VOLTAMP TRANSFORMERS LIMITEDA GUIDE TO INSTALLATION , COMMISSIONING, OPERATION AND MAINTENANCE OF OIL FILLED TRANSFORMERS INDEX x 1. 1.1. 1.1 1.2 1.3 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 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 INTRODUCTION TRANSPORT &HANDLING. GENERAL TRANSPORT. UNLOADING & HANDLING STORAGE. 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. 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. PAGE NO. 3 4 6 13 1 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 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 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 COMMISSIONING PRE-COMMISSIONING TESTS. RATIO TEST. VECTOR GROUP CHECK TEST. MAGNETISING CURRENT TEST. MAGNETIC BALANCE TEST. MEASUREMENT OF INSULATION RESISTANCE. SHORT CIRCUIT TEST. PARALLEL OPERATION. OTHER RELEVANT DETAILS. CHECK POINTS. ENERGISING. TOOLS & INSTRUMENTS. COMMISSIONING REPORT. 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. MAINTENANCE SCHEDULE. TROUBLE SHOOTING. 27 16 29 2 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. 3 Routine Tests in accordance with I. 20). sight glass etc.2 TRANSPORT. can be supplied on request. for active part. Following should be particularly observed: (a) Dents on tank wall. Transformers are dispatched in one of the following modes : (a) Completely filled with oil. They should be handled in their upright position as indicated on the cases. They will give long and trouble-free service when properly installed. 40mm below top cover). Each jacking pad is designed to take approximately 25% of the total load. Lifting lugs provided for partial lifting (e. with asterisks against list of fittings with an appropriate note. Roller axles or radiators should not be slinged for the purpose of towing. 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. 2026/I. Rollers should be used for shifting the transformer from one place to other. dismantled for transport. All lifting lugs must be used to avoid unbalanced lifting and undue stresses on lugs. jacks should be used anywhere else other than these specially provided pads.3 UNLOADING & HANDLING : On receipt at site. in the packing list.g.S.S. Packed components should be carefully unpacked and all parts/components received should be examined for transit damages. the transformers supplied may differ in minor details from the data here under. Space above Oil level is filled with air at normal atmosphereic pressure. oil filled bushings etc. Transformers should be carefully examined for transit damages. transformers should be unloaded by means of crane or lifting devices of adequate capacity. 1180 are carried out on all transformers.) must not be used for lifting complete transformer. manufactured and tested with due care.VOLTAMP TRANSFORMERS LIMITED 1. conservator etc. Under no circumstances. 1. (b) With oil covering coils and top yoke (approx. (Refer Fig. Transformers of higher ratings are provided with four jacking pads. (b) Damage to protruding parts like valves.1 GENERAL: All our Transformers are designed. Pulling holes provided on the tank for this purpose should only be used. Parts other than lifting lugs must not be used for lifting. which are dispatched in different packages are given numbers and these numbers are indicated together with contents. 4 . filling in radiators etc. All parts which are dismantled are packed either separately or in a group as appropriate. Any additional information. radiators. External damages could be indicative of severe internal damages. 1.1) All other parts and case containing accessories should be unloaded by using lifting lugs. As efforts are being constantly made to improve designs and services. While slinging care should be taken to avoid sling touching other parts. 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. 2. TRANSPORT & HANDLING 1.. Each packing case is marked or numbered and is included in the packing list alongwith the description of contents. Fig. . operated and maintained. Oil for topping up. (Ref. if required. (c) Oil leakage around or through welds. Accessories such as conservator. In case anything abnormal occurs during the service. is dispatched separately in sealed drums. External arrangement drawings indicate various accessories. Drums should not be stored standing on end but should be placed on their sided with the bung at 45degree downwards. The breather incorporates an oil sealing device which must be filled with oil to the marked level to be effective. they are likely to be damaged. all pipe work. . It is very important that drums are stored free from fire and explosion hazards. 5 . In case. it is advisible to flush them with clean transformer oil before use. Down Voltage (BDV) of oil atleast once in a month and should be maintained at a level of 50K.VOLTAMP TRANSFORMERS LIMITED 1. this is not possible. If these are stored for longer period like six months or so. . dial type temperature indicator. the drums should be stored in a covered space where temperature variation is minimum. If it is necessary to store the drums outside. . If they are not stored properly. in position. it is recommended to mount rollers by jacking –up the transformers to enable free flow of air underneath. radiator. terminal box. OIL DRUMS.It is advisable to check the condition of silica gel during storage atleast once a week and Break.4 STORAGE: On receipt of the Transformer at site. the silica-gel breather should be fitted. buchholz relay.Even during temporary storage. adequate protection must be provided. Two or three runs from one end of the range to the other are considered sufficient. The conservator pipe work and radiators are dispatched with blanking plates and these are to be stored with their blanking plates. A periodic watch should be kept on the silica-gel breather to ensure that the gel is blue. should be stored indoors till such time they are not required.The tap changer should be operated at six monthly intervals.Accessories like bushings. The gel should be replaced or dehydrated immediately on its turnings pink. it is desirable to install and commission the transformer with minimum delay. 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 . If oil received in drums is not likely to be used immediately. it is necessary that switch handle assembly is dismantled before untanking. No. 2. The earthing terminals should be connected to the earthing. The switch mechanism is such that it can be locked only when it locked in its position and not in any intermediate position. The locking device is fitted to the handle to lock in any tap position. The transformer is normally fitted with an off-circuit tap changing switch to obtain required voltage ratio. THE TRANSFORMERS MUST BE ISOLATED FROM ALL LIVE LINES.5 6 . BEFORE OPERATING THE SWITCH. All lugs are designed for simultaneous use and must be accordingly. Two earthing terminals are provided on the transformer tan. voltage ratio. 2.3 2. etc. The plate contains information concerning the rating . The automatic voltage regulation can also be provided as an optional fittings. Valves are fitted with plugs/blanking plates to stop oil coming out. Two/Four lifting lugs are provided for untanking the core and windings of larger capacity transformers. Operating the switch when transformer is energized . In case of conservator units. and year manufacturing.2 2. please refer to the attached manual of OLTC and schematics. Tap changing arrangement: Off-Circuit Switch.2. and filter valve at top of the tank.2. oil level has to be lowered below the inspection cover before the unbolting inspection cover. The plate also includes unit Sr. The on-load tap changes are provided with local manual control. When the switch handle is provided on the side wall. 2.2. will damage the switch contacts due to serve arcing between the contracts and may damage transformer winding.VOLTAMP TRANSFORMERS LIMITED 2. weights.1 FITTINGS & ACCESSORIES Rating & Terminal marking Plate : (R & D Plate) The transformer is supplied with rating and terminal marking plate made out of non-corrosive metal.4 2. Valves: Every transformer is provided with drain cum filter valve at bottom of the tank. oil quantity vector group. 2. Links are accessible from the inspection cover. The tappings are located on high voltage winding.2 Off-Circuit Ratio Changing links: Sometimes links are provided inside the transformers tank to obtain required voltage ratio. (ii) Butterfly Valves. On –Load Tap Changer: The on-load tap changer is an optional fitting. (i) Wheel Valves. Lifting Lugs: Two/Four lifting lugs of adequate capacity are provided on tank sides/top cover to lift fully assembled transformer filled with oil.3 Earthing Terminals: The core lamination assembly is connected to core clamping frame which is in turn connected to the tank. All heavy fittings are also provided with individuals lifting lugs. Mainly two types of valves are provided. For further details. local electrical control and remote electrical control.1 2. Links are required to be loosened and fixed in new required position as given in R &D Plate. It can be hand-operated by switch handle mounted either on tank or on the tank side . 