INSTRUCTIONS FOR
INSTALLATION, COMMISSIONING, OPERATION AND MAINTENANCE OF TRANSFORMERS AND REACTORS
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Sr. No. PARTICULARS PAGE NO.
1.0 LIST OF STANDARDS RELATED TO OUR PRODUCTS
1.1 LIST OF INDIAN STANDARDS REFERRED 1
1.2 LIST OF IEC STANDARDS REFERRED 2
2.0 TRANSPORTATION, DESPATCH AND STORAGE
2.1 TRANSPORTATION 3
2.2 RECEIPT OF TRANSFORMER AT SITE 3
2.3 STORAGE 5
3.0 INSTALLATION
3.1 LOCATION AND SITE PREPARATION 6
3.2 ASSEMBLING THE TRANSFORMER 6
3.3 GASKETS 7 3.4 BUSHINGS 7 3.5 TAP CHANGERS 11 3.6 COOLING OF TRANSFORMERS 14 3.7 RADIATORS 14 3.8 COOLING FANS 15 3.9 OIL PUMP 15
3.10 OIL FLOW INDICATOR 16
3.11 HEAT EXCHANGER 17
3.12 DIFFERENTIAL PRESSURE GAUGE 17
3.13 CONSERVATOR TANK 18
3.14 MAGNETIC OIL LEVEL GAUGE 18
3.15 COMMISSIONING OF AIR CELL 19
3.16 GAS AND OIL OPERATED (BUCHHOLZ) RELAYS 20
3.17 SILICA GEL BREATHER 22
3.18 PRESSURE RELIEF VALVE (PRV) 23
3.19 DOUBLE DIAPHRAGM EXPLOSION VENT 24
3.20 MARSHALLING BOX 25
3.21 OIL TEMPERATURE INDICATOR 25
3.22 WINDING TEMPERATURE INDICATOR 25
3.23 CURRENT TRANSFORMER 28
3.24 CONTROL CABLING 28
3.25 ASSEMBLY OF VALVES 28
3.26 ASSEMBLY OF PIPE WORK 28
3.27 OIL FILLING 28
3.28 EARTHING 31
3.29 COMPLETION OF ERECTION WORK 31
3.30 TOUCH-UP PAINTING 31
4.0 COMMISSIONING
4.1 GENERAL CHECK POINTS 32
4.2 DO’S & DON’TS FOR POWER TRANSFORMER 33
4.3 INSULATION RESISTANCE TEST (MEGGER) 34
4.4 VOLTAGE RATIO TEST 34
4.5 MAGNETIZATION CURRENT 35
4.6 VECTOR GROUP 35
4.7 MAGNETIC BALANCE 36
4.8 WINDING RESISTANCE 36
4.9 OLTC CONTINUITY CHECK 36
4.10 OIL CHARACTERISTICS 37
4.11 TESTING OF ON LOAD TAP CHANGER 37
4.12 OFF CIRCUIT TAP CHANGER 37
4.13 TEST ON CT 38
4.14 TESTING OF COOLING CIRCUIT 38
4.15 TERTIARY WINDING PROTECTION 38
4.16 PROTECTION AND ALARMS 38
4.17 DETAILS OF CIRCUIT BREAKER 39
4.18 ENERGIZING 39
4.19 RECORD AFTER CHARGING 39
5.0 MAINTENANCE AND OPERATION
5.1 GENERAL 40
5.2 ROUTINE MAINTENANCE INSPECTION OF OLTC 40
5.3 OIL FILTRATION AND MOISTURE REMOVAL 42
5.4 TEMPERATURE SUPERVISION 43
5.5 IR TEMPERATURE RELATION 43
5.6 SUPERVISION AND CONTROL OF OIL 44
5.7 TROUBLE SHOOTING 44
5.8 GAS ANALYSIS ON TRANSFORMER OIL 44
• TARIL Transformers are designed, manufactured and tested with care. With proper attention during installation and use, the user should receive from it the maximum expected performance.
• This maintenance procedure gives a good understanding about handling and maintenance of the transformer.
• It is recommended to go through all information contained in this before installing, operating and maintenance of the transformer.
• These instructions have been prepared to provide information on assembly, installation, commissioning and regular maintenance of the transformers and shall form part of the Instruction Manual.
• In operating the Transformer, care should be taken that loading limits as specified are strictly followed. For instructions regarding, general information on accessories such as OLTC, WTI, OTI, Buchholz relay, fan, pump, etc. may please be referred.
• In case there is doubt about any portion or wants more details. Please contact us in the following address.
• If any problem occurs during operation, please inform T&R at following address by specifying the following.
1. SL. NO.
2. YEAR OF MANUFACTURE 3. VOLTAGE
4. PROBLEM FACED
TRANSFORMERS & RECTIFIERS (INDIA) LTD.
Survey No. 344 to 350, Sarkhej Bavla Highway, N.H. 8-A, Village: Changodar, Ta. Sanand, Dist. Ahmedabad - 382210. Gijarat, INDIA
Phone: +91-2717-661661 Fax: +91-2717-661716 Email: [email protected] www.transformerindia.com
1. LIST OF STANDARDS RELATED TO OUR PRODUCTS
1.1 LIST OF INDIAN STANDARDS REFERRED
Sr No IS/EC NO AND YEAR SPECIFICATIONS
POWER TRANSFORMERS A1. SPECIFICATIONS 1 IS 1885 (Part 38) : 1977 Electrical Vocabulary Part 38 Transformers 2 IS 2026 (Part 1) : 1977 Power Transformers: General
3 IS 2026 (Part 2) : 1977 Power Transformers: Temperature Rise
4 IS 2026 (Part 3) : 1981 Power Transformers: Insulation level & Dielectric Tests
5 IS 2026 (Part 4) : 1977 Power Transformers: terminal Marking, Tappings & Connections
6 IS 2026 (Part 5) : 1994 Transformer/Reactor bushings minimum external clearance in air- Specification 7 IS 6600 : 1972 Guide for loading of oil immersed Transformers
8 IS 10561 : 1983 Application guide for Power Transformer 9 IS 335 : 1993 Insulating Oil
10 IS 10028 (Part 1) : 1985 Code of practice for selection installation & maintenance of Transformers 11 IS 10028 (Part 2) : 1981 Installation
12 IS 10028 (Part 3) : 1981 Maintenance
13 IS 1180 Outdoor Type three-phase distribution transformers up to & Including 100 KVA in 11 KV.
14 IS 1180 (Part 1) : 1989 Non Sealed Type 15 IS 1180 (Part 2) : 1989 Sealed Type
A2. MATERIALS, FITTINGS & ACCESSORIES OF POWER TRANSFORMERS. 1 IS 1576 : 1992 Solid Pressboard for electrical purpose
2 IS 2312 : 1976 Propeller type AC ventilating fans 3 IS 3024 : 1965 Electrical steel sheets (oriented) 4 IS 3231 : 1986 1987 Electrical relays for Power Transformers 5 IS 3402 : 1992 Silica gel.
