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0 02-02-2002 Approved Issuerev. date Description/issued for prepared authorised

client: ADWEAproject: STANDARD SPECIFICATIONS FOR WATER WORKStitle: SPECIFICATION FOR TRANSFORMERS

tender: project: document: W-E-SS-003 rev: 0 sheet: 1 of: 16

SPECIFICATION FOR TRANSFORMERS

Client ADWEAProject: STANDARD SPECIFICATIONS FOR WATER WORKSTitle: SPECIFICATION FOR TRANSFORMERS


Table of Contents page

1. SCOPE...................................................................................................31.1 General........................................................................................3

2. APPLICABLE STANDARDS.................................................................32.1 IEC Standards .............................................................................32.2 Other Standards ..........................................................................32.3 Local Standards...........................................................................3

3. SITE CONDITIONS................................................................................43.1 General........................................................................................43.2 Altitude ........................................................................................43.3 Special Design Conditions...........................................................4

4. DESIGN CONSIDERATIONS ................................................................44.1 General........................................................................................44.2 Ratings ........................................................................................54.3 System Variations........................................................................54.4 Temperature Rise........................................................................54.5 Impedance Voltage and Short Circuit Currents ...........................54.6 Vector Group ...............................................................................54.7 Noise Level..................................................................................54.8 Installation ...................................................................................6

5. CONSTRUCTION REQUIREMENTS.....................................................65.1 Internal Arrangement...................................................................65.2 Tank or Enclosure .......................................................................65.3 Windings......................................................................................65.4 Insulation .....................................................................................75.5 Oil and Fillings .............................................................................75.6 Terminals.....................................................................................75.7 Cable Connection ........................................................................85.8 Off-Load Tap Changers...............................................................85.9 Earthing .......................................................................................95.10 Fittings and Accessories..............................................................95.11 Rating Plate...............................................................................13

6. INSPECTION AND TESTING ..............................................................146.1 Inspection ..................................................................................146.2 Testing.......................................................................................14

7. PACKING AND SHIPMENT ................................................................15

8. VENDOR DOCUMENTATION .............................................................15



1. SCOPE

1.1 General

This specification covers the general requirements of Medium Voltage to Low VoltageDistribution For Transformers for the water works project. This specification sets theminimum acceptable requirements for design, construction, testing and delivery oftransformers.

In case of differences between this specification and the international standards specified inclause 2 below, the more stringent requirements shall prevail.

2. APPLICABLE STANDARDS

2.1 IEC Standards

Unless specified otherwise transformers shall conform in design, material, construction andperformance to the latest editions of the IEC Standards and in particular to the followingpublications:

- Power transformers IEC 60076- Thermal evaluation and classification of electrical

insulation IEC 60085- Insulating liquids determination of the break down

voltage at power frequency IEC 60156- Specification for unused minerals insulating oils IEC 60296

for transformers and switchgear- Loading guide for oil-immersed power transformers IEC 60354- Determination of transformers and reactors IEC 60551

sound levels- Dry type power transformers IEC 60726

Note :In case Transformer terminal box is provided with CTs then relevant IEC standard for CTis also applicable.

2.2 Other Standards

If different standards, namely BS or VDE are specified on the data sheets and/oraccompanying documents, the latest editions of the specified standards shall be applicable.

2.3 Local Standards

Further to the international standards, transformers shall in any case conform to the localstandards (ADWEA), if these are higher, more stringent or of special nature and shall bepreviously approved by ADWEA.



3. SITE CONDITIONS

3.1 General

For general climatic conditions applicable to the project installations, refer to Specification forGeneral Technical Requirements.

3.2 Altitude

Altitude where transformers will be installed shall not be more than 1000 metres above sealevel.

3.3 Special Design Conditions

The transformers shall be designed for an ambient temperature of 55 deg. C in outdoor areaswithout sunshade.