2. 2.5. These are of gun-metal/cast iron type. Typical Bushing Assemblies are shown in Figs. (v) Suitably raise the bushing and remove the protective cover at the oil end of the bushing. Fig .2 Condenser Bushings : Generally. Assembly and dismantling of single piece type bushing is possible without disturbing the active part. These bushings contain their own oil and are sealed to retain the same.6).6 2. Continue the operation till the bushing rests on its flange pocket. These bushings are not detached at the time of transportation. (iv) Remove the blanking plate and uncoil the draw through type lead.whereas all other bushings are of single piece porcelain type. (vii) During the lowering operation.6. do not mount that bushing. 2.S. The shape and the size of the bushing depend on the voltage class. They are packed as per manufacturer’s instructions. Generally. Also do not attempt to fill oil at site as such bushing is most likely to fall in service. Condenser Bushings are used for 72. Type procedure for mounting is as follows: (i) Open the bushing case carefully and check it for transit damage and clean the bushing thoroughly.VOLTAMP TRANSFORMERS LIMITED The wheel Valves are used either with female screw threads or with flangs. In case it is not visible. Dimensional details and associated parts generally conform to IS-3 upto 36KV class. (xi) Fix upper and lower arcing horns and adjust the gap setting as per the required Insulation Coordination.6.4. 7 . of suitable length.S.3. The bushings are installed on the cover or. The cable bolt to be used on the unit is brazed to the end of the flexible draw through type lead mentioned above. The draw through type lead is coiled and kept temporarily below the bushing blanking plate (Ref. 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. These bushings are detached from the transformers and dispatched separately. For bushing of two piece construction. type of current. 2099 & I. thread the flexible steel wire through the inside tube of the bushing and pull it. clean the seat of the gasket and replace it by new one. remove the flexible wire and insert the locking pin (3) to hold the cable bolt downward. If not. on side walls of the transformer tank. (Ref.5KV and above. (viii) Hold the cable bolt in position. unscrew the terminal cap and press the terminal bolt downward. Bolt the two flanges and remove the slings. Electrical performances of these bushings conform to I. (ix) Fix the terminal cap (1) in position by screwing it on the terminal bolt. tank cover is required to be removed for necessary access to the inner (lower) end of the bushings. 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.2 BUSHING: Oil Communicating type : Transformers windings are connected to the external circuit through terminal bushings. Bushings of 1000 Volts are of two piece construction without arcing horns. one Isolating Valve also known as shut off valve is provided for transformer upto 2000KVA between conservator and buchholz relay.7) (vi) Check that Oil Level in the bushing is appearing in the Oil Level indicating glass. (iii) Remove the locating pin (3). (x) For removing air from the central tube after oil filling. Whenever these bushings are mounted on bushing pockets or raised truncated portions. 2mm in dia . (ii) Check whether the gasket on the pocket is in order. Fig.7421. 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. The butterfly type cast-steel valves with the machnical flanges are used at points of connection between tank and detachable radiators. The equipment required for mounting the bushings are (i) rope sling (ii)flexible steel wire approx. VOLTAMP TRANSFORMERS LIMITED 2. etc. 8 . 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. Busduct is supplied by some other agency. The capillaries from OTI & WTI come from the bottom of the Marshalling box through suitably recessed gland plate thus preventing ingress of dust. 2. When cable Boxes are provided with disconnecting chambers they permit removel of transformers for servicing without disturbing cable terminations. The Marshalling box is made of sheet metal and is provided with a glass window for observing OTI & WTI. This box called marshalling box. 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. Earthing terminals are also provided on these cables boxes for earthing the armouring of individual cables. the cables from all such contracts are wired upto a weather-proof terminal box. bushing terminal details. (b) Surge of oil is developed on account of sudden increase in pressure inside the transformer due to severe fault. However. conservator or relay itself. The cable box in such case must be filled with compound as marked as indicated in the drawling. gas and oil operated apparatus which detects formation of gas or development of sudden pressure Inside the oil filled transformers. as result of incipient fault. It has a detachable gland plate with glands through which cables enter and leave.10 Buchholz relay : Buchholz Relay is a very sensitive. (c) Oil level in the relay is reduced below the minimum level. The level of the busduct flanges from ground /rail level is indicated in the General Arrangement drawings of the transformer. It has hinged door with locking facility to prevent unauthorized access. 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.9 Marshalling Box : The transformer is provided with certain fittings directly mounted on the transformer at various locations. Bus-duct/trunkings : Some users prefer connections to load by means of busduct. It has a rain shed provided on top to prevent rain falling directly overit. bolt spacing. 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. 2. These cable boxes are provided with brass wiping glands and are designed with clearances inside the box suitable for compound filling. is also used for housing Oil Temperature Indicator (OTI) and winding Temperature Indicator (WTI). Cable boxes for PVC ar XLPE cables are designed with air clearances and hence these boxes are not required to be filled with compound.6 KV and above are provided with detachable gland plate. Other probable reasons for dropping of oil level in the relay are: (a) Leakage of oil from main tank.7 Cable Boxes : Cable boxes are designed for receiving and protecting cable ends. Cable boxes of 3. The complete details of busduct flange is furnished by us giving complete dimensional details for the matching flanges. Due to gas collection. we provide suitable flanges/trunkings around transformer bushings for receiving the busduct. In order to facilitate connections of all such devices to the protective scheme. All these provisions make Marshalling Box a Weather-Proof enclosure. 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 relay is fitted in the oil connection between conservator and tank. Insulating paper is most hygroscopic and all paper insulated cable ends must be protected by suitable insulating compound.8 2. 18). Upper bucket contracts (A) are connected to audible alarm -‘A’. The relay is mounted in position with associated piping and isolating valves at works.circuit and lower bucket contracts -(T). External surface is cleaned off all rust and one coat of Red oxide primer is applied which is followed by final painting. However. Distribution Transformers are normally provided with Radiators welded to tank. a window for observation of oil level and an oil filling hole with gasket and plug. made from M. Each radiator consists of number of “Sections made from presses CRCA Sheets forming channels for oil flow. Mount the Buchholz Relay between conservator and transformer tank cover along with piping & valves without straining the pipe line. Lifting Lug. At the time of dispatch. Owing to transport limination and possible transit damages. The number of section per radiator and the number of radiators per transformer will depend upon the losses and permissible temperature rise. After filling oil in the transformer. The lower part of the casing has at its lower end an oil seal arrangement.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.VOLTAMP TRANSFORMERS LIMITED (b) Collection of air in the relay which is trapped earlier in the tank and in the winding. & hence in the volume of oil.S Flanges at Top & Bottom. checks the relay for any damage to window glasses and mercury switches. air trapped inside the relay is to be realized through the valve/petcock provided on top of buchholz collection. 