are compatible with each other.

    If possible, one should check zero voltage between the corresponding phases to be paralleled.

    3.2.9 Other Relevant Details:

    Other controlling and protecting equipments like C.T.s, Breakers, relays etc., from a part of the transformer

    installation. Note their details in Commissioning Report.

    3.2.10 Check points :

    After completing installation and precommmissioning test, check that the various points mentioned in the

    Commissioning Report have been complied with. Note the compliance in the Commissioning Report.

    3.2.11 Energising:When all the pre-commissioning tests are found satisfactory and all the check points are confirmed the

    transformer can be energized on No load. It is preferable to keep settings of all protective relays to theminimum. The transformer should be allowed to run on No-Load for about 3 hours. During this period, the

    transformer should be observed for any abnormality in the hum and gas collection in the Buchholz Relay.

    Sometimes during this period, trapped air is released and gets accumulated in Buchholz Relay.

    At the end of this 3 hours period, transformer should be de-energised and air released from Bushings,

    Bushing pockets, Buchholz Relay, Main tank cover, Radiators etc. The transformer should , then be

    energized again and then relays set at their desired settings. Transformer should then gradually loaded

    reaching full load in about 3 hours time. During the period and for further 3 hours, (i.e total of 6 hours)transformer should be under observation. Check that all instruments, O.T.I. & W.T.I., M.O.G. are reading

    properly and that all radiators are uniformly hot. Check that there is no gas collection in Buchholz Relay. If

    everything is found in order, the transformer can continue working.

    The Commissioning Report should be duly signed by the Authorised representatives of all the

    participating organizations.

    3.2.12 TOOLS & INSTRUMENTS REQUIRED FOR INSTALLATION / MAINTENANCE :The following tools are required at the time of installation of transformers.

    (a) 20 mm or 12mm Vinyl hose to take oil samples from drums. 1 No.

    (b) Drum Opener. 1 No.

    (c) Crow bar, Pipe roll, hammers, etc. for package shifting and opening. As required.

    (d) 25 mm dia Manila Rope. 50 Meters.(e) Chain Pully Block-1 Ton capacity and lift about 10 meters 1 No.

    (f) Small size screw spanners-100 mm long for

    nuts upto 6mm size. 2 Nos.(g) Hand lamp for inside working. 1 No.

    (h) Screw driver-200 mm & 300 mm long. 1 No. each.

    (i) Pipe Wrench- 250 mm size. 1 No.(j) Cutting Pliers (Insulated) 2 Nos.

    (k) PVC Wire for connecting meters. As required.

    (l) Spanners M-24, M- 20, M-16, M-12, M-10, M-8 .. 2 NOS. OF EACH SIZE

    The Following instruments are required for testing :

    (a) Oil testing kit to test the break- down voltage of transformer oil.(b) 2500 volts megger to measure the Insulation Resistance (IR) values.

    (c) Two Voltmeters, one of 0-100V range and another of 0-500V range, to read the L.T side and the applied

    voltage during voltage ratio test.(d) One AVO meter.

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    3.2.13 COMMISSIONNING REPORT

    CLIENT : DATE:

    TRANSFORMER DETAILS :

    TRANSF. SR. NO : MAKE:

    RATING : VOLTAGE RATIO :

    TAPPING RANGE : BY OFF CKT. SWITCH/ OL.T.CCONNECTION : VECTOR GROUP :

    SUPPLIED ON :

    INSTALLED AT :

    (1) Oil Test Results :Details of Oil Test Set Make : Type : Motorised/ Manual , Gap : 2.5 mm

    Observed BDV

    (a) Main Tank Oil : Before Filteration:

    : After Filteration:

    (b) O.L.T.C : Before Filteration :After Filteration :

    (c) Cable Box Oil : Before Filteration :

    After Filteration ;

    (2) Details of Bushings:(1) H.V. Bushings Make

    KVSr. Nos.

    (2) Arching Horn Gap on H.V. Bushings

    adjusted to mm

    (3) L.V Bushinga make

    KVSr. Nos.