4. DESIGN CONSIDERATIONS

4.1 General

4.1.1 Purpose of Equipment

All components utilised in the construction of the transformer shall be of latest design, newand in current production. Material and equipment shall be approved by the appropriateauthority where applicable.

- The power/distribution transformer will be used to supply power to the electrical systems.

The design shall allow continuous full load operation of complete transformer underconditions specified.

4.1.2 Safety and reliability

- The transformer shall be of a standard, well tested and proven design which ensuresmaximum safety to personnel, maximum service reliability and economic operation for anoperational lifetime of at least 15 years. Design and construction shall be simple andshall provide good accessibility to components and parts.

- All equipment, materials and parts shall be brand new and unused, of currentmanufacture, of modern design and of the highest industrial grade, free from allimperfections that might affect the performance.

- Transformers feeding frequency converters shall be provided with static screening tosuppress the radio frequency interference (RFI).



4.2 Ratings

4.2.1 Standard ratings

Transformers kVA and voltage rating shall comply with the preferred values of the standardsspecified. Unless otherwise specifically stated to the contrary the rated kVA shall be based onnatural air cooling. Voltage insulation of windings shall be for unearthed system.

For oil immersed and dry type transformers manufacturer shall indicate the base rating of thetransformer for operation in an ambient of 40C and furnish the de-rating factors forequipment rating at different ambient temperatures.

4.3 System Variations

Transformers shall be capable of continuous operation at their maximum kVA ratings andwithin their limits of temperature rise at system continuous deviation of up to and including thefollowing percentage values of the rated system :

- Voltage : 10%

- Frequency : 5%

4.4 Temperature Rise

Temperature rise of the oil immersed type transformers shall not exceed the following valueswhen operating continuously at the maximum kVA ratings, at the rated voltage and frequencyand with the provisions of clause 4.3 and climatic/installation conditions of clause 3.0 above:

- Top oil temperature risemeasured by thermometer 50C

- Winding temperature risemeasured by resistance 55C

4.5 Impedance Voltage and Short Circuit Currents

Unless parallel operation with existing transformers, having different characteristics, isspecified, transformers shall have the impedance voltage and short circuit current values asper IEC requirements or as indicated in the data sheets.

4.6 Vector Group

The vector group shall be as specified in the data sheets.

4.7 Noise Level

The noise pressure level produced by transformers operating at the rated voltage andfrequency at either no load or full load shall be below the level specified in IEC unlessspecified otherwise on the data sheets.



4.8 Installation

Unless otherwise specified in the data sheets or accompanying documents transformers shallbe suitable for outdoor installation (without sunshade). Ventilation requirement for indoorinstallation of dry type transformers shall be specified by the manufacturer.

5. CONSTRUCTION REQUIREMENTS

5.1 Internal Arrangement

Transformer core shall be of robust design adequately braced to prevent displacement due toelectromagnetic stresses of short circuits, and the mechanical shocks of normal moving andhandling of the transformer without any need for special shipping braces.

The core laminations shall be evenly secured to prevent settling of the core and minimizenoise and vibration when transformer is in operation.

The core construction shall be such that removal and replacement of the coils would requirethe removal of minimum possible number of core laminations.

5.2 Tank or Enclosure

For oil immersed transformers the tank, cover, radiators and any other attachedcompartments, shall be rigid steel construction.

Radiator tubes or fins shall be so arranged that external cleaning and repainting can becarried out at site without dismantling.

For sealed type transformers the tank cover shall be welded with continuous joint. Boltedconnection with tack-welded bolts is not acceptable. After filling the tank with oil the fillingorifice shall be permanently sealed in a tamperproof manner.

The tank cover, radiators etc. shall have adequate strength to withstand without deformation.The internal pressure of the oil, air and gas under operation conditions.

Pressure relief valves, when specified, shall be fitted and set to operate at static pressure ofless than the hydraulic test pressure of the tank.

Minimum degree of protection for dry type transformers shall be IP 31 for indoor installationand IP 55 for outdoor installation.