2.are connected to trip circuit. In such cases. It has a flange connection at the top for connecting the breather to the breather pipe. These contaminants deteriorate the insulation properties of oil. A typical – Silica Gel Breather has following main components: (1)A casing. Increase in oil volume. When gas is collected. Fig. (2) Silica Gel Crystals.S Flat are provided on radators to prevent vibration of sections. On receipt at site. MOUNT RELAY SUCH THAT AROW DIRECTION POINTS TOWARDS CONSERVATOR. These “Sections” are welded to Header Pipes at Top & Bottom. 2. the buchholz relay assembly is dismantled and sent separately. these radiators are detached and sent separately keeping the valves in position on tank flanges. In larger transformers . Hence Silica Gel Breather is provided which arrests moisture and dust from the air drawn in. Flanged radiators are fitted with Air Release Plug. 9 . Detachable radiators are provided with M. Thus the transformer “Breathes”. To ensure successful operation of the relay the pipe work on either side of the relay is set inclined to horizontal by 3-5degree. it sent in ‘Test’ position to prevent damage in transit. - Radiators are cleaned Internally to remove scales and a coat of varnish is applied. it must be ensured that this valve is kept open and the pipe is full of oil. Drain Plug. important function of this relay is to disconnect transformer from circuit under sudden development of pressure indide the transformer due to severe internal fault. power transformers are normally provided with detachable radiators with radiator valves (Ref. The casing has a window at the upper part for observation of the colour of the gel crystals. Isolating valve must be fully opened after mounting is completed. Bracing Straps. 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. causes the air above the oil level in the conservator to be pushed out and decrease causes air to be drawn in. When air is breathed in. oil from pipe will flow outn first and then gas will come out.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. When Test Lever is provided. The lower bucket operates similar to upper bucket when level in the relay drops further . etc. (3) An oil seal at the lower end of casing. there is possibility of moisture and dust from atmosphere to be sucked in. The dial has three positions marked. The oil acts as a coarse filter and removes the dust from the outside air when it passes through oil.When this magnet is at a position corresponding to low oil level the mercury switch close the Normally open (NO ) contacts.T.A Typical – Oil temperature indicator consist of a . . as it would break communication between bulb and Bourdon tube. 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 contacts are brought to a terminal box at the lower end of the dial. This protection feature and clear visibility justify the cost of MOG on a bigger transformer It consists of two compartments. The movement of float is. Both the pointers are independently adjustable and can be set to desired temperature. they absorb moisture from the drawn in. There is a temperature sensing bulb which communicates to the Bourdon tube through the armoured capillary. In large transformers conventional glass oil level indicators are difficult to observe due to their heights and colour change/dust accumulation on the glass. when duly wired give an alarm.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. of oil. On the oil side compartment.The OTI is generally housed and wired upto terminal strip in the marshalling box having a glass window on the door for observation. Setting of these pointers at required temperature can be done from outside through the knob by using special keys. 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. for external connections. Guide for loading of oil immersed transformers.S. Movement of the float due to rise and fall of oil level in the conservator results into circular motion of driving magnet. - 10 .Bourdon tube with pointer arrangement mounted in a case comprising of a reading dial and a glass cover. eliminating direct oil light mechanical coupling. there is a bevel gear wheel and it is positioned near the diaphragm. If the oil temperature increases beyond set limit due to overload or inadvertent closure of radiator valves or insufficient air draft.The oil temperature indicator is provided with two pointers and associated contracts for protection of transformers. therefore . The length of capillary does not influence the accuracy of measurement and extra length of capillary tubing must not be cut. These Compartments are sealed against leakage of oil by a metallic diaphragm. (b) The pointer side compartment. The follower magnet has also a cam fitted on it which operates a mercury switch. The colour of crystal can be observed from outside of the casing. . (a) The oil side compartment which is fixed on the opening in the conservator. The direct reading pointer arrangement in this Instrument greatly facilitates observation of working temp. 2. It also helps. A follower magnet is positioned in the pointer side compartment neat the diaphragm.I) : Oil Temperature indicator (O.I) is generally provided on all transformers except for very small ratings.VOLTAMP TRANSFORMERS LIMITED Due to the chemical affinity possessed by Silica Gel Crystals. . The Colour of silica gel is blue when dry and turns pink when it is saturated with moisture. These contacts are normally wired to give audible alarm. Further. the indicating pointer touches the present alarm pointer and actuates the alarm contacts. 2. The alarm contacts. transferred through the diaphragm. 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.14 Oil Temperature Indicator (O.T. 6600-1972. deciding the permissible overloads in accordance with I. This magnet has its poles face to face to the poles of driving magnet from the oil side compartment coupling them magnetically. if need be. The dial and the pointer area housed behind the front glass. Silica gel breather is dispatched in a separate case. If the alarm is not attendedand threr and isolate the transformer from mains. It is fitted to the transformer tank similar to a radiator with provision of isolating valves. the adsorbent material) and in the process.can be operated by RTDs. the shunt is adjusted at factory for the applicable Winding Gradient WTI also has Alarm &Trip contracts. DETECTORS (RTSs) Temp. They are housed inn UNIT BOX mounted on the transformer.I) : A Winding Temp. In this case also Power Supply Unit and RCXT Unit will be required and they are provided in the Unit Box. UNIT BOX and RTCC Panel are supplied along with transformer.I.I.19 FLEXIBLE SEPARATOR Also known as ‘Diaphragm Conservator’ or ‘Rubber Diaphragm’. The bulb of the instrument is placed in an oil filled pocket located on the top cover of the transformer similar To O.ISH For the particular transformer. coated externally to resist transformer oil and internally to resist external atmosphere. organic acids etc. For Fan cooled transformers auxiliary contracts of WTI are used for fan switching.VOLTAMP TRANSFORMERS LIMITED 2.e. They are generally provided in the RTCC Panel.I. sensing load current.17 2. drain valve etc. It is an optional fitting and is provided when ordered.T. Due to the convection current set up in oil . when it is a part of contract. nonporous flexible bag of a highly resistant fabric. And is adjusted to read HST = [ Top Oil Temp] + 1.c Digital Repeater (d) 4-20 mA. The Heater Coil is fed by the W.T . D. It is a container having perforated trays filled with Activated Alumina. The adjustable shunt by-passes certain amount of current (ISH ) from the C. REPEATER OTI & WTI INSTRUMENTS Repeater OTI & WTI instruments are Optional Fittings and are provided when ordered. Wiring Diagrams and Interconnection Diagrams necessary for the wiring of Marshalling Box.18 2. D.(c) &(d).15 WINDING TEMPERTURE INDICATOR (W. When. 2. oil flows continuously over the exposed surface of Activated Alumina (i. contaminants like moisture. Rise of winding over surrounding oil) which is dependent on Load Current. The ‘Flexible Separator’ is a sealed. Thus Heater Coil Current ISH = IS . A typical WTI arrangement comprises of the following: (a) WTI Instrument having a temp. In case (b).1 x Gradient The heater coil is provided with an adjustable resistive shunt (Ref. Sensing bulb and capillary similar to O. Detectors (RTDs). (b)A current Transformer mounted on one of the transformer leads. 