transformer manual

MADHYA PRADESH POWER TRANSMISSION CO. LTD.

SHAKTI BHAWAN RAMPUR: JABALPUR

VOLUME II

PART-1

Technical Book Serial No. MPPTCL/TECH/PROC/01/MAY13

TECHNICAL SPECIFICATION FOR SUPPLY OF EHV EQUIPMENTS AND MATERIAL FOR

SUB-STATIONS AND FEEDER BAYS

O/o CHIEF ENGINEER (PROCUREMENT)

MPPTCL, JABALPUR

Volume-II contains four booklets as under:-

Section Description Technical Book Serial No.

Part-1 TECHNICAL SPECIFICATION FOR SUPPLY OF 132KV, 40MVA POWER TRANSFORMERS

MPPTCL/TECH/ PROC/03/MAY13

Part-2 Book I of III

TECHNICAL SPECIFICATION FOR SUPPLY OF EHV EQUIPMENTS/ MATERIALS


Part-2 Book II of III



Part-2 Book III

of III



All the above four booklets are in the form of separate books. This book refers to:-

PART-1

TECHNICAL SPECIFICATION FOR SUPPLY OF 132KV, 40MVA POWER TRANSFORMERS

Please note that the modifications in technical specifications

are indicated in Appendix-1, enclosed in Volume-I of the Tender document.

Contents

Description of document Page No.

Technical specification for transformer 1-66

Annexures and appendix for 132KV, 40MVA Power Transformer

Annexure I - Principal Technical particulars 67-69

Annexure II - List of Fittings and Accessories 70-73

Annexure III - Test certificates to be furnished foraccessories 74-76

Annexure IV - Schedule of Inspection Windows 77

Annexure V - Schedule of Valves 78-79

Annexure VI(A)- Drawings & Data to be furnished 80-82

Annexure VI(B)- List of drawings to be furnished alongwith bid

83

Annexure VII - Calculations required to be furnished

84-87

Annexure VIII - Details of Inspection Program 88-92

Annexure IX - List of Hand Tools and Jacks 93

Annexure X - Description of equipment for schedule of rates & prices

94

Appendix I - Calculation for Hot Spot winding temperature for EHV transformers

95-96

Appendix II - Technical particulars to be filled-in by bidder

97

List of abbreviations used in technical specification 98-99

MPPTCL/TECH/PROC/03/MAY13 1 of 99 40 MVA TRANSFORMER

VOLUME II, PART-1

TECHNICAL SPECIFICATION FOR 40 MVA , 132/33 KVPOWER TRANSFORMERS

1.0 SCOPE 1.1 This specification covers design, engineering, manufacture, assembly, stage inspections and testing before supply and delivery including unloading on plinth at our substation sites of 132/33KV,40 MVA, three phase transformers complete with all fittings, accessories, associated equipment including oil for first filling including wastage & 10% extra of that quantity specified herein which are required for efficient and trouble free operation as specified hereunder. Scope of supply also includes services to be provided by the supplier/Bidder for supervision of erection and supervision of commissioning of each transformer unit at each project site anywhere in MP. 1.2 It is not the intent to specify completely herein all the details of the design and construction of equipment. However, the equipment shall conform in all respects to high standards of engineering, design and workmanship and shall be capable of performing the duties specified herein. The offered transformers shall be complete with all components necessary for their effective and trouble free operation. Such components shall be deemed to be within the scope of Bidders supply irrespective of whether those are specifically brought out in this specification or not. The transformers should be free from Polychlorinated Biphenyls (PVB/PCB). 1.3 The Purchaser will interpret the meanings of drawings and specification and shall have the power to reject any work or material which, in his judgment is not in accordance therewith. The offered transformers shall be complete with all components necessary for their effective and trouble free operation. Such, components shall be deemed to be within the scope of Bidders supply irrespective of whether those are specifically brought out in this specification and/or the commercial order or not. 2.0 STANDARDS 2.1 The transformers and associated accessories shall conform to the latest issues/amendments of standards as given below, except to the extent explicitly modified in this specification. Transformers conforming to any other authoritative standards meeting better quality and ensuring better performance are also acceptable. Bidder shall specifically indicate deviations if any from the INDIAN STANDARDS.

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THE APPLICABLE INDIAN/INTERNATIONAL STANDARDS FOR POWER TRANSFORMERS AND ASSOCIATED ACCESSORIES ETC.

INDIAN STANDARD

NUMBER TITLE

INTERNATIONAL AND

INTERNATIONALLY RECOGNISIED

STANDARD IS-2026 (Part 1 to 5 )

Power Transformers IEC-60076(Part I to 5)

CBIP Publi-cation No.295

Manual on Power Transformers

IS-335 Insulating oil for transformers IEC-296,BS-148. IS1866-2000

Electrical maintenance and Supervision of mineral insulating oil in equipment.

IS-2099 Bushings for alternating Voltage above 1000V.

IEC-60137(2008)

IS-2312 Fans (Cooler fans) IS-2705. Current Transformers. IEC 60044 IS-325. Three phase Induction motors. IEC-34. IS-375 & IS-996

Marking & arrangements for switch gear, bus bars, main connections & auxiliary wiring.

IS-3407. Gas & oil operated relays. IS-10028 (Part 1to3)

Code of practice for installation and maintenance of transformers.

IS-2147. Degree of protection provided by enclosures for low voltage switch gear and control.

IEC 60529,IEC60947

IS-5. Colours for ready mix paints. IS-6272 Industrial cooling fans. DOC.ETD16 (3703)

Draft standard by BIS for revision of IS-6600 for Guide for loading of oil immersed transformers.

IEC 60354

OLTC IEC 60214 IS 8478 Application Guide for OLTC IEC 60542 IS 10561 Application Guide for Power

Transformer. IEC 60076-8

IS 13964 Method of measurement of Transformer Sound levels.

NEMA-TR1

IS 2071 (Part 1 to 3)

Methods of High Voltage Testing IEC 60060

IS 6209 Methods for Partial Discharge Measurements

IEC 60270

IS 2165 Insulation Coordination IEC 60071 IS 5561 Terminal connectors

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INDIAN STANDARD

NUMBER TITLE

INTERNATIONAL AND

INTERNATIONALLY RECOGNISIED

STANDARD Short Circuit Current calculation of

effects IEC 865(part I & II)

IS-5553 Shunt Reactors, Neutral/Earthing Reactor and Arc Suppression Coil

IEC 60289

IS:335 Insulating oils for transformers and switchgears

IEC:60296, BS:223

IS -1886 Code of practice for installation and maintenance of transformers.

Supervision and Maintenance guide for Mineral Insulating Oil in Electrical Equipment

IEC 60422

Method of Sampling of Liquid dielectrics IEC 60475 Guide for the Sampling of Gases and of

Oil from Oil-filled Electrical Equipment for the Analysis of Free and Dissolved Gases

IEC 60567

Digital Recorders and Software for High Voltage Impulse testing

IEC 61083

Specification for radio disturbance and immunity measuring apparatus

CISPR 16

Guidelines for conducting design reviews for transformers 100 MVA and 123 kV and above.

Cigre Publication 202

Metal oxide surge arrestors without gaps

IEC 99-4

Selection and application recommendation

IEC 99-5

Indian Electricity Rule 1956

2.2 In case equipment conforms to other International standards which ensure equivalent or better performance than specified under cl 2.1 then the English version of such standards or the relevant extracts of same shall be forwarded with the bid and the salient features of comparison shall be brought out separately. 2.3 The electrical installation shall meet requirements of Indian Electricity Rules, 1956 and IS-1886,"Code of practice for installation & maintenance of Transformers" as amended till date.