5.3 Windings

Transformers shall have separate low and high voltage windings.

The neutral point of star connected windings shall be brought out separately to a terminal onthe respective winding side.

The MV winding shall have tapping at 2.5% and 5.0% of the rated MV voltage unlessspecified otherwise on the data sheet.



The winding coils shall be adequately braced to prevent distortion of the windings ormovement of the coils on the core limbs under short circuit condition or normal moving andhandling of the transformer.

LV winding of dry type transformers shall be made of Aluminium sheet to reduce axialstresses under short circuit. The layers of windings shall be insulated by class F insulatingmaterial. The HV windings shall be made from insulated aluminium wires and shall be castunder vacuum in filled epoxy resin.

5.4 Insulation

All windings shall be fully insulated and the insulation shall be free from any composites likelyto soften, shunt or collapse during service. The insulating material shall be of a type that doesnot shrink, disintegrate, carbonize or become brittle in hot oil for oil immersed transformer.

Insulation varnish treatment shall be accomplished by vacuum impregnation.

5.5 Oil and Fillings

Mineral oil for immersed type transformers shall be Shell DIALA B,D or AX alternative oilscomplying IEC 60296.

Oil shall be dried prior to filling of the transformer which shall be performed under vacuum.

PCB synthetic liquids (Poly Chlorinated Biphenyls) or other chlorinated hydro carbons withtrade names Askarel, Pyranol, Clapnen, Pyralene, etc. are not acceptable and shall not beused.

Instructions for cleaning and filtering of the liquid used shall be furnished with eachtransformer.

The dielectric strength of oil or synthetic liquid shall be more than 125 kV/cm.

Oil immersed type transformers shall be filled with the oil at the manufacturers works.

The brand and type of oil shall be stated on the rating plate.

5.6 Terminals

To provide a 4-wire system, the low voltage starpoint connections shall be brought out on aseparate terminal.

Terminals shall be marked in accordance with the connection diagram marked on the ratingplate.

The stems and bushing of the terminals shall be sealed in leakproof manner into the tank wallor cover, rotations of terminal stems shall be prevented by effective locking.



External terminals for the connection of cables shall be provided with bolted type conductorconnections of adequate dimensions and ratings and if two or more conductors per terminalare required, provision shall be made to accommodate the same.

All bushings shall be self-contained and shall be sealed into the enclosure air/gas and liquidtight with non-deteriorating gaskets suitable for the liquid used.

All transformers shall be provided with external earthing terminal. This shall be either athreaded bolt or bolted clamp. The minimum diameter shall be 8 mm.

5.7 Cable Connection

5.7.1 Cable Boxes

Cable entries into the boxes shall be located such that conductors can be clamped straightinto the terminal connectors without being bent into tortuous shapes inside the box.

Extension pieces bolted to the actual terminal with additional bolted conductor clamps in linewith the cable entry may be required.

Cable boxes for PVC or XLPE insulated cables shall be dry type. Single core type cablesshall be glanded to non-magnetic plates.

5.7.2 Terminations and glands

Cable terminations for lower voltages shall be with double compression type glands. Singlecore cable entries shall be mounted on non-magnetic plates.

For star point earthing an extra gland, suitable for PVC insulated cable shall be provided.

5.7.3 Supports and clamps

Cable clamp supports shall be delivered as an option.

5.8 Off-Load Tap Changers

Tap changing on the MV winding shall be done by externally hand operated off-load tapchanging switch. The switch shall preferably satisfy the following requirements:

- The switch shall be operable by its handle without the need of additional tool and withoutrisk to personnel safety.

- The contact changing shall be positive snap action arranged so that it is impossible forthe contacts to be left in a position where the circuit remains interrupted.

- The stops shall be robust type to prevent overrunning.

- Padlocking of the switch shall be provided.

- Tap positions shall be clearly marked.



- The driving rod through the tank cover or wall shall be sealed to prevent leakage of air,gas or liquid under all service conditions.