6 IS 3588 : 1987 Electrical Axial Flow fans 7 IS 3637 : 1966 Gas Operated relays
8 IS 3639 : 1966 Fittings & Accessories for Power Transformers 9 IS 4253 (Part 1) : 1980 Specification for cork composition sheets 10 IS 4253 (Part 2) : 1980 Cork & Rubber
11 IS 6088 : 1988 Oil to water heat exchangers for Transformers
12 IS 7404 (Part 2) : 1991 Paper covered Copper conductors. Rectangular conductor 13 IS 8468 : 1977 On-load tap changers
14 IS 9147 : 1979 Cable sealing boxes for oil immersed transformers 15 IS 9700 : 1991 Activated Alumina
16 IS 8478 : 1977 Application guide for On Load Tap Changers 17 IS 5561 : 1970 Electric Power Conductors
1.2 LIST OF IEC STANDARDS REFERRED
SR NO IEC NO EDITION YEAR DESCRIPTION1 60-1 SECOND 1989-11 HIGH-VOLTAGE TEST TECHNIQUES (GENERAL DEFINITIONS AND TEST REQUIREMENT) 2 60-2 SECOND 1994-11 HIGH VOLTAGE TEST TECHNIQUES (MEASURING SYSTEMS)
3 76-1 SECOND 1993-03 POWER TRANSFORMERS (GENERAL)
4 76-2 SECOND 1993-04 POWER TRANSFORMERS (TEMPERATURE RISE)
5 76-3 SECOND 2000-03 POWER TRANS. INSULATION LEVELS ,EXTERNAL CLEARANCE & DIELECTRIC TESTS 6 76-3-1 FIRST 1987 POWER TRANSFORMERS (INSULATION LEVELS AND DIELECTRIC TESTS EXTERNAL
CLEARANCES IN AIR)
7 60076-5 SECOND 2000-07 POWER TRANSFORMER – ABILITY TO WITHSTAND SHORT CIRCUIT 8 60076-5 THIRD 2006-02 POWER TRANSFORMER – ABILITY TO WITHSTAND SHORT CIRCUIT 9 60076-7 FIRST 2005-12 LOADING GUIDE FOR OIL-IMMERSED POWER TRANSFORMERS 10 60076-8 FIRST 1997-10 POWER TRANSFORMERS-APPLICATION GUIDE
11 60076-10 FIRST 2001-05 POWER TRANSFORMER-DETERMINATION OF SOUND LEVELS 12 60076-10-1 FIRST 2005-10 DETERMINATION OF SOUND LEVELS-APPLICATION GUIDE 13 60076-11 FIRST 2004-05 POWER TRANSFORMERS-DRY TYPE TRANSFORMERS
14 TS 60076-14 FIRST 2004-11 DESIGN & APPLICATION OF LIQUID-IMMERSED POWER TRANSFORMERS USING HIGH-TEMPERATURE INSULATION MATERIAL
15 60137 FIFTH 2003-08 INSULATED BUSHING FOR ALTERNATING VOLTAGES ABOVE 1000V 16 289 SECOND 1988 BOBINES D’INDUCTANCE (REACTORS)
17 296 SECOND‘ 1982 SPECIFICATION FOR UNUSED MINERAL INSULATING OILS FOR TRANSFORMERS 18 317-0-2 2.1 2000-01 SPECIFICATION FOR PARTICULAR TYPES OF WINDING WIRES
19 396 SECOND 1991-02 TEST METHOD FOR INDUCTION CHANNEL FURNACES
20 554-1 FIRST 1977 SPECIFICATION FOR CELLULOSE PAPER FOR ELECTRICAL PURPOSES 21 554-3-3 FIRST 1980-01 SPEC.. FOR CELLULOSE PAPER FOR ELECTRICAL PURPOSES
22 641-1 FIRST 1979 SPEC. FOR PRESSBOARD & PRESS PAPER FOR ELECTRICAL PURPOSE 23 641-3-1 FIRST 1992-04 SPEC. FOR PRESSBOARD & PRESS PAPER FOR ELECTRICAL PURPOSE 24 60038 6.2 2002-07 IEC STANDARD VOLTAGES
25 60044-1 2000-07 CURRENT TRANSFORMER
26 60214-1 FIRST 2003-02 TAP CHANGERS-PERFORMANCE REQUIREMENTS & TEST METHODS 27 60214-2 FIRST 2004-10 TAP CHANGERS-APPLICATION GUIDE
28 60270 THIRD 2000-12 HIGH VOLTAGE TEST TECHNIQUES - PARTIAL DISCHARGE MEASUREMENT 29 60317-27 THIRD 1998-01 SPEC. FOR PARTICULAR TYPES OF WINDING WIRES
30 60404-8-7 SECOND 2008 MAGNETIC MATERIAL
31 60554-2 SECOND 2001-11 CELLULOSE PAPERS FOR ELECTRICAL PURPOSES
32 60599 SECOND 1999-03 MINERAL OIL IMPREGNATE ELECTRICAL EQUIPMENT IN SERVICE GUIDE TO THE INTERPRETATION OF DISSOLVED AND REC GASES ANALYSIS
33 62271-209 FIRST 2007-08 HIGH VOLTAGE SWITCHGEAR AND CONTROL GEAR - CABLE CONNECTION FOR GAS INSULATED METAL ENCLOSED SWITCHGEAR FOR RATED VOLTAGE ABOVE 52 KV
2. TRANSPORTATION, DESPATCH AND STORAGE
2.1 TRANSPORTATION
“Transformers,” depending upon the restriction imposed by transport weight and/or other considerations, have to be transported either filled with Oil or Nitrogen as per the description given below.
WITH OIL
The Transformer is filled with oil such that sufficient tank volume is left clear for expansion to limit the excess internal air pressure to 0.35 kg/cm2. Fittings dismantled before transport is packed in packing cases in line with packing list. All openings resulting from removal of fittings for shipment are sealed with suitable blanking plates during transport. The balance oil quantity required for the complete filling of the transformer is supplied separately.
A transformer dispatched according to this method can be stored at site or elsewhere for one year provided, that all insulating materials are covered with oil and silica gel breather is mounted and quality of oil is maintained as per IS: 1866.
WITHOUT OIL (FILLED WITH NITROGEN N2)
Large oil filled transformers are not normally oil filled during shipping due to weight limitations. To protect the active parts against moisture the transformer tank is filled with dry Nitrogen at a low internal pressure 0.2kg/cm2 at TARIL works before dispatch.
All openings resulting from the removal of fittings for shipment are sealed with suitable gasketted blanking plates during transport.
The gas pressure & temperature at the time of dispatch from factory are painted on the tank cover. Full quantity of oil is sent in separate sealed drums.
For control of gas pressure and maintaining the pressure during transport and possible storage before assembling, the transformer is equipped with two back up N2 Cylinders and is kept in a steel frame provided on tank side.
N2 regulator reduces cylinder high pressure of 120 to 140 kg/cm2 to required low pressure of 0.2kg/cm2. One gauge provided on the first stage indicates the cylinder pressure, whereas other gauge provided on second stage indicates the tank pressure.
The gas consumption during transport and possible storage is difficult to estimate as it depends on ambient temperature variation, possible leakages as well as on the duration of transport and storage. However, two back up cylinders are provided to meet the gas requirement. Normally one cylinder is kept open and the other shut. When the pressure of first cylinder falls to 0.5 kg/cm2 this should be considered as empty and immediately its valve should be closed and the valve of second cylinder should be opened.
Use only dry Nitrogen gas to IS: 1747 with 50 ppm moisture and 1% oxygen by volume.
If the storage time exceeds 3 months, the transformer is filled with oil according to directions given. If for some reason oil filling is not possible, then nitrogen must be continuously maintained at a positive pressure.
INSTRUCTIONS FOR FILLING DRY PURE NITROGEN GAS WITH BACK UP CYLINDERS (AT WORKS)
1. Lower the oil level to the minimum necessary to dismantle the items (such as bushing and turrets) which must be removed for shipping.
2. Pull 500mm. mercury vacuum after blanking off all openings.
3. Break the vacuum by admitting dry nitrogen through a convenient valve at the top of the tank and drain the oil completely.
4. Continue to supply nitrogen until it maintains a steady pressure of 0.14 ± 0.02 kg/cm2 above the atmosphere. 5. Pressure of nitrogen gas shall be maintained at 0.14 ± 0.02 kg/cm2 at same reference temperature. Pressure
would be monitored by taking three readings within 24 hours to ensure that there is no leakage of gas 6. Shut off the gas supply valve and fit dry nitrogen back up cylinders through nitrogen regulator valve.
2.2 RECEIPT OF TRANSFORMER AT SITE
To ensure that a Transformer will function satisfactorily it is important that handling, lifting, storing and assembling are carried out with great care and cleanliness by experienced personnel who are thorough with various working operations.
This section gives instructions how handling, lifting, storing and assembling should be carried out. For large Transformers it is recommended that the work is done by TARIL or is under supervision by experts from TARIL.
INSPECTION
In connection with receiving and unloading at site, and at the final storing place before assembling, the transformers shall be inspected carefully for external visible damages as dents, paint damages etc.
After the arrival of the material at receiving points, the customer should, in case of possible damage/loss of any component, make the necessary claims with the contractor’s representatives under intimation to supplier so that such claims can be registered with the transport agents. Before unloading, the condition of packing and of the visible parts should be checked and possible traces of leaks verified (condenser bushings). If necessary, appropriate statements and claims should be made.