11 . get collected in the absorbent material and thus improve the quality of oil. Thus the Temperature indicated by WTI accounts for (i) Temp. It is set to read Hot Spot Temperature (HST).I pocket. generated due ti ageing of insulation.C.T. of Top oil and (ii) Winding Gradient (Temp. Here again Repeater Instruments are provided when ordered. Thus O.I &W.T.T. so ordered. They are available in one of the following types : (a) Simple Analog Repeater (b) 4-20 mA.T. Indicator (WTI) is an optional fitting and is provided when ordered.24) in parallel which allow the Instrument to be adapted for a range of winding gradients. OTI & WTI INSTRUMENTS OPERATED BY RESISTANCE TEMP.16 2. Resistance to Current Converter (RCXT) and /or Current Converter (CCXT) etc. they are provided accordingly. they also require Auxiliary Devices like Power Supply Unit.T. Periodic recharging of adsorbent material is necessary.c Analog Repeater (c) 4-20 mA. THERMOSYPHON FILTER : Thermosyphon Thermosyphon Filter is a device which continuously improves the quality of oil in the transformer tank.c Digital Repeater Plus a signal for SCADA They all require the Local Instrument to be provided with a precision potentiometer. Fig.T. They enable readings being taken in Control Room also. air release plug. It is optional fitting and is provided when ordered. Secondary Current (ISH). sensing can alternatively be done by Resistance Temp. On addition it is provided with a heater coil around its operating bellow. D. inflate the separator with a pressure of less then 2 p. ON LOAD TAP CHANGER (OLTC) : OLTC is an optional device and is provided when ordered. 27 (c). In both the types. Pressure will slightly increase. Separator will deflate. the Coarse tap winding is included in or excluded from the circuit. (a) shows the separator in inflated condition corresponding to low oil volume. 2. In the other type.0 p. One type of OLTC is fitted external to transformer main tank as shown in Fig . A typical arrangement is illustrated in Fig. 1) Set up the separator inside the conservator by suspending it from the hooks provided. Open this valve slightly to maintain pressure. IMPORTANT WARNINGS: (1) When conservator provided with Flexible Separator is filled with oil as mentioned abov. Fig. A typical arrangement of Air inlet is shown in Fig. of tap position is moderate. Close the valves. contracts mounted on insulated cylinder are immersed in the transformer main tank as shown in Fig. SSF wheel valves at the top of the conservator open. are taken up by the Flexible Bag. It is an optional fitting and is provided when ordered. Drive Mechanism (DM) is contained in separate box.20. the ½ “Valves mentioned above must never be opened. 5) Admit oil under slight pressure from the lower part of the conservator.20 OIL FILLING PROCEDURE FOR A CONSERVATOR PROVIDED WITH A FLEXIBLE SEPERATOR. tap positions) are obtained for one position of moveable arm.e.e. (b) Coarse/Fine : By means of a change –over contract. Adding ) or Reverse(i. (c) Reverse/Forward : By means of a change-over contact.t. of tap positions is large. 2. main winding.2. (ii) Transducer which gives e. the tapping winding is connected in Forward (i. If opened by mistake. 22(a). Continue admitting oil slowly while maintaining pressure. Tappings are located on High Voltage Windings of the Transformer. If there is leakage contact us.i. 4) If there is no pressure drop.VOLTAMP TRANSFORMERS LIMITED It is fitted inside the conservator such that variations in oil volume due to variations of temp. Oil in conservator is sealed from the outside atmosphere moisture and gases connot contaminate the oil inside the conservator. Open the Air Inlet Valve completely to equalise pressure inside the bag with atmospheric pressure. OIL LEVEL TRANSMITTER: When oil level in conservator is to be remotely monitered Oil level transmitter is to be provided . Thus two voltages (i.5 & 2. Atmosphere inside the separator is exhaled and the separator bag deflated as shown in Fig. 2) Keep the 2 Nos. Stop filling when the MOG indicates filling level. Subtracting) direction w.i.ectrical signal dependent on the oil level. till oil flows steadily from the valves mentioned in (2) above. Observe for pressure drop for 24 hours. Oil filling in the conservator is to be done as per the procedure given in 2. then the separator is leak-proof 7 proceed for oil filling.i and lock it. (2) When it is necessary to open these valves.s. 22(b). and then only open these valves. 3) Adjust the pressure to a valve between 1.s.e. Arrangement (b) or (c) is used when no. Different arrangements used to effect tap changing are shown in Fig. (iii) Power supply / V-I Module which provided 4-20 mA signal from the transducer output. (3) Do not carry out any welding work on the conservator shell while separator is inside as it can damage the separator. tap positions ) are obtained for one position is large. 6) Admit further oil.s.3 12 .21 2. Inflate the separator carefully with an air pressure of not more than 2 p.r. Thus two voltage (i. ½ “ . When oil expands due to increase in temp.e. Remove compressor connection from the Air Inlet Valve. (b). 28. Transmitter System comprises of : (i) Stainless Steel Rod which goes inside the conservator tank. the air-pressure acting on the separator will deflate the separator. 23 They are : (a) Linear : Commonly used arrangement when no. are to be set by means of adjustable knobs. connecting transformer to load . is controlled. 13 . In such a case . When Automatic Voltage Regulating (AVR) Relay is ordered and Voltage Transformer (V. These details are given in the plate fitted to OLTC. R&X of the cable. Only some types are suitable for Full Power Flow –in terms of current and no. voltage at the end of the cable and not at transformer terminals.in the reverse direction. 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. Other type have restrication on the current and no. Direction of Power Flow is an important consideration in OLTC. along with a selector switch for Local or Remote Control. please refer to the OLTC manual and Schematic & Wiring Diagrams supplied along with the transformer.VOLTAMP TRANSFORMERS LIMITED OLTC is generally operated electrically through a Remote Tap Control Cubicle (RTCC) LOCATED IN Control Room. of operation.T) wired on the Transformer output side (generally in user’s scope). of operation in the reverse direction. Thus the output voltage is automatically controlled to the preset value. For further details. A local electrical control is also provided in the Dm. an operating handle is provided. A Line Drop Compensator (LDC) is included in the AVR when specifically ordered. For emergency manual operation. suitable ralls should be provided.1 General: This section illustrates procedure for installation & Commissioning of our transformers. Note details of these Breathers also in the “Commissioning Report”. if separate.2 Bushing : Clean the bushing and check that there are no hair-crakcks or other damages.4 3. Lock the rollers to prevent any accidental movement on ralls. When there is an OLTC its conservator is some times provided separately or by making a partitioned compartment in the main conservator. Similarly mount the OLTC breather. 3.2. should also be mounted. similarly mount “Oil Surge Relay”.1 Location: The transformer should be kept in a well ventilated place.VOLTAMP TRANSFORMERS LIMITED 3. Result of various precommissioning tests as well as conformation of check points are to be recorded in this Report. Check that the colour of Silica Gel in Main Breather is Blue.2 Foundation: Foundation should be firm.1 Main Tank: Keep the main tank in its permanent position of operation. Test IR value of each bushing with a 500V Megger.G in the “Commissioning Report”. Adequate ventilation is necessary for tank and radiators so that they can dissipate heat. 3. in the “Commissioning Report”. There should be clear space of about 1.G is provided with a locking leaver. Mount the conservcator.5 Breathers: Note details of Breathers. Note details of Bushings in the “ Commissioning Report”. should be made by way of oil Soak Pits.4.2. Fire separation walls should be provided when necessary. Remove the rubber cap closing the breather pipe and fit the breather. it should be in the working position. OLTC conservator.O.6. 3. in the event of a fire .4. INSTALLATION & COMMISSIONING 3. This Report then would serve as a handy record for further reference. free from excessive dust. 14 . Fill oil in the oil cup and remove the seal which closes the breather opening. horizontal and dry .O.4. it may have its own separate breather. 3.O. Assembly of Dismantled Components: Various components dismantled for transporation should be duly assembled. thus positively grounding the same.2. Also if ‘Test’ lever is provided. They should be released. where rollers are fitted. Adjust the Arcing Horn Gaps in accordance with the Insulation Coordination Note these values in the “Commissioning Report”.3 3. 3. Provisions for Oil Draining : Necessary provisions for oil draining . 3.2. Draw an oil sample from the bottom of the tank and test it for Break-Down –Vlotage (BDV) Note this value in “Commissioning Report”. If the M.4 Buchholz Relay : Note details of “Buchholz Relay” for the transformer and of “Oil Surge Relay “ for the OLTC in the “Commissioning Report”.10. It should be 100M ohms or greater. 