5.9 Earthing

MV cable boxes shall have an earthing terminal of adequate dimensions for the cableearthing wires. LV cables boxes shall have earthing terminals of adequate dimensions foreach cable earthing sheath wire.

For connection to the external earthing network, the enclosure shall have earthing pads withthreaded holes for connection to a 70 sq mm stranded copper earthing cable.

5.10 Fittings and Accessories

The following shall be provided for all transformers as a minimum:

- Pressure relief device.

- Winding temperature indicator with contacts.

- Oil temperature indicator with contacts (for oil immersed transformers).

- Oil level switch with contacts (for oil immersed transformers).

- Lifting lugs for lifting the entire transformer.

- Skid under base with bi-directional rollers.

- Rating plate.

- Any special tools required for erection, operation, or maintenance of the transformer.

All VENDOR cabling/wiring on the transformer shall be run through cable trays fitted ontransformer.

Further to the above the following shall be provided for breather type transformers:

- Air dryer with silica gel dehydration capsule and suitable air lock to prevent externalatmosphere from coming into direct contact with insulation liquid.

- Liquid conservator with connection pipe to transformer tank and extending into theconservator for collection of any water or sludge. A drain plug shall be provided at thelowest part of the conservator.

- Liquid level indicator fitted on the conservator.

- Thermometer pocket with sealing cap. Pocket shall be approximately 150 mm deep and20 mm inside diameter and welded into the tank wall such that a thermometer orthermoprobe can be inserted to measure the top liquid temperature even at the lowestliquid level.



- Gas and liquid activated Buchholz relay with suitable valves and flanges to enableremoval for maintenance without dismantling the transformer.

- Filling cap for topping of liquid.

- Valves for filtration and draining of liquid.

- Liquid sampling device, separately fitted or combined with the drain valve.

Lifting lugs for lifting tank cover with or without core and coil assembly. If without, further liftinglugs for core an coil assembly shall be provided.

5.10.1 Pressure Relief Valve

A pressure relief device of sufficient size, capable of functioning without electrical power shallbe provided for the rapid release of any pressure that may be generated within the tank andwhich might result in damage to the equipment. It shall also be capable of maintaining the oiltightness of the transformer under all conditions of normal service.

The device shall operate at a static pressure of less than the hydraulic test pressure fortransformer tanks and shall be designed to prevent further oil flow from the transformerfollowing its operation.

5.10.2 Conservator

Conservator shall have an adequate sump, a filling cap and a drain valve. To permit cleaningof internal side conservator, one end of the conservator to have removable cover with facilityfor lifting.

Level gauge with markings to be provided on conservator. The level gauge to indicatemaximum, minimum and normal level.

The main feed pipe from the conservator vessel to the transformer shall be connected to thehighest point of tank and shall be arranged at a rising angle towards the conservator at about5 degree to horizontal. A valve shall be provided at the conservator to cut off the oil to thetransformer.

Conservator to be connected to a dehumidifying breather which shall be mounted at about 1.5metres above ground level.

5.10.3 Valves

Valves shall be of the fully sealing full-way type suitable for minimum and maximumtemperatures specified without any deterioration. Valves to open when turned counterclockwise. All valves other than 'drain' and 'filter' to be fitted with an indicator readily visiblefrom ground level clearly showing position of valve. All valves opening to atmospheres shallbe fitted with blanking plates.



5.10.4 Explosion Vents

Explosion vents with single diaphragm to be provided which shall be connected toconservator by an equaliser pipe.

5.10.5 Cooling

Detachable radiators with valves to be provided and shall be through connected to the maintank. Radiator thickness to be 1.20mm (minimum) and shall be fitted with lifting lugsmachined, flanged inlet and outlet pipes.

Plugs shall be fitted at the top and bottom of each radiator for filling and draining. The oilcircuit of all coolers shall be provided with the following as appropriate to tank mounted onseparate bank coolers :-

A valve at each point of connection to the transformer.

