200-25v4-33kv earthing transformers for use with 1 - nie

SPECIFICATION 200-25

33kV Earthing transformers for use with 110/33kV power

transformers

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Specification 200-25

33kV Earthing Transformer for use with 110/33kV Power Transformers

Table of Contents

1 General .................................................................................................................................... 5

1.1 Scope ............................................................................................................................... 5

1.2 Standards ......................................................................................................................... 5

1.2.1 European Standards ................................................................................................ 5

1.2.2 International Standards ........................................................................................... 6

1.2.3 British Standards...................................................................................................... 6

1.2.4 NIE Networks Specifications ................................................................................... 6

1.3 Service Conditions .......................................................................................................... 6

1.4 System Conditions .......................................................................................................... 7

2 Electrical Characteristics (Refer to technical contents for specifics) .................................. 8

2.1 Type .................................................................................................................................. 8

2.2 Rated Power .................................................................................................................... 8

2.3 Voltage ratio ..................................................................................................................... 8

2.4 Winding Connection and vector group .......................................................................... 8

2.5 Insulation Levels .............................................................................................................. 8

2.6 Impedance voltage .......................................................................................................... 9

2.7 Zero sequence impedance using low and high impedance earthing transformers ... 9

2.8 Short Circuit Performance .............................................................................................. 9

2.9 Over-fluxing ...................................................................................................................... 9

2.10 Losses ............................................................................................................................ 10

3 Design and Construction ...................................................................................................... 10

3.1 Quality Systems ............................................................................................................. 10

3.2 Tanks and Accessories ................................................................................................. 10

3.2.1 General ................................................................................................................... 10

3.2.2 Tank vacuum/pressure .......................................................................................... 10

3.2.3 Conservator ............................................................................................................ 10

3.2.4 Gas operated relay ................................................................................................ 10

3.2.5 Gas sampling device ............................................................................................. 10

3.2.1 Breathers ................................................................................................................ 11

3.2.2 Pressure relief device ............................................................................................ 11

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3.2.3 Oil Filtration ............................................................................................................ 11

3.2.4 Lifting lugs .............................................................................................................. 11

3.2.5 Earthing Terminals................................................................................................. 11

3.2.6 Oil Valves ............................................................................................................... 11

3.2.7 CT mounting arrangement .................................................................................... 11

3.3 Transformer Oil .............................................................................................................. 11

3.4 Bushings, cable boxes and terminals .......................................................................... 12

3.4.1 General ................................................................................................................... 12

3.4.2 Bushings ................................................................................................................. 12

3.4.3 Cantilever Operating Loads .................................................................................. 12

3.4.4 Clearances ............................................................................................................. 12

3.4.5 Cable Boxes ........................................................................................................... 13

3.4.6 Terminals ................................................................................................................ 13

3.4.7 Terminal Markings ................................................................................................. 13

3.4.8 400 Volt LV Cable Isolator Box ............................................................................. 13

3.5 Noise and vibration ........................................................................................................ 13

3.6 Labels and rating plates ................................................................................................ 14

3.6.1 General ................................................................................................................... 14

3.6.2 Rating plate ............................................................................................................ 14

4 Cleaning and Painting........................................................................................................... 15

4.1 General ........................................................................................................................... 15

4.2 Surface Preparation ...................................................................................................... 15

4.3 Coating Systems ........................................................................................................... 15

4.4 Paint Finish .................................................................................................................... 15

4.5 Inspection ....................................................................................................................... 15

4.6 Other requirements ....................................................................................................... 15

5 Tests....................................................................................................................................... 16

5.1 General ........................................................................................................................... 16

5.2 Type Tests ..................................................................................................................... 16

5.3 Routine Tests ................................................................................................................. 16

5.4 Site Tests ....................................................................................................................... 18

5.5 Test Certificates ............................................................................................................. 18

6 Documentation ...................................................................................................................... 19

6.1 Drawings ........................................................................................................................ 19

6.2 Assembly, Operation and Maintenance Instructions .................................................. 20

7 Quality Assurance ................................................................................................................. 20

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7.1 Quality System and Inspection ..................................................................................... 20

8 Delivery and Service ............................................................................................................. 20

8.1 Packing, Despatch and Delivery .................................................................................. 20

8.2 Spare Parts .................................................................................................................... 20

9 Schedule of Requirements ................................................................................................... 21

SCHEDULE A ................................................................................................................................... 21

SCHEDULE B .................................................................................................................................... 22

SCHEDULE C .................................................................................................................................... 23

SCHEDULE D .................................................................................................................................... 24

SCHEDULE E..................................................................................................................................... 29

SCHEDULE F ..................................................................................................................................... 30

SCHEDULE G ...................................................................................................................................... 1

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1 General

1.1 Scope

This specification states the requirements with regard to 33kV/400V high impedance earthing transformers with neutral coupler, for use in conjunction with 110/33kV power transformers.