    (4) Arching Horn Gap on L.V Bushing

    adjusted to .mm

    (3) Details of Magnetic Oil level Gauge:Make: Type:

    Wired } : Alarm Yes/ Nofor } : Trip Yes / No

    Tested } : Alarm Yes/ No

    for } : Trip Yes/ No

    4. Details of Buchholz & oil Surge Relays :

    4.1 Buchholz Relay :

    Make : Type :

    Tested} : Alarm Yes /Nofor } : Trip Yes / No

    4.2 Oil Surge Relay (on OLTC) ;Make : Type :

    Tested for : Trip Yes /No

    Notes :

    (1) Both relays connected in

    control circuitry Yes /No

    (2) Control circuit Checked for Operations through:(a) Buchholz Relay Yes / No

    (b) Oil Surge Relay Yes / No

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    5. Details of Breathers :

    CHECK Main Tank

    Breather

    OLTC Breather

    MAKE

    TYPE / MODEL

    Colour of Silica Gel Blue /Pink Blue /Pink

    Oil level in Breather OK /Not ok OK / Not Ok

    6. Details of Radiators & Radiators Valves :

    6.1 RadiatorsMake :

    Type :

    No :

    6.2 Radiators Valves :Make :

    Type :

    No :

    7. Oil and winding temperature indicators :

    CHECK OTI WTI

    MAKE

    TYPE

    ALARM SET0 C 0 C

    TRIP SET0 C 0 C

    TESTED FOR

    ALARM

    Yes / No Yes / No

    TESTED FOR

    TRIP

    Yes / No Yes / No

    7.1 Pressure Relief Valve :Make :

    Type :Tested } : Alarm Yes / No

    For } :Trip Yes /No

    Note :

    (1) O. T. I & W.T.I. connected incontrol circuitry. Yes / No

    (2) Control Circuit : OTI Yes / No

    Checked for operation : WTI Yes / No

    through. : P.R.V Yes / No

    8. Details of Cooling Fans :Make :

    Type :

    Nos :

    Fan control through } : OK /Not OKW.T.I } :

    Group I of fans set for 0 C.

    Group II of Fans set for 0 C.

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    9. Ratio Test :Apply single phase ,415 or 240 Volts, AC. to those H.V. terminals, which will energise U phase of transformer.

    (This can be found from the R & D plate ). Measure L.V Voltage for the same phase. Likewise measure for V &

    W phases also.

    H. V VoltageApplied

    Between

    Terminals =

    Do Do Remarks

    Tap. L.V. VoltageMeasured

    Between

    Terminals =

    Do Do

    1

    2

    17

    (1) Checked Ok for

    Consistent

    Variation

    Yes / No(2) Checked Ok for

    Rated VoltageRatioYes /No

    10. Vector Group Check Test :Terminals 1U & 2U connected together. 3 Phase voltage applied to terminals 1U, 1V, 1W. Measured Voltage

    Between Terminals :

    Between

    terminals

    Voltage Between

    terminals Voltage

    Vector Diagram ;

    Observed Voltage confirms Vector Group :

    11. Magnetising Current Test :

    3Phase Voltage applied to H.V Winding- Star / Delta connected.Voltage 1U 1V = 1V -1W = 1W 1U =

    Tapping Switch in position no :..

    Line Currents : U = mA, V= mA, W= mA

    Line current checked Ok for .Connected H.V Yes / No

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    12. Magnetic Balance Test :

    SrNo Voltage between terminals

    CorrespondingTo U Phase

    CorrespondingTo V phase

    CorrespondingTo W Phase

    1 Applied

    Voltage =

    Current

    Drawn =

    2 Applied

    Voltage =

    CurrentDrawn =

    3 Applied

    Voltage =

    CurrentDrawn =

    Observed distribution of voltage confires absence of any shorted turns. Yes / No

    13. Measurement of Insulation Resistance :

    (a) For Transformer :

    (1) Between H.V. and Earth = . Mohms

    (2) Between H.V. and L.V. = . Mohms.

    (3) Between L.V. and Earth = . MohmsTransformer Top Oil Temp. = 0 C.

    Details of Megger :(1) Make : (2) Sr. No. :

    (3) Voltage : (4) Range :

    (b) For Power Cable :

    Type :Temp : .0 C.

    (1) U Phase to earth Mohms.

    (2) V Phase to earth Mohms.(3) W Phase to earth Mohms.

    (4) U Phase to V Phase Mohms.

    (5) V Phase to W Phase Mohms.(6) W Phase to U Phase Mohms.

    REMARKS :

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    14. Short Circuit Test :

    Applied Voltage = 3 phase , 50 Hz.1U 1V = 1V 1W = 1W -1U = Volts.