2.4 It has been experienced that the weight of core lamination, weight of copper, weight of steel, weight of Transformer Tank along with Fittings and Accessories and quantity of oil for first filling including wastage & 10% extra

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of that quantity, total weight of core + winding after assembly and total weight of transformer are indicated in the technical bid by the manufacturers on tentative basis and at the time of submission of drawing, wide variations in these quantities take place. This is not in order and it will be obligatory on the part of the Bidder to ensure that all these details are worked out carefully and only correct figures after proper design are offered in the technical bid. It may be noted that at the time of submission of final drawings, variation in these weights beyond the limits of (+) 5% shall not be permitted. 2.5 It will also be obligatory on the part of the manufacturer to furnish details of calculations for quantity (weight & size) of core material, quantity (weight & size) of copper material, calculations for thermal and dynamic short circuit withstand capability of transformer, calculations for pressure relief valve, adequacy of size of AIRCELL Bag, volume of oil for adequate cooling with calculations of size of conservator and other details as called for in the specification. Furnishing of these calculations along-with technical bid is a must. All the data should be supported with calculation details. 2.6 Interconnection : The transformers are meant for service as interconnecting transformers and shall be capable of being energized either from 132 KV side or 33 KV side. The power transformer shall be capable of being loaded at rated power on the 132 KV and 33 KV sides at its full rating (lagging or leading or mixed load). On Load Tap Changer shall be suitable for such operation. The OLTC shall be suitable for bidirectional flow of power. 3.0 SERVICE CONDITIONS 3.1 Climatic Conditions : The transformers and its accessories to be supplied against this specification shall be suitable for satisfactory continuous operation under the following tropical conditions. 1. Location At various substations within

the State of Madhya Pradesh 2. Max. Ambient air temp. (oC) 50 3. Min ambient air temp (oC) -5 4. Maximum daily average ambient air

temperature(oC) 40

5. Maximum yearly weighted average temperature (oC)

32

6. Maximum Relative humidity (%) 95 (sometimes reaches saturation.)

7. Average annual rainfall (cm) 125 8. Max. Wind pressure (Kg/sq.m.) 150 9. Max. Altitude above mean sea level

(Metres) 1000

10. Isoceraunic level (Average number of thunderstorm days per year)

50

11. Seismic level (horizontal acceleration) 0.3g

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Moderately hot and humid tropical climate, conducive to rust and fungus growth. Tropical Protection Shall conform to IS:3202 titled climate proofing of electrical equipments and BS: 1014 : titled protection of electrical power equipments against the climatic condition. The transformer tank fittings and radiators including all accessories shall be designed to withstand seismic acceleration equivalent to 0.3 g. Special precautions shall be taken to prevent mal-operation of Buchholz relay under such condition. 3.2 Auxiliary Power Supply : Auxiliary electrical equipment shall be suitable for operation on the following supply system.

a. Power Devices

(like drive motors) 433V, 3phase, 4wire 50Hz. neutral grounded AC supply.

b. DC Alarm, control & protective devices

220V or 110volts DC, ungrounded 2wire (Substation wise exact details shall be furnished to the successful Bidder).

c. Lighting. 250V, single phase, 50Hz. AC supply. Bidders scope include supply of interconnecting cables, terminal boxes etc. The above supply voltage may vary as indicated below and all devices shall be suitable for continuous operation over the entire range of voltages.

i) AC supply : Voltage Variation of 25% to +10%;Frequency +/- 4%

ii) DC supply : Voltage Variation of -20% to + 10%. All accessories requiring AC or DC supply shall perform satisfactorily for voltage variation as above. 4.0 GENERAL TECHNICAL REQUIREMENTS 4.1 Duty Requirements

a) The transformers and all its accessories like CTs etc., shall be designed to withstand without injury, the thermal and mechanical effects of any external short circuit to earth and of short circuits at the terminals considering infinite bus arrangement of values specified as under :

132KV - 40KA for 3 secs.

33KV - 31.5KA for 3 secs.

b) Over Loading : The transformer shall be capable of being loaded in accordance with IS:6600. There shall be no limitation imposed by windings, bushings, tap changer etc. of transformer. Transformer & all its accessories shall be liberally rated to allow 10% over loading at all taps on continuous basis without exceeding the temperature limits specified in clause 6.0.

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The transformer shall be capable of being operated without danger on each tapping at the rated KVA with specified voltage variation corresponding to the voltage of that tapping with normal temperature rise. The design adopted to achieve this shall be indicated in detail in the Bid.

Transformer shall be capable of operating under the natural

cooled condition up to the specified load i.e. as ONAN rating. The forced air cooling equipment shall come into operation by pre-set contacts of winding temperature indicator and the transformer shall operate as a forced air cooled unit i.e. as ONAF. Cooling shall be so designed that during total failure of power supply to cooling fans the transformer shall be able to operate at full load for Ten(10) minutes without the calculated winding hot spot temperature exceeding 140 deg.C. Also stopping of two cooling fans should not have any effect on the cooling system. Transformers fitted with two coolers (cooling banks) each capable of dissipating 50 per cent of the loss at continuous maximum rating shall be capable of operating for 20 minutes in the event of failure of the blowers associated with one cooler, without the calculated winding hot spot temperature exceeding 140oC at continuous maximum rating.

c) Over Voltage : The transformers shall be capable of being

operated on continuous basis at 10% excess voltage than the rated voltage specified at each tap.

4.2 Radio Interference & Noise Level 4.2.1 The transformers shall be designed with particular attention for suppression of maximum harmonic voltage especially the third and fifth so as to eliminate wave form distortion and minimize interference with communication circuits. 4.2.2 The noise level, when energized at normal voltage and frequency with fans running shall not exceed, when measured under standard conditions, the values specified in NEMA,TR-I. 4.3 Stresses : Transformer shall be capable of withstanding Electrical, thermal and mechanical stresses on any winding caused by forces due to symmetrical or asymmetrical external fault. 4.4 Frequency & Magnetic Induction 4.4.1 The transformers shall be suitable for continuous operation for a frequency variation of (+) plus (-) minus 4% from normal 50Hz without exceeding the specified temperature rise. For considerations of over fluxing, the transformer shall be suitable for continuous operation for values of over fluxing factor up to 1.1. V FN The over fluxing factor being { -- x -- } VN F

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4.4.2 The working flux density shall not exceed 1.65 Tesla for offered no load losses and the maximum flux density in any part of core and yoke at 110% rated voltage combined with (-) 4% frequency variation shall preferably not exceed the value of 1.90 Tesla as per CBIP manual no 295. For manufacturing of Power transformer, core laminations of various specifications are available and therefore while selecting the working flux density, the Bidders will have to comply with the requirements of cl.4.4.1 & 4.4.3. 4.4.3 For the selected flux density, the transformer shall have minimum of following over fluxing capabilities , such that while meeting the above requirement saturation of transformer core shall not take place under any circumstances. Transformer shall accept, without injurious heating, combined voltage & frequency fluctuation, which produces the following over fluxing conditions :

Over Fluxing Factor Period 1.50 Less than 2 seconds 1.40 5.0 seconds 1.25 60 seconds 1.10 Continuous

The Bidder shall also indicate 160% & 170% over voltage/over fluxing withstand capability period. Over fluxing withstand characteristics up to 170% shall be submitted along with the bid. 4.4.4 Detailed calculations for maximum flux density and magnetizing current for core material shall be furnished to substantiate the above requirement. The manufacturer shall enclose details of Core Material with thickness of lamination, type designation and source of raw material and its characteristic curves. All characteristic curves of material including Voltage Vs Flux Density and Loss per Kg Vs Flux Density are to be enclosed with Bid clearly indicating Flux Density selected for calculation of core losses (No load loss). On the basis of these data, for the Flux Density and core material chosen verification of Saturation Flux Density shall be done by the purchaser, to know the margin considered in operating Flux Density . 4.4.5 The maximum current density for design of power transformers within specified limits of transformer losses shall not exceed the limits of 300 amps per sq.cm. 4.4.6 All other requirement of magnetic circuit shall be as per latest issue of CBIP Manual no 295. 4.4.7 The transformers shall be either core type or shell type construction, oil immersed, ONAN/ONAF with external heat exchangers and shall be suitable for outdoor service as inter connecting and/or step-down transformers suitable for parallel operation with the existing transformer having tertiary winding already in service at the EHV substation where these transformers are to be commissioned. The rating and electrical characteristics of the transformers shall be strictly as specified in this specification. For matching the parameters required for parallel operation with existing unit, details shall be intimated to successful Bidder.

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4.5 All the transformers shall be suitable for continuous operation with frequency variation of +/- 4% from normal 50 Hz . Combined voltage & frequency variation should not exceed the rated V/f ratio by 10 %. 5. INSULATION 5.1 Impulse & Power Frequency Voltage Withstand Values : For rated nominal system voltage of 33KV & 132KV following minimum power frequency and impulse withstand voltage should be offered for the windings.

System Voltage

Highest System Voltage

Power Frequency Withstand Voltages

Impulse Withstand

Voltage

33KV 36KV 95KV rms 250KVp

132KV 145KV 230KV rms 550KVp 5.2 The HV winding of the transformers shall have graded insulation. The insulation class of the neutral end of the winding shall be graded to 95 KV. The 33KV winding shall have full insulation for 33KV i.e. 250 KVp impulse and 95KVrms power frequency. 6.0 TEMPERATURE RISE : Each transformer shall be capable of operating continuously at its normal rating & 10% over load condition without exceeding temperature limits as specified below. The maximum ambient temperature shall be taken as 50 degree C and type of cooling be suitably adopted to limit the temperature rise within the safe limit of operation.

