PREPARATION OF TRANSFORMER SPECIFICATIONS

By

VALLAMKONDA SANKAR P.Eng.

E-mail: powertransformer@hotmail.com

THANKS TO

IEEE NORTHERN CANADA SECTION, EDMONTON, ALBERTA.

THANKS TO

MR. PETER ROTHWELL

MR. BLAINE LARSON

ACKNOWLEDGEMENTS

Mr. Frank David, FD Consulting Services, Winnipeg.

Mr. Peter Franzen, Manitoba Hydro, Winnipeg.

Mr. Izy Polischuk, Hydro One, Toronto.

Mr. Ronnie (Rashed) Minhaz, McGregor Construction, Calgary.

THANKS TO

MR. BILL BERGMAN, Consultant, PowerNex Associates Inc., Calgary, Alberta.

MR. JEFF TENNANT, Senior Engineer, Ontario Power Generation Inc, Niagara Falls, Ontario.

MR. JOHN van KOOY, van Kooy Transformer Consulting Services Inc., Hamilton, Ontario.

Presentation Schedule

45 minutes first half of the presentation.

10 minutes interactions (questions/comments).

10 minutes break.

45 minutes second half of the presentation.

10 minutes interactions (questions/comments).

OBJECTIVES•To procure reliable transformers at economical prices per schedule.•To use the standards to achieve above goals.•To determine transformer parameters that meet system requirements.•To prepare the specifications that make the design and the manufacturing simple and economical.•To obtain maximum benefits from Globalization.•To establish effective interactions between users and manufacturers for mutual benefits.•To conduct effective and useful Tender Review and Design Review meetings.•To initiate innovations.

FUNCTIONS OF TECHNICAL SPECIFICATIONS•To formally and fairly communicate exactly what the contractor has to deliver.•To be able to accurately offer services and products which provide a satisfactory solution to user.•To avoid relationship mishaps associated with costly variation work.•To give an opportunity for manufacturer to apply improved design and manufacturing methods and to use advanced materials and accessories. •To procure lowest life cycle cost transformers.•A record of parameters of transformers purchased.•A chance for users and manufacturers to work together for advancement of transformer industry.

TOPICS FOR FIRST HALF OF THE PRESENTATION

• Ratings• Standards• Single phase versus three phase • Winding connections• Vector group• Insulation levels• Terminals• Accessories• Types of cooling• Sound levels• Taps (range, location etc.)• Types of taps• Impedance

RATINGS•Available generation (GSU transformers).•For security of supply, unit service and system service transformers are mostly with double LVs and LVs of two transformers are interconnected. •Load growth (System transformers).•Return on investment.•Difference in definitions in CSA, IEEE and IEC standards.•LV and HV ratings per CSA and IEEE based on:

Location of the tap-changer (in HV or in LV).

Use of the tap-changer (for input voltage fluctuations, to

compensate for output voltage regulation, step-up or

step-down. •Specifying the MV.A to be delivered by output windings and the type of loading (Arithmetic, vectorial or simultaneous).•Specifying current to which each winding has to be designed for.•In stations also where security of supply is critical, the transformers are with double LVs (LVs of two transformers are interconnected).

RATINGS (continued)When a transformer is specified per CSA C-88 or IEEE C.57.12.00, calculation of winding ratings.

HV has 1000 turns and current per specified MV.A is 100 Amps.LV has 100 turns and current per specified MV.A and rated tap is 1000 Amps.LTC is in LV for ±10% tap range. LTC turns are 10.Operation of the transformer is step-down.Taps are to compensate for regulation.

While delivering the full load (1000Amps), to keep the LV voltage constant, the tap changer moves to the maximum turns position.Ampturns on LV = (100+10)1000 = 110000.Ampturns on HV must be same as that on LV.HV winding current rating = 110000/1000 = 110 Amps.

