TRANSFORMER MANUAL.pdf

VOLTAMP TRANSFORMERS LIMITED

A GUIDE TO INSTALLATION , COMMISSIONING, OPERATION AND MAINTENANCE OF OIL FILLED TRANSFORMERS

INDEX PAGE NO. 3

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INTRODUCTION

1. 1.1. 1.1 1.2 1.3

TRANSPORT &HANDLING. GENERAL TRANSPORT. UNLOADING & HANDLING STORAGE.

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2. 2.1 2.2 2.2.1 2.2.2 2.2.3 2.3 2.4 2.5 2.6 2.6.1 2.6.2 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15

FITTINGS & ACCESSORIES . RATING & TERMINAL MARKING PLATE TAP CHANGING ARRANGEMENT. OFF-CIRCUIT TAP CHANGING SWITCH. OFF- CIRCUIT RATIO CHANGING LINKS. ON LOAD TAP CHANGER. EARTHING TERMINALS. LIFTING LUGS. VALVES. BUSHINGS. OIL COMMUNICATING TYPE BUSHINGS. CONDENSER BUSHINGS CABLE BOXES. BUS-DUCT TRUNKINGS. “MARSHALLING BOX”. BUCHHOLZ RELAY. RADIATORS. SILICA GEL BREATHER. MAGNETIC OIL LEVEL GAUGE. OIL TEMPERATURE INDICATOR. WINDING TEMPERATURE.

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3. 3.1 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.4.1 3.2.4.2 3.2.4.3 3.2.4.4 3.2.4.5 3.2.4.6 3.2.4.7 3.2.4.8 3.2.4.9 3.2.5 3.2.6

INSTALLATION & COMMISSIONING. GENERAL INSTALLATION. LOCATION FOUNDATION. PROVISION FOR OIL DRAINING. ASSEMBLY OF DISMANTLED COMPONENTS. MAIN TANK BUSHINGS. CONSERVATOR & M.O.G BUCHHOLZ RELAY. BREATHER. RADIATORS. MARSHALLING BOX. CABLE BOX. OTHER FITTINGS. OIL SAMPLING & FILTRATION. AIR RELEASE.

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VOLTAMP TRANSFORMERS LIMITED

INDEX 3.3 3.3.1 3.3.1.1 3.3.1.2 3.3.1.3 3.3.1.4

COMMISSIONING PRE-COMMISSIONING TESTS. RATIO TEST. VECTOR GROUP CHECK TEST. MAGNETISING CURRENT TEST. MAGNETIC BALANCE TEST.

3.3.1.5 3.3.1.6 3.3.1.7 3.3.2 3.3.3 3.3.4 3.3.5 3.3.6

MEASUREMENT OF INSULATION RESISTANCE. SHORT CIRCUIT TEST. PARALLEL OPERATION. OTHER RELEVANT DETAILS. CHECK POINTS. ENERGISING. TOOLS & INSTRUMENTS. COMMISSIONING REPORT.

4. 4.1 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.2.6 4.2.7 4.2.8 4.2.9 4.2.10 4.2.11 4.2.12 4.2.13 5.0 5.1

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OPERATION & MAINTENANCE. OPERATION. MAINTENANCE. GENERAL. OIL. CORE & WINDING. O.L.T.C. CONSERVATOR & M.O.G. BREATHER. BUCHHOLZ RELAY. PIPE WORK. EXPLOSION VENT. GASKETS. TEMP. INDICATORS. BUSHINGS. EXTERNAL CONNECTIONS.

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MAINTENANCE SCHEDULE. TROUBLE SHOOTING.

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VOLTAMP TRANSFORMERS LIMITED

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. I.S. 2026 parts I TO IV I.S.3639 I.S. 335 I.S. 10028- parts I to III I.S. 1866 I.S. 2099 I.S.3347 I.S. 6792 I.S. 8468 I.S.8478 I.S.1646 I.S.3043 I.S 2705 I.S. 3637 I.S. 6600 I.s. 6272

TITLE Power Transformers. Fittings & Accessories for power Transformers. New insulating Oil for Transformers & Switchgears. Code of Practice for selection, Installation & maintenance of Transformers. Code of Practice for maintenance of Insulating Oil. Bushings. Dimensions of Porcelain Transformer Bushings for use in lightly polluted atmosphere. Method of determination of electric strength of insulating oil. On- Load Tap Changers. On – Load Tap Changers Application Guide. Code of Practice for fire safety of Building (General)Electrical Installation. Code of Practice for Earthing. Current Transformers. Specification for Gas-Operated Relay. Guide for loading of oil immersed transformers. Industrial Cooling Fans. - C.B.I.P.-Manual on Transformers. - Indian Electricity Rules.