Type Of Cooling Temperature-Rise

Windings Oil

ONAN (Air natural). 50oC 45oC

ONAF (Air forced) 50oC 45oC. 7.0 FREQUENCY : All the transformers shall be suitable for continuous operation with a frequency variation of + 4% to -4% from normal 50 Hz without exceeding the specified temperature rise. 8.0 IMPEDANCE : The percentage impedance of the power transformer shall be 10% on 40 MVA base. manufacturer shall indicate the guaranteed impedance, tolerances and also the impedance on all taps for the offered transformers. Impedance shall include positive and zero sequence and shall be expressed in terms of the branches of the star connected equivalent diagrams on all the specified MVA base and the range shall be given for each branch of the equivalent circuit turn. It may be noted that if required the percentage impedance should be designed identical to the existing transformer of any make in case parallel operation is desired. The IS tolerance on all matching taps are acceptable. Confirmation regarding requirement of parallel operation should be given in the Bid.

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It may be noted by the manufacturer that for the purpose of matching impedance of transformer, included in scope of this Bid, between 132KV & 33KV windings, the Bidders are not permitted to use reactor or reactor/capacitor assembly. The design of the main winding should take care of the requirement of impedances as specified in this Bid document and for this purpose, no reactor or reactor/capacitor should be used. 9.0 MAXIMUM LOSSES: 9.1 Maximum Losses : While the Bidders may offer their own design, it may be noted that the transformer losses at 75 deg. C. at rated Output. Rated Voltage and rated frequency should not exceed the following maximum limits which include tolerances as per IS :

a) No load losses (Iron losses). : 20 KW

b) Load(Copper losses) + Auxiliary losses. : 100 KW including stray loss in KW 9.2 The losses in kilowatts (including BIS tolerance) at rated voltage and rated frequency and the total load losses in kilowatts at rated output, rated voltage and rated frequency at 75oC shall be guaranteed by the Bidder. It may be noted that the losses of the Transformer shall not exceed during final testing of the transformer, if the same exceeds from the maximum Ceiling limit of Transformer losses as detailed in 9.1 above the Transformer shall not be accepted 9.3 Heat Run Test:

One 40 MVA 132 KV power transformer of each manufacturer (if there are more than one manufacturer) shall be subject to heat run test (Temperature rise test).

10.0 COOLING : The Bidder may offer ONAN / ONAF type of cooling for these transformers. The ONAF rating for each transformer winding shall be 125% of ONAN rating achieved by cooling. The ONAF cooling shall be in two groups each of 50% capacity. Adequate no. of standby cooling fans shall be provided for 20% additional cooling per bank, in line with requirement indicated in clause 15.1 ( C ). 11.0 CONSTRUCTION DETAILS : The features and construction details of power transformer shall be in accordance with the requirements stated hereunder 11.1 Tank

(A) As required in CBIP specification, the tank shall be of Bell type construction for 40 MVA transformers covered under this specification. Top cover of Bell type construction shall be welded to the tank body .

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(B) Tank shall be of welded construction and fabricated from tested quality low carbon steel suitable for welding & of following minimum sheet thickness.

Tank cover - 20 mm, Sides including inspection covers- 10 mm ,

Base - 20 mm.

(C) All seams and those joints not required to be opened at site shall be factory welded and wherever possible they shall be double welded. After completion of tank construction and before painting, 'Dye Penetration Test' shall be carried out on welded parts of jacking bosses, lifting lugs and all load bearing members.

(D) Tank stiffeners shall be provided for general rigidity and these shall be designed to prevent retention of water.

(E) The tanks shall be designed to withstand the following without permanent distortion.

(i) Mechanical shocks during transportation.

(ii) Vacuum filling of oil at 10 milli torr in transformer with all fittings.

(iii) Continuous internal pressure of 35 kN/m2 over normal hydrostatic pressure of oil.

(iv) Short circuit forces &

(v) Under seismic condition /events both horizontal/vertical.

(F) Where ever possible the transformer tank and its accessories shall be designed without pockets wherein gas may collect. Where pockets can not be avoided, pipes shall be provided to vent the gas into the main expansion pipes if any.

(G) The shields shall be such that no magnetic fields shall exist outside the tank. They shall be of magnetically permeable material. If required impermeable shields shall be provided at the coil ends. Tank shield shall not resonate when excited at the natural frequency of the equipment.

(H) The tank shall be provided with :

(i) Lifting lugs suitable for lifting the equipment complete with oil.

(ii) A minimum of four jacking pads in accessible position at 500mm height to enable the transformer complete with oil to be raised or lowered using hydraulic or screw jacks. The location of jacking pads shall be such that there should not be any interference with the civil foundation of rails in either direction i.e. longitudinal or transverse. A typical drawing no. MPPTCL/TR-57/ 40MVA/01 for providing jacking pad is enclosed with the Bid specification.

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(iii) Suitable haulage holes shall be provided.

(I) (i) Inspection cover/access windows & Manholes: Suitable man-hole with a welded flange and a properly gasketted bolted cover having of minimum thickness of 10 mm shall be provided on the tank cover, weight of which shall not be more than 50Kg each. The man- hole shall be of sufficient size to offer easy access to the lower ends of the bushings, terminal etc. The requirement of inspection windows and manholes have been stipulated in Annexure-IV & Bidders have to confirm compliance of the same in their Bid.

(ii) Space for free movement in Transformer Tank for inspection: Details of passage & free space provided inside the main tank should be indicated in concerned drawing to allow free movement of at-least two persons for inspection of active parts etc. To be more specific it may please be noted that minimum clearance from outer most winding/connection leads to tank shall not be less than 300 mm. on all 4 sides with suitable platform on bottom of the tank to facilitate free movement of person all around inside the tank.

(J) All bolted connections to the tank shall be fitted with suitable oil tight gaskets which shall give satisfactory service under all operating conditions. Special attention shall be given to the methods of making the hot oil tight joints between the tank and the cover as also between the cover and the bushings and all other outlets to ensure that the joints can be remade satisfactorily and easily with the help of semi skilled labour. Where compressible gaskets are used, stoppers/ runners shall be provided to prevent over compression.

(K) Suitable guides shall be provided for positioning the various parts during assembly or dismantling. Adequate space shall be provided between the cores and windings assembly and the bottom of the tank for collection of any sediment.

(L) The design of the tank, lifting lugs shall be such that the complete transformer assembly filled with oil can be lifted with the use of these lugs without any damage or distortions.

(M) For the complete transformer we have clearly brought out our requirement of various types of valves in Annexure V enclosed brings out details of type, size and quantity of valves which are to be provided at various locations. This requirement has to be confirmed by the Bidders without any deviation.

(N) It may be noted that all gasketted joints shall be grooved one using O rings of nitrile rubber or better, such as the joints between bushing turret and bushing flange, inspection covers of inspection windows and all other openings provided for the

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purpose of inspection of internal parts of the transformer etc. The main bell tank gasket between upper tank and bottom tank shall be single piece O ring cord/gasket of nitrile rubber or material of better quality. The gasketting arrangement shall be grooved one with proper stopper to avoid over compression.

(O) One detachable bolted type mild steel (MS) ladder with anti-climbing arrangement shall be provided. Ladder for climbing up to & over top cover of power transformers shall be mechanically sturdy enough to bear the load of healthy maintenance staff without any shake/jerks. The arrangement shall not be detached after erection and commissioning of the unit, hence shall be provided with padlock locking arrangement for anti-climbing device. On the upper top of the ladder, provision for support shall be made. However, the arrangement of the ladder shall be to purchasers approval. Collapsible ladder shall not be acceptable to us.

11.2 Tank Cover

(a) The tank cover shall be sloped to prevent retention of rain water and shall not distort when lifted.

(b) Inspection cover/man holes shall be provided as per Annexure-IV.

(c) The tank covers shall be fitted with pockets at the position of maximum oil temperature of MCR (Maximum Continuous Rating) for inserting bulbs of oil and winding temperature indicators. It shall be possible to remove these bulbs without lowering the oil in the tank.

(d) Bushings, turrets, covers of inspection openings, thermometer, pockets etc., shall be designed to prevent ingress of water into or leakages of oil from the tank.

(e) All bolted connections shall be fitted with weather-proof, hot oil resistant gasket in between, for complete oil tightness. If gasket is compressible, metallic stoppers shall be provided to prevent over-compression.

(f) A minimum of three nos. PRD shall be provided above each phase winding.

11.3 Undercarriage

(a) The transformer tank shall be supported on a structural steel base equipped with forged steel or cast steel single flanged wheels suitable for moving the transformer completely filled with oil.