STANDARDS• Referencing the standards in the specifications.• Differences in CSA, IEEE and IEC standards: Normal or usual service conditions Rated power Over voltage conditions Overload capability at low ambient temperature Suggested impedances Tests and test levels Insulation levels Dimensions of bushings Air clearances Types of taps and tap range Tolerances on impedances, losses and magnetization current• Use of standards in preparation of specifications.

SINGLE-PHASE VERSUS THREE-PHASE•Dimensional and weight limitations.•Transport restrictions.•Air clearances.•Reliability (Risk assessment).•Specifications for replacement transformer:

Current ratings of neutral bushing

Current rating of tertiary bushings

Type of core

Design of stabilizing winding

Tertiary delta voltages

Polarity (subtractive or additive)

WINDING CONNECTIONS•Wye, delta or zig-zag.•Wye:

Design of windings (graded insulation)

Neutral is available

Many types of LTCs are available

Winding and phase currents same (need for series transformer)•Delta:

Design of windings

Grounding transformer is required to get a neutral

Limited types of LTCs are available

Winding current is √3 times lower than the phase current•Zig-zag.

Design of windings

Compared to wye and delta windings difficult and costly to have taps

Zero sequence impedance and need for a grounding reactor •Limitations and advantages of each connection.

VECTOR GROUP•Time angle expressed in degrees between line-to-neutral voltages of two or more systems.•Per the book ‘Transformer Engineering’ by L.F. Blume only three phase three legged core form is recommended for wye/wye vector group. For all the other types of cores, a delta tertiary is required.•In delta connected winding, if neutral is required then a grounding transformer is used.•Relative costs of Yd, Dy, Yz and Dz vector groups depend on voltage rating of each winding, current rating of each winding and in which winding the taps are needed.•Technical limitations of different vector groups (One o’clock vectors of Yd1, Dy1 and Yz1, twelve o’clock vectors of Yy0, Dd0 and Dz0 etc.).

INSULATION LEVELS•Insulation levels are to be based on insulation coordination design.•Higher insulation level for bushings than windings is not preferred.•Decide insulation levels prior to inviting the bids, rather asking alternate bids with different insulation levels.•Specify chopped wave and front-of-wave tests only when needed by the system.•When wave shape of the switching surge in the system is different to that in the standards then give the wave shape in the specifications. •Unless there is a logical reason do not increase the test levels from those in the standards.•Users and bidders should discuss and agree on test connections and test levels in the Design Review meeting.

TERMINALS•Consider the cost and delivery time before specifying the bushings to CSA or IEEE or IEC standards.•Get copies of routine tests from the manufacturer.•Specify the tests that are required and not covered under routine tests in the standards.•Check the suitability of the bushings for Low-ambient Temperature Load Capability.•Transformer manufacturer’s approval is recommended to interchange corona shields of the bushings.•Specifications should give details of bus-duct and enclosures.•Preferable for manufacturer to determine the current rating.•Check the withstand value of the peak fault current also.•Check the design of horizontal mounted terminals (need for a conservator etc.).

ACCESSORIES•List all required accessories. If preferred, specify the manufacturer and type or model.•Instruction manuals to include pamphlets describing the function, construction and operation of the accessories.•Before specifying air bag in the conservator, check the compatibility with the inhibitor in oil.•Specify if certification for revenue metering is required.•For valves specify the size, function and the type.•In Design Review discuss the details of packing and shipping.•Shipping list to include instructions for storage (outdoor, indoor etc.)•Tender price to include training of user’s personnel is a good idea.

TYPES OF COOLING•Specify 65 C rise per CSA and IEEE standards. Avoid ⁰specifying 55 rise or 55/65⁰ ⁰ rise.•Do not call OA, FOA etc. designations, many young engineers may not know them. Specify only the designations ONAN, ONAF, OFAF, ODAF etc. in the current CSA and IEEE standards•Economics of type of cooling based on site location.•On pumped units, check oil velocities to avoid electrostatic charge build-up.•With OFAF cooling, check oil velocities and gradients of the windings.•With OD cooling, correlation of time constants of WTI and windings is to be checked. •When self-cooled rating is not required, allow the bidders to quote with industrial type coolers or with radiators.•Give air flow restriction (fire walls, enclosures etc.) details. •For water coolers specify leak detector type.