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VOLTAMP TRANSFORMERS LIMITED 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 constantly made 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 to the 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 is marked 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. All lifting 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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VOLTAMP TRANSFORMERS LIMITED 1.4 STORAGE: On receipt of the Transformer at site, it is desirable to install and commission the transformer with minimum delay. 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. It is 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 the transformers 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 oil before 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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VOLTAMP TRANSFORMERS LIMITED 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 2.2.1

Tap changing arrangement: 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 to the 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 to be 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 assembled transformer 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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VOLTAMP TRANSFORMERS LIMITED The wheel Valves are used either with female screw threads or with flangs. These are of gun-metal/cast iron type. Generally, one Isolating Valve also known as shut off valve is provided for transformer upto 2000KVA between 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 2.6.2

BUSHING: 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 the tank 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 be removed 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 are sealed 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 per manufacturer’s 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 by new 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 main lead 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 not visible, 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 and pull 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 terminal bolt downward. (xi) Fix upper and lower arcing horns and adjust the gap setting as per the required Insulation Coordination.

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VOLTAMP TRANSFORMERS LIMITED 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 provided with 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.

2.8

When cable Boxes are provided with disconnecting chambers they permit removel of transformers for servicing without disturbing cable terminations. 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 for the 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 from mains. 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 on top 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 or development 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 to severe 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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VOLTAMP TRANSFORMERS LIMITED (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 the transformer 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. -

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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 air is 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 its lower 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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VOLTAMP TRANSFORMERS LIMITED Due to the chemical affinity possessed by Silica Gel Crystals, they absorb moisture from the drawn in. The Colour 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 high level 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 low level. 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 in the 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 small ratings. 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 glass cover. 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 protection of 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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VOLTAMP TRANSFORMERS LIMITED 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 Spot Temperature (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 similar To 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 the Instrument 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 - ISH For the particular transformer, the shunt is adjusted at factory for the applicable Winding Gradient WTI also has Alarm &Trip contracts. For Fan cooled transformers auxiliary contracts of WTI are used for fan switching.

2.16

REPEATER OTI & WTI INSTRUMENTS Repeater 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 SEPARATOR Also 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 to resist transformer oil and internally to resist external atmosphere.

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VOLTAMP TRANSFORMERS LIMITED It is fitted inside the conservator such that variations in oil volume due to variations of temp. are taken up by the Flexible 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 FLEXIBLE SEPERATOR. 1) Set up the separator inside the conservator by suspending it from the hooks provided. 2) Keep the 2 Nos. ½ “ , SSF wheel valves at the top of the conservator open. Inflate the separator 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 pressure drop 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 the MOG 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 ½ “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 an optional 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 is connected 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.

12

VOLTAMP TRANSFORMERS LIMITED OLTC is generally operated electrically through a Remote Tap Control Cubicle (RTCC) LOCATED IN Control Room. 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 user’s 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 the current 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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VOLTAMP TRANSFORMERS LIMITED

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 precommissioning tests 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 “ Commissioning Report”. 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 Coordination 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 times provided 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 Relay” and 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 own separate 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.

14

VOLTAMP TRANSFORMERS LIMITED 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. This oil 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.Fit by 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 steadily from 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 next radiator 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 local conditions. 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 cableboxes 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 terminal connector. 3.2.4.9 Other Fittings: Note the details of other important fittings like fans in the “Commissioning Report”and mount these fittings. 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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VOLTAMP TRANSFORMERS LIMITED

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 to do 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 voltages on 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 equal while 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 in the 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 & W phase 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 manufactures’ works. 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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VOLTAMP TRANSFORMERS LIMITED 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 oppose establishment 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 that case 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 “Commissioning Report”. 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 power Cables. 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 an OFF-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.