Drums containing oil which have been dispatched separately should be examined carefully for leaks or any sign of tampering. All drums are dispatched filled up to their capacity and any shortage should be reported. As a principle we never supply partly filled drums.
In order to protect the active part against moisture, the transformer tank is filled with nitrogen during transport at an over pressure of 0.2kg/cm2 approximately at room temperature.
Check immediately the gas pressure at the arrival. A positive pressure indicates that the tank and the transformer components respectively are tight, and that the active part including the insulation materials is dry.
If there is no positive gas-pressure, transformer should be immediately filled with dry Nitrogen gas at pressure of 2 PSI without loss of time.
DAMAGE/LOSS
Damage or loss of any component should be reported to Supplier immediately. Photographs or other useful evident should be submitted wherever possible.
When the transformer is dispatched filled with oil, level in transformer main tank should be checked & if the level is below the indicated level in main tank the same should be reported to the supplier immediately & also the same should be mentioned in LR copy. When the transformer is dispatched filled with oil, a sample of oil should be taken from bottom of the tank and tested to IS: 1866. If the dielectric strength is below 50KV, when tested on standard IS: 1866, the matter should be reported to supplier along with insulation resistance values of the various windings to earth.
Drums containing transformer oil which have been dispatched separately should be examined carefully for leaks or any signs of tempering. All drums are dispatched filled up to their capacity and any shortage should be reported to us immediately.
UNLOADING
The transformer should be unloaded by means of crane or suitable device of sufficient capacity (Please refer rating plate for weight detail).
For lifting purpose lifting lugs are provided on the top cover & on the sides of tank. Lifting lugs on the sided of tank are lifting the complete transformer, whereas the lugs provided on the tank cover should be used only for lifting the cover. Lifting lugs for transformer lifting are painted red. Check at lifting of complete transformer that the lifting wires/ropes are not in contact with bushing or other components on the cover.
Four jacking pads are also provided for lifting the transformer with the help of jacks.
Bidirectional skids are also provided on the bottom of the transformer, in the form of channels having towing holes on both the sided & also holes for foundation of transformer.
Transformer should be jacked up using the projections specially provided for that purpose. Jack should never be placed under any valves.
To avoid undue mechanical stresses the transformers must be kept on reasonably level foundation.
ASSEMBLY OF WHEELS
Whenever wheels are supplied with transformer, movement of transformer at site is carried out by mounting these wheels.
Mounting of wheels under transformer is to be done as per roller arrangement drawing. In power transformer wheels are designed such a way that conservator side wheels are of slight higher in height fin the view of keeping transformer shortly inclined to release trapped air from main tank and to avoid accumulating rain water on the tank top cover. While fixing the rollers, the flange should come on the inner side of the rails.
Transformer placement can be with or without rollers as per applicable GA/foundation drawing. When the transformer is in the final position, the wheels shall be locked to prevent accidental movement of the transformer.
2.3 STORAGE
1. After arrival at site, it is desirable to erect and commission the transformer with minimum delay. In case this is not possible the transformer shall be erected at its permanent location with conservator and breather fitted and dry oil filled to the correct level. Whether storage or in use, the dehydrating breather must be fitted on all the transformers which are oil filled. The breather incorporates an oil sealing device which must be filled with oil, to the level marked, to be effective. The condition of silica gel must be checked periodically, particularly during monsoons.
2. Dismantled equipment and components are packed to be protected against normal handling and transport stresses.
3. All other accessories should be stored in a covered dry place. It should be ensured that there is no damage to the gasketted joints and that all the blanked joints are tight.
4. Goods stored outdoors must not be placed directly on the ground, and should be covered carefully with tarpaulin or similar material.
5. The tap changer, if provided, should be operated at 6 monthly intervals. Two of three runs from one end of the range to the other and back are sufficient.
6. Heaters on Marshalling kiosks, etc. should be kept energized. If for this purpose, power supply at the appropriate voltage to suit the heater is not available, temporary heaters should then be installed to suit the site voltage. The provision of heaters is important and failure to provide them may result in extensive damage to the contents of the kiosk because of condensation.
7. If oil received in drums is not likely to be used immediately the drums should be stored in a covered space where the temperature variation is minimum. If it is necessary to store the oil outside, adequate protection must be provided at all times. Oil drums should be stored in horizontal (lying) position with both the bungs also in horizontal position.
INDOOR STORAGE
The following items shall be stored indoor. • All the Bushings.
• Insulating Materials & Paints.
• M.Box R.T.C.C. & Motor Drive of OLTC. • Turrets with C.T. mounting.
• Components like B. Relay, MOO, PRy, Pressure gauges & Flow Indicators, Breather. • Cooling fans & Pumps.
OUT DOOR STORAGE
• Oil Drums: To be kept Horizontal and over two wooden planks. Care is taken that the caps shall be at 45 deg. from Vertical
• Radiators & Conservator. • Frames, Pipes & Pipe supports. • Rollers, Cable Box.
3 INSTALLATION
3.1 LOCATION AND SITE PREPARATION
1. Transformer should be placed on the foundation so that easy access is available all around and diagram plates, thermometers, valves, oil gauges, etc. can be easily reached or read. Adequate electrical clearances are also to be provided from various live points of the transformer to earthed parts.
2. ONAN type transformers depend entirely upon the surrounding air for carrying away the heat generated due to losses. For indoor installation, therefore, the room must be well ventilated so that the heated air can escape readily and be replaced by cool air. Air inlets and outlets should be of sufficient size and number to pass adequate air to cool the transformer. The inlets should be as near the floor as possible and outlets as high as the building will allow. Where necessary, exhaust fans can be installed for the purpose.
3. The transformers should always be separated from one another and from all walls and partitions to permit free circulation of air.
Where walls are provided, it should be ensured that the transformer gets good ventilation as mentioned above for indoor transformers. Provision should be made for the emergency drainage of the oil from the transformers (e.g. in case of fire in neighboring apparatus or bushing or the transformer tank), by surrounding the transformer plinth with sump filled with small pebbles.
3.2 ASSEMBLING THE TRANSFORMER
By means of the Part list and the Transformer GA Drawing, the assembling of a fully completed transformer is carried out according to the following Instructions. The following precautions are to be taken:
1. Fire-fighting equipment shall be available near the oil-treatment equipment as well as at work on and adjacent to the transformer.
2. Transformer oil is inflammable and under certain circumstances in a confined space may become explosive. Naked lights & flame should never be used near a transformer.
3. Check that there is no overpressure in the transformer when blanking plates or connection lids are to be opened. 4. Workmen having access to the interior of a transformer should empty their pockets of all loose articles. Any spanners or other tools used should be securely tied with a tape so that they can be recovered, if accidentally dropped.
5. All loose objects, tools, screws, nuts etc., shall be removed from the transformer cover before opening the connection and blanking lids.
6. All loose objects (tools, pencils, spectacles etc.,) shall be removed from the boiler-suit pockets etc. Before starting the work through man holes.
7. Tools to be used inside the transformer/reactor -e.g. for tightening of screw-joints- shall be fastened to the wrist or another fixed point by means of cotton tape or string.
8. Tools with loose sleeves and tools with catches must not be used at work inside the transformer.
9. Fibrous cleaning material should not be used as it can deteriorate oil when mixed with it. The presence of loose fibers in suspension in transformer oil can reduce its insulating properties. The presence of loose fibers in suspension in transformer oil can reduce its insulating properties. If any cleaning or wiping is necessary this should be done with clean and dry oil, using soft non-fluffy cloth.
10. Check healthiness of all the accessories and components dispatched separately with respect to GA Drawing and packing list.
11. All components dispatched separately should be cleaned inside and outside before being fitted.
12. A transformer is best protected from damp hazard by circulating warm, dry oil through it until temperature is 5° C to 10° C above ambient. This should be done before allowing external access to the interior of the tank. The warm oil should be circulated as long as transformer is open to atmosphere,
13. Oil pump & all joints in the oil pipe work should be airtight to avoid entrance of air through leakage joints. 14. The active part (core and winding) should be exposed to the surrounding air as short time as possible. Open
therefore only one blanking plate or connection lid at a time for remounting of bushings, valves etc. 15. Check Conditions of Leads, Connections, Tap changer, General conditions of insulation etc.
16. Check that the bushing leads set without being too close to ground or other points of different potential. 17. Core-ground; this is checked with the megger after removing earth connection.