SOUND LEVELS•Check CSA and NEMA sound levels before specifying as they are very old.•Effect of sound level on cost.•Sound level on bridging position with reactor LTC.•Series transformer sound level at different tap positions.•Sound level with constant flux taps and variable flux taps.•Effects of sound level reduction methods (core binding etc.) on life of the transformer.•Sound levels at different stages of cooling.•Sound level at no-load and at load.

TAPS (range, location etc.)•Function of the taps.•IEEE tutorials on www.transformerscommittee.org or on Google. “TAPS” – 2004 in Las Vegas by V. Sankar. “Taps in autotransformers” – 2010 in Toronto by Dr. T. Kalicki and V. Sankar.•Tap ranges in C57.12.10 (DETC ±5% and LTC ±10%).•Avoid DETC taps, specially when there is LTC.•DETC taps in autotransformers.•Formation of oxide film on DETC tap changer contacts.•Adequacy of LTC range to meet regulation.•Specifying the tap range by the user versus specifying system requirements for bidders to calculate the tap range.

TAPS (range, location etc. continued)•Location of the taps: On input winding. On output winding. In wye or delta or zig-zag windings. Series transformer.•LTC selection: Voltage across the tap range. Number of steps and step voltage. Step KV.A. Number of tap turns. RMS and peak fault currents.• Autotransformers: DETC. DETC and LTC. Taps in LV line. Taps in TV.

TAP RANGE•If system requires +5% to -15% taps, do not specify ±15% taps.•Tap range of ±10% in C57.12.10 and system requirement.•Specify the tap range such that a reversing or linear type tap changer can be offered. Instead of 230KV±10% tap range in ±16 steps, specify that the taps are required for voltage variation from 207KV to 253KV in 32 steps.•For taps below normal, load loss reduction with linear taps compared to reversing taps. •With vacuum LTC no need to meet the minimum inductance requirement between coarse and fine windings, where as this requirement must be met with non vacuum LTC.

OTHER CONSIDERATIONS FOR THE TAPS•Reliability and cost of non-linear elements (Zno discs) across the taps verses the designs without the non-linear elements.•To specify tap changer make and type only when specifically needed.•At tender review to check tie-in elements effect in service.•Not to state that selector contacts must not be in main oil.•RCBN and FCBN.•Type of tap changer influence on buckling forces on tap winding.•Current splitting.•Step-up and step-down operations. Also how the taps are used.•Vacuum verses non-vacuum tap changers.

TYPES OF TAPS•Constant flux taps (CFVV).•Variable flux taps (VFVV).•Mixed regulation taps (Cb.VV).•Change in types of taps based on step-down operation, step-up operation, used for input voltage fluctuations or used to compensate for regulation.•Types of taps effect on the following: Impedance Short-circuit current Sound level Losses TV voltage

LTC location and core flux in two winding transformers

Taps Location Operation Constant Voltage Varying Voltage Core Flux HV step-down HV LV variable LV HV constant step-up HV LV variable LV HV constant  LV step-down HV LV constant LV HV variable  step-up HV LV constant LV HV variable

LTC location and core flux in autotransformersLTC

LocationOperation Compensate for

Input VoltageCompensate forLoad Regulation

CoreFlux

Series Step-down   constant

      variable

  Step-up   variable

      almost constant

         

LV Line Step-down   variable

      almost constant

  Step-up   constant

      variable

         

Common Step-down   variable

      variable

  Step-up   variable

      variable

TYPES OF TAPS (continued)•Based on user preference or special requirement the following should be specified in the specifications. Resistor type / Reactor type Tank mounted / In-tank Vacuum / Non-vacuum with filters Reversing / Coarse-fine / Linear Series transformer, acceptable or not Non-linear devices, acceptable or not Tie-in elements, acceptable type Extra continuous current rating, 1.5 p.u. or 2 p.u. etc. Taps in body of main winding or taps in a separate winding

TYPES OF TAPS (continued)•Some other considerations are given below.