3. A format of “Commissioning Report” is included at the end of this section.2.4. Buchholz Relay floats are tied to prevent transit damage.2.2 Installation: 3.4. Ensure that the test cap is fully tightened.25m on all sides of the transformers if it is enclosed in a room.2.G : Note details of M. it should be removed. Mount the “Buchholz Relay” and the shut off valves as described in 2. Mount all the bushings as described in 2.3 Conservator & M.2.2. corrosive fumes etc. If OLTC is provided. 3.4. Buchholz Relay. if available. Ensure that tank gasket is in position. (ii) Oil required to fill in the radiators is sent separately in drums. When oil comes out steadily from the air release plug and no more air comes through.T. Air. (viii) Open the bottom radiator valve using the operating handle. should be fitted in position in their respective pockets. If gaskets are damaged. (vii) Bring the radiator flanges close to the flanges on the tank. Test oil sample from each drum for BDV. Main Tank Cover.9 Other Fittings: Note the details of other important fittings like fans in the “Commissioning Report”and mount these fittings.2. They can be worked out to suit local conditions.5 Oil Sampling & Filteration: Taking usual precautions. Note details of O.7 Marshalling Box. Set the ‘Alarm’ & ‘Trip’ contracts of O. From plain porcelain bushing of 11.I at required values. This oil should be collected in a clean container at the time of removing top and bottom blanking plates. 1866 for new transformers.Release : Release air by slowly unscrewing Air Release Plugs provided at Bushings.air can be release by loosening the nut pressing the rubber gasket and pressing the metal part down.I & W.T.22. Assembly of radiators should be proceeded in only one direction-clockwise or anticlockwise . 3.4.I and their settings in the “Commissioning Report”. Restore the oil level and assemble the next radiator in the same manner. Ensure it is more than minimum specified in I. Oil from main tank will now flow in the radiators.T. Hey should be tested for BDV. Gradually unscrew the air release plug on the top of the radiator. Oil filled cableboxes should be duly filled with oil.T.S.8 Cable Box : When cable Boxes are provided they should be mounted and cable terminations done.6 15 . Mount the radiators as outlined below: (i) Radiators are to be assembled only one at a time. (v) If blanking plates are not in position and it is suspected that foreign material might have entered the radiators.4.T.After filling last radiator.T.& 33 KV. If they meet the requirements of I.T. Air release plug should not be removed from the engaging threads as it would be difficult to control oil coming out of it. However if they do not meet the requirements.T.I should be filled with transformer oil.I setting of A -950 C & T= 1050 C are considered good.Fit by means of bolts. (iii) Fill the conservator full using an oil filter machine. until air starts escaping . use spare gaskets. Oil level in the conservator would now have fallen.4. Open the top radiator valve.I. Remove blanking plates and clean the gaskets and radiator flanges .T.I settings of A=850 C & T = 950 C W. Oil Surge Relay etc. oil needs to be filtered till the required BDV is obtained. (vi) Oil might seep through the tank side radiator valves and be retained by the blanking plates. Due connection and fitting should be done tio over-head line by a terminal connector. 3. driving out air from air release plug. (iv) Clean one radiator externally. Note the BDV values in the “Commissioning Report”.T. 1866 for New transformer.VOLTAMP TRANSFORMERS LIMITED 3. In case of “Bus-Duct” connections.2. draw oil samples from Bottom & Top of main tank and from OLTC. Bulbs of O. nuts.2. spring washers etc.2. oil level in conservator should be restored only up to the filling mark. no further processing is required.6 Radiators : Note the details of Radiatiors and Radiators Valves in the “ Commissioning Report”. Pockets of O.I & W. Bushing Pockets. 3. Check that there is no oil leakage from the radiator itself and gasketted joints. Marshalling box should be fitted in position. 3.2.S.2.I & W. clean them internally by flushing fresh and clean transformer oil. O. close the air release plug.I & W. When OLTC compartment is provided in the main conservator. this compartment is to be Separately filled upon its filling mark. transformer is provided with a flange to receive the bus-duct. 2. Measure the 3 line currents. Referring to R &D plate. a simple test of measuring voltages can also serve the purpose.V. V & W phase currents will be approximately equal and U phase current around 110%.2. the 3 line currents will be approximately equal & v phase current around 805 of either of them. AC. Repeat for the other two phases.g for a vector Group of Dyn-11.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. 415V.V. 1V.2.V. If H.3 Magnetising Current Test : Apply 415 volts.V. 2N correspond to U phase.V. Measure voltages between terminals 1V-2V. terminals 1U. When done at site and results compared with the factory test confirms that there are no transit damages to the core and windings. Vectors are redrawn as shown. keeping the L. 415V or 240V. Apply 3 Phase . For the condition 1U & 2U connected together. These observation should indicate a consistent trend of variation in line with the details given in R & D plates.V phases is to be measured on all taps. AC. With this configuration.7 COMMISSIONING 3. 3. L. IV.V. the method is illustrated below. Because the 3phase of the magnetic current of the core are not similar.2.V. 2U together. or supply. Note the observations in the “Commissioning Report”. This method can be extended to any other Vector Group. Numerical values should approximately check with the voltage ratio.V terminals.2 Vector Group Check Test : Connect terminal 1U.. Check that the measured voltages confirm the relative position of H. &L. such a test is done. 3. Measure these voltages on all taps and note them in “Commissioning Report”. several pre-commissioning tests are done . 1W. terminals open and tapping switch in the normal position. For vector group Dyn-11. find out which terminals of H.V. otherwise one after the other. 1V-W (for suitable other voltage if required).V. Apply single phase. H.V. to the H.8 Pre-Commissioning Test : Prior to energising the transformer. & L.V. 50Hz. 3. Voltages 1V-2V 7 1V-2W will be equal while 1W-2V will be greater than 1W-2W.1 Ratio Test : Ratio between all the three corresponding H. It is desirable to do this test by a Radio-meter. But if it is not available. AC.8. correspond to one phase e.V.V. vectors are shown independently positioned for Dyn-11.VOLTAMP TRANSFORMERS LIMITED 3. to H. side and measure voltage on the L. alongwith routine tests at the manufactures’ works.8. is delta connected. Note the observations in the “Commissioning Report”.50Hz to H. if possible simultaneously. some times. 16 . & L. 2 phase.8.2. In case of Power Transformers. side.V. H. & L. vector group. terminals 2U. Terminals 1U.V & L. then. When other phases are energized.8.R reading continues to increase initially and for comparison purpose.t centre limb. In that case L. Also. side.R.V. carry out one tap changing operation over the entire range increasing as well as decreasing. supply has to be disconnected before changing tap. As both the outer limbs are symmetrically located w. 3.R value dependent on temperature. Check the other modes of OLTC operation and note in “Commissioning Report”. Compare the I. flux will divide equally between them. Also measure and note the I. Note the observations in the “Commissioning Report”.VOLTAMP TRANSFORMERS LIMITED 3. the following conditions must be fulfilled by the incoming transformer: (1) Its voltage ratio is same as the existing transformer on all tappings. A Consistent trend indicates healthiness. This test can . generally. the infinity setting of the Megger.V. more flux passes through it and less flux in the outer limb.4 Magnetic Balance Test: This is a simple test to detect shorted turns ion a winding. Voltage is 66KV and above the current drawn may be very small. If required using Carbon Tetrachloride. flux and hence voltage in the shorted phase eill be significantly reduced.V.V side voltage and the % impendence. side shorted.7 Parallel Operation: Sometimes the transformer to be commissioned is required to run in parallel with an existing transformer. Side. 17 . 415 or 240V. otherwise hand-driven. check and adjust. it would be possible to calculate the current which would flow in the H. Note also details of OLTC. It is also known that I. reading is to be taken at 1 minute of energizing. keeping L. there should be no external connections to the transformer terminals.2 apply single phase. 3. In case the H . if any. Centre limb being nearer ti the energized limb. Measure the voltage induced in the V phase (Centre limb and W phase (other outer limb). side shorted. AC to such H.415V.r. energise W phase and measure the other two voltages as before. Also .2. 