    Tap IU IV IW ILTNo A A A A

    123

    4

    5

    6

    78

    9

    10

    1112

    13

    1415

    16

    17

    15. Details of Control Panel/ Protective System :

    (1) H.V Circuit Breaker :

    Make : Type :

    MVA : I-rated

    KV : ReleaseSetting =

    (2) H.V.C.T.s :

    Make : Type :

    No. of. Cores Accuracy Class

    1.2.

    3.

    4.

    ------------------------------------------------------------------------------------------------------------------------------------

    (3) Earthfault Relay (H.V.Side ):Make : Type :

    Mounted on Phase :

    Current Setting : TimeSetting :

    (4) Over-Current Relay (H.V. Side ):

    Make : Type :

    Mounted on Phase :Current Setting : Time

    Setting :

    (5) L.V. Circuit Breaker :

    Make : Type :MVA : I-rated :

    KV : Release Setting :

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    (6) L.V.C.T.s :

    Make : Type :

    No of Cores Accuracy Class1.2.

    3.

    4.

    (7) Earthfault/ Overcurrent/Different Relay on L.V. side :Make : Type :

    Mounted on Phase

    Current : Time :

    Setting : Setting :

    16. Details of O.L.T.C :

    Make : Type :Sr. No Year :

    (a) Manual Operation OK / Not OK

    (b) Local Electrical Operation OK / Not OK(c) Remote Electrical Operation OK / Not OK

    17. COMMISSIONING CHECK POINTS ;1. Oil Samples from main Tank

    O.L.T.C. have passed BDV requirement. Yes / No.

    1a. Bushing surfaces are cleaned. Yes /No.2. Test Tap Caps are fully tightened. Yes /No.

    3. Arching Horn-gaps are duly adjusted. Yes /No.4. Oil level main conservator is upto mark. Yes / No.

    5. Oil level in O.L.T.C Conservator in separate Yes / NoConservator or Compartment in main

    conservator6. M.O.G. lock is released. Yes / No.

    7. Buchholz Relay lock is released. Yes / No.

    8. Buchholz Relay Test Lever is kept in Yes / No.

    S position.

    9. Buchholz Relay shut off valves on Yes / No.both sides are open.

    10. Air Release valve of Buchholz Relay Yes / No.

    is closed.11. Buchholz Relay arrow head is Yes / No.

    pointing towards conservator.

    12. Lock of Oil Surge Relay (OSR ) on Yes / No

    O.L.T.C. is released.13. OSR shut off valve is open. Yes / No.

    14. OSR arrow-head is pointing towards Yes / No.

    conservator.

    15. Colour of silica Gel in main breather Yes /No.is blue.

    16. Oil is filled in main Breather upto Yes / No.

    level mark.17. Sealing Tape of main Breather is Yes /No.

    removed.

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    18. Colour of Silica Gel in O.L.T.C. Yes /No.

    breather is blue.19. Oil is filled in O.L.T.C breather Yes /No.

    upto level mark.

    20. Sealing Tape of O.L.T.C. breather is Yes / No.

    removed.

    21. All radiator Valves-Top and bottom Yes /No.are open.

    22. Valve connecting min Tank to Cable Yes /No.

    Box is open.23. Oil is filled in disconnecting Cable Yes /No.

    Box upto Level Mark.

    24. All sampling, drain and filteration Yes /NoValves are closed.

    25. Oil filling cap on main conservator is Yes /No

    duly filled.

    26. There is no oil leakage from any where. Yes / No.

    27. Explosion vent diaphragms are intact Yes / Noand there is no oil in explosion vent.

    28. Oil is filled in O.T.I /W.T.I Yes /No.

    pockets.29. Air released from :

    (i) All Bushings Yes /No.

    (ii) All Bushings Pockets Yes /No.(iii) Buchholz Relay. Yes /No.

    (iv) Main Tank Cover. Yes /No.

    (v) All radiators. Yes / No.

    (vi) OSR on O.L.T.C Yes / No

    (vii)O.L.T.C. Tank Cover. Yes /No30. O.L.T.C. /Off Circuit Tap Switch is in Yes /No

    the desired position and is properly locked.