Type and design of tap winding.

Leads bring-out.

Eccentric duct winding arrangement.

Series transformer rating based on reversing or

linear taps.

Low ambient temperature capability.

Measurement of tap winding temperature rise.

Lead supports strength.

Clearances between tap leads of different phases

and from tap leads to ground.

Eccentric duct winding arrangement

Eccentric Duct

Core

Tap winding

LV winding

Tap leads

Centerline of

HV & LV

Centerline of

Tap & Core

IMPEDANCE

•Specifications must give impedance value •Reference MVA•Impedance value on cost•Effects of low impedance and high impedance•Impedance values recommended in standards•Impedance values at extreme taps•Effect of CFVV and VFVV taps on impedance•TV to LV and TV to HV impedances•Impedance of zig-zag transformers

TOPICS FOR SECOND HALF OF THE PRESENTATION•Capitalization of losses•Short-circuit withstand•Special requirements (altitude, over excitation, GIC etc.)•Overloads•Parallel operation•Rating plate•Alternatives•Interesting clauses in the specifications•Globalization•Data sheets•Tests•Tender and Design Review meetings•Transportation and limiting dimensions/weights•Conclusions

CAPITALIZATION OF LOSSES•IEEE C57.12.120 ‘Evaluation Guide for Power Transformers and Reactors’ is a very good reference.•Following should be stated in the specifications. No-load loss $/KW Load loss $/KW at a reference MV.A. Cooler losses if different to load loss $/KW•Do not specify rate per KWH.•Do not specify no-load and load losses, give only the loss evaluation values.•Reference temperatures for losses if different from the standards.•Penalty for losses tested above the guaranteed values.•Incentives for innovations to reduce the losses.•Users and manufacturers to work together to develop green-transformers.

SHORT-CIRCUIT WITHSTAND•Following should be specified in the specifications. System impedances if different from the standards. Pre-fault voltage if different from the standards. System and transformer grounding details. For transformers directly connected to the generators; the duration the voltage source is connected. Details of impedances connected to limit short-circuit current magnitude. For three-circuit transformers the in-feed is from which circuits. Requirement and details of the devices that relieve the tank pressure during the short-circuit.•Short-circuit test is very expensive. Design and manufacturing practices of the bidders to withstand short-circuit forces should be thoroughly evaluated in the Tender Review meeting.

SHORT-CIRCUIT WITHSTAND (continued)•Manufacturers normally calculate the following stresses from the short-circuit forces. In the Design Review meeting user to check the stresses and withstand strengths. Mean hoop tensile stress on outer windings. Mean compressive stress on inner windings. Radial bending stress on inner windings. Axial bending stress on all coils. Compressive stress on radial spacers (duct sticks). Compressive stress on axial spacers (keyed spacers) and on the paper insulation of the winding conductors. Compressive stress on clamping ring (pressure ring). Tensile stress on clamping structure. Compressive stresses on inner windings. Free buckling stresses on inner windings. Short-circuit stresses on lead structures.

SPECIAL REQUIREMENTS•Where economical and needs by the system, deviate the following from the standards. Ambient temperature. Low-ambient temperature capability. System over voltage. Pre-fault voltage. LTC current rating.•Operating temperature, viscosity of the oil in the LTC and the LTC cut-out temperature setting are to be properly coordinated.

SPECIAL REQUIREMENTS (continued)•Requirements from one station to another station differs. Information to be included in the specifications of some requirements is given below. Operating altitude when above 1000 meters. Polluted environments. Transport dimensions/weights/profile restrictions. GIC requirements. Oil preservation system. Special oils like FR3. Fiber optics. On-line monitoring devices. Painting. Wheels and similar requirements. Positions of control box, conservator etc.