50Hz to H. Hence the voltages measured on outer phases will be approx. thoroughly clean all the bushings with clean cotton cloth. (2) Its % Impedance is within ± -1% of value of existing transformer. with the Factory results keeping in view the temperature at the time of measurement. Note the observation in “Commissioning Report”. If short-circuit test is not possible due to limitation of source. Its principle is that shorted turns oppose establishment of flux in that limb because of the current that circukates through the shorted turns. /the division is around 70-30% & hence the measured voltages will be having approx this proposition. would .V. Hence all three observations will indicate the shorted phase.8. This test would confirm proper contract engagement at all tap positions. line terminals which would energies U phase (outer limb) Use an averaging instrument like a Multimeter. Then energise V phase (Centre limb0. Currents drawn when outer phases are excited the healthiness of the windings.V.6 Short-Circuit Test : For the H. side. Lead wires from the Megger to the transformer should run independently and be permanently clamped.8.R. Note the observations in the “Commissioning Report”. equal .V. They should not have any joints. When the Magnetic Balance Tes5t indicates a shorted phase.2. 3. In case one of the phases has shorted turns. if required. values of the power Cables.5 Measurement of Insulation Resistance: Measure Insulation Resistance (IR) between windings and between windings and earth with a 2500/1000v Megger. Apply 3Ph.8. Before measuring I. Next. Measure the 3 line currents at all tap positions.2.R values measured. for reasons explained earlier. be carried out on L. Hence temperature at the time of measurement should be noted.V.V . Results should be similar to previous ones.3. it will draw a comparatively large current when it is energized. If the 415V source can feed that current. As indicated in 3. It is known that the I. be 11KV or more. In is case. commissioning cannot be undertaken contact us immediately giving detailed test results. a short-circuit test can be carried out. Measure also the current drawn by the energised phase. while keeping L.2. preferably motor driven. with 415V applied to it. If the switch is an OFF-CIRCUIT switch. for package shifting and opening. The transformer should be allowed to run on No-Load for about 3 hours. Check points : After completing installation and precommmissioning test. Buchholz Relay. M-12. each. 3. check that the various points mentioned in the “Commissioning Report” have been complied with.2.. At the end of this 3 hours period. OF EACH SIZE 3.s. If possible. Pipe roll. Check that all instruments.T. the other would share less than its rated load. M-8 ….2.I.20.2. Sometimes during this period. (h) Screw driver-200 mm & 300 mm long. … 1 No. (l) Spanners –M-24.down voltage of transformer oil. Note their details in “Commissioning Report”.G.T. (d) One AVO meter. the combination can supply load less than the sum of the two KVAs.11 The Following instruments are required for testing : (a) Oil testing kit to test the break. … 50 Meters. one should check zero voltage between the corresponding phases to be paralleled. (i) Pipe Wrench. 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. (c) Crow bar. M. are reading properly and that all radiators are uniformly hot. M-16. (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. The “Commissioning Report” should be duly signed by the Authorised representatives of all the participating organizations. Breakers.T side and the applied voltage during voltage ratio test. If everything is found in order. It is preferable to keep settings of all protective relays to the minimum. O.12 TOOLS & INSTRUMENTS REQUIRED FOR INSTALLATION / MAINTENANCE : The following tools are required at the time of installation of transformers.e total of 6 hours) transformer should be under observation. During the period and for further 3 hours.VOLTAMP TRANSFORMERS LIMITED NOTE : Due to difference in % impedances. one of 0-100V range and another of 0-500V range. … 2 Nos.2. … 1 No.. (c) Two Voltmeters.I. from a part of the transformer installation. The transformer should .250 mm size. then be energized again and then relays set at their desired settings. relays etc. (k) PVC Wire for connecting meters. … 1 No. … As required. As a result. trapped air is released and gets accumulated in Buchholz Relay. (i. … As required. 2 NOS. Note the compliance in the Commissioning Report. 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. (f) Small size screw spanners-100 mm long for nuts upto 6mm size. (j) Cutting Pliers (Insulated) … 2 Nos. & W. (d) 25 mm dia Manila Rope. when one transformer reaches its rated load. Main tank cover. Radiators etc. etc. (4) Vector group is compatible. Check that there is no gas collection in Buchholz Relay. M. 3. to read the L. M-10. (a) 20 mm ĭ or 12mm Ɏ Vinyl hose to take oil samples from drums.T.. the transformer should be observed for any abnormality in the hum and gas collection in the Buchholz Relay. During this period.O.10 3. transformer should be de-energised and air released from Bushings. 18 . the transformer can continue working. hammers.9 Other Relevant Details: Other controlling and protecting equipments like C. Hence only certain Vector Groups are compatible with each other. (e) Chain Pully Block-1 Ton capacity and lift about 10 meters … 1 No. … 1 No. (g) Hand lamp for inside working. … 1 No. (b) Drum Opener. Transformer should then gradually loaded reaching full load in about 3 hours time. Bushing pockets. (b) 2500 volts megger to measure the Insulation Resistance (IR) values. Gap : 2. NO : RATING : TAPPING RANGE : CONNECTION : SUPPLIED ON : INSTALLED AT : COMMISSIONNING REPORT DATE: MAKE: VOLTAGE RATIO : BY OFF CKT. Nos.V Bushinga make KV Sr. Make KV Sr. Details of Buchholz & oil Surge Relays : 4. Nos.V. (4) Arching Horn Gap on L.5 mm : : : : Before Filteration: After Filteration: Before Filteration : After Filteration : Before Filteration : After Filteration .1 Buchholz Relay : Make : Tested} : Alarm for } : Trip 4. (2) Arching Horn Gap on H.L. SR. Bushings Type : Motorised/ Manual . 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 Type: Yes/ No Yes / No Yes/ No Yes/ No Type : Yes /No Yes / No Type : Yes /No Yes /No Yes / No Yes / No 19 .2 Oil Surge Relay (on OLTC) .C VECTOR GROUP : (1) Oil Test Results : Details of Oil Test Set Make : Observed BDV (a) Main Tank Oil (b) O.C (c) Cable Box Oil (2) Details of Bushings: (1) H.V Bushing adjusted to ……….T.T.VOLTAMP TRANSFORMERS LIMITED 3.2. Bushings adjusted to ………mm (3) L. SWITCH/ OL.V.13 CLIENT : TRANSFORMER DETAILS : TRANSF.mm (3) Details of Magnetic Oil level Gauge: Make: Wired } : Alarm for } : Trip Tested } : Alarm for } : Trip 4. 1 Radiators Make : Type : No : 6.T. connected in control circuitry. Details of Radiators & Radiators Valves : 6.2 Radiators Valves : Make : Type : No : 7. I & W. Oil and winding temperature indicators : CHECK MAKE TYPE ALARM SET TRIP SET TESTED FOR ALARM TESTED FOR TRIP OTI 0 0 WTI 0 0 C C Yes / No Yes / No C C Yes / No Yes / No 7.T. 20 .VOLTAMP TRANSFORMERS LIMITED 5.I } : Group I of fans set for Group II of Fans set for OK /Not OK 0 0 C. (2) Control Circuit Checked for operation through. C.I.V Yes / No Yes / No Yes / No Yes / No 8. Details of Cooling Fans : Make : Type : Nos : Fan control through } : W.1 Pressure Relief Valve : Make : Type : Tested } : Alarm For } :Trip Note : (1) O.R. T. Details of Breathers : CHECK MAKE TYPE / MODEL Colour of Silica Gel Oil level in Breather Main Tank Breather OLTC Breather Blue /Pink OK /Not ok Blue /Pink OK / Not Ok 6. Yes / No Yes /No : OTI : WTI : P. V= mA.V Voltage for the same phase. Line Currents : U = mA. Voltage 1U –1V = 1V -1W = 1W – 1U = Tapping Switch in position no :…………………………. AC.Star / Delta connected. 1W. (This can be found from the R & D plate ).V Winding. V Voltage Applied Between Terminals = Tap. Voltage Measured Between Terminals = 1 Do Do Remarks Do Do 2 17 (1) Checked Ok for Consistent Variation Yes / No (2) Checked Ok for Rated Voltage Ratio Yes /No 10. Observed Voltage confirms Vector Group : 11. which will energise ‘U’ phase of transformer.V Yes / No 21 . 3 Phase voltage applied to terminals 1U. Magnetising Current Test : 3Phase Voltage applied to H. Likewise measure for ‘V’ & ‘W’ phases also. H. 1V. Measure L.VOLTAMP TRANSFORMERS LIMITED 9. Measured Voltage Between Terminals : Between terminals Voltage Between terminals Voltage Vector Diagram .. L. terminals.V. Ratio Test : Apply single phase . Vector Group Check Test : Terminals 1U & 2U connected together. to those H.415 or 240 Volts. W= mA Line current checked Ok for ……………………………. Connected H.V. 0 C.V. = (3) Between L. Yes / No Voltage between terminals Corresponding To V phase Corresponding To W Phase 2 3 13. and Earth = Transformer Top Oil Temp.V. and L. Measurement of Insulation Resistance : (a) For Transformer : (1) Between H. Mohms. ……….VOLTAMP TRANSFORMERS LIMITED 12. = Details of Megger : (1) Make : (3) Voltage : (b) For Power Cable : Type : Temp : ………. 