18. Before entering into a N2 filled transformer make sure that sufficient Oxygen is available inside.
3.3 GASKETS
The sealing system normally used against oil and gas in transformers and belonging components has rubber bonded cork gaskets at joints.
Whenever the blanking plates are removed to fix detached parts such as bushing turrets, etc., a new gasket shall be used while fixing the same. A set of new unused gaskets of correct size and thickness is supplied with every transformer for this purpose.
Gaskets are best stored in such a way, that they must be protected from damp, oil and grease
To make a gasket joint, first clean the metal surfaces ensuring that they are free from oil, rust, scale etc.
Using one of the flanges as a template, punch the necessary bolt holes. Insert the bolts and tighten the bolts sequentially, a little every time so that uniform pressure is exerted on the gasket until the gasket is compressed to about 2/3 of its original thickness.
Joints should not be subjected to pressure until tightening is complete. If care is taken in making joints, and in handling the gasket, it is possible to break and remake a joint several times, using the same gasket.
Bolts/studs should be tightened lightly and diagonally in the sequence. Do not over tighten, otherwise gasket will get crushed.
3.4 BUSHINGS
After completing the internal connections, windings leads are brought out through suitable bushing. Normally three types of bushings are used.
PLAIN PORCELAIN TYPE
Assembly and dismantling of this type of bushing is possible without disturbing active part, tank cover and tank.
PLAIN OIL FILLED TYPE
Bushings supplied are oil communicating type. Oil communicating type bushing must be filled with transformer oil in operation and this is achieved by keeping conservator above bushing level so that bushing remain always filled with oil.
CONDENSER TYPE
DESIGN AND CONSTRUCTION
The active part of the bushing consists of an oil impregnated paper core built up around a centre pipe/rod with Aluminum foils at pre-designed locations for best possible internal & external dielectric strengths. The active part is built under heat and pressure on microprocessor controlled broadband winding machine.
The active part is dried under heat and vacuum and impregnated with insulating oil. The impregnated core is assembled inside porcelains Aluminum flange, and conservator with oil resistant synthetic rubber seals and are held together by a spring pack which also takes care of expansion & contraction of the centre pipe/rod. The annular space between the core and the porcelain is filled with the same oil. A nitrogen gas cushion is provided in conservator to take care of expansion and contraction of oil. An oil level gauge (prismatic / magnetic) is provided on the conservator. At the mounting flange an air vent plug is provided for air release of the transformer turret or for connecting to a Buchholz relay.
The outermost condenser layer of core is taken out electrically through the test tap and grounded through a screwed - on cap.
Arcing horns are provided (If ordered) and are kept inside the packing case itself. The upper arcing horn fixing arrangement is shown in the lower arcing horn support should be fixed to any of the mounting bolts.
CAUTION: THE TEST TAP MUST ALWAYS BE EARTHED BY THE SCREWED ON CAP AND SHOULD NEVER BE REMOVED DURING OPERATION.
PACKING AND TRANSPORT
The bushings are packed horizontally in sturdy wooden cases with oil level indicator facing down to avoid Nitrogen gas to come in contact with active part. Immediately on receipt, inspect the bushing thoroughly for any damage after opening top cover of the case. It is recommended to use the same packing case for storage/further transport. CAUTION OIL LEVEL INDICATOR SHOULD ALWAYS FACE DOWN DURING STORAGE / TRANSPORT
HANDLING AND STORAGE
Bushing can be lifted from packing case It is recommended to use two point lifting arrangement. The bushing can be stored in the same packing case with oil level indicator facing down or can be kept vertical on stands with flange firmly fixed stand.
Generally condenser type bushings are used for 72.5 KV and above. Design of this bushing is such that their mounting is independent of oil level in conservator, whenever this bushing are mounted on bushing pockets or raised truncated portions. Air vent pipes are provided for carrying away air or gases from these pockets to Bucholz relay during service. The bushing should be examined for damage at oil end and as well as the porcelain before fixing which may have occurred during transit.
The bushing shall be lifted by using the lifting eyes and soft ropes. Steel wire ropes or slings shall not be used. The turrets are often individually adapted; check therefore that they are remounted in correct places, which appear from the GA drawing and, part list.
1 Oil Impregnated Core
2 Central Metal Tube
3 Fixing Flange 4 Porcelain - Upper 5 Porcelain - Lower 6 Gaskets 7 Springs 8 Expansion Bowl 9 Cable Bolt
10 Air Releasing Screw 11 Test Tap
12 Top Terminal 13 Oil Filling Plug 14 Oil Sight Glass 15 Base Plate /
Stress Shield
16 Upper Arcing Horn 17 Lower Arcing Horn 18 Nitrogen Filling Plug
Bushings should be cleaned by dry & non fluffy cloth. Bushing insulator and metal parts are dispatched separately. Refer to G.A. Drawing for the position of bushing on transformer.
Ensure that the oil level is below the tank cover. (Please check prismatic oil level gauge on main tank or Check it by unscrewing air release plug provided on the tank cover. No oil should come out).
Remove blanking plates from tank cover. Check the gasket is OK. Replace it if required.
Put the lock washer over the connecting stud. Screw the connecting stud to the connecting plug.
BUSHING ARCING HORN GAP SETTING
KV RATING BIL RECOMMENDED VALUES
66kV 325 380 mm
132Kv 650 / 550 800 / 635 mm 220kV 1050 / 900 1400 / 1250 mm
400kV 1425 2250 mm
NOTE: IN CASE LIGHTNING ARRESTERS ARE FIXED CLOSE TO TRANSFORMER ARCING HORNS ARE NOT REQUIRED.
ASSEMBLY OF PLAIN PORCELAIN & PLAIN OIL FILLED TYPE OF BUSHING USED FOR VOLTAGE RATING UP TO 36KV.
1. Fix the stem on the top of the connecting stud and then lock them with lock nuts.
2. Insert the clamping ring over the bottom of the insulator before kept in the position. Place the insulator on the cover property, insert threading stem assembly and insulating tube through it. Ensure that stem is properly engaged inside the groove of the bushing.
3. Insert seal ring, cap and fix them in position by hexagonal nut.
4. Clamp the insulator by means of clamping ring, clamp, washer and hexagonal nut. See that the insulator is tightened evenly and carefully at all places. Turn the cap so that mounting locations for spark gap horns which are fitted later are in the position.
5. Fix the hexagonal nut, plain washer and spring washer.
ASSEMBLY OF CONDENSER TYPE OF BUSHING USED FOR VOLTAGE RATING 72.5KV & ABOVE
1. The line lead of HV winding if coiled inside the transformer is drawn through the bushing using a string when the bushing is lowered into position.
2. The thimble brazed at the end of line lead is fixed in position at the top of the bushing brass tube. Fix the stem on top of the end cap and lock them with lock nut. Fix the washer over the end cap 3. The lower end of the bushing shall be inspected from inspection
window for proper sealing.
4. The line connection should be tight and should not strain the terminal.
Fix the upper and lower spark gap horn and adjust gap setting as per required.
Release the trapped air inside the bushing by unscrewing hexagonal nut and depressing the stem slightly or unscrewing the vent screw on the top side of the metal part till a little quantity of oil comes out.
Before mounting on transformer, clean the bushing thoroughly and check for any damage. The lower part and inside of the centre pipe (in case of draw load/rod type bushing) should be further cleaned with transformer oil.
BUSHINGS WITH DRAW LEAD/DRAW ROD CONNECTIONS
Remove the terminal and pass a pilot wire through the centre pipe and lift the bushing upright of any desired inclination as shown in fig.. Gently rock it back and forth to release any gas trapped inside insulation before lifting up. After tying the transformer lead/rod to the pilot wire, bring down the bushing while pulling up the wire. Fix the flange to the transformer after checking the direction of oil level indicator, tightening the mounting bolts in a fraction of a turn at a time, working progressively in one direction until the bolts are uniformly tight. The thimble/rod is located by means of the pin and the terminal is screwed down fully with the gasket. The centre pipe can be deaerated by loosening the terminal. In case of 245 & 420 kv bushings, an additional cover is to be fixed after the terminal is tightened, for compressing the gasket. Bushings as per terminations as per CEA requirements.