OVERLOADS•Information below should be included in the specifications. Overload profile. Number of occurrences in a year. Information per clause 9.7 of C57.91. Limits of hot-spot temperature and top oil rise. Loss of insulation life. Operation (step-down or step-up). Load on the tertiary (also arithmetic, vector loading etc.). Ambient temperature at each load. Requirement of overload test. Acceptable DGA levels during the overload test.

OVARLOAD (continued)•Some of the risks during the overload are listed below. Evaluation of free gas. Loss of insulation life. Leaks on gaskets. Reduced mechanical strength of the insulation. Permanent deformation of materials. Tap changer thermal runaway condition. Operation of relief devices. Excessive pressure built-up in bushings. Risk of damage of internal parts (CTs, current limiting devices, tap changers etc.). Increase in regulation.

PARALLEL OPERATION•When parallel operation with the existing transformers is required following should be included in specifications: Rated MV.A. Exact turns ratio of the windings at all the taps. Impedance on rated and tap extremes. Diagram of connection and phasor relationship between windings. Compatibility of controls to maintain the correct tap positions on all transformers while minimizing the circulating current. Type of paralleling method preferred.•Impedances should be same at maximum rating (For transformers of 60/80MV.A and 60/80/100MV.A impedance of 8% at base rating of 60MV.A is not correct; should be impedance of 10% at 80MV.A for the first unit and 10% at 100MV.A for the second unit).

PARALLEL OPERATION (continued)•Some paralleling methods are given below: Master / Follower Power factor Negative reactance Circulating current Circulating reactive current•Paralleling information on the existing units is not proprietary.•If the tolerances on impedances lesser than those in the standards are required, then the required tolerances should be stated in the specifications.•Parallel operation is user responsibility. Manufacturer designs the transformer to the specifications.•IEEE standard C57.153 ‘Transformer Paralleling Guide’ and IEEE April 2009 tutorial ‘Transformer Paralleling’ are good references.

RATING PLATE•Most important and readily accessible record.•Data inscribed should not fade away after a few years.•Suggest to include the following in the specification along with the data stated in CSA C-88: Tap changer nameplate. Phasor diagram including hour clock designation (Dyn11, Dyn1 etc.). Step-up operation suitability. Suitability of reversal of power flow. Current transformers, voltage transformers etc. No detectable PCB (less than 2ppm). Standard number including the year. Impedances on extreme taps. Nameplates for bushings, tap changers etc. Vacuum withstand capability of oil circulating parts.

RATING PLATE (continued)•Users should consider to include the following also: Diagram of location of emergency man-holes. Diagram of location of major valves. Tie-in resistors including their rating. Make and serial number of LTC reactor. Make and the impedance of current limiting reactors. Location diagram and the type of fall arrest system. Pressure settings on nitrogen pressurized units. User specification number. A statement that the voltages and the currents marked are based on by not considering the regulation. Zero sequence impedance. Make and serial numbers of series transformer, compensating transformer etc., when used. Common winding maximum current for autotransformers. Type of oil (Voltesso 35, Luminal etc.)

ALTERNATIVES•Users should consider the bids with alternatives meeting the system needs without the main bid per specifications.•Management of users should nourish the cost saving and reliability ideas of their engineers.•Asking the bids for only the required ratings than all the ratings in the system saves money and time for both users and manufacturers.•Consult the manufacturers to determine the parameters rather asking alternatives with different parameters (impedance, insulation levels, winding connections etc.).•Encouraging the alternatives not only saves money to the user but also helps to the advancement of the industry.