0 C. Mohms (2) Sr. Mohms.V. : (4) Range : Mohms. and Earth = (2) Between H. REMARKS : 22 .V. Mohms. Mohms. Mohms Mohms. Magnetic Balance Test : Sr No Corresponding To U Phase 1 Applied Voltage = Current Drawn = Applied Voltage = Current Drawn = Applied Voltage = Current Drawn = Observed distribution of voltage confires absence of any shorted turns. Mohms. No. (1) (2) (3) (4) (5) (6) 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 ………. ………. 1U – 1V = 1V – 1W = 1W -1U = Volts. Details of Control Panel/ Protective System : (1) H.V.s : Make : Type : No. 3. Short Circuit Test : Applied Voltage = 3 phase . 2. Side ): Make : Type : Mounted on Phase : Current Setting : Time Setting : (5) L. Cores Accuracy Class 1. 4.V.Side ): Make : Type : Mounted on Phase : Current Setting : Time Setting : (4) Over-Current Relay (H.VOLTAMP TRANSFORMERS LIMITED 14. Tap No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 IU A IV A IW A ILT A 15. 50 Hz.T.V.C. Circuit Breaker : Make : Type : MVA : I-rated : KV : Release Setting : 23 . of.V.V Circuit Breaker : Make : Type : MVA : I-rated KV : Release Setting = (2) H. -----------------------------------------------------------------------------------------------------------------------------------(3) Earthfault Relay (H. Buchholz Relay Test Lever is kept in ‘S’ position.C. No (a) Manual Operation (b) Local Electrical Operation (c) Remote Electrical Operation 17. Buchholz Relay lock is released. 14. 24 . 8. Yes /No.O. Yes / No. Yes / No. Yes / No. 4. Air Release valve of Buchholz Relay is closed. Bushing surfaces are cleaned. side : Make : Mounted on Phase Current : Setting : 16. Test Tap Caps are fully tightened. Oil is filled in main Breather upto level mark.T. Buchholz Relay shut off valves on both sides are open. 2.L. Yes / No. 12. Colour of silica Gel in main breather is blue.T.G. Yes / No. Details of O. Yes / No. Oil Samples from main Tank O. 3. is released. 1a.L. 3. 9. 17.C. Yes /No. M. 2. OSR shut off valve is open.s : Make : No of Cores 1.C.L. Yes / No.C Conservator in separate Conservator or Compartment in main conservator 6. 10. 4. 13.T. 1. Yes / No Yes / No. Oil level main conservator is upto mark. Arching Horn-gaps are duly adjusted. Yes / No Yes / No.V. OSR arrow-head is pointing towards conservator. 15. 16. 5. Type : Accuracy Class Type : Time : Setting : Type : Year : OK / Not OK OK / Not OK OK / Not OK Yes / No. COMMISSIONING CHECK POINTS . have passed BDV requirement.V. Sealing Tape of main Breather is removed.T. Oil level in O. Yes /No.T. Yes / No. 7. Buchholz Relay arrow head is pointing towards conservator.L. Lock of Oil Surge Relay (OSR ) on O. (7) Earthfault/ Overcurrent/Different Relay on L.C : Make : Sr.VOLTAMP TRANSFORMERS LIMITED (6) L. 11. Yes /No. lock is released. Yes /No. Yes /No. Yes /No. 19.I pockets. the transformer was commissioned on ……………………………………. Alarm & Trip contracts of O. Tank Cover. breather is blue. Oil is filled in O.I & W.T. Yes /No.I.at No load in our presence Subsequently Load was also taken. Oil is filled in O. Colour of Silica Gel in O. O. Yes /No. Yes / No.T. 35. 25.T. are set at the required valves. secondary terminals. External connection are duly tightened. (iv) Main Tank Cover.at ………………………………….T. Yes /No. Yes / No.C. 33. /Off Circuit Tap Switch is in the desired position and is properly locked. Valve connecting min Tank to Cable Box is open. if not wired.L. 24.L. drain and filteration Valves are closed. 20. Yes / No Yes /No Yes /No Yes /No.C. 27. Yes /No Yes /No Yes / No.T.L. Tank earthing is done. Oil filling cap on main conservator is duly filled. Oil is filled in disconnecting Cable Box upto Level Mark. 36. There is no oil leakage from any where.Hrs. Explosion vent diaphragms are intact and there is no oil in explosion vent.C. Yes /No.T. For Customer : for VOLTAMP 25 . 22.T. C. 23.VOLTAMP TRANSFORMERS LIMITED 18.T. Sealing Tape of O.C breather upto level mark. Yes /No Yes /No Yes / No. Commissioning : After carrying out installation and pre-commissioning tests and ensuring all check points.C.. (vi) OSR on O. Rollers are locked. Yes / No. Yes /No.T. breather is removed. Yes /No. Nothing abnormal was observed during these operation. All sampling. Air released from : (i) All Bushings (ii) All Bushings Pockets (iii) Buchholz Relay. All radiator Valves-Top and bottom are open.L. 34. (v) All radiators. Neutral earthing is duly done. 18. 26.T. 29. 32. Yes /No. Yes / No Yes /No.T.C (vii)O. 21. 28. 31. are shorted and earthed.I /W. Yes /No. 30.L.L. Removel of sludge is important as otherwise it can stick to coil and hamper the heat dissipation from coils. It is necessary to maintain required oil level and to maintain this oil in good condition. It may be noted that the products of decompositions viz.1981. 4.335. if the results indicate that acidity needs to be improved. 1866. sludge etc. corrective actions must be immediately taken. Samples of oil should be taken at regular intervals and tested. reduces the life by 50% ). The filteration will remove moisture. If the dielectric strength is below the value recommended in I. (i) (ii) (iii) (iv) Check if there is any leakage of oil.1 OPERATION : I. acids etc.S.S.S.e. the oil should be duly filtered. remain in the oil and accelerate the rate of ageing.T is lower than 980 C. Guidance on overloading is provided by I.S. Thus.e. topping up should be done with oil complying with I.S.S. Sometimes a transformer may be required to deliver load higher than its rating.T exceeds 980 C.ageing. A few guide liners are given here.General : Compared to moist electrical equipments transformer requires relatively less maintenance. then a simple filteration would not be sufficient and a Fullers Earth treatment would be required. Naked light and flames should be kept well away from the transformer.2 Oil: In the transformer.VOLTAMP TRANSFORMERS LIMITED 4. The insulation ageing (which decided the life of transformer) increases with increase of H. The oil level should be checked at frequent intervals and if necessary.T) is 980 C for an air temperature at 320 C. if noticed. The insulation ageing decreases thus increases the life of transformer. Precautions must be taken to secure tools with tapes to prevent them from falling inside the tank. increase of H. dust. it must be properly maintained. I. dirt and high temperature causes insulation deterioration i. Detailed guidance on Maintenance is given in I. Principal object of maintenance is to maintain the insulation in good condition. the H. When the ambient air temperature is lower than 320 C.S. 6600 basis for this recommendation is as follows: In a 24 hours loading. 10028 (part II). Maintenance consist of regular inspection. The H.2. 2026-1977 states that a Power Transformers loaded at its rated KVA will fulfil its normal life when its hottest spot temperature (H. Hence they must be prevented.1. No work should be done on the transformer unless it is disconnected from all external circuits and all windings have been solidly earthed. 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. water. 26 . by 60 C doubles the rate of ageing (i. However in order to obtain a long and trouble-free service from the transformer. timely treatment of oil is a must.S. It is considered (by the I.S.As the ambient air temperature exceeds 320 C.2.S. Moisture . testing and reconditioning when necessary.S. OPERATION & MAINTENANCE 4.6600-1972) that periods of accelerated ageing due to higher ambient temperature are compensated by the periods of reduced ageing due to lower ambient temperature. Recommended frequency of maintenance is given at the end of the chapter. oil is used as an insulating liquid as well as for cooling. 4.T.T.1866 gives recommendations in details for the maintenance of oil.S. Maintenance hints on main constituents of the transformer are given in the following paragraph.2 MAINTENANCE: 4. However. The mechanism should be inspected and cleaned . 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 . .C oil in which arcing takes place is not allowed to mix with the main tank oil. Flat should be checked to see that there is no oil in the float . may have to be disconnected before lifting up core and windings assembly. Buchholz Relay : Routine operation and mechanical insepection should be carried out as per the manufacturer’s instructions.2.The operation of alarm and trip contracts should to be checked. Joints should be remade. 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. and leakage stopped.L. is housed in the main tank by suitable mounting on the top cover. In bigger transformers.T. 4.5 Conservator & Oil level Indicator : The inside of conservator should be cleaned by flushing.T. 4. Depending upon the arrangement provided.L. 4. Explosion Vent : The diaphragm at the exposed end of the explosion vent should be inspected and replaced if damaged .C.