1.2 Standards

The transformers shall in general comply with the requirements and related documents below. Where any provision of this NIE Networks specification differs from those listed, the provision of this specification shall apply.

1.2.1 European Standards

BS EN 50181 Plug-in type bushings above 1kV up to 36kV and from 250A up to 1.25kA for equipment other than liquid filled transformers

BS EN 60071-1: Insulation Co-ordination. Definitions, principles and rules

BS EN 60071-2: Insulation Co-ordination. Application guide

BS EN 60076-1: Power Transformers. General

BS EN 60076-2: Power Transformers. Temperature rise.

BS EN 60076-3: Power Transformers. Insulation Levels, dielectric tests and external clearances in air.

BS EN 60076-4: Power Transformers. Guide to the lightning impulse and switching impulse testing. Power transformers and reactors.

BS EN 60076-5: Power Transformers. Ability to withstand short circuit.

BS EN 60076-10: Power Transformers. Determination of sound levels.

BS EN 60137: Insulated bushings for alternating voltages above 1000V.

BS EN 60214-1: Tap changers. Performance requirements and test methods.

BS EN 60529: Specification for degrees of protection provided by enclosures. (IP code)

BS EN 60567: Oil-filled electrical equipment. Sampling of gases and of oil for analysis of free and dissolved gases. Guidance.

BS EN 60599: Mineral oil impregnated electrical equipment in service. Guide to the interpretation of dissolved and free gases analysis.

BS EN 61672: Electroacoustics. Sound level meters.

BS EN 60296: Fluids for electrotechnical applications. Unused mineral insulating oils for transformers and switchgear.

BS IEC 60076-7: Power transformers. Loading guide for oil - immersed power transformers.

BS EN ISO 1461: Hot dip galvanized coatings on fabricated iron and steel articles. Specification and test methods.

BS EN ISO 12944-1: Paints and varnishes. Corrosion protection of steel structures by protective paint systems. General introduction.

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BS EN ISO 9001: Quality management systems. Requirements.

BS EN ISO 1461: Hot dip galvanized coatings on fabricated iron and steel articles. Specifications and test methods.

BS EN ISO 12944: Paints and varnishes. Corrosion protection of steel structures by protective paint systems.

BS EN ISO 14713: Zinc coatings. Guidelines and recommendations for the protection against corrosion of iron and steel in structures.

1.2.2 International Standards

IEC 60289: Reactors

IEC 60296: Fluids for electrotechnical applications. Unused mineral insulating oils for transformers and switchgear.

IEC 60076-8: Power transformers. Application guide.

IEC 60542: Application guide for on-load tap-changers

IEC 60616: Terminal and tapping markings for power transformers

IEC 60076-4: Power transformers. Guide to the lightning impulse and switching impulse testing. Power transformers and reactors.

IEC/ 60815: Selection and dimensioning of high – voltage insulators intended for use in polluted conditions – Part 2: Ceramic and glass insulators for a.c. systems.

IEC 60997: Determination of polychlorinated biphenyls (PCBs) in mineral insulating oils by packed column gas chromatography (GC)

1.2.3 British Standards

BS 148: Reclaimed mineral insulating oil for transformers and switchgear. Specification.

BS 381C: Specification for colours for identification, coding and special purposes

BS7870 - 4.10 Specification for distribution cables with extruded insulation – Single core 11kV and 33kV Cables

1.2.4 NIE Networks Specifications

211-03 Ancillary Electrical Equipment

1.3 Service Conditions

The transformers will be located outdoors in an electrically exposed location less than 1,000 metres above sea level, in a salty atmosphere with high humidity.