INTERESTING CLAUSESThe clauses that are either ambiguous or will add considerable cost with almost no benefit should not be included in the specifications. A few are given below.•Missing technical information per industry standard.•Assembled in a manner best suited for the application.•Best materials should be used.•Adequate barriers shall be provided.•LTC selector contacts shall not be in transformer main oil.•No exceptions, no deviations and no alternatives will be accepted.•Per manufacturer’s standard.•Life of the transformer must be 40 years.•Tank should have adequate stiffeners.•Only bids from the manufacturers with a skilled labour force will be considered.•Core should be built with high grade laminations.

INTERESTING CLAUSES (continued)•Oil should be of good quality.•Test voltages should be 25% higher than those in the standards.•Calculations must be by computer programs only.•Top oil limit of 105⁰C and hot-spot limit of 120 C for over ⁰loads also.•Design of the taps should be as CFVV and also as VFVV.•All components shall provide utmost reliability.•No abnormal deterioration of insulation in service.•Should conform to high standards of engineering, design and workmanship.•Impedance shall be stated in the order.•Materials used shall be of established quality.

Globalization•Specifications are the first and the most important tool in procuring reliable transformers at economical prices from the global market.•Many transformer manufacturers are in the countries whose first language is not English. As such, the specifications should be in simple English with globally known terminology.•For the fear of losing the competitive edge many bidders do not wish to post the clarifications on the web site.•Repair cost and time to repair are important on whom to place the order.

Globalization (continued):•Due to stiff competition safety margins between stresses and strengths are reduced by almost all the manufacturers.•Provides an opportunity to update the specifications from the beneficial experiences in other countries (use of coarse/fine taps, non-linear devices etc.).•Specifications should include user maintenance practices, safety requirements and transport limitations.•Some countries give subsidies for export. This makes local manufacturers bankrupt and the local knowledge to evaporate.•CSA, IEC and IEEE should be combined to develop one global standard.

DATA SHEETS•Data sheets should ask the information needed in evaluating the bids. •Data sheets should not ask the information that the user can not explain what to be filled.•Suggest not to ask the following. Efficiency and regulation at various loads and power factors. Impulse, applied and induced test levels per standards. Voltages on all DETC tap positions. No-load and load losses at 20⁰C and at 85 C.⁰ Load losses at base MV.A and at maximum MV.A.•Electronic Data Forms should allow the bidders to fill different to the drop down menu and enough space to fill. •Data sheets are not a substitute to the Tender Review meeting.

TESTS•Routine and Design tests (Type tests) on fully assembled and oil filled transformers are listed in CSA, IEEE and IEC standards.•Recommend that the specifications specifying the tests per standards unless the system conditions require to test differently. (switching surge wave shape, single phase induced test etc.).•Obtain test certificates of all accessories and components (DETC tap changers, bushings, CTs, pressure relief devices, bolts used for lead clamping structures, glue used on insulating items etc.).•Not possible to do sound level test on load in the factory.•Tests before shipping, after receiving at the station, before energization should also be specified.•Specifying the actions to be performed when a transformer fails in a factory test is a good practice.

TENDER AND DESIGN REVIEWS•Tender Review meeting is very important and strongly recommend for all the tenders.•Tender & Design Reviews cost to the bidders. As such, the specifications should state these requirements.•Suggest to discuss the following in Tender Review: Manufacturing and test capabilities. Quality and inspections. Delivery track record (past 3 years). Shop failures, investigation & corrections (past 5 years). Field problems and how rectified (past 10 years). Exceptions/comments in the tender. Design of core, coils, tank etc. Taps effects on transformer parameters. Processing practices of core & coils and oil. Short-circuit with stand, overload calculations etc.•User technical consultant should attend Tender review.

TENDER AND DESIGN REVIEWS (continued) Suggest to discuss the following in Design Review.Magneic circuit•Flux density in legs and yokes at maximum system voltage (specially in 5 legged cores and split cores).•Type of core (core or shell) and joints (step-lap etc.).•Laminations surface insulation.•Clamps design for short-circuit forces and for lifting.•Cooling ducts and core maximum temperature.•Core grounding.•Undesirable hot-spots due to the leakage flux.