    31. Tank earthing is done. Yes /No.

    32. Neutral earthing is duly done. Yes / No.

    33. Rollers are locked. Yes /No.34. C.T. secondary terminals, if not Yes /No

    wired, are shorted and earthed.35. Alarm & Trip contracts of O.T.I & Yes /No

    W.T.I. are set at the required valves.

    36. External connection are duly Yes / No.

    tightened.

    18. Commissioning :

    After carrying out installation and pre-commissioning tests and ensuring all check points, the transformer was

    commissioned on .at ..Hrs.at No load in ourpresence Subsequently Load was also taken. Nothing abnormal was observed during these operation.

    For Customer : for VOLTAMP

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    4. OPERATION & MAINTENANCE

    4.1 OPERATION :

    I.S. 2026-1977 states that a Power Transformers loaded at its rated KVA will fulfil its normal life when its

    hottest spot temperature (H.S.T) is 980 C for an air temperature at 320 C.As the ambient air temperature exceeds

    320 C, The H.S.T exceeds 980 C. The insulation ageing (which decided the life of transformer) increases with

    increase of H.S.T. increase of H.S.T. by 60 C doubles the rate of ageing (i.e. reduces the life by 50% ). When theambient air temperature is lower than 320 C, the H.S.T is lower than 980 C. The insulation ageing decreases thus

    increases the life of transformer.

    It is considered (by the I.S.6600-1972) that periods of accelerated ageing due to higher ambient temperature are

    compensated by the periods of reduced ageing due to lower ambient temperature.

    Sometimes a transformer may be required to deliver load higher than its rating. Guidance on overloading is

    provided by I.S. 6600 basis for this recommendation is as follows:

    In a 24 hours loading, if ambient temperature is low and load for a substantial time duration is also low a short

    time over load may be permitted such that equivalent ageing due to this varying load will be the same as that ofloading over a period of 24 hours.

    4.2 MAINTENANCE:

    4.2.1.General :

    Compared to moist electrical equipments transformer requires relatively less maintenance. However in order to

    obtain a long and trouble-free service from the transformer, it must be properly maintained. Maintenance consist ofregular inspection, testing and reconditioning when necessary. Principal object of maintenance is to maintain the

    insulation in good condition. Moisture , dirt and high temperature causes insulation deterioration i.e.ageing. Hence

    they must be prevented.

    No work should be done on the transformer unless it is disconnected from all external circuits and all windings

    have been solidly earthed.

    Naked light and flames should be kept well away from the transformer.

    Precautions must be taken to secure tools with tapes to prevent them from falling inside the tank.

    Maintenance hints on main constituents of the transformer are given in the following paragraph.

    Recommended frequency of maintenance is given at the end of the chapter. Detailed guidance on Maintenance is

    given in I.S. 10028 (part II)- 1981.

    4.2.2 Oil:

    In the transformer, oil is used as an insulating liquid as well as for cooling. It is necessary to maintain requiredoil level and to maintain this oil in good condition. I.S.1866 gives recommendations in details for the

    maintenance of oil. A few guide liners are given here.

    (i) Check if there is any leakage of oil. if noticed, corrective actions must be immediately taken.(ii) The oil level should be checked at frequent intervals and if necessary, topping up should be done with

    oil complying with I.S.335.

    (iii) Samples of oil should be taken at regular intervals and tested.

    (iv) If the dielectric strength is below the value recommended in I.S. 1866, the oil should be duly filtered. It

    may be noted that the products of decompositions viz. water, acids etc. remain in the oil and acceleratethe rate of ageing. Thus, timely treatment of oil is a must. The filteration will remove moisture, dust,

    sludge etc. Removel of sludge is important as otherwise it can stick to coil and hamper the heat

    dissipation from coils. However, if the results indicate that acidity needs to be improved, then a simplefilteration would not be sufficient and a Fullers Earth treatment would be required.

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    4.2.3 Core & Winding :It is recommended that the core and winding are removed from the tank for visual inspection as per the

    maintenance schedule given. Depending upon the arrangement provided, tap switch handle, connections to

    bushings etc. may have to be disconnected before lifting up core and windings assembly.

    The windings should be examined and if sludge has been deposited it should be washed away with oil Jet. Any

    loose nut and bolt should be tightened.

    Adjust the rods/coil clamping screws provided tomremove any slackness of windings. This is important as

    slackness in windings will permit movement of coil under the action of Short Circuit force and repeated coilmovement can wear out insulation and give rise ti a fault.