A valve in the main oil connection at the bottom of each cooler.

Loose blanking plates to permit the blanking off of the main oil connection to the top of eachcooler.

A 50 mm oil filtering valve at the top and bottom of each cooler, the bottom valve shall alsofunction as a drain valve.

A thermometer pocket fitted with a captive screwed cap on the inlet and outlet oil branches ofeach cooler.

5.10.6 Disconnecting And Sealing End Chambers

Where M.V. cables of rating 11 kV and above are terminated in a cable box, an air insulateddisconnecting chamber with removable links shall be provided. The disconnection chambershall have a removable cover and the design of the chamber shall be such that ampleclearances are provided to approach the terminations of the disconnecting links, and alsofacilitates either the transformer or each cable to be subjected separately to high voltagetests.

Cable termination box shall be provided with suitable arrangement to provide supportingstructure from floor.

Cables boxes for 6.6 kV and below, need not be attached with disconnecting link chambers.

All terminal boxes to be provided with bushings with Air clearance and creepage suitable foroutdoor mounting type transformer.

An earthing terminal shall be provided in each disconnecting or sealing end chamber to whichthe connections from the transformer or reactor winding can be earthed during cable testing.

Terminals shall be marked in a clear and permanent manner.



5.10.7 Temperature Indicating Devices And Alarms

Oil temperature indicating (OTI) devices shall be fitted with one set of contacts adjustableover the range 60C to 110C for initiating a DC operated alarm.

Winding temperature indicating (W.T.I.) devices shall indicate the temperature of the hottestspot of the winding and shall have a load-temperature characteristic approximating to that ofthe main winding. Two sets of contacts shall be provided for initiating of alarm and trip relays.

Separate C.T. shall be used for W.T.I.

Temperature indicating devices shall incorporate a dial and a pointer indicator and a separatepointer to register the maximum temperature reached.

The capillary connected sensing bulbs of temperature indicators shall be positioned inseparate oil-tight pockets arranged in the top oil.

The temperature indicating devices shall be so designed that it shall be possible to move thepointers by hand for the purpose of checking the operation of the contacts and associatedequipment. The working parts of the instruments shall be made visible by the provision ofdials and glass fronted covers.

The characteristics of the winding temperature indicating devices shall be forwarded to theADWEA/ENGINEER for approval prior to the delivery of the transformers and shall also beincluded in the operating and maintenance instructions.

All temperature indicators shall be housed in the marshalling kiosk or box and shall bemounted so that they will not be affected by vibration.

5.10.8 Bushings

a) The bushing insulator shall be rated for maximum system voltage and comply withrequirements of IEC.

b) Minimum current rating shall be 400 Amps or as per load, whichever is higher.

c) In case of overhead line connected transformers, bushing shall suitable with creepagesfor outdoor and to be provided with arcing horns.

d) Neutral bushings to be provided for Earthing the neutral.

e) A separate box shall be provided to accommodate neutral C.T. for restricted fault relay.

f) All bushings shall be marked with symbols as per rating plate and connecting diagram.

5.10.9 Gas and Oil Actuated Relays (Buchlotz Relay)

Each transformer shall be provided with Bucholtz relay for operation during fault conditionsresulting in production of excessive gas inside the tank.



This relay is to make an Alarm contact during low oil level conditions and make trip contactduring upsurge.

The normally open, Electrically separate alarm and tripping contacts shall not exposed to oil.

The relays shall be fitted in the expansion pipe connecting the transformer tank to theconservator.

Each relay shall be provided with a test block to take a flexible pipe connection for checkingthe operation of the relay.

Bucholtz relay shall be fitted with flange on both ends and a valve to isolate oil supply forease of removal of the relay and assembly.

5.10.10 Painting

Paints chosen for Transformer should be carefully selected to withstand Tropical heat andextreme weather. The paint shall not scale off, crinkle or removed by abrasion due to normalhandling.