Windings•Design of coils and their construction.•Types of conductors and their suitability.•Impact of taps location on short-circuit forces and on insulation design.

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TENDER AND DESIGN REVIEWS (continued)•Cooling design to avoid undesirable hot-spots.•Stresses in oil and in solid insulation.•Construction of static shields, stress rings etc.•On pumped units velocities in different parts.•Leads exists.•Off-set, modeling etc. for calculations of forces.•Design and construction of counter shields, interleaving, transpositions etc..•Review of purchasing specifications of winding conductors, all components and materials.

External to the coils•Design and construction of current limiting reactors, tap changer reactor, series transformer etc.•Design of core shunts, clamp shunts, tank shields etc. •Leads layout, leads structures, clearances etc.

TENDER AND DESIGN REVIEWS (continued)Accessories•Principle of operation, construction, mounting etc.•Safety systems design and location (fall arrest systems, pressure relief devices, emergency exits etc.).•Gaskets material and design.

Manufacturing and processing•Machinery to cut laminations to avoid burrs.•Air gaps during core assembly and binding of the core.•Method of core lifting after the assembly.•Maintaining tightness of the windings.•Winding methods, removing from the lathe and sizing.•Workmanship of installation of counter shields, making interleaved joints, cross-overs, transpositions etc.•Vapour-phase process, pre-tanking, moisture control etc.•Painting specifications and painting process.

TENDER AND DESIGN REVIEWS (continued)Inspection and testing•Quality standards and procedures.•Inspection and tests of raw materials and accessories.•Pre vapour-phase tests (ratio, vector group etc.).•Oil tests before filling.•Factory tests on completely assembled unit.

Shipping and installationMarking, packing and shipment of the parts.Preparation of the main unit for shipment.Transportation method and the route of shipment.Type and location of impact recorders.Pre-shipment tests (SFRA, core megger, power factor etc.).Inspection and tests at site before unloading.Erection steps and processing at site.Pre-commissioning tests.

TRANSPORTATION AND LIMITING DIMENSIONS/WEIGHTS•Specifications should include a schedule for civil drawings, control drawings, outline, rating plate etc. •Manufacturers’ drawings to have correct weights and dimensions.•Manufacturers should not use users as checkers for drawings.•Manufacturers should realize that after receiving the drawings user has to make ready the foundations, spill containments, control schemes etc. by the time the transformer arrives in the station.•Specifications should clearly give the transportation details like station location, siding details, dimensional and weight restrictions.•Enquiries for replacement transformer specifications mostly have the drawings of the old transformer, but often they are not readable or critical dimensions missing. Users should rectify this.•Specifications should also give dimensional and weight restrictions for the parts.•Manufacturers should ship all the parts in time with proper packing.•Based on site location, complications of the transformer etc. a pre-tender site meeting is a good idea.•Many damages had occurred in the transportation.•Many users had problems due to the large differences on dimensions and weights between initial and final drawings of the manufacturers.

CONCLUSIONS•User’s management should provide adequate resources and time to their Technical Departments to prepare the specifications.•At the time of preparation of specifications users should interact with manufacturers to finalize on cost effective parameters meeting system needs.•Standards are to complement the specifications and are not to use as specifications.•CSA-C88 is not updated for a longtime. Canadian utilities and manufacturers should take initiative and update CSA-C88 soon.

CONCLUSIONS (continued)•Specifications should be revised based on the work done by organizations like IEEE, IEC etc. and the developments in the transformer world.•Users should give freedom to manufacturers to offer alternatives without a main bid exactly to the specifications.•Technical Departments of the users and the manufacturers must have direct, fast and reliable communication paths.•Developments are not manufacturers’ arena only. Users’ management should encourage their engineers for innovations.•Users and manufacturers are not just buyers and suppliers they are a team.

INTERACTIONS(Comments, questions etc.)