The following ambient temperature conditions detailed in Table 1 shall apply:

Environmental conditions Value

Minimum temperature -25C

Annual average temperature +20C

Maximum temperature +40C

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Maximum daily average temperature +30C

Table 1: Environmental conditions

1.4 System Conditions

110kV Network Nominal voltage: 110kV

Highest system voltage: 123kV

3 phase, 50Hz, with neutral point directly earthed

33kV Network Nominal voltage: 33kV

Highest system voltage: 36kV

3 phase, 50Hz, earthed through earthing transformer

Network short circuit levels and duration

3 phase single phase duration

110kV network 40kA 40kA 3 secs

33kV network 31.5kA 10kA 3 secs

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2 Electrical Characteristics (Refer to technical contents for specifics)

2.1 Type

The transformer shall be three phase 50Hz, oil immersed.

2.2 Rated Power

2.2.1 The transformer shall have a continuous rating of 200kVA unless otherwise specified by NIE Networks. 2.2.2 The transformer shall be capable of supplying its rated power continuously with maximum voltage on the high voltage winding. 2.2.3 The transformer shall be capable of supplying its rated power continuously under the stated ambient temperature conditions, without the temperature rise of the top oil exceeding 60K, and without the temperature rise of the windings, as measured by resistance, exceeding 65K. The temperature rise on any part of the tank up to 2.6m above the ground level, when operating at rated power, shall not exceed 60C. Above 2.6m, it shall not exceed 80C.

2.3 Voltage ratio

The no-load voltage ratio shall be 33,000/400 Volts.

2.4 Winding Connection and vector group

The transformer shall be connected as follows:

H.V. Winding: Zig-zag connected.

L.V. Winding: Star connected.

Vector Group: ZN, yn1 also with links for alternative yn11 connection.

Links for alternative yn11 reconnection shall be provided and all such links shall be easily accessible through inspection openings in the tank cover. The links and their fastenings shall be CAPTIVE.

2.5 Insulation Levels

The complete transformer arranged for service shall be designed and tested to the following insulation levels, detailed in Table 2, in accordance with BS EN60076 Part 3:

Line Terminals HV Neutral

Nominal voltage 33kV 400V -

Highest voltage for equipment 36kV - -

Min Induced Overvoltage withstand (kV rms) 70kV 2.5kV -

Min Lightning Impulse Voltage withstand (kVp) 170kV - -

Min separate source power frequency voltage withstand (kV rms) - - min 38

Table 2 Insulation levels

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2.6 Impedance voltage

The design impedance voltage shall be 4.75%.

2.7 Zero sequence impedance using low and high impedance earthing transformers

The zero sequence impedance shall be such that it will limit the earth fault current flowing in the HV neutral to 750 amps. This can be accomplished in one of three ways as described in 2.8.1, 2.8.2 and 2.8.3.

2.7.1 Typical low zero sequence impedance, earthing transformer complete with external neutral earthing resistor. (For asset replacement requirements only).

2.7.2 High impedance earthing transformer design with magnetically shielded neutral coupler connected to the LV winding. The neutral coupler is an interconnected star winding.

2.7.3 High impedance earthing transformer design with magnetically shielded 200kVA Delta/Star auxiliary transformer providing the function of the LV winding.

Tolerances shall be +20% to 0%.

Explanatory Note – During earth faults, zero sequence stray magnetic flux within the core of high impedance earthing transformers can induce an overvoltage upon the LV windings if wound upon the same magnetic core. The neutral coupler and the auxiliary transformer are known solutions to this problem.

Either the neutral coupler or auxiliary transformer, may be in the same tank as the 33kV earthing transformer but it must be magnetically shielded from it.

High impedance earthing transformers must include type tests which prove the neutral coupler or auxiliary transformer prevent overvoltages appearing on the LV winding during 33kV earth faults. The manufacturer shall propose type tests for approval by NIE Networks.

2.8 Short Circuit Performance

The transformer shall be capable of withstanding for 3 seconds a metallic short circuit on the terminals of LV winding with rated voltage on the HV winding. The HV winding shall be capable of withstanding without damage for 3 seconds the maximum single phase to earth short circuit on the HV terminals.

The transformer shall be capable of withstanding for 30 seconds the earth fault current in clause 2.7. For earthing transformer design using an external NER, the transformer is also to be capable of carrying for 5 seconds the maximum value of earth fault current that would flow if the NER is replaced by a short circuit.

2.9 Over-fluxing

The transformer shall be designed and guaranteed to meet the following overfluxing requirements while carrying the rated current without exceeding the temperature rise specified in section 2.2.3.