17

VOLTAMP TRANSFORMERS LIMITED 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 two KVAs. (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 connected in 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 the minimum. 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 Φ or 12mm Ф 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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VOLTAMP TRANSFORMERS LIMITED 3.2.13

COMMISSIONNING REPORT

CLIENT :

DATE:

TRANSFORMER DETAILS : TRANSF. SR. NO : RATING : TAPPING RANGE : CONNECTION : SUPPLIED ON : INSTALLED AT :

MAKE: VOLTAGE RATIO : BY OFF CKT. SWITCH/ OL.T.C VECTOR GROUP :

(1) Oil Test Results : Details of Oil Test Set Make : Observed BDV (a) Main Tank Oil

Type : Motorised/ Manual , Gap : 2.5 mm

(b) O.L.T.C

: : :

(c) Cable Box Oil

:

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

Before Filteration: After Filteration: Before Filteration : After Filteration : Before Filteration : After Filteration ; Make KV Sr. Nos.

(2) Arching Horn Gap on H.V. Bushings adjusted to ………mm (3) L.V Bushinga

make KV Sr. Nos.

(4) Arching Horn Gap on L.V Bushing adjusted to ……….mm (3) Details of Magnetic Oil level Gauge: Make: Wired } : Alarm for } : Trip Tested } : Alarm for } : Trip 4. Details of Buchholz & oil Surge Relays : 4.1 Buchholz Relay : Make : Tested} : Alarm for } : Trip

Type: Yes/ No Yes / No Yes/ No Yes/ No

Type : Yes /No Yes / No

4.2 Oil Surge Relay (on OLTC) ; Make : Tested for : Trip Notes : (1) Both relays connected in control circuitry (2) Control circuit Checked for Operations through: (a) Buchholz Relay (b) Oil Surge Relay

19

Type : Yes /No Yes /No Yes / No Yes / No

VOLTAMP TRANSFORMERS LIMITED 5.

Details of Breathers : CHECK

Main Tank Breather

MAKE TYPE / MODEL Colour of Silica Gel Oil level in Breather

OLTC Breather

Blue /Pink OK /Not ok

Blue /Pink OK / Not Ok

6. Details of Radiators & Radiators Valves : 6.1 Radiators Make : Type : No : 6.2 Radiators Valves : Make : Type : No : 7.

Oil and winding temperature indicators : CHECK MAKE TYPE ALARM SET TRIP SET TESTED FOR ALARM TESTED FOR TRIP

7.1 Pressure Relief Valve : Make : Type : Tested } : Alarm For } :Trip Note : (1) O. T. I & W.T.I. connected in control circuitry. (2) Control Circuit Checked for operation through.

OTI

WTI

0

0

C C Yes / No

C C Yes / No

Yes / No

Yes / No

0

0

Yes / No Yes /No Yes / No Yes / No Yes / No Yes / No

: OTI : WTI : P.R.V

8. Details of Cooling Fans : Make : Type : Nos : Fan control through } : W.T.I } : Group I of fans set for Group II of Fans set for

OK /Not OK 0 0

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C. C.

VOLTAMP TRANSFORMERS LIMITED

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 Voltage Applied Between Terminals = Tap. L.V. Voltage Measured Between Terminals =

Do

Do

Do

Do

1

Remarks

(1) Checked Ok for Consistent Variation Yes / No (2) Checked Ok for Rated Voltage Ratio Yes /No

2 17

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

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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Voltage

VOLTAMP TRANSFORMERS LIMITED

12. Magnetic Balance Test : Sr No

Voltage between terminals Corresponding To U Phase

1

Corresponding To V phase

Corresponding To W Phase

Applied Voltage = Current Drawn =

2

Applied Voltage = Current Drawn =

3

Applied Voltage = Current Drawn = Observed distribution of voltage confires absence of any shorted turns. 13. Measurement of Insulation Resistance : (a) For Transformer : (1) Between H.V. and Earth = (2) Between H.V. and L.V. = (3) Between L.V. and Earth = Transformer Top Oil Temp. =

………. ………. ………. 0 C.