    4.2.4 On Load Tap Changer:On load tap changer is, normally, mounted on the tank in the separate housing and connected to winding leads

    through copper studs fixed on an insulated terminal board. is oil-tight. Hence oil in the tank need not be

    lowered for attending O.L.T.C.

    In some other types, O.L.T.C. is housed in the main tank by suitable mounting on the top cover. Here againO.L.T.C oil in which arcing takes place is not allowed to mix with the main tank oil.

    Please refer to O.L.T.C. manual for operation and maintenance instructions of O.L.T.C.

    4.2.5 Conservator & Oil level Indicator :The inside of conservator should be cleaned by flushing, clean transformer oil to remove sludge and other

    impurities. In bigger transformers, detachable end plate is provided to facilitate cleaning of conservator.

    - Oil gauge glass should be cleaned. If the glass is found broken, the same should be replaced.

    - Magnetic oil gauge is also to be attended while cleaning the conservator. The mechanism should

    be inspected and cleaned . Flat should be checked to see that there is no oil in the float .Theoperation of alarm and trip contracts should to be checked.

    4.2.6 Silica Gel Dehydrating Breather :

    Breather should be examined to ascertain if the silica gel requires changing. More frequent inspection are

    needed when the climate is humid and when transformer is subjected to fluctuating load. The colour of SilicaGel crystals in the breather acts as an indicator as it changes from blue to pink when saturated with moisture.

    When majority of crystals have turned pink, the silica gel should be reactivated by heating in oven or a shallowpan at a temperature of 1500 C to 2000 C until the original colour is gained . This usually takes 2 to 3 hours. Oil

    cup should be cleaned to removes dust and dirty oil.

    Oil seal should be filled with fresh oil.

    4.2.7 Buchholz Relay :Routine operation and mechanical insepection should be carried out as per the manufacturers instructions.

    4.2.8 Pipe Work :The pipe work should be inspected for leakages, which may be due to bad seated joints. Joints should be re-

    made, and leakage stopped.

    4.2.9 Explosion Vent :The diaphragm at the exposed end of the explosion vent should be inspected and replaced if damaged . Failure

    to replace the diaphragm quickly may allow the ingress of moisture in the transformer.

    Whenever bottom diaphragm ruptures, oil rises inside the explosion vent pipe and is visible in the oil level

    indicator on explosion vent. If diaphragm is broken because of fault in the transformer, inspection should be

    carried out to determine the nature and cause of the fault.

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    4.2.10 Gaskets :Gaskets sometimes shrink during service. It is , therefore, necessary to check the tightness of all bolts/fasteners

    of gasketted joints. The bolts should be tightened evenly around the joints to avoid uneven pressure. Leaky

    gaskets should be replaces as soon as the circumstances permit.

    4.2.11 Temperature Indicators :

    The capillary tubing should be fastened down again if it has become loose. Dial glass should be kept clean. Itshould be replaced if damaged, to prevent damage to the pointer. Temperature indicators found reading

    incorrectly should be calibrated with standard thermometer using hot water bath. Check the pocket/s for

    presence of water and if found ,clean the pocket and refill with fresh oil and seal the opening properly. Ifarmour of capillary is exposed, then retaping must be done by PVC tapes.

    4.2.12 Bushing :Porcelain insulators should be cleaned and minutely examined for any cracks, chipping off & other defects. All

    such bushing should be replaces. In case of any sign of oil leakage from the condenser bushing the matter

    should be referred to us.

    4.2.13 External connections Including Earthing :Check all external electrical connections including earthing . They should be tight. If they apper blackened or

    corroded, unbolt the connection and clean with emery paper. Re,ake the connecteions and give a heavy coating

    of conducting grease. It is particularly important that heavy current carrying connections are properly made asany loose connections give rise to heat generation & temperature rise which could be detrimental to the

    connection.

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    5.0 MAINTENANCE SCHEDULE

    Recommended maintenance schedule is given below. However, depending on the local situation and importance

    of transformer, frequently may be increased.

    Sl Inspection Items to be Inspection Notes Action required if inspection shows

    No. Frequency inspected unsatisfactory conditions-------------------------------------------------------------------------------------------------------------------------------------------------

    1 2 3 4 5

    1. Hourly (i) Ambient Temp - -

    (ii) Winding Temp. Check that the temp. Shut down the transformer and

    investigate(iii) Oil Temperature. rise is reasonable if either is persistently higher

    than normal.