STEM TYPE BUSHINGS
In stem type bushings, the central conductor itself acts as .the current carrying part and the transformer lead is to be connected at the bottom terminal through the inspection window of the transformer. The busbar/conductor can be connected directly to the top terminal with the help of a proper terminal connector.
PRE-COMMISSIONING CHECKS
1. Check capacitance/tan delta of the bushing preferably at 600 V and less than 10 KV, between High voltage terminal and test tap (after removing the cap) and compare with factory test results. Any abnormality should immediately be reported to TARIL. After the test, put back the cap.
CAP SHOULD NOT BE LEFT OPEN UNDER ANY CIRCUMSTANCES.
2. Check oil level of the bushing. In vertical condition, oil level should be at the middle of the indicator/gauge. 3. Check that the HV terminal is firmly tightened with the gasket to avoid passage of moisture to transformer. 4. Ensure that the transformer is energized minimum 36 Hrs. after mounting the bushing.
ROUTINE CHECKS AND MAINTENANCE
As the bushings are hermetically sealed, these are practically maintenance free. How ever, a periodic check of oil level and cleaning of the porcelain insulator will suffice. It is recommended to check capacitance and tan delta and compare with pre commissioning test results every year. Tan delta value of 0.01 or more, and increase in capacitance by 10% or more, should be viewed seriously and should be immediately informed to TRAIL.
3.4.8 DEMOUNTING AND PACKING
Demounting of the bushing from transformer should be done in the reverse fashion as illustrated under “INSTALLATION”. Repacking of the bushing is to he done in sturdy wooden cases and in the same way it is received.
3.5 TAP CHANGERS
OFF CIRCUIT TAP CHANGER
The off circuit tap changer is an integral part of transformer & its operation is to be carried out from outside. The actual position of tap changer is confirmed when the ratio tests are done.
That tap change is complete only when the tap switch handle hole matches with the hole provided on indicating plate.
The transformer must be de-energized from both primary and secondary sides before handling Off Circuit Tap Changer. In no case should the tap switch handle be left half way and unlocked to prevent damage due to inadvertent operation.
Off circuit tap changer should be operated only after de-energizing the transformer.
ON LOAD TAP CHANGER:
On load tap changer (OLTC) function in the same as off circuit tap changing switch. However, in case of OLTC the transformer need not be electrically isolated from HV & LV side. The tap changer can be operated on load. The tap changer is an integral part of the transformer and is suitable for power flow in the direction indicated on the OLTC name plate. It is used for transformer where the system voltage fluctuations are frequent and over wide range. It has local manual, local electrical and remote electrical controls and the panel located in the control room has the necessary
switches for raising or lowering the taps and is provided with a remote tap changer control cubical (R.T.C.C). Automatic voltages regulation can be provided as an optional fitting.
Where transformers have to operate in parallel, special circuits are employed such as Master - Follower and will be given with each scheme by the supplier in agreement with user.
For constructional details, refer manuals of manufacturer.
It is advisable to fit the tap changer on the transformer even during storage & connect it to the conservator and breather.
It should be ensured that the selector switch & diverter switch are filled with clean dry processed oil to keep selector switch & diverter switch moisture & dust free.
OIL SURGE RELAY
A Protective oil operated relay is supplied and the dispatched loose. This relay is sensitive to both low oil level and oil surge conditions. The relay must be fitted in a pipe connection from the tap changer conservator pad to the conservator and its contacts must be connected to the inter tripping system so as to isolate both sides of the transformer. The pipe work rising to the conservator should be arranged at an angle of 5° above the horizontal to ensure the effective operation of the protective relay. The connection of the relay contacts in the trip circuit such that the transformer is fully isolated will prevent damage to the tap changer the in case of low oil level.
Extensive damage will also be prevented in remote cases of incipient faults in the tap changer.
If the relay is painted at site care should be taken to see that the vent and drain holes in the terminal box are not clogged. A separate indication to show operation of tap changer oil surge relay should be available to avoid unnecessary inspection of tap changer in case only the transformer gas and oil surge relay operates.
OIL
The oil in the tap changer should conform to IS 335 and thus be thoroughly dried out by filtration. The electrical withstand level of Oil should be minimum 50kV when tested as per IS 335 - and IS: 5792-1972. The oil should be free from solid contaminations as well.
HEATER
Heater is provided in the drive mechanism in order to eliminate condensation troubles due to changes in ambient temperature. The heater is controlled by an ON-OFF Switch and should be switched on when there is a possibility of moisture condensation such as during monsoons.
COMMISSIONING OF THE TAP CHANGER
It is absolutely - important that the Drive Mechanism and the Tap changer Head show the same tap number, other wise the electrical and mechanical limits which are contained only in the Drive Mechanism become inoperative for the main Tap changer.
Fit the protective Relay, to a suitable outlet using pipe Connection Fill the Oil Vessel and Protective Relay completely with oil. COMMISSIONING CHECKS
1. The associated transformer should be de-energized, isolated and earthed during these checks to prevent any unintended damage to life equipment. Switch off auxiliary supply to tap changer.
2. Inspect the outside of the tap changer and inside of the drive mechanism to ensure that nothing is damaged or removed and that the mechanism chamber is clean. Touch up paint and lubricate if required.
3. Ensure that the tap changer is filled with oil to the level required in the conservator. Test oil. 4. Check that the breather charge is blue.
5. Check tripping operation of surge relay.
6. Operate the tap changer manually to extreme position, and check the operation of the limit switches and crank handle interlock visually. Bring the tap changer manually to a position in the middle of the tapping range. 7. Switch on mechanism auxiliary supply.
8. Stall motor by holding coupling and ensure that the motor protection relay trips. 9. Check that the damper is locked.
10. Check that the mechanism travels in the correct direction when operated electrically. 11. Check that the friction device is pressing tightly on the coupling drum.
12. Check that during electrical operation the pointer is approximately in the middle of the white sector when the motor comes to rest after tap change.
13. Check that the heaters are working. 14. Check counter operation.
15. Carry out approximately 100 electrical operations through the full range. 16. Air Release as follows:
• From the Head Cover: Note that there is provision of a small air cushion on top of oil in the Head and therefore you may see an air bubble under the numbering disk glass window.
• From Suction pipe, where this is provided
• From Transformer Tank Space under head, through plug.
17. Before commissioning the Tap changer must be taken at least once over the entire range manually using the crank handle. During this operation the following checks should be carried out.
• The number on the Tap changer Head and the Drive Mechanism should tally at each tap. • At the end positions, the electrical limits should be operative.
• If the Drive Mechanism is driven by crank handle beyond the end position, then the mechanical limit should operate, thereby decoupling the drive to the tap changer.
18. Only after carrying out the above checks, should power be switched on to the Motor Drive. 19. See also separate Operating Instruction for Motor Drive.
20. Check operation of all electrical control both local and remote as well as paralleling where provided.
21. Operate the tap changer one complete cycle with the transformer energized. It is not essential that the transformer be loaded for this test. If the tap changer oil surge relay trips during this test do not operate tap changer further. Isolate the whole equipment electrically and examine the tap changer completely, including the selector switch. Rectify any faults found and recommission.
PUTTING INTO OPERATION
Before connecting the motor drive to the mains, check whether voltage, current and power of the supply should coincide with the required values. When checking the voltage for the motor circuit take care that the RYB phase sequence is clockwise.
As the gearing and the ball bearings of the driving motor are sufficiently supplied with grease a regular maintenance is not necessary. We recommend, however, Check that all wiping faces, gear teeth, cam faces etc. are lubricated with special molybdenum disulphide lubricant. No oil should be used for lubrication. Ensure that drive mechanism chamber is clean and free from dust.
3.6 COOLING OF TRANSFORMERS
TYPE OF COOLING
1. OIL NATURAL AIR NATURAL COOLED TRANSFORMER (ONAN) 2. OIL NATURAL AIR FORCED COOLED TRANSFORMER (ONAF) 3. OIL FORCED AIR FORCED COOLED TRANSFORMER (OFAF) 4. OIL FORCED WATER COOLED TRANSFORMER (OFW)
COOLING EQUIPMENTS USED IN TRANSFORMER AS PER THEIR COOLING SYSTEM
TYPE OF COOLING ONAN ONAF OFAF OFW
COOLING EQUIPMENTS USED
RADIATORS √ √ √
FAN √ √
OIL PUMP √ √
OIL FLOW INDICATOR √ √
HEAT EXCHANGERS √
DIFFERENTIAL PRESSURE GAUGE √
The cooling equipments & associated pipe work & fittings are to be thoroughly cleaned thoroughly before assembly. Valves which are not dismantled like shut-off valves for radiators, coolers and possible headers shall be provided with blanking plates during the transport.