The surface to be painted shall be shot or sand blasted to remove all dust and scale orforeign adhering matter. All traces of oil and grease should be removed by suitable treatment.

All surfaces exposed to outside shall be painted with suitable anti rust and anti-corrosivepaints.

The colour shall be as per data sheet or subject to ADWEA/ENGINEER approval.

5.11 Rating Plate

The rating plate(s) shall be of non-corrosive material. Enamelled plates are not acceptable.The rating plate(s) shall give the following information:

- The international specification to which the transformer conforms to.

- Vector group and winding connection.

- Percentage tapping positions of rated voltage.

- Rated MV voltage at zero tapping.

- Rated LV voltages at no load and full load at above condition.

- Rated ambient temperature.

- Rated kVA at self air cooling at above conditions.

- Rated full load current and short circuit current withstand for 3 seconds.

- Impedance Voltage at principal tap.



- Rated reactance.

- Make, type, volume, and weight of insulation liquid.

- Enclosure class of transformer.

- Lifting weight of the core and winding assembly.

- Lifting weight of the entire transformer with liquid.

- Transformer type, make, serial number, year of manufacture and purchase ordernumber.

6. INSPECTION AND TESTING

6.1 Inspection

Visual inspection of the transformer or its parts and accessories may be required by theADWEA/ENGINEER or authorised inspector representing ADWEA at the following stages ofconstruction:

- Before core and winding assembly is placed in the transformer tank.

- Before final packing of transformer and its parts for shipment.

The manufacturer has to inform ADWEA/ENGINEER two weeks in advance of the events'dates.

6.2 Testing

The transformers shall be tested by the manufacturer to the requirements of the specifiedinternational standards. Some or all of the tests may be witnessed by ADWEA/ENGINEER orthe authorised inspector representing them. The witnessed tests shall be indicated on thetest sheets or accompanying documents and the manufacturers have to informADWEA/ENGINEER two weeks in advance of the test dates.

6.2.1 Routine tests

All transformers shall be subjected to the following routine tests:

- measurement of winding resistance; on all taps

- measurement of voltage ratio on all taps and check of voltage vector relationship;

- measurement of impedance voltage (at zero tapping), shortcircuit impedance and loadloss;

- measurement of no-load loss and current;



- the insulation resistance of each winding in turn to all other windings, core and frame ortank connected to earth shall be measured and recorded. The coil and windingtemperatures shall be measured immediately prior to the test and be recorded.

6.2.2 Type tests

The manufacturer shall carry out the following type tests if requested on the data sheets oraccompanying documents, if not, evidence of such type tests carried out on similartransformers will be accepted:

- temperature rise test;

- impulse voltage withstand test (on oil immersed type transformers).

6.2.3 Special tests

Any one or more of the following tests may be requested to be carried out on the transformer,if indicated on the data sheets or accompanying documents:

- measurement of zero sequence impedance;

- short-circuit test capabilities of transformer;

- measurement of the harmonics on the no-load current;

- measurement of acoustic sound level.

7. PACKING AND SHIPMENT

Transformers shall be packed in wooden type seaworthy crates having sufficient strength towithstand normal ship handling and transport.

The crates shall be marked with the place of destination, the Owner's name, order number,type of equipment etc.

8. VENDOR DOCUMENTATION

The following shall be provided by the manufacturer :

- Foundation fixing arrangement drawings(s)

- General arrangement drawing

- Name/tag plate lists

- Component arrangement drawing(s)

- Material lists

- Material descriptive literature



- Performance data/curve(s)

- Connection/terminal - diagram(s)

- Type test certificate(s)

- Routine test certificate(s)/report(s)

- Weight data sheet(s)

- Transport/lifting instructions.

- Installation instruction(s)

- Operating instructions

- Maintenance instructions

- completed data sheets.

- priced list of spare parts recommended to be on hand during plant start-up and two (2)years of operation.

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