Continuous : 110% of rated volts/Hz

1 minute : 125% of rated volts/Hz

10 seconds : 140% of rated volts/Hz

2.10 Over-loading

The transformer shall be designed so that over loading in accordance with IEC 60076-2 is possible.

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2.11 Losses

The design of the transformer shall be such that it complies with the requirements of Commission Regulation (EU) No 548/2014 Table 1.1. The no-load and load losses shall be stated in Schedule D.

3 Design and Construction

3.1 Quality Systems

The supplier shall be accredited to BS EN ISO 9001 or submit satisfactory evidence to demonstrate that their quality system and inspection procedures are such as to ensure compliance with this standard.

3.2 Tanks and Accessories

3.2.1 General

The tank construction shall be such as to prevent water from lodging on it.

3.2.2 Tank vacuum/pressure

The Tender shall state the maximum vacuum/internal pressures which the main tank is designed to withstand.

3.2.3 Conservator

The transformer shall be provided with a conservator tank that has an appropriate oil level gauge, which shall be so located that a person standing at ground level can easily read it. The range of indicated oil level shall correspond to average oil temperatures from -10oC to 80oC and the position for the oil level at 15oC shall be indelibly and clearly marked, bearing the inscription '15oC Oil Level'.

3.2.4 Gas operated relay

A double float gas relay with 2 x trip and 1 x alarm contacts shall be provided in the pipe connection from the main tank to the oil conservator tank. This relay shall be such that a slow release of gas closes an alarm circuit while a sudden pressure rise results in the operation of an alarm and trip circuit. NIE Networks will require evidence that the particular equipment is suitably adapted and rated for the transformer offered.

3.2.5 Gas sampling device

The gas release connection from the gas relay shall be brought down to a gas sampling arrangement, which shall be accessible to a person standing at ground level.

A relay test connection from the gas relay shall be brought to the gas sampling device, if suitable, or may be terminated beside it.

Isolating valves shall be provided in both the gas sampling and test connections. These valves shall be accessible to a person standing at ground level.

The gas sampling device shall have the following facilities:

(a) Gas connection from the Gas relay through an isolating valve on the gas sampling device

(b) Coupling in the pipe connections to enable the device to be removed from the transformer.

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(c) Gas sampling valve at the top, with outlet approximately 3mm diameter to make rubber tube connection. The outlet shall have a captive screwed cap.

(d) Oil drain valve at the bottom with blanking plug.

(e) The oil level in the device shall be visible from the front.

3.2.1 Breathers

The conservator tank shall be fitted with an approved desiccant breather. The breather shall be located at ground level.

3.2.2 Pressure relief device

A pressure relief device with 1 x alarm and 2 x trip contacts, which are set to open on excess pressure, and to reseal automatically shall be fitted to the main tank. It shall be located to ensure that discharge is directed towards the ground so as not to cause danger to personnel.

3.2.3 Oil Filtration

The transformer shall be fitted with 25mm combined drain and filter valves.

A 25mm bore filter valve shall be fitted to the tank.

3.2.4 Lifting lugs

Lifting lugs shall be provided for supporting the weight of the transformer including core, windings, fittings and with the tank filled with oil.

3.2.5 Earthing Terminals

Earthing terminals shall be provided close to each of the four corners of the tank to facilitate earthing of the transformer by NIE Networks using two copper lugs each having 14mm holes for fixing bolts.

3.2.6 Oil Valves

All oil valves shall be lockable in the open and closed positions. The use of loose fittings to lock valves in the open or closed positions, other than a pad lock, is not acceptable.

They shall clearly indicate whether they are in their open or closed positions and shall be fitted with appropriate blanking plates.

All oil valves shall be made of brass or otherwise protected against corrosion to NIE Networks' approval.

3.2.7 CT mounting arrangement

Provision shall be made on the earthing transformers for the mounting of an outdoor, cast resin primary bar type CT for restricted and standby earth fault considerations. The CT shall be supplied by others.

The mounting plate shall be drilled with 4x15mm diameter holes on the corners of a 90x140mm rectangle. (140mm dimension on the vertical). The mounting arrangement shall be in a suitable position to connect between the CT and the HV (33kV) neutral.