Remove the blanking plates when the assembling of the coolers is to be started. Check first that the valves are closed. The pressure gauge, differential pressure gauges, etc. should be fitted in position.
Check that each radiators and possible headers are assembled in the correct positions according to GA drawing. The shut-off valves against the transformer tank shall be closed until the oil-filling is started.
The cooler and associated pipe work is then filled with clean dry oil keeping all the cooler circuit open. Air is released from all the pipe work during filling.
3.7 RADIATORS
Transformer is provided with detachable pressed sheet radiators with isolating valve. Due to transport limitation and considering possible transit damages, the radiator valve are closed at the time of dispatch and radiators are detached and sent separately keeping the valve in position on tank flange. The valve blanking plate is to be removed only when the radiator is ready for mounting on flanges. On removal of blanking plate, oil will seep out. After filling the oil in radiators and venting air from them, radiator valves at top and bottom must be kept in OPEN position and sealed. In large transformers the radiators are sometimes separately mounted. In such cases there will be a header each at top & the bottom, which are supported on frames. Flanges are provided on these headers for fixing the radiators. Radiators valves are fitted to the headers and dispatched. The end frames are to be erected first. The frames should be positioned correctly with respect to the transformer. The distance between centre lines of transformer and cooler should be strictly as per GA drawing otherwise the connecting pipe work will not match. After erecting the end frames
the top and bottom headers are mounted. The headers will have to be properly leveled so that the connecting pipe work can be easily fixed. Radiators should be mounted in last.
If the conservator is to be provided on the cooler bank, the same may be mounted on it and all fittings for the same attached.
The interconnecting pipe work may be done taking care to connect correct pieces at the correct location. Usually expansion joints are provided in the pipeline connecting the transformer tank to cooler. Special care should be taken to see that these are installed correctly.
MOUNTING OF RADIATORS
Ensure that the transformer and radiators are not damaged in transit.
Special care should be taken while removing radiators from crates subsequent handling operations and while mounting on tank. Any damage while handling may result in cracks and oil may leak when fitted on tank and filled.
1. Lift the radiator vertically. Bring the radiator nearer to the valve. Remove the blanking plates from valve. Slide the radiator on the bolt from pipe flange the radiator valve and tighten using plain washer, spring washer and nuts. Tighten nuts in sequence applying uniform pressure on the gasket to make a proper leak proof fitting. Assembly all the radiators in the same manner.
2. Clamping arrangement at outer ends of the radiators is to be fitted to minimize the vibrations of radiators. Required number of bracing straps in standard lengths are sent separately with hole arrangement.
3. Make arrangements to fill the transformer oil through the main conservator. It is recommended to use hot filtered oil directly from the filter.
4. Fill only one radiator at a time. Open the bottom valve. Slowly unscrew the air release plug on the top of the radiators until the air starts escaping. The oil from the main tank will now flow in the radiator. Start putting fresh oil in the conservator.
5. After filling open valve at top.
6. Fill the remaining radiators in the same manner.
3.8 COOLING FANS
Cooling fans are provided whenever transformer is designed for dual rating. This are mounted on brackets which are fixed on tank wall or ground. The fans are controlled from Fan Cooling Control and some times from remote tap changer control (RTCC) panel and can be operated manually and on auto mode. When fans are on auto mode they are switched on using one of the mercury switches of the WTI mounted FCC. The setting of the switch should be such that no hunting takes place. For this the temperature differential should be minimum 5º C to 7º C between switching on and off the fans.
3.9 OIL PUMP
The pump and driving motor are assembled as a single unit or a common shaft. The transformer oil circulates through the windings thus eliminating cooling fan, shaft seal and avoiding the danger of oil leakage or entry of air. The complete unit is weather proof and can be arranged for horizontal or vertical mounting. Lubrication of the bearing and cooling of the motor windings is achieved with the circulated transformer oil. This results in a very efficient rate of cooling of the motor windings with minimum recirculation losses and maximum utilization of cooling of the motor windings with minimum utilization of available motor power.
In Case of forced oil cooled transformer, oil pumps are provided for circulating the oil. The pumps are dispatched separately after blanking both suction and delivery sides. The pump should be connected at proper position as per the GA drawing. New gaskets provided with the accessories should be used at the joints and the bolts should be tightened. In some pumps an air release plug is provided on the body. This plug should be checked for tightness.
3.10 OIL FLOW INDICATOR
FUNCTION
Flow indicators are mainly designed as a safety device looking to the need of an electrical signal on failure of forced circulation of liquid in pipe line. They perform following functions:
1. Indicate the rate of full flow in proper direction in specified pipe.
2. Operate one or two mercury switches when rate of flow drops near to 70% of specified full flow. These switches can be used to initiate precautionary systems of safety devices.
3. To introduce these Flow Indicators in a pipe line a “T-Mounting” is necessary.
CONSTRUCTION & WORKING
A suspended vane is used as sensor. Its surface is kept at right angle to direction of flow. When liquid starts flowing through pipe, the vane gets deflected along with vane shaft. This deflection is used to indicate flow inside the pipe and to operate mercury switches as follows:
A pair of permanent magnets is used as glandless coupling. The driving magnet is connected with vane; therefore it rotates with vane and remains in liquid. The follower magnet, separated by a nonmagnetic wall, is kept outside in air and acquires position corresponding to driving magnet. The follower magnet carries a pointer and a cam. The pointer is set to read the specified rate of full flow and the cam is set to operate one or two mercury switches when flow drops near to 70% of full flow. A return spring is used which acts in the opposite direction of flow. Hence any steady position of pointer is the result of equilibrium of force due to impinging liquid on vane spring tension & weight of vane. The pointer does not remain steady for unsteady flows. The size and shape of vane and tension on return spring is adjusted to suit specified full flow. The vane occupies very small area out of full cross section of pipe at NO-FLOW position. At full flow it becomes almost parallel to flow. Hence there is practically no head-loss across Flow Indicator. The flow indicators are distinguished in two series 4021 & 4022. Basic difference between two series is that in Series 4021 only one mercury switch is provided. Whereas in Series 4022 two mercury switches are provided. Proportionately, number of terminals, size of switch-box and size of terminal box differ.
DIAL MARKING
Usually PUMP ON-PUMP OFF or FULL FLOW-NO FLOW type of limit markings are printed. Intermediate markings such as ALARM, TRIP are also printed if required. Besides, specifications such as value of full flow, liquid, pipe size and direction of flow are also printed. The background of dial is white. Direction indicating arrow is in red color and all other markings in black color.
SWITCHES
One or two mercury switches are provided. Their contact position can be set on NO or NC at full flow. If required, switch can be changed from NO to NC or vice versa at site.
In case of single switch, it is set to operate near 70% when flow is fallen. In case of two switches, both are mounted on same plate. Hence both operate at same rate of flow. But in order to satisfy design requirements, one switch can lie set to operate near 80% and the other near 70% or one near 70% and the other near 60%. It is not possible to set a switch to operate at lower value than 60%. Even when both switches are set to operate at same rate of flow, some switching differential is observed due to use of mercury as switching element. We can modify setting suitably if switching requirements are clearly specified.
WIRING
Leads from mercury switch/switches are brought into a terminal box at the bottom of indicator. Terminals are accessible for wiring after removing cover. A hole with conduit threads is provided for fixing cable gland to box. Terminals are marked. Wiring should be done as per respective wiring diagrams.
NOTES:
1. Flow indicators are not interchangeable direction of flow or rate of flow. 2. Locking pin in the terminal box should be removed before taking into service.