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. The colour of Silica Gel crystals in the breather acts as an indicator as it changes from blue to pink when saturated with moisture. manual for operation and maintenance instructions of O.2. Any loose nut and bolt should be tightened.2. If diaphragm is broken because of fault in the transformer.VOLTAMP TRANSFORMERS LIMITED 4.4 On Load Tap Changer: On load tap changer is. oil rises inside the explosion vent pipe and is visible in the oil level indicator on explosion vent. The windings should be examined and if sludge has been deposited it should be washed away with oil Jet.C. normally.9 27 .6 4. Adjust the rods/coil clamping screws provided tomremove any slackness of windings. detachable end plate is provided to facilitate cleaning of conservator. mounted on the tank in the separate housing and connected to winding leads through copper studs fixed on an insulated terminal board. which may be due to bad seated joints.2.L. More frequent inspection are needed when the climate is humid and when transformer is subjected to fluctuating load. .2. This usually takes 2 to 3 hours.T.Magnetic oil gauge is also to be attended while cleaning the conservator.7 4. Oil seal should be filled with fresh oil. Whenever bottom diaphragm ruptures. inspection should be carried out to determine the nature and cause of the fault. tap switch handle.2. Oil cup should be cleaned to removes dust and dirty oil.8 4. Silica Gel Dehydrating Breather : Breather should be examined to ascertain if the silica gel requires changing. O. Pipe Work : The pipe work should be inspected for leakages. Here again O. the same should be replaced. In some other types.C. is oil-tight. connections to bushings etc.Oil gauge glass should be cleaned. Hence oil in the tank need not be lowered for attending O. When majority of crystals have turned pink. If the glass is found broken.L. Failure to replace the diaphragm quickly may allow the ingress of moisture in the transformer.2. clean transformer oil to remove sludge and other impurities.T.T. Please refer to O.C.L. 11 4. If they apper blackened or corroded. Temperature indicators found reading incorrectly should be calibrated with standard thermometer using hot water bath.2. In case of any sign of oil leakage from the condenser bushing the matter should be referred to us. 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. It should be replaced if damaged. unbolt the connection and clean with emery paper. Check the pocket/s for presence of water and if found . Leaky gaskets should be replaces as soon as the circumstances permit.VOLTAMP TRANSFORMERS LIMITED 4. therefore.clean the pocket and refill with fresh oil and seal the opening properly. They should be tight. necessary to check the tightness of all bolts/fasteners of gasketted joints. Bushing : Porcelain insulators should be cleaned and minutely examined for any cracks. If armour of capillary is exposed.12 4.13 28 . External connections Including Earthing : Check all external electrical connections including earthing . chipping off & other defects. Dial glass should be kept clean. 4. All such bushing should be replaces. Re.2. It is . then retaping must be done by PVC tapes. The bolts should be tightened evenly around the joints to avoid uneven pressure. Temperature Indicators : The capillary tubing should be fastened down again if it has become loose.2.ake the connecteions and give a heavy coating of conducting grease.2. to prevent damage to the pointer.10 Gaskets : Gaskets sometimes shrink during service. Frequency inspected unsatisfactory conditions ------------------------------------------------------------------------------------------------------------------------------------------------1 2 3 4 5 1. Daily (i) Oil level in transformer on load tap changer (ii) Explosion (iii) Dehydrating breather Check that the temp. Examine contracts. check oil. examine transformer for leakes. check gear box.. However. depending on the local situation and importance of transformer. If silica gel is pink change by spare charge. Lubricate bearings. The old charge may be reactivated for further use. check for dielectric strength and water content. Replace if cracked or broken. Quarterly (i) Bushing (ii)Oil in transformer and tap changer (iii) Cooler fan and pump bearings and motors & operating mechanism. Replace burnt or worn out contracts or other parts. top up with dry oil. rise is reasonable check against rated figure check against transformer oil temperature. Control load. check colour of the active agent and that opening is not clogged. (iii) Oil Temperature.VOLTAMP TRANSFORMERS LIMITED 5. - (vi) Dehydrating breather (vii) Ventilators (in case of indoor transformers) check all circuits independently Check step by step operation including limit switches. - Make up oil if required. Sl Inspection Items to be Inspection Notes Action required if inspection shows No. check oil level in oil cup. If low. - 29 . Adjust tap. check manual conrol and interlocks. Hourly (i) Ambient Temp (ii) Winding Temp. Check that air passages are free. (v) On load tap changer automatic control. Shut down the transformer and investigate if either is persistently higher than normal. frequently may be increased. 3.0 MAINTENANCE SCHEDULE Recommended maintenance schedule is given below. Take suitable action to restore quality of oil. (iv) Load (amperes ) (v) Voltage 2. (iv) On load tap changer driving mechanism. Clean or replace as necessary. Examine for cracks and dirt deposists. Examine compound for craks. etc. Check for sealing Replace gaskets. transformer can convieniently to be taken out for checking). if required. Frequency inspected unsatisfactory conditions ------------------------------------------------------------------------------------------------------------------------------------------------1 2 3 4 5 4. (iii) Gasketted joints. (vii) Dial type Oil gauge. Examine relay and alarm contracts and their operation fuses. Compare with valves at the time of commissioning. Internal inspection above care Filter oil regardless of condiation. Adjust floats. (v) Relay alarms. check the acidity Filter or replace. Adjust if required. if leaking arrangements for filling holes. Two years (xi) Nonconservator transformer (xii) Coil conservator (xiii) Buchholz Relay Check pointer for freedom of movement should be inspected Oil to be replenished. 30 .VOLTAMP TRANSFORMERS LIMITED Sl Inspection Items to be Inspection Notes Action required if inspection shows No. Any painting or retouching should be done if necessary. Take suitable action if earth resistance is high. -do-do- Internal inspection Mechanical inspection Should be thoroughly cleaned. Clean the components or replace contracts and fuses. - Examine for cracks and dirt deposits. if necessary. as required. Yearly (or (i) Oil in transformer earlier if and sludge. Process if required. etc. switches etc. change the setting if necessary. (viii) Paint Work (ix) Earth resistance (x) Surge diverter and gap. (vi) Temperature Pockets holding indicator thermometers should be checked. Check moisture condensate If any in air filled boxes. clean or replace. 5. theircircuits etc. (ii) Insulation resistance. (iv) Cable Boxes Tighten the bolts evenly to avoid uneven pressure. Check relay accuracy. In the case of severe fault or if alarm is not attended the transformer is tripped by the Tripping circuits. 7 to 10 years 5. -do- 7. . indication of trouble is given by the various alarms provided. be avoided.1 Trouble –Shooting : At the time of commissioning or periodic maintainece if any abnormalities are observed. If tripping and subsequent investigation indicates internal faults. 31 . Analysis of gas collected in Buchholz Relay can give indication regarding nature of fault. transformer has to be taken out of service. nuts if loose. Guidance for this is given in I. These alarms must be accepted and corrective action initiated immediately. 5Years (xiv) Transformers Overall inspection upto 3 MVA including lifting of core and colts (xv)Transformers above 3MVA -do- wash by hosing down with clean dry oil. Frequency inspected unsatisfactory conditions ------------------------------------------------------------------------------------------------------------------------------------------------1 2 3 4 5 6. possibly. 10028 (part III ) – Maintenance. This is a very undesirable situation and should . corrective action should be taken immediately. For a transformer in service. Tighten coil clamping arrangements and other bolts. Several other methods of testing to assist preventive maintenance are available.VOLTAMP TRANSFORMERS LIMITED Sl Inspection Items to be Inspection Notes Action required if inspection shows No.S.