Details of Megger : (1) Make : (3) Voltage : (b) For Power Cable : Type : Temp : ……….0 C. (1) (2) (3) (4) (5) (6)

Mohms Mohms. Mohms

(2) Sr. No. : (4) Range :

U Phase to earth V Phase to earth W Phase to earth U Phase to V Phase V Phase to W Phase W Phase to U Phase

Mohms. Mohms. Mohms. Mohms. Mohms. Mohms.

REMARKS :

22

Yes / No

VOLTAMP TRANSFORMERS LIMITED 14. Short Circuit Test : Applied Voltage = 3 phase , 50 Hz. 1U – 1V = 1V – 1W = 1W -1U =

Tap No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

IU A

Volts.

IV A

IW A

ILT A

15. Details of Control Panel/ Protective System : (1) H.V Circuit Breaker : Make : Type : MVA : I-rated KV : Release Setting = (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 : Time Setting : (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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VOLTAMP TRANSFORMERS LIMITED

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

Make :

Type :

No of Cores 1. 2. 3. 4.

Accuracy Class

(7) Earthfault/ Overcurrent/Different Relay on L.V. side : Make : Mounted on Phase Current : Setting : 16. Details of O.L.T.C : Make : Sr. No (a) Manual Operation (b) Local Electrical Operation (c) Remote Electrical Operation

Type : Time : Setting : Type : Year : OK / Not OK OK / Not OK OK / Not OK

17. COMMISSIONING CHECK POINTS ; 1. Oil Samples from main Tank O.L.T.C. have passed BDV requirement. 1a. Bushing surfaces are cleaned. 2. Test Tap Caps are fully tightened. 3. Arching Horn-gaps are duly adjusted. 4. Oil level main conservator is upto mark. 5. Oil level in O.L.T.C Conservator in separate Conservator or Compartment in main conservator 6. M.O.G. lock is released. 7. Buchholz Relay lock is released. 8. Buchholz Relay Test Lever is kept in ‘S’ position. 9. Buchholz Relay shut off valves on both sides are open. 10. Air Release valve of Buchholz Relay is closed. 11. Buchholz Relay arrow head is pointing towards conservator. 12. Lock of Oil Surge Relay (OSR ) on O.L.T.C. is released. 13. OSR shut off valve is open. 14. OSR arrow-head is pointing towards conservator. 15. Colour of silica Gel in main breather is blue. 16. Oil is filled in main Breather upto level mark. 17. Sealing Tape of main Breather is removed.

Yes / No. Yes /No. Yes /No. Yes /No. Yes / No. Yes / No Yes / No. Yes / No. Yes / No. Yes / No. Yes / No. Yes / No. Yes / No Yes / No. Yes / No. Yes /No. Yes / No. Yes /No.

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VOLTAMP TRANSFORMERS LIMITED 18. Colour of Silica Gel in O.L.T.C. breather is blue. 19. Oil is filled in O.L.T.C breather upto level mark.

Yes /No. Yes /No.

20. Sealing Tape of O.L.T.C. breather is removed. 21. All radiator Valves-Top and bottom are open. 22. Valve connecting min Tank to Cable Box is open. 23. Oil is filled in disconnecting Cable Box upto Level Mark. 24. All sampling, drain and filteration Valves are closed. 25. Oil filling cap on main conservator is duly filled. 26. There is no oil leakage from any where. 27. Explosion vent diaphragms are intact and there is no oil in explosion vent. 28. Oil is filled in O.T.I /W.T.I pockets. 29. Air released from : (i) All Bushings (ii) All Bushings Pockets (iii) Buchholz Relay. (iv) Main Tank Cover. (v) All radiators. (vi) OSR on O.L.T.C (vii)O.L.T.C. Tank Cover. 30. O.L.T.C. /Off Circuit Tap Switch is in the desired position and is properly locked. 31. Tank earthing is done. 32. Neutral earthing is duly done. 33. Rollers are locked. 34. C.T. secondary terminals, if not wired, are shorted and earthed. 35. Alarm & Trip contracts of O.T.I & W.T.I. are set at the required valves. 36. External connection are duly tightened.

Yes / No. Yes /No. Yes /No. Yes /No. Yes /No Yes /No Yes / No. Yes / No Yes /No. Yes /No. Yes /No. Yes /No. Yes /No. Yes / No. Yes / No Yes /No Yes /No Yes /No. Yes / No. Yes /No. Yes /No Yes /No Yes / No.