3.11 HEAT EXCHANGER
In case of forced water-cooled transformers the oil to water shell tube heat exchangers are dispatched separately and properly blanked. On receipt at site, it shall be checked whether blanking is all right. The bracket for mounting the heat exchanger may be attached to the transformer first. The heat exchanger should be mounted on the support as per GA drawing. The oil pump, OFI & the connecting pipe may be fixed after this, in the correct position. In the water circuit necessary pies may be fitted. A water flow mater is placed on the outlet pipe to indicate that there a positive water flow. It is to be made sure that there is no restriction in the water outlet pipe as any obstruction in this pipe will increase the pressure in the water circuit and may result in the water pressure exceeding the oil pressure and creating leakage of water into oil circuit, which is detrimental to the transformer. Water discharge shall be of free flow type. The heat exchanger oil circuit is sealed from the water circuit with special seals. Pressure Gauges & Temperature Gauges should be mounted in water & oil pipe line inlet & outlet the heat exchanger to monitor the pressure & temperature, of inlet & outlet, water & oil. Temperature of outlet oil should be lower that the inlet while opposite phenomena should be in water circuit.
3.12 DIFFERENTIAL PRESSURE GAUGE
Differential Pressure Gauge is mounted to ensure that the water circuit pressure should not increase the oil circuit pressure.
Differential Pressure Gauge Consisting of two bourdon tubes, one for oil and one for water line and the pointer of the instrument give direct reading of differential pressure. Each bourdon tube can take maximum pressure of 1.3 times of maximum pressure shown on the dial. Oil side tube should be connected to Oil pipe line at outlet of Heat Exchanger and water side tube should be connected to Water pipe line at inlet of Heat Exchanger.
3.13 CONSERVATOR TANK
The conservator, which may be with or without air cell is assembled either on the transformer, or on a separate frame. Before the conservator is assembled it shall be checked that belonging equipment -e.g. Oil-level indicator -functions satisfactorily. Before erection of conservator make sure that all gasketted joints are oil tight and pipe work is clean and free of moisture.
The breather is connected to the oil conservator, and it is very important that joints and couplings in the pipe between breather and conservator are air tight.
3.14 MAGNETIC OIL LEVEL GAUGE
This model of indicator is manufactured considering Transformer application. It can also be used as Content Gauge on other tanks where level of liquid inside the tank is required to be indicated continuously on a dial. This is direct oil level indicator devices provided on conservator. 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 prevents the damages of the transformer from damages attributed to loss of oil due to any reason.
During dispatch, the indicator & the arm and float are detached to prevent damage to the bevel gear and mercury switch. The mercury switch operating arm and bevel gear are also locked in position.
CONSTRUCTION, WORKING & FEATURES
A float is used as sensor of liquid level inside the conservator (tank). Swing of float due to change in liquid level is utilized to indicate level on a calibrated dial and to operate a switch for external alarm unit.
Use of magnetic coupling in the indicator achieves complete sealing off the liquid inside the conservator from surrounding atmosphere. This results in avoiding any leakage of costly oil and avoiding contamination of insulating oil due to seepage of surrounding air in the conservator.
The glass mercury switch is nylon encapsulated to avoid breakage and spilling of mercury.
Switch is accessible for servicing while indicator is mounted on the conservator without any necessity of draining the oil. The detail of the subassembly/parts are as below.
1. Gear Assembly 2. Magnetic Couple 3. Float with arm
4. Cam assembly with Mercury Switch 5. Dial with pointer
The Schematic diagram of the full assembly is shown here.
EXAMPLES OF APPLICATION OF MOG
The float is hinged and swings up or down when oil level rise or falls. This rise or fall rotates the bevel gear and thus the pinion of the gear assembly. The pinion in turn rotates the driving magnet inside the conservator. The follower magnet positioned outside carries a pointer and a cam. The pointer reads oil level and the cam set to operate the mercury switch at a predetermined low level. MGOs are with different specifications are not interchangeable.
3.15 COMMISSIONING OF AIR CELL
1. Before assembly, ensure that there is no leakage in the air cell. Keep the air cell fixed inside the conservator. Inflate air cell by dry air or Nitrogen to a pressure of 0.08 kg/sqcm max. through the opening for breather connection. There should be one valve and a pressure gauge fitted in between this valve and air cell close the valve after required pressure is achieved. Keep in this condition for 24Hrs ensure no leakage in air cell with the help of pressure gauge.
2. Assemble the air cell conservator on the transformer.
3. Connect the conservator to transformer tank through Bucholz relay pipe line. 4. Close the valve between Bucholz relay & conservator.
5. Fill the oil in the transformer up to upper tank flange level under vacuum.
6. Keep the air cell inflated to a pressure of 0.08 kg/sqcm by Nitrogen / dry air through the opening for breather. 7. Open the valve between Bucholz relay & conservator.
8. Start further filling through the transformer lower filter valve slowly. Continue filling till the oil appears through ‘C1’. Close vent holes ‘C1’ and when oil appears through vent holes ‘C2’ close it. During oil filling, the pressure gauge should be kept 0.08 kg/sqcm.
9. Start further filling through the transformer lower filter valve slowly. Continue filling till the oil appears through ‘C1’. Close vent holes ‘C1’ and when oil appears through vent holes ‘C2’ close it. During oil filling, the pressure gauge should be kept 0.08 kg/sqcm.
10. Now remove the pressure supply connection of conservator & fix the breather with its pipeline. Keep further filling of oil and stop at the value selected for the filling temperature.
11. Before applying pressure or vacuum close the valve between Bucholz relay & conservator perfectly.
12. While air cell in service never open the vent holes ‘C1’ & ‘C2’ to check oil level. This will cause sudden fall in oil level. If oil level is to be checked first inflate the separator to 0.08kg/sqcm pressure and then open the vent holes.
3.16 GAS AND OIL OPERATED (BUCHHOLZ) RELAYS
Buchholz relay is very sensitive, gas and oil operated instrument which detects low oil level, formation of gas or development of sudden pressure inside the oil filled transformer. It has to be connected to protection circuits to give any early audible alarm in case of low oil level/gas collection and to disconnect the transformer from supply in case of severe fault inside the transformer. When mounted on the pipe work, the correct direction is maintained with the help of arrow provided. The angle of inclination is also to be checked and should be between 3 to 7’.
CONTENTS
Protective devices In the ideal case must be sensitive to all faults, simple in operation, robust for service and economically feasible. The relay operates on the fact that almost every type of electric fault in oil filed transformer gives rise to gas. This gas is collected in the body of the relay and is used in some way or other to cause the alarm or the tripping circuit to operate. The Relay is capable of indicate incipient fault thereby preventing further spreading of the fault and extensive damage and thus saving expensive and protracted repairs.
Double element relays are being used in detecting minor or major faults in transformer. The alarm element will operate, after a specified volume of gas has collected to give an alarm indication. Examples of incipient faults are. 1. Broken - down core bolt insulation,
2. Shorted laminations 3. Bad contacts
4. Overheating of part of windings.
The alarm element will also operate in the event of oil leakage and if air gets into the oil system. The trip element will be operated by an oil surge in the event of more serious faults such as 1. Earth faults
2. Winding short circuits 3. Puncture of bushings 4. Short circuit between phases
The trip element will also be operated if a rapid loss of oil occurs. Single element relays can be used to detect either incipient or major faults in oil filled potential transformers, reactors, capacitors etc. A special single element relay is available for the protection of on load tap-change equipment.
CONSTRUCTION
The Buchholz relay essentially consists of enclosure i.e. an oil tight container and an inserted assembly comprising of two floated elements fitted with switches. The enclosure is provided with inlet and outlet for the liquid. To allow connection of pipes, the enclosure openings can be designed with pipe thread or flange. The front inspection glass is provided with a graduation to allow reading the accumulated volume of gas and observe color of gas for fault analysis. For checking the function of the inserted assembly a Test Key is provided. There is also a visual indication on the scale
of service and Test/Locking position, in the form of movement of red indicator on the reading scale. This allows the testing of the alarm and Trip circuits before installation and even when the transformer is in service. Just above the inspection glass an arrow shows the specified direction of flow of the insulation liquid to the conservator. Enclosure and its inserted Assembly cover are made out of Cast iron/weather resistant light alloy.
FUNCTIONAL TEST
1. Testing the relay function with the Test Key.
A test system is provided in the Buchholz relay that allows the functional test of the upper and lower switching system. To test the relay function loosen the nut on the Test Key and rotate the key with a screwdriver in the Anticlockwise direction the SLOT on the Test Key points towards the T/L position Both the alarm (upper switching system) and Trip (lower switching system) will show continuity.
On bringing the SLOT on the Test Key to S (Service) position by rotating the key clockwise the Alarm and Trip circuits will not show continuity. The circuits will be actuated to ‘ON’ position only when there will be a fault in the transformer. Repeat the functional test each time a relay is started or maintenance completed.
2. Testing the relay function with draining the oil. Close the valves both the side of the relay. Put continuity tester across the alarm & trip contacts of the relay terminal box. Open the air vent lug on the top of the relay. Drain the oil from relay from drain plug at the bottom of the relay. As oil start draining alarm & trip contact will close.
INSTALLATION
Mount the Buchholz relay as close as possible to the tank in the pipeline between transformer and conservator. Keep pipe bends as wide as possible. Avoid close bends.
Make sure pipe ascends to the conservator at angle between one degree to nine degrees. Make pipe bends as wide as possible between transformer and conservator.
See that the relay enclosure is not subjected to stress. If necessary, use expansion compensators.
Ensure that the slot on the Test Key remains in the T/L (Test/Locking) position during storage or loose transportation of the relay.
Ensure that the slot on the Test key remains in the ‘S (Service) position and the Test Key Bolt is tightened just before commissioning of the relay.
MAINTENANCE
No servicing is needed during operation. On routine inspections of the protection equipment test the function of the Buchholz relay as described earlier and check the alarm and trip devices connected to them.
BASIC CHARACTERISTICS
The Gas and Oil relay provides protection against a number of internal faults but it is also able to indicate in several cases the tyke of fault. This is possible because the gas collected in relay can, from its color, odor and composition, indicate where the fault may be and what its nature is. By examining the gases collected it is possible to identify the nature of the fault.
DIAGNOSIS
I. If the gas is colorless and odorless or with only a faint odor of oil, the gas is air trapped in the oil or the insulation. 2. If the gas is Greyish White with sharp and penetrating odor and be non-inflammable it is due to overheated or
faulty insulation.
3. If the gas is Yellowish in color and inflammable it may be due to surface leakage on material like wood. 4. If the gas is dark Grey and inflammable it may be due to a flashover in oil or due to excessive overheating of the
oil caused by a fault in the winding or the core.
On the operation of the alarm if investigation of the collected gas does not indicate a serious fault it is possible to leave the transformer In service till it Is convenient to carry out a thorough inspection. This occurrence is possible on a newly commissioned transformer due to air trapped in the oil, or the
insulation. On repeated and frequent alarm signals the transformer should be taken out of service for thorough check up.
FUNCTION
The function of a double element relay will be described here. During normal operation of a transformer the Buchholz relay is completely oil filled.
In the event some fault in the interior of the transformer tank gas bubbles are produced and accumulate in the Buchholz relay on the way to the conservator. In consequence, the oil level in the relay enclosure drops which in turn lowers the upper bucket.
This causes the mercury switch/Reed switch to operate an alarm signal.
The lower bucket does not change its position, because when the gas reaches the upper inside wall of the pipe it can escape into the conservator. Hence, minor fault in the transformer tank will not trigger the lower switching assembly and will not trip the transformer.
In case the liquid continues to drop due to loss of oil, the lower bucket also goes down in consequence lower switching system operates if the level of oil goes below the bottom level of the pipe connected the relay.
Alternately in the event the liquid flow exceeds a specific value the lower bucket is forced down, thus triggering the lower switching system to operate.
As the liquid flow rate decreases or the level of the liquid raises the bucket returns to its original position.
The single element relay has only one operating element and it responds to either gas collection or oil surges. The single element OIL SURGE RELAY has been specifically designed for use with on load tap change equipment and it will bypass normal amounts of gas which are generated by tap change operations and will only responds to oil surges and loss of oil.
OPERATING CHARACTERISTICS
Normally Relays of the double element type are made in three sizes GOR1, GOR2 & GOR3 according to the diameter 25, 50 and 80 mm respectively of the bore of the oil pipe connecting the transformer to the conservator tank. All relays are normally open types.
When transformers are required for use in areas subject to earthquakes or for traction application, we can supply special relays which use magnetically operated Reed Switches instead of mercury switches.
3.17 SILICA GEL BREATHER
OPERATION
Dry silica gel crystals which are dark blue in color have a very good capacity to absorb moisture. When the air from outside is breathed in the conservator, it passes through the crystals and the moisture in the air is absorbed. Thus the air that reaches the conservator is dry. Dust particles are partly trapped in the oil seal and partly trapped by the crystals of the silica gel. Silica gel crystals change their color from dark blue to pink depending upon absorption of certain quantity of moisture.
Silica gel crystals can be reactivated a numbers of times and therefore, they can be used over a long period. They should be observed for the color of the silica gel on weekly basis. Change oil in oil seal once the color changes from light yellow to dark brown.
BREATHING PROCESS OF THE TRANSFORMER:
When Transformer is loaded or unloaded, the oil temperature inside the transformer tank rises or falls. Accordingly the air Volume inside the tank changes, by either sucking in or pushing out the air.
impurities and/or Humidity which changes dielectric strength of transformer oil. Hence, it is necessary that, the air entering into the transformer is free from moisture & foreign impurities.
OPERATION & WORKING
The Breather- is connected to an outlet pipe of the Conservator Vessel and the air which Is being sucked by transformer is made to pass through the Silica Gel Breather to de humidify the air and to remove foreign impurities. The Silica Gel which is filled in the Breather Is hard blue Crystals, which has considerable absorption power for moisture. When, it gets saturated with moisture, it changes it color to pinkish white. For proper dehumidification of air, its is absolutely necessary that this charge of Silica Gel is reconditioned from pinkish white to deep blue by heating it. The air, which is passed through Gel is first made to pass through the oil compartment of the Breather. This oil removes all foreign Impurities from air which enters the Gel compartment.
Hence, Oil sealed type Silica Gel Breather will keep the oil properties constant, thereby ensuring proper working and hence longer life of the transformer.
INSTALLATION
The Breather is connected to transformer by either threaded or flanged joint (after removing the Seal) as per details mentioned below. Before putting the Breather Into service, remove the Oil Cup and fill it up with fresh transformer oil up to the line marked on Cup. Remove the seals on the air holes of the Cup and fit the Cup to the Breather The Breather is how ready for installation.
MAINTENANCE
As the color of the Silica Gel changes to pinkish whit after use, it needs recharging.
Take out the Silica Gel and heat it, until color of Gel changes to deep blue. The Gel content or the size of the Breather is determined by the Volume contents of the air passing through the Breather, the Oil Transformer and the atmospheric conditions of installation. Hence, the Transformer Manufacturer or the ultimate user should decide the size of Breather would shut the transformer.
3.18 PRESSURE RELIEF VALVE (PRV)
Pressure Relief Valve should be mounted as per GA drawing. Check operation of alarm/trip contacts. The purpose of the pressure relief valve is to prevent mechanical damage to the transformer tank by releasing any excess pressure over the set limit. This valve is basically a spring loaded device which closes automatically when the pressure inside the tank drops to the set limit after venting excess pressure over the set limit.
APPLICATION
This PRV is designed to be used on power Transformer. When pressure in the tank rise above, predetermined safe limit this valve operates and allows the pressure to drop by instantaneously opening a port of about 150 mm diameter & give valve & operation by raising a flag and also operates a switch. This switch has 1 NO and 1 NC contacts (As per requirement). Hence switch can be effectively used in control circuit.
SPECIFICATIONS
Normally PRVs are used of two sizes T-3 & T-6 each are having variety of three pressure ratings of 0.42 kg/sqcm (6 PSI), 0.49 kg/sqcm (7 PSI) and 0.56 kg/sqcm (8 PSI).
CONSTRUCTION & WORKING
The Pressure Relief Valve consists of a pressure die cast Aluminum flange (1) with Nitrile gasket (2) for mounting on transformer. The stainless steel diaphragm (3) is loaded with two reverse wound calibrated springs (4) and seals the 75/ 150mm port against top and side gasket (5 & 6). The deep drawn cover (7) retains and is held in place by six screws (8). The cover and the operating disc have specially designed retainers to prevent dislocation of springs during repeated operations.
The switch assembly and houses one/two NO and NC contact as per requirement. It also has a visual indicator (10). When pressure in the tank rises above the safe limit, the operating disc moves slightly upwards from top gasket. This