3.3 Transformer Oil

The insulating oil shall be Class 1 mineral oil to BS 148/BS EN 60296. The complete first filling shall be new oil provided by the Supplier. If an anti-oxidant is recommended, its use shall be subject to NIE Networks approval.

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The oil shall not include polychlorinated biphenyls (PCB), polychloroterphenyls (PCT) or polychlorobenzyltoluene (PCBT). The material used for the transformers, such as insulating materials, varnishes, paints etc. shall also not contain PCB, PCT or PCBT. The concentration of PCB shall be less than the detection limit of the measurement method specified in IEC 60997.

NIE Networks may require evidence that the oil is not contaminated by PCB.

If an anti-oxidant is recommended, its use shall be subject to NIE Networks' approval.

3.4 Bushings, cable boxes and terminals

3.4.1 General

The high voltage windings and phases shall be routed via a disconnection chamber to a cable termination chamber. The cable termination chamber and disconnecting chamber may be combined. Alternatively outdoor bushings may be provided as specified in Schedule A.

The HV neutral shall be brought out through a fully rated outdoor porcelain bushing.

3.4.2 Bushings

Were outdoor bushings are specified they shall comply with BS EN60137, be fully rated and preferably have alternate long-short profile porcelain sheds. The minimum nominal creepage distance for the insulator between phase and earth shall be in accordance with IEC 60815 for the case of heavy pollution levels. (Based on nominal specific creepage distance of 25mm/kV, system highest voltage of 36kV and the appropriate shed diameter factor, kD.)

If HV bushings are oil filled they shall be fitted with oil-level gauges, clearly readable from ground level. All bushings shall be mounted on turrets.

The HV bushings shall be 36kV insulated.

The colour of the bushings is to be grey.

3.4.3 Cantilever Operating Loads

Bushing cantilever operating loads are to be to level II of BS EN 60137, clause 4.5 and table 1.

3.4.4 Clearances

Where outdoor bushings are specified, the minimum design clearances (in accordance with BS EN 60076-3) and creepage distances (in accordance with IEC/ 60815 for heavily polluted conditions) are:

33kV System

(a) Phase-to-phase 630mm (b) Phase-to-earth (steelwork or transformer) 500mm (c) Creepage distance - 900mm

Neutral Bushing

Creepage distance 450mm

N.B. NIE Networks require the above minimum clearances to meet the requirements of NIE Networks safety rules and UK standards whilst allowing for an increase of electrical clearances for the fitting of bus bar clamps.

The earthing transformer shall be installed on a plinth such that if outdoor air insulator bushings are provided, the height from ground level to the nearest live point on the HV bushing shall be a minimum of 3.2 metres.

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3.4.5 Cable Boxes

Where the HV cable termination chamber option is selected in Schedule A, then the HV cables shall be terminated in a combined cable termination/disconnection chamber. The cable termination bushings provided within the chamber shall be in accordance with BS EN50181, inside cone, size 3 and shall be suitable for size 3; Pfisterer Connex plugs (typical arrangement as shown in Diagram 1). The supplier shall provide suitable stainless steel base plates for the inside cone bushings, complete with fixings, to permit the connection and disconnection of the HV cable plugs. (a typical arrangement is shown in Diagram 2)

NIE Networks use 1 x single core 240sqmm2 XLPE copper cable per phase. The cable is generally in accordance with BS7870-4.10. The position of the cable termination chamber should take account of the bending radius of this cable and all supporting steelwork and clamps suitable for 46mm diameter cable shall be provided by the supplier.

Earthing in the form of copper bus bar shall be provided close to the cable terminations for terminating the cable screen wires using flat palm cable lugs. The lugs used by NIE Networks have M12 clearance holes and the earth bar should be drilled to suit. There shall be one earthing point per cable. All the necessary nuts, bolts, washers and split washers shall be provided.

3.4.6 Terminals

The HV neutral terminal shall be round copper as follows:

33kV Bushing 40mm diameter x 150mm long

The LV terminal arrangement shall comprise an approved type three-pole, air-break, weatherproof combined switch-fuse unit incorporating a bolted neutral link and a gland entry for 4-core cable.

3.4.7 Terminal Markings

The HV bushings shall be identified in accordance with NIE Networks practice as follows:

An observer facing the HV side of the transformer shall read from left to right

HV Terminals L1, L2, L3

LV Terminals l1, l2, l3

These markings shall be clearly and permanently shown on the cover plate and on the side walls of the main tank below each bushing location and also to the left hand side of the LV cable boxes.