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 our presence Subsequently Load was also taken. Nothing abnormal was observed during these operation. For Customer :

for VOLTAMP

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VOLTAMP TRANSFORMERS LIMITED

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 the ambient 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 of loading 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 of regular 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 required oil 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) (ii) (iii) (iv)

Check if there is any leakage of oil. if noticed, corrective actions must be immediately taken. The oil level should be checked at frequent intervals and if necessary, topping up should be done with oil complying with I.S.335. Samples of oil should be taken at regular intervals and tested. 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 accelerate the 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 simple filteration would not be sufficient and a Fullers Earth treatment would be required.

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VOLTAMP TRANSFORMERS LIMITED 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 coil movement 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 again O.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 .The operation 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 Silica Gel 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 shallow pan 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 manufacturer’s 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 remade, 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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VOLTAMP TRANSFORMERS LIMITED 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. It should 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. If armour 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 as any loose connections give rise to heat generation & temperature rise which could be detrimental to the connection.

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VOLTAMP TRANSFORMERS LIMITED

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.

2.

3.

Hourly

Daily

Quarterly

(i) Ambient Temp (ii) Winding Temp.

Check that the temp.

(iii) Oil Temperature.

rise is reasonable

(iv) Load (amperes ) (v) Voltage

check against rated figure

(i) Oil level in transformer on load tap changer

check against transformer oil temperature.

If low, top up with dry oil, examine transformer for leakes.

(ii) Explosion (iii) Dehydrating breather

check colour of the active agent and that opening is not clogged.

Replace if cracked or broken. If silica gel is pink change by spare charge. The old charge may be reactivated for further use.

(i) Bushing

Examine for cracks and dirt deposists. check for dielectric strength and water content.

Clean or replace as necessary.

(iii) Cooler fan and pump bearings and motors & operating mechanism.

Lubricate bearings, check gear box. Examine contracts. check manual conrol and interlocks.

Replace burnt or worn out contracts or other parts.

(iv) On load tap changer driving mechanism. (v) On load tap changer automatic control.

check oil.

-

(ii)Oil in transformer and tap changer

(vi) Dehydrating breather (vii) Ventilators (in case of indoor transformers)

check all circuits independently Check step by step operation including limit switches. check oil level in oil cup. Check that air passages are free.

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Shut down the transformer and investigate if either is persistently higher than normal. Control load. Adjust tap.

Take suitable action to restore quality of oil..

-

Make up oil if required. -

VOLTAMP TRANSFORMERS LIMITED 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 earlier if and sludge. transformer can convieniently to be taken out for checking). (ii) Insulation resistance.

check the acidity

Filter or replace.

Compare with valves at the time of commissioning.

Process if required.

(iii) Gasketted joints.

5.

Two years

-do-do-

Tighten the bolts evenly to avoid uneven pressure.

(iv) Cable Boxes

Check for sealing Replace gaskets, if leaking arrangements for filling holes. Examine compound for craks, Check moisture condensate If any in air filled boxes.

(v) Relay alarms, theircircuits etc.

Examine relay and alarm contracts and their operation fuses, etc. Check relay accuracy, etc.

Clean the components or replace contracts and fuses, if necessary, change the setting if necessary.

(vi) Temperature Pockets holding indicator thermometers should be checked.

Oil to be replenished, if required.

(vii) Dial type Oil gauge.

Check pointer for freedom of movement

Adjust if required.

(viii) Paint Work

should be inspected

Any painting or retouching should be done if necessary.

(ix) Earth resistance

-

Take suitable action if earth resistance is high.

(x) Surge diverter and gap.

Examine for cracks and dirt deposits.

clean or replace.

(xi) Nonconservator transformer

Internal inspection above care

Filter oil regardless of condiation.

(xii) Coil conservator (xiii) Buchholz Relay

Internal inspection

Should be thoroughly cleaned.

Mechanical inspection

Adjust floats, switches etc. as required.

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VOLTAMP TRANSFORMERS LIMITED 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 upto 3 MVA including lifting of core and colts

7.

7 to 10 years

(xv)Transformers above 3MVA

-do-

wash by hosing down with clean dry oil. Tighten coil clamping arrangements and other bolts, nuts if loose. -do-

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. .

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