    (iv) Load (amperes ) check against Control load.(v) Voltage rated figure Adjust tap.

    2. Daily (i) Oil level in check against If low, top up with dry oil, examine

    transformer on transformer oil transformer for leakes.load tap changer temperature.

    (ii) Explosion - Replace if cracked or broken.

    (iii) Dehydrating check colour of If silica gel is pink change by sparebreather the active agent and charge.

    that opening is not The old charge may be reactivated for

    clogged. further use.

    3. Quarterly (i) Bushing Examine for cracks Clean or replace as necessary.

    and dirt deposists.

    (ii)Oil in transformer check for dielectric Take suitable action to restore

    and tap changer strength and water quality of oil..

    content.

    (iii) Cooler fan and Lubricate bearings, Replace burnt or worn out contracts

    pump bearings and check gear box. or other parts.motors & operating Examine contracts.

    mechanism. check manual conrol

    and interlocks.

    (iv) On load tap check oil. -

    changer driving

    mechanism.(v) On load tap check all circuits

    changer automatic independently -

    control. Check step by stepoperation includinglimit switches.

    (vi) Dehydrating check oil level in Make up oil if required.

    breather oil cup.(vii) Ventilators Check that air passages -

    (in case of indoor are free.

    transformers)

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    Sl Inspection Items to be Inspection Notes Action required if inspection shows

    No. Frequency inspected unsatisfactory conditions-------------------------------------------------------------------------------------------------------------------------------------------------

    1 2 3 4 5

    4. Yearly (or (i) Oil in transformer check the acidity Filter or replace.

    earlier if and sludge.transformercan convieniently

    to be taken out for

    checking).

    (ii) Insulation Compare with valves Process if required.resistance. at the time of

    commissioning.

    (iii) Gasketted Tighten the bolts evenly tojoints. avoid uneven pressure.

    (iv) Cable Check for sealing Replace gaskets, if leakingBoxes arrangements for

    filling holes. Examine

    compound for craks,

    Check moisture condensate

    If any in air filled boxes.

    (v) Relay Examine relay and Clean the components or

    alarms, alarm contracts and replace contracts and fuses,theircircuits their operation if necessary, change the

    etc. fuses, etc. Check setting if necessary.

    relay accuracy, etc.

    (vi) Temperature Pockets holding Oil to be replenished,

    indicator thermometers should if required.

    be checked.

    (vii) Dial type Check pointer for Adjust if required.Oil gauge. freedom of movement

    (viii) Paint should be inspected Any painting or retouching shouldWork be done if necessary.

    (ix) Earth - Take suitable action if earthresistance resistance is high.

    (x) Surge Examine for cracks clean or replace.

    diverter and dirt deposits.and gap.

    5. Two years (xi) Non- Internal inspection Filter oil regardless of condiation.

    conservator above caretransformer

    -do- (xii) Coil Internal inspection Should be thoroughly cleaned.

    conservator-do- (xiii) Buchholz Mechanical inspection Adjust floats, switches etc. as

    Relay required.

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    Sl Inspection Items to be Inspection Notes Action required if inspection shows

    No. Frequency inspected unsatisfactory conditions-------------------------------------------------------------------------------------------------------------------------------------------------

    1 2 3 4 5

    6. 5Years (xiv) Transformers Overall inspection wash by hosing down with clean dryupto 3 MVA including lifting oil. Tighten coil clamping arrangements

    of core and colts and other bolts, nuts if loose.

    7. 7 to 10 years (xv)Transformers -do- -do-

    above 3MVA

    5.1 Trouble Shooting :At the time of commissioning or periodic maintainece if any abnormalities are observed, corrective action should

    be taken immediately. Guidance for this is given in I.S. 10028 (part III ) Maintenance.

    For a transformer in service, indication of trouble is given by the various alarms provided. These alarms must be

    accepted and corrective action initiated immediately.

    In the case of severe fault or if alarm is not attended the transformer is tripped by the Tripping circuits. This is a

    very undesirable situation and should , possibly, be avoided.

    If tripping and subsequent investigation indicates internal faults, transformer has to be taken out of service.

    Analysis of gas collected in Buchholz Relay can give indication regarding nature of fault.

    Several other methods of testing to assist preventive maintenance are available.

    .