3.4.8 400 Volt LV Cable Isolator Box

The LV cable box shall be constructed from stainless steel over painted. It shall include for a fuse/isolator unit suitably rated for the full load current of the transformer. The isolator switch shall be operated externally of the cable box and be padlockable in the open and closed positions. The door of the cable box shall open only with the isolator switch in the off position.

3.5 Noise and vibration

3.5.1 Transformers and auxiliary plant shall be designed and manufactured to reduce noise and vibration.

The sound pressure level of transformers shall not exceed 59 dB(A). All measurements shall be guaranteed by the Supplier and shall be taken in accordance with BS EN 60076-10.

3.5.2 To minimise the affects of ground and structure borne vibration, anti-vibration mountings shall be provided between the transformer base and the foundations. The mounting arrangement shall:

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(i) Take cognizance of the irregularities in the tank under-base and the plinth surface,

(ii) be of an oil and weather resisting material comprising either a rubber or other approved compound, capable of operation at temperatures between minus 10oC and 80oC,

(iii) have a total unloaded depth (excluding load spreader plates) not exceeding 40mm,

(iv) at 100Hz, have an attenuation of at least 32 dB (assuming an infinite ground impedance value) when loaded, at room temperature, to the same pressure as in service.

3.6 Labels and rating plates

3.6.1 General

All markings including labels, rating and diagrams plates and instructions shall be clear, indelible and in English. Cast-in or moulded words other then in English shall be covered with a permanently fixed non-ferrous label inscribed in English. Painted markings are not acceptable.

3.6.2 Rating plate

A rating plate in accordance with BS EN 60076 shall be fitted. The plate shall be so designed that by means of a hinged section or otherwise, the connection diagram for each alternative vector group is displayed when the links specified in Clause 2.4 previously are positioned as appropriate.

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4 Cleaning and Painting

4.1 General

Transformers may be exposed to coastal atmospheric conditions and therefore must be able to resist the corrosive effects of the environment.

All fixings and fastenings used in the fabrication of the transformer shall be of suitable material or treated to the same performance level as the tank to prevent corrosion, having regard for the corrosion effects of different adjacent materials.

The painting and corrosion protection system proposed by the Manufacturer is subject to approval by NIE Networks. A full description of the proposed system shall be given including surface preparation, rust inhibition, paint thickness, treatment of bolts, nuts, threads etc.

4.2 Surface Preparation

Prior to coating, all surfaces shall be thoroughly cleaned of scale, rust and foreign matter by shot blasting or other method approved by NIE Networks, and all rough surfaces shall be carefully filed.

4.3 Coating Systems

The treatment and protective coating of the transformer shall comply with BS EN ISO 12944 and BS EN ISO 14713. The coating shall be according to the 'Long' category, typically 10 - 20 years as defined in Section 2, 'Life required of coating'.

As defined in Table 1 of BS EN ISO 12944-2, 'Atmospheric-corrosivity categories and examples of typical environments', the category shall be 'coastal and offshore areas with high salinity'.

4.4 Paint Finish

The final colour of the transformer shall be Cement Grey, RAL colour 7033.

4.5 Inspection

Inspection shall be carried out in accordance with BS 5438 Section 4 Table 8 and clear and adequate records of inspection as defined in paragraphs 39-43 shall be provided.

4.6 Other requirements

Radiators shall be hot dip galvanised in accordance with BS EN ISO 1461.

The interior of the conservator and any tank internal surfaces above oil level shall be given a coat of oil-resisting paint and varnish.

Fixing studs for access covers shall be coated with a wax based rust inhibitor paint to facilitate cover removal.

The interior surfaces of the control cubicle and all air-filled chambers shall receive a minimum of one priming coat, an undercoat and a finishing coat of paint applied to the thoroughly cleaned metal. The final coat shall be of a light coloured anti-condensation finish.

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5 Tests

5.1 General

Tests shall be carried out on each transformer in accordance with BS EN 60076 and as specified in the following clauses. NIE Networks shall have the right to reject a transformer if test results do not comply with the standards/values specified and information/data preferred in the tendered schedules.

Before and after acceptance testing, samples of oil shall be taken from the transformer and analysed for dissolved gases using the procedures specified in BS EN 60567 and BS EN 60599. Results of the analysis of gases dissolved in the oil shall be included in the Acceptance Test Report.

5.2 Type Tests

The following shall be regarded as type tests and shall be carried out on one transformer.

(a) Test of temperature rise to BS EN 60076-2. This test shall be carried out on the tap having maximum losses.

(b) Measurements of open circuit and short circuit zero sequence impedances of the HV and LV windings at 10% of rated current to BS EN 60076-1.

(c) Impulse test to BS EN 60076-3 clause 13.

(i) Full wave impulse voltage withstand test. The test voltage shall be applied to each HV line terminal. The applied voltage shall be the relevant lightning impulse voltage specified in Clause 2.5: Insulation Levels.

(ii) Chopped wave impulse voltage withstand test. The test voltage shall be applied to line terminals only. The applied voltage shall be 100% of the relevant lightning impulse voltage specified in Clause 2.5: Insulation Levels.

Tests (i) and (ii) shall be combined in a single sequence as follows:

- One reduced full impulse (calibration).

- One 100% full impulse.

- One or more reduced chopped impulse(s).

- Two 100% chopped impulses.

- Two 100% full impulses.

(d) Noise level measurement, in accordance with BS EN 60076-10 using a precision sound level meter conforming to BS EN 61672.

5.3 Routine Tests

The following shall be regarded as routine tests and shall be carried out on each transformer.

Routine test Relevant Standards

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Measurement of winding resistance BS EN60076-1

Measurement of voltage ratio BS EN60076-1

Voltage vector relationship BS EN60076

Measurement of impedance voltage at all taps BS EN60076

Measurement of short circuit impedance BS EN60076

Measurement of load loss BS EN60076

Measurement of no-load loss & current including harmonics BS EN60076

Induced overvoltage power frequency withstand BS EN 60076-3

Separate source power frequency withstand BS EN 60076-3

Switching impulse test BS EN 60076-3

Partial discharge measurements BS EN 60076-3

Applied voltage to all auxiliary circuits BS EN 60076-3

Tests on bushings BS EN60137

Tests on painting and galvanizing BS EN ISO 12944

Measurement of acoustic sound level BS EN 60076-10

Notes on Routine tests:

1. Induced overvoltage, separate source voltage, and switching impulse tests shall be

carried out in accordance with BS EN 60076-3 at levels specified.

2. Partial discharge measurements shall be made at line terminals of each phase of the transformer during induced overvoltage routine tests. This test shall be carried out using a broadband instrument. The voltage time envelope shall be as described in Clause 11.3 of BS EN 60076-3.

3. Noise level measurement to be in accordance with BS EN 60076-10 using a precision sound level meter conforming to BS EN 61672.

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5.4 Site Tests

If the contract includes the complete range of site work the following tests on site shall be carried out after the plant is fully assembled:

Site Tests

Ratio and vector group checks.

Insulation resistance (between windings and windings to earth).

Oil tests including moisture content and breakdown voltage.

The Supplier shall provide all necessary test equipment and personnel under the contract, shall be responsible for calibration of instruments, where required, and shall supply to the Purchaser three copies of the reports of site tests.

Should the contract exclude assembly of the transformer on site by the supplier, the above tests will be carried out by NIE Networks' Staff under the general direction of the Supervisor mentioned in Clause 6.2.

5.5 Test Certificates

Routine, type and special test certificates shall be forwarded to the Asset Management Operational Manager, NIE Networks Ltd, Fortwilliam House, Edgewater Road, Belfast BT3 9JQ, Northern Ireland.

Test certificates shall include relevant details and calculation methods. In the case of lightning impulse tests, copies of the response shall be attached and in the case of temperature rise tests, the extrapolation curve shall be provided.

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6 Documentation

6.1 Drawings

6.5.1 The following drawings and information shall be submitted with the tender. In addition all drawings will include the equipment serial number and contract number.

(a) Overall dimensioned drawings of the transformer.

(b) Dimensioned drawings of the main unit arranged for transport.

(c) Winding disposition for the transformer.

(d) Over-excitation curve.

(e) General description of cubicle, dial thermometers, buchholz and gas-pressure relays, breathers, etc.

(f) Detailed specification of the transformer oil including oxidation inhibitor if recommended.

(g) Details of surface treatment.

(h) Outline transport plan.

(i) Statement of acceptance of guarantee.

(j) Financing details, if applicable.

(