(b) Jacking pads/steps shall be provided. It shall be possible to change the direction of the wheels through 90 deg. when the

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transformer is lifted on jacks to permit movement of the transformer both in longitudinal and transverse direction.

(c) The track/rail gauge shall be 1676 mm along the longer side, as well as along the shorter axis. However Rails shall be placed perpendicular to the bushing line.

(d) Pulling eyes shall be provided to facilitate movement/pulling of the transformers and these shall be suitably braced in a vertical direction so that bending does not occur when the pull has a vertical component.

11.4 Axles And Wheels

(a) The transformers are to be provided with flanged bi-directional wheels and axles. These shall be so designed as not to deflect excessively to interfere with the movement of the transformer. Wheels shall be provided with suitable bearings which shall be rust and corrosion resistant. Fittings for lubrication shall also be provided.

(b) Suitable locking arrangement along-with foundation bolts shall be provided for the wheels to prevent accidental movement of transformer. The locking arrangement shall be such that it can be locked with plinth of transformer. The length of the arrangement should be adequate to cover height of the rail. No floating type locking arrangement shall be accepted.

(c) The wheels are required to swivel and they shall be arranged so that they can be turned through an angle of 90 degrees when the tank is jacked up to clear of rails. Means shall be provided for locking the swivel movements in positions parallel to and at right angles to the longitudinal axis of the tank (i.e. longitudinal & transverse directions).

(d) To facilitate uniform distribution of transformer weight two nos. props each on front & rear side along longer axis to be provided.

11.5 Anti Earthquake/Transport Clamping Device

(a) To prevent transformer movement during earthquake, clamping device shall be provided for fixing transformer to the foundation. The Bidder shall supply necessary bolts for embedding in the concrete foundation. The arrangements shall be such that the transformer can be fixed to or unfastened from these bolts as desired. The fixing of the transformers to the foundations shall be designed to withstand seismic events to the extent that a static co-efficient of 0.3g. applied in the direction of least resistance to that loading will not cause the transformer or clamping devices as well as bolts to be over stressed..

(b) Locking arrangement to eliminate relative movement between top yoke/active parts with the transformer tank shall be sturdy

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enough to bear transport hazards taking in to account the poor road conditions and also considering that road transportation of transformer will not be on hydraulic trailers

11.6 Conservator Tank

(a) The conservator tank shall be of minimum thickness of 8 mm and it shall have adequate capacity between highest and lowest visible levels to meet the requirement of expansion of the total cold oil volume in the transformer and cooling equipment from minimum ambient temperature to 100oC.

(b) The conservator tank shall be bolted into position so that it can be removed for cleaning purposes.

(c) Magnetic oil gauge (MOG) & prismatic oil level gauge having three overlapped windows on one side of conservator and on opposite side of conservator, plain oil gauge with three overlapped windows shall be provided to indicate oil level inside the conservator at each location. Proper arrangement to ensure visibility of oil level from ground be also ensured .

(d) Conservator shall be provided in such a position as not to obstruct the electrical connections to the transformer.

(e) In order to avoid congestion and to facilitate operation and maintenance activities, the main conservator and OLTC conservator shall be provided on opposite sides of the main tank. Further, there shall be adequate space for manual operation of OLTC.

(f) Separate conservator tank shall be provided for OLTC.

(g) The size of the conservator shall be so designed as to accommodate approximately 10% volume of total quantity of oil in the transformer.

(h) Suitable arrangement shall be made for providing a foot rest with easy & access arrangement to facilitate maintenance/operation at top of the conservator, on magnetic oil level gauge and buchholz relay.

(i) The design of conservator shall be such that the air is not trapped between air cell and main conservator.

11.7 Tank Earthing Arrangement : Two earthing pads complete with two number tapped holes M10 bolts plain and spring washer suitable for connection to 50X8 mm GI flat shall be provided each at position close to two diagonally opposite bottom corners of tank. Earthing strips up to the ground level and its connection with station earth pit shall be provided by the Bidder. 11.8 Pressure Relief Device : A minimum of 3 (three) number of pressure relief devices of reputed make and reliable quality shall be provided on each transformer and these shall be mounted preferably

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on the tank cover above each phase winding. Bidders must submit calculations to prove that the no and capacity of pressure relief device with location of each PRV provided on the transformer will adequately meet our requirement. The quantity of three numbers is on the basis that two numbers will be required as per design calculation and one number additional PRD shall be provided from the point of view of additional safety.

Constructional and design details of pressure relief device must be furnished and it should be proved by calculation that the size and operating pressure setting of pressure relief device is adequate, considering the rating of the transformer and quantity of oil in the transformer. Furnishing of this information is a must. These PRD's shall be of sufficient size for rapid release of any pressure that may be generated in the tank and which may result in damage to the equipment. The device shall operate at a static pressure of less than the hydraulic test pressure of transformer tank. It shall be mounted directly on the tank. One set of electrically insulated contacts shall be provided for alarm & tripping along-with the recommendations. 11.9 Relays 11.9.1 Buchholz Relay : A double float type Buchholz relay along with suitable moulded type cover to avoid ingress of moisture/ rain water shall be provided. All the gases evolved in the transformer shall collect in this relay. The relay shall be provided with a test cock suitable for a flexible pipe connection for checking its operation and for taking gas sample. A copper or stainless steel tube, shall be connected from the gas collector to a valve located about 1200mm above ground level to facilitate sampling of gas while the transformer is in service. The device shall be provided with two electrically independent ungrounded contacts, one for alarm on gas accumulation and the other for tripping on sudden rise of pressure. The contacts of relay shall be properly housed, sealed and gasketted to make the arrangement water proof. Entry of moisture/water in the contact chamber needs to be eliminated. Cable entry to terminal box of buchholz relay should be made through bottom of relay. 11.9.2 Oil Surge Relay (OSR) : From our past experience, it is found that undesired tripping of Power Transformers is occurring on oil surge relay (OSR)and Buchholz relay operation actuating due to accumulation of water inside relay pockets. The water accumulation takes place through entry point of cable gland. In view of above, the design and placement of Alarm & trip contact assembly of OSR and Buchholz Relay should be improved to take care of the following requirements:

(a) The cable entry to terminal box of OSR should be made through bottom of relay. Also the OSR relay should be protected from rain water by providing proper cover on it.

(b) In order to ensure exit/drainage of accumulated water from inside the relay, a fine hole should be made in terminal box of relay.

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Note : The Bidders shall ensure that the compartments housing relay contacts of Pressure Relief Valve , Buchholz Relay and Oil Surge Relay are made absolutely water and vermin proof. The compartment housing contacts of OSR,PRV and Buchholz Relay shall be tested for water proof at the time of inspection and effectiveness of water proofing shall be demonstrated at the time of inspection. This should be noted carefully by the Bidder and specifically confirmed in their bid. 11.10 Temperature Indicator 11.10.1 Oil Temperature Indicator (OTI) :Transformers shall be provided with a 150mm dial type thermometer with maximum pointer for top oil temperature indication. The thermometer shall have adjustable two electrically isolated heavy duty alarm and trip contacts, maximum reading pointer and resetting device mounted in the Fan control cubicle (FCC). A temperature sensing element suitably located in a pocket on top oil shall be provided. This shall be connected to the OTI by means of capillary tubing. Accuracy class of OTI shall be plus or minus 1.0% or better. The OTI shall be provided with anti vibration mounting . 11.10.2 Winding Temperature Indicator (WTI)

(a) WTI for measuring the winding temperature of the windings shall be provided. It shall comprise of the following

(i) Temperature sensing element.

(ii) Image coil.

(iii) Auxiliary CTs, if required, to match the image coil, shall be provided.

(iv) 150mm dia local indicating instrument with maximum reading pointer mounted in FCC/marshalling box and with four adjustable electrically isolated heavy duty contacts (two for control of cooling equipment, one for high winding temperature alarm and other for trip) shall be provided. The WTI shall be provided with anti vibration mounting.

(v) Calibration device.

(b) In addition to the (a) above, repeater dial of WTI for each winding shall be provided for Remote winding temperature indication. It shall be suitable for flush mounting on RTCC panel. A precision potentiometer mounted inside the case shall function as a transmitter to operate a repeater for RWTI. The transmitter shall be directly connected to the repeater.

(c) Auxiliary supply, if required in RTCC panel for RWTI, shall be 220V or 110V DC only.

(d) Accuracy class of WTI shall be plus or minus 1.0% or better.

(e) Any special cables required for shielding purpose for connection between cooler control cabinet and remote winding temperature indicator control circuit shall be in Bidders scope of work.

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(f) WTI CT ratio shall be embossed on secondary winding terminal box.

Note Some of the manufacturers have a practice to directly install winding temperature indicator (WTI) and oil temperature indicator (OTI) on the body of the transformer in open. This is not acceptable & it is obligatory on the part of the Bidders to enclose OTI & WTI and all such accessories in a separate Fan Control Cubicle (FCC) cum Marshalling Box .

11.11 Core

a) The core shall be constructed from high grade, non- ageing, low loss, Cold Rolled Super Grain oriented (CRGO) silicon steel laminations of HI-B grade steel or better. All stipulations under clause 4.4 should be considered while selecting material of core. Interlamination resistance shall be as per BS601 Part 5 method of July 1973. The Bidder shall furnish the details of steel laminations i.e. type alongwith hysterisis loss curve (B-H curve) etc.

(b) After being sheared, the laminations shall be treated to remove all burrs and shall be re-annealed to remove all residual stresses.

(c) The design of the magnetic circuit shall be such as to avoid static discharges, development of short circuit paths within itself or to the earthed clamping structure and production of flux component at right angles to the plane of laminations which may cause local heating.

(d) The core shall be provided with lugs suitable for lifting complete core & coil assembly of transformer.

(e) Core Belting : The core shall be rigidly clamped by belting to ensure adequate mechanical strength. Core and winding shall be capable of withstanding the vibrations & shock during transport, installation, service and adequate provision shall be made to prevent movement of core & winding relative to tank during these conditions. The location, size and material of belting shall be clearly indicated in drawing which shall be submitted with Bid. Bolted type core construction shall not be acceptable.

(f) All steel sections used for supporting the core shall be thoroughly sand blasted after cutting, drilling and welding.

(g) Each core lamination shall be insulated with a material that will not deteriorate due to pressure and hot oil.

(h) The insulation of core to bolts and core to clamps plates shall be able to withstand a voltage of 2KV RMS for one minute.

(i) The maximum flux density in any part of the core and yoke at rated MVA, 110% voltage and (-) 4% frequency at any tap shall not exceed 1.90 Tesla. The Bidder shall provide saturation curve of the core material proposed to be used and

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calculations to demonstrate that the core is not over fluxed under stringent condition of transformer operation.

(j) Bidder will offer the core for inspection & approval by the purchaser during the manufacturing stage. Bidder's call notice for this purpose should be accompanied with the following documents, as applicable, as a proof towards use of prime core material. i) Invoice of the supplier ii) Mill's Test Certificate iii) Packing List iv) Bill of lading v) Bill of entry certificate by customs.

(k) Core material shall be directly procured either from the manufacturer or through their accredited marketing organization of repute and not through any agent.

(l) Bidder should have in-house Core Cutting facility for proper monitoring & control on quality and also to avoid any possibility of mixing of prime material with defective/second grade material.

(m) Oil ducts shall be provided wherever necessary to ensure adequate cooling. The winding structure and major insulation shall not obstruct the free flow of oil through such ducts. Where the magnetic circuit is divided into pockets by cooling ducts parallel to the plane of laminations or by insulating material above 0.254 mm. Thick, tinned copper strip bridging pieces shall be inserted to maintain electrical continuity between pockets. The design of the magnetic circuit shall be such as to avoid static discharge development of short circuit path within itself or to the earthed clamping structure and production of flux components at right angles to the plane of the laminations which may cause local heating.

(n) Core shall not directly rest on the bottom metal sheet of transformer tank. Around 3 mm or more free space for oil insulation shall be made between the core and bottom sheet of transformer tank. A 5 mm FRP Insulating sheet shall be provided to take care of core earthing due to accidental slippage of stampings. Also in addition to this extra insulation thickness of 5 mm or more FRP sheet be provided at the bottom of resting shoes of end frame with proper fixing arrangement to avoid accidental slippage, damages etc.

11.12 Windings

(a) The Bidder shall ensure that windings of all transformers are made in dust proof, conditioned atmosphere. The Bidder shall furnish the facilities available at their works alongwith the bid.

(b) The conductors shall be of electrolytic grade copper as per relevant IS. The maximum current density for design of

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transformers within specified limits of transformer losses shall not exceed the limits of 300 amps per sq.cm.

(c) The insulation of transformer windings and connections shall be free from insulating compounds which are liable to soften, ooze out, shrink or collapse or be catalytic and chemically active in transformer oil during service.

(d) Coil assembly and insulating spacers shall be so arranged as to ensure free circulation of oil and to reduce the hot spot of the winding. The conductor shall be transposed at sufficient intervals in order to minimize eddy currents and equalize the distribution of currents and temperature along the winding.

(e) The LV winding should withstand short circuit faults/forces of the transformer upto the prescribed fault levels on HV & LV sides against mechanical and thermal stresses.

(f) Best insulating material shall be used and compression of the windings after drying out shall be carried out at a pressure exceeding one and a half to twice the force which can occur in the transformer; to impart greater mechanical strength to the windings against heavy short circuit stresses.

(g) The windings shall be so designed that all coil assemblies of identical voltage ratings shall be interchangeable and field repairs to the windings can be made readily without special equipment. The coils shall be supported between adjacent sections by insulating spacers, and the bracings and other insulation used in the assembly of the winding shall be arranged to ensure free circulation of the oil to reduce hot spots in the windings.

(h) The coil insulation shall be treated with suitable insulating varnish or equivalent compound wherever necessary to develop the full electrical strength of the winding. All materials used in the insulation and assembly of the winding shall be insoluble, non-catalytic and chemically inactive in the hot transformer oil and shall not soften or otherwise be adversely affected under the operating conditions.

(i) All threaded connections shall be provided with locking facilities. All leads from the winding to the terminal connectors and bushings shall be rigidly supported to prevent injury from vibration. Guide tubes shall be used where practicable.

(j) Windings shall be subjected to a shrinkage treatment before final assembly so that no further shrinkage occurs during service. Adjustable device shall be provided for taking up any possible shrinkage of coils in service. After shrinkage process, the windings shall be clamped securely in place so that they will not be displaced or deformed during short circuits. The assembled core and windings shall be vacuum-dried and suitably impregnated before removal from the treating tank. The copper conductors used in the coil structure shall be best suited to the requirements and all permanent current carrying

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joints in the windings and the leads shall be crimped or brazed preferably by high frequency brazing system.

It is observed that many manufacturers are using sectored clamping arrangement at top as well as bottom for clamping of the windings. This type of arrangement is considered to be not suitable for EHV grade power transformers. In this regard, it may be noted that both top & bottom clamping rings to be provided for clamping of windings shall be of one piece single ring. The top & bottom clamping rings should be of minimum thickness 60 mm thk with proper safety margins based on design and shall be in one piece to make the clamping arrangement sturdy. Sectored pressure/clamping rings are not acceptable. The single pressing/clamping ring shall be provided with adequate number of pressure/jacking points as per design. Since sectored ring arrangement shall not be accepted hence bidder should ensure and confirm this specific requirement in the technical questionnaire.

(k) Bidder will offer the Copper and insulating material for windings for inspection & approval by the purchaser during the manufacturing stage. Bidder's call notice for the purpose should be accompanied with the following documents, as applicable, as a proof towards use of prime Copper and insulating material for windings .

i) Invoice of the supplier

ii) Mill's Test Certificate

iii) Packing List

iv) Bill of lading

v) Bill of entry certificate by customs.

(l) Core, Copper and insulating material for windings shall be directly procured either from the manufacturer or through their accredited marketing organisation of repute and not through any agent.

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(m) Certificate : Supplier shall provide purchaser details of procurement of raw materials i.e., core, insulation & copper. Supplier shall also record a certificate as under :

" CERTIFICATE "

It is certified that the Transformer shall be manufactured by --------- (Name of manufacturer) out of the core, insulating and winding material procured as per details indicated in specification. We are agreeable to undertake third party inspection of Transformer during its manufacture or of raw materials, at the sole discretion of MPPTCL without any extra cost.

If at any stage it is found that the transformer is not manufactured out of the raw material indicated specification, the transformer shall be liable for rejection by MPPTCL and transformer shall be replaced by (name of manufacturer) at no extra cost to MPPTCL.

Signature of Authorised Signatory with Seal of manufacturer

(o) The Purchaser also reserves the right to carry out stage inspections at other stages also, for which advance intimation shall be given and all necessary cooperation shall be rendered by the supplier.

11.13 Bushings

(a) The electrical & mechanical characteristics of bushings shall be in accordance with IS-3347 & IS-2099 ( latest version ) & IEC 60137(2008 or latest version).

(b) The bushings shall have high factor of safety against leakage

to ground and shall be so located as to provide adequate electrical clearances between bushings and also between the bushings and grounded parts. Bushings of identical voltage rating shall be inter changeable. All bushings shall be equipped with suitable terminals of approved type and size and all external current carrying contact surfaces shall be adequately silver plated. The insulation class of the high voltage neutral bushing shall be properly coordinated with the insulation class of the neutral of the high voltage winding.

(c) All main winding and neutral leads shall be brought out

through outdoor type bushings which shall be so located that the full flashover strength will be utilized and the adequate phase clearance shall be realized.

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(d) Each bushing shall be so coordinated with the transformer insulation that all flashovers will occur outside the tank.

(e) All porcelain used in bushings shall be of the wet process,

homogeneous and free from cavities or other flaws. The glazing shall be uniform in color and free from blisters, burns and other defects.

(f) (i) For 33KV winding & neutral , the bushing shall be of OIP

condenser of 72.5KV class of draw rod type/solid stem type.

(ii) The bushings of 145 KV class shall be of OIP condenser of draw rod type (DR) only.

(iii) Tan-delta of all bushings shall be 0.005 (max.)during testing at manufacturers works.

(g) All bushings shall have puncture strength greater than the dry

flashover value. (h) Main winding terminals shall be solder-less terminals and shall

be of the type and size specified. (i) The spacing between the bushings must be adequate to

prevent flashover between phases under all conditions of operation. The clearances shall be as follows :

S. No

Nominal

System

Voltage

Voltage Class

Of Bushin

g

Current

Rating

Impulse Withsta

nd Voltage (Kvp)

1min.Power

Frequency

withstand Voltage Kv(rms)

Creepage

Distance

in mm

Clearance in mm

Ph to Ph.

Ph to E

1 132KV 145KV 1250A 650 275 3625 1430 1270 2 33KV 72.5KV 2000A 325 140 1813 700 660

The Bidders are required to confirm clearances and no change/

reduction in clearances shall be acceptable. The clearances shall be clear distances in air after accounting for clamps/connectors dimensions to be mounted on the stud of bushings.

(j) Special adjustable arcing horns shall be provided for the HV bushings. For 72.5KV class bushings, arcing horns are not required.

(k) The Bidder is requested to furnish the guaranteed withstand voltage for the above and also furnish a calibration curve with different settings of the coordination gap to the purchaser to decide the actual gap setting. Bidder's recommendations are also invited in this respect.

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(l) The bushings shall be capable of withstanding without injury the electrical, thermal and mechanical effects of external short circuits. The 145 KV bushings shall be rated for short time thermal current rating of 40 KA for 3 seconds and 72.5 KV Bushings, for 31.5KA for 3 seconds.

(m) All the transformers covered under this specification shall be utilized in heavily polluted atmosphere. In view of this the Bidders while offering prices for the transformers against this contract may please note that the offer should be made out based on the creepage for the bushings @ 25mm per KV based on the voltage of 72.5KV/145KV. Thus in the quoted prices of transformer cost of bushings should be included based on a creepage distance of 25mm per KV.

(n) All O.I.P. Condenser bushings shall be provided with :

(i) Oil level gauge.

(ii) Oil filling plug and drain valve, if not hermetically sealed.

(iii) Tap for capacitance/tan delta test.

(o) When bushings have an under-oil end of reentrant form, the pull through lead shall be fitted with a gas bubble deflector.

(p) The bushings with current transformers are specified, hence the bushings shall be removable without disturbing the current transformers.

(q) Porcelain used in bushing manufacture shall be homogenous, free from laminations, cavities and other flaws or imperfections that might affect the mechanical or dielectric quality and shall be thoroughly vitrified tough and impervious to moisture. Glazing of porcelain and bushing shall be of uniform brown color free from blisters and burrs.

(r) Bushing turrets shall be provided with suitable vent pipes which shall be connected to route any air/gas collection through the Buchholz relay.

(s) For Bushings of all voltage class, the arrangement for connection of winding/neutral terminal shall be indicated .

(t) From the end point of the condenser of the bushing which will protrude inside the transformer OR the bottom termination point of bushing, sufficient clearance should be available so that in case any other make bushing is installed problem in this regard may not arise. Maximum length of condenser portion, which can be easily accommodated, should be clearly indicated by the Bidder.

(u) The LV take off arrangement within the transformer is of utmost importance hence due care shall be taken while providing this arrangement inside the transformer tank. The connecting lug of LV winding with the bushing bottom terminal pad should match with the current rating of the bushing. The

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size of the LV winding lug shall be of suitable rating to match with the maximum load current of the transformer to be fed through extreme tap of OLTC meeting requirements of IS-6600. In this regard, the clamping arrangement of LV winding with two lugs having two holes with two hole terminals on counter part of the bushing pad are not acceptable. In case of such arrangement, it will have to be ensured that the counter part of winding lead/lug i.e. bushing terminal is with four holes or vice versa.

11.14 Bushing Current Transformers

(a) Current transformers shall comply with IS:2705.

(b) One no. bushing CT of Ratio 200/1 on each phase of HV winding & one no. CT of Ratio 800/1 on each phase of LV winding i.e 3 nos for HV & 3 nos for LV winding, one no. bushing CT of Ratio 200/1 for HV neutral and 800/1 for LV neutral shall be provided for each out door Transformer .

(c) It shall be possible to remove turret mounted CTs from the transformer tank without removing the tank cover. Necessary precaution shall be taken to minimize the eddy currents and local heat generated in the turret.

(d) All secondary leads shall be brought to a terminal box near each bushing. These terminals shall be wired out to cooler control cabinet using separate cables for each core.

(e) For the thermal image coil of winding temperature indicator, CT with suitable ratio and class may be used.

11.15 Terminal Marking : The terminal marking and their physical position shall be in accordance with IS:2026. 11.16 The positioning of HV & LV bushings shall be such that skew jumpering is avoided. The middle phase primary & secondary bushing center line shall be parallel to side axis of the transformer body. 12.0 EARTHING ARRANGEMENT 12.1 NEUTRAL EARTHING ARRANGEMENT: The neutral terminal of the star connected HV / LV winding shall be brought up to the ground level through two tinned copper flat strips of size 50x6mm which shall be supported on transformer tank horizontal/vertical by porcelain insulators of adequate voltage class. The number of insulators shall be sufficient to provide a mechanically sturdy arrangement. Necessary mechanical supports on the tank for mounting of the insulators shall be made. The KV class rating of insulators shall commensurate with the rating /KV class of neutral design. It may be ensured that connection of the neutral strips to neutral bushings at one end shall be made using a terminal connector suitable for connection to the neutral bushing terminal and to receive 2x50x6 mm tinned copper strips on the other side. The connection between the bushing and transformers earth pit shall be through 2x50x6 mm tinned copper strips single run without any joint connection/brazing/ welding etc. The other end of the earth connection

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to the earth pit shall also be through terminal connector suitable to receive 2x50x6 mm copper strips at one end and to receive MS flat and /or twin ACSR zebra conductor on the other end. The length of the copper strips shall be suitable for providing a joint less connection between transformer neutral and earth pit and details in this regard shall be intimated to the successful bidder based on transformer/substation layout design. A typical arrangement is shown in drg. No: MPPTCL/TR-57/40MVA/02 of this specification for neutral earthing. 12.2 CORE EARTHING ARRANGEMENT : The bidder should note our requirement in this regard very clearly. It is required to bring out leads from core, end frame and tank to the top of the transformer through only three insulated bushings. The arrangement shall be housed in a box at the top cover of transformer tank with provision for interconnection between the studs of bushings. The bushing housing shall have a suitable cover with gasket to make the arrangement waterproof. A clear marking (engraved/punched) shall be made to indicate that the housing contains core/end frame/ tank earthing arrangement. Please note that stickers/flags/tags/painted marking for identification shall not be accepted. A typical sketch of general arrangement needed by purchaser is shown in drawing no. MPPTCL/TR-57/40MVA/03 of this specification. Arrangement shall be such that even after removal of connections, oil shall not leak. Removable shorting strips between the three bushing shall be provided. It may be noted that internal earthing of any nature between core and End frame should not be provided. Earthing at site shall be done by interconnecting the three bushings through shorting strips. This arrangement is to facilitate checking of multiple core earthing in the transformer. It may be noted that :

a) any alternative arrangement is not acceptable and therefore bidder must confirm provision of three bushings as desired above.

b) Once transformer reaches site, before unloading from the trailor the position of core earthing shall be checked and in case any problem of multiple core earthing is observed, delivery of Transformer will not be taken.

The insulated cable to be used for core to Bushing connection & end frame to Bushing connection should be of good quality with proper grounding arrangement. The size and number of strands of cable shall be subject to purchasers approval. 13.0 AUXILIARY POWER SUPPLY FOR OLTC, COOLER CONTROL

AND POWER CIRCUIT

13.1 Duplicate (Two) auxiliary power supplies of 433volt, three phase, four(4) wire shall be provided by the purchaser at cooler control cabinet and for OLTC drive.

13.2 All loads shall be fed by one of the two feeders through an electrically interlocked automatic transfer switch housed in the cooler control cabinet, for tap changer control and cooler control circuits.

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13.3 Design features of the transfer switch shall include the following :

i) Provision for the selection of one of the feeders as normal source and other as standby.

ii) Upon failure of the normal source, the loads shall be automatically transferred after an adjustable time delay to the standby source.

iii) Indication to be provided at cooler control cabinet for failure of normal source and for transfer to standby source and also for failure to transfer.

iv) Automatic re-transfers to normal source without any intentional time delay following re-energisation on the normal source.

v) Both the transfer & re-transfer shall be dead transfers and AC feeders shall not be paralleled at any time.

13.4 AC feeder shall be brought to the OLTC cabinet (Cooler Control Cabinet) by the Bidder, after suitable selection at cooler control cabinet. The Bidder shall derive AC power for control circuit from the AC feeder as mentioned above by using appropriately rated dry type transformers. If the control circuit is operated by DC supply then suitable converters to be provided by the Bidder to be operated from AC Power source.

13.5 Necessary isolating switches and HRC fuses shall be provided at suitable points as per approved scheme of purchaser. 14.0 TAP CHANGING EQUIPMENT 14.1: GENERAL REQUIREMENT

a) OLTC gear shall be motor operated for local as well as remote operation. An external hand wheel/handle shall be provided for local manual operation. This hand wheel/handle shall be easily operable by a man standing at ground level.

(b) Arrangement shall be made for securing and padlocking the tap changer wheel in any of the working positions and it shall not be possible for setting or padlocking the wheel in any intermediate position. The arrangement shall be such that no padlock key can be inserted unless all contacts are correctly engaged and switch set in a position where no open or short circuit is possible. An indicating device shall be provided to show the tap in use.

(c) The design of OLTC shall be on the principle of Constant Flux Design

(CFVV) wherein HV (132KV ) voltage would be varied in the range of (+)5 % to (-)15 % in steps of 1.25 % so as to provide constant voltage of 33 KV on LV side. While through current rating of OLTC shall be based on cl.2.3.2 of IS 8478,the purchaser desires to obtain OLTC with higher voltage and current rating from the point of view of better performance. In view of this, the bidder shall offer OLTC for 40 MVA transformer suitable for rated voltage and rated current as mentioned in the following table :

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Transformer Rating

OLTC on Winding

(HV)

Rating of OLTC

Voltage Rating

Minimum Current Rating

Tap Range (In steps of

1.25%)

132 KV, 40 MVA

132KV 66KV/132KV* 300 Amp. (+)5% to (-)15%

*Suitable for 132KV neutral end d) The OLTC motor should be capable of smooth and trouble free operation

with supply voltage variation of 433 V +10% & -25%. 14.2 ON LOAD TAP CHANGING GEAR (OLTC) (a) The details of the method of diversion of the load current during tap

changing, the mechanical construction of the gear and the control features for OLTC gear alongwith detailed drawings on the inner view and the arrangement of connections shall be submitted with the Bid. Information regarding the service experience on the gear and a list of important users shall also be furnished. The tap changer shall change the effective transformation ratio without producing phase displacement.

(b) The current diverting contacts shall be housed in a separate oil chamber

not communicating with the oil in main tank of the transformer. (c) The contacts shall be accessible for inspection without lowering oil level in

the main tank and the contact tips shall be replaceable. (d) The Bidder shall indicate the safeguards employed to take care of harmful

arcing at the current diverting contacts in the event of operation of the OLTC gear under overload conditions (overloading capability as per IS 6600) of the transformer. Necessary tools and tackles shall be provided alongwith main supply for maintenance of OLTC gear.

(e) The OLTC oil chamber shall have oil filling and drain valves, oil sampling

valve, relief vent and oil level gauge/glass. It shall also be fitted with an oil surge relay. For accommodating oil expansion of OLTC a separate conservator tank shall be provided.

(f) The diverter switch or arcing switch shall be designed so as to ensure that

its operation once commenced shall be completed independently of the control relays or switches, failure of auxiliary supplies etc. To meet any contingency which may result in incomplete operation of the diverter switch, adequate means shall be provided to safeguard the transformer and its ancillary equipments.

(g) Drive mechanism chamber shall be mounted on the tank in accessible

position. It should be adequately ventilated and provided with anti condensation metal clad heaters. All contactors, relay coils and other

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parts shall be protected against corrosion, deterioration due to condensation, fungi etc.

(h) The control feature shall provide the following :

i) LOCAL-REMOTE selector switch mounted in the local control cubicle shall switch control of OLTC for lower/ raise functions in local or remote mode as selected.

ii) The LOCAL-REMOTE selector switch shall have at-least two spare

contacts per position which are closed in that position but open in the other position.

iii) A RAISE-LOWER CONTROL SWITCH shall be provided in the local control cubicle. The switch shall be spring loaded to return to the Centre "OFF" position and shall require movement to the RIGHT to raise the voltage of the transformer. Movement to the left shall lower the voltage. Alternatively push button type arrangement of standard design may be provided.

iv) An OFF-ON tap changer control switch shall be provided in the OLTC local control cabinet of transformer. The tap changer shall be inoperative in the OFF position. Also the OFF-ON switch shall have atleast one spare contact per position which is closed in that position but open in the other position.

v) Operating mechanism for on load tap changer shall be designed to go through one step or tap change per command. Subsequent tap changes shall be initiated only by a new or a repeat command.

vi) On load tap changer shall be equipped with a time delay in complete STEP alarm consisting of a normally open contact which closes, if the tap changer fails to make a complete tap change. The alarm shall not operate for momentary loss of auxiliary power.

vii) The selsyn units or approved equivalents shall be installed in the local OLTC control cabinet to provide tap position indication for the transformer. Complete mounting details shall be included with approved diagram.

viii) Transformer load tap changer shall be equipped with a fixed resistor network capable of providing discrete voltage steps for input to the supervisory system. Any other approved / established design for remote indication of tap position shall also be acceptable.

(i) Limit switches shall be provided to prevent overrunning of the mechanism and in addition, a mechanical stop shall be provided to prevent over-running of the mechanism under any condition.

(j) Limit switches may be connected in the control circuit of the operating motor provided that a mechanical-de-clutching mechanism is incorporated.

(k) Thermal device or other means shall be provided to protect the motor and control circuit. All relays, switches, fuses etc. shall be mounted in the

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drive mechanism chamber and shall be clearly marked for the purpose of identification.

(l) A permanently legible lubrication chart shall be fitted within the driving mechanism chamber.

(m) Any "DROP DOWN" tank associated with the tap changing apparatus shall be fitted with guide rod to control the movements during lifting or lowering.

(n) A five digit counter shall be fitted to the tap changing equipment to indicate the number of operations performed.

(o) All relays and operating devices shall operate correctly at any voltage between the limits specified.

(p) It shall not be possible to operate the electric drive when the manual operating gear is in use.

(q) It shall not be possible for any two controls to be in operation at the same time.

(r) The equipment shall be suitable for supervisory control and indication with make before break multi-way switch, having one potential free contact for each tap position. This switch shall be provided in addition to any other switch/switches which may be required for remote tap position.

(s) Operation from the local or remote control switch shall cause one tap movement only until the control switch is returned to the off position between successive operations.

(t) All electrical control switches and the local operating gear shall be clearly labeled in a suitable manner to indicate the direction of tap changing.

(u) Transfer of source failure of one AC supply shall not affect tap changing operation.

(v) For the purpose of operation of OLTC, based on design of manufacturer, transition resistor could be used. However, no component of OLTC including transition resistor shall be housed inside main transformer tank. The design of the transition resisters should be liberal to ensure suitability during tap change operation at rated current including over loading capability and system short circuits.

(w) The location and design of OLTC shall be such that in the event of any repair / maintenance , it should be possible to take out various parts from the OLTC and other accessories and fittings mounted on the transformer particularly equalizing pipes etc do not infringe /obstruct.

14.3 MANUAL CONTROL : The cranking device for manual operation of the OLTC gear shall be removable and suitable for operation by a man standing on ground level. The mechanism shall be complete with the following :

i) Mechanical tap position indicator which shall be clearly visible to the person operating tap changer manually at the transformer.

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ii) A mechanical operation counter.

iii) Mechanical stoppers to prevent over-cranking of the mechanism beyond the extreme tap positions.

iv) The manual control considered as back up to the motor operated load tap changer control shall be interlocked with the motor to block motor start-up during manual operation. The manual operating mechanism shall be labeled to show the direction of operation for raising the voltage and vice-versa.

14.4 ELECTRICAL CONTROL This includes Local Electrical control and Electrical remote control from remote control panel. The control circuits shall have the following features:

(i) An interlock to cut off electrical control automatically upon recourse being taken to the manual control in emergency.

(ii) Reinforcement of the initiating impulse for a tap change, ensuring a positive completion once initiated to the next (higher or lower) tap.

(iii) Step-by-step operation ensuring only one tap change from each tap changing impulse and lock-out of the mechanism if the control switch (or push button) remains in the "Operate Position".

(iv) An interlock to cut-out electrical control when it tends to operate the gear beyond either of the extreme tap positions.

(v) An electrical interlock to cut-off a counter impulse for reverse step change being initiated during a progressing tap change and until the mechanism comes to rest and resets circuits for a fresh position. Suitable interlocks shall be provided to prevent operation of OLTC beyond extreme tap with a mechanical/electrical lockable switch.

(vi) Protection apparatus, considered essential by the Bidder according to specification.

14.5 REMOTE ELECTRICAL GROUP CONTROL The OLTC control scheme offered shall have provision of remote electrical group control during parallel operation of transformers. This is in addition to independent control of OLTC.

(i) A four position selector switch having MASTER, FOLLOWER, INDEPENDENT and OFF position shall be provided in the remote OLTC control panel for each transformer. This shall be wired to enable operator to select operation of OLTC in either Master, Follower or Independent mode.

(ii) Out of step relays with timer contacts shall also be provided to give alarm and indication in case of tap positions in all the transformers under group control being not in same position.

(iii) Master Position : If the selector switch is in MASTER position, it shall be possible to control the OLTC units in the FOLLOWER mode by operating the controls of the MASTER unit Independent operation of the

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units under FOLLOWER mode shall have to be prevented. However, the units under independent mode will be controlled independently.

(iv) Follower Position : If the selector switch is in FOLLOWER mode, control of OLTC shall be possible only from MASTER panel.

(v) Independent Position : In this position of Selector Switch, Control of OLTC of individual unit only shall be possible.

14.6 LOCAL OLTC CONTROL CUBICLE The Auxiliary devices for electrical control of the OLTC shall be housed in a weather proof cubicle. It shall be complete with the following :

i) A circuit breaker/contactor with thermal overload devices for controlling the AC auxiliary supply to the OLTC motor.

ii) Cubicle light with door switch.

iii) Space heaters to prevent condensation of moisture.

iv) Padlocking arrangement for hinged door of cabinet.

v) Cable terminal glands for power and control cables to the OLTC gear. 14.7 REMOTE TAP CHANGER CONTROL PANEL (RTCC)

Remote tap changer control panel to be supplied by the Bidder shall consist of :

i) Actuating switch for electrical raise/lower control.

ii) Remote tap position indicator.(preferred digital type)

iii) Signal lamps for Tap changer in progress and Tap changer out of step.

iv) Auxiliary devices for remote electric group control of OLTC.

v) Annunciation scheme with the following :

(a) Fan fail (for all fans individual windows). (b) AC supply fail. (c) Stand by fan fail. (d) Stand by fan on. (e) OLTC motor over loaded. (f) OLTC control supply fail. (g) OLTC at extreme position i.e. lowest & highest voltage tap. (h) Two spare windows.

vi) Indicating Devices : Following lamp indications shall be provided in Remote tap changer control cubicle /panel

- Fan "ON", Fan "OFF" - Cooling system "On Automatic Control". - Cooling system "On Manual".

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- Selector switch in auto or manual. - 433volts cooler supply auto changeover. - Control supply failure main and standby. - one potential free initiating contact for all the above indications

shall be wired independently to the terminal blocks of cooler control cabinet exclusively for owner's use.

vii) Remote OTI with repeater unit.

viii) WTI repeater unit.

ix) Voltmeter for indicating HV & LV voltage.

x) Schedule of equipments for RTCC panel shall be as under:

1. Name plate remote OLTC and cooler control cubicle

2. Indicating lamp-OLTC control supply on ( red)

3. Indicating lamp-tap change in progress ( yellow)

4. Indicating lamp-OLTC out of step ( red)

5. Indicating lamp-OLTC motor trip ( red)

6. Cooler mode selector (auto-off-on)

7. OLTC sequence selector switch.(OFF-INT-FOLL-MAST.)

8. Emergency stop push button for tap change operation. (red)

9. Auxiliary contactor for OLTC out of step monitoring.

10. Out of step timer.

11. Voltmeter for HV. (0-150 KV)

12. Remote oil temperature indicator.

13. Voltmeter for LV. (0-40 KV)

14. Terminal blocks.

15. Cubicle lamp.

16. Door switch.

17. HRC cartridge fuse holder with link for cubicle illumination circuit.

18. Neutral link.

19. Earth bus.

20. HRC cartridge fuse holder with link for HV volt meter.

21. HRC cartridge fuse holder with link for LV volt meter..

22. HRC cartridge fuse holder with link for RWTI and ROTI circuit.

23. Selector switch for HV volt meter.

24. Selector switch for LV volt meter.

25. Remote winding temperature indicator.

26. Ammeter for HV & LV winding current measurement.

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27. Selector switch for amp. meters

28. OLTC control switch

29. Tap position indicator (digital).

xi. a. HV digital Voltmeter of accuracy class 0.5 provided for indicating HV voltage shall be scaled for voltage range 0-150 KV (phase to phase) and shall be suitable for use with PT ratio 132KV/110 volt. The HV digital voltmeter shall be precisely calibrated so as to indicate 132KV Voltage on voltmeter scale corresponding to input voltage of 110 Volt (phase to phase).

b. LV digital Voltmeter of accuracy class 0.5 provided for indicating LV voltage shall be scaled for voltage range 0-40 KV (phase to phase) and shall be suitable for use with PT ratio 33KV/110 volt. The LV digital voltmeter shall be precisely calibrated so as to indicate 33KV Voltage on voltmeter scale corresponding to input voltage of 110 Volt (phase to phase).

xii. a. HV digital Ampere meter of accuracy class 0.5 provided for measurement of HV winding current shall be for use with 132KV CT having CT ratio 200/1 with 20% over range reading scale. The HV digital Ampere meter shall be precisely calibrated so as to read 200 HV side current in ampere on Ampere meter scales corresponding to input current of 1 Amp. from 132KV CT.

b. LV digital Ampere meter of accuracy class 0.5 provided for

measurement of LV winding current shall be for use with 33KV CT having CT ratio 800/1 with 20% over range reading scale. The LV digital Ampere meter shall be precisely calibrated so as to read 800 LV side current in ampere on Ampere meter scales corresponding to input current of 1 Amp. from 33KV CT.

15.0 COOLING EQUIPMENT 15.1 The design shall take into account the following requirements

a) The oil cooling system of transformer shall be designed using 2x50% radiator banks. The radiator banks shall be mounted on two different sides of transformer tank. The arrangement shall be subject to approval by the purchaser based on substation layout and positioning of other neighboring switch yard equipments. Coolers/radiators shall with stand pressure / vacuum conditions specified for the tank. All coolers/ radiators shall be attached on the transformer tank through header having suitable expansion joints (flexible coupling) to ensure adequate mechanical strength against vibration etc. subject to specific approval from the purchaser. Radiators directly mounted on transformer tank are not acceptable.

b) Each radiator bank / block shall have its own set of cooling fans, shut off valves, lifting lugs, top and bottom oil filling valves, air release plugs, drain valves and if considered

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necessary based on design thermometer pocket fitted with captive screw cap on the inlet and outlet, in line with valve schedule as per Annexure-V.

c) Each radiator bank shall be provided with at least 20% standby (spare)cooling fans. These spare fans shall be duly mounted and shall also be wired up complete with required protective devices and be identified with each radiator bank. While working out number of spare fan for 20% additional cooling per bank, if 20% quantity works out in fraction , the spare fans to be provided shall be next whole number.

d) Cooling fans shall be designed to meet overloading requirements as per clause 4.1 (b)

e) The exhaust air flow from cooling fan shall not be directed towards the main tank in any case.

f) Cooling fans for each radiator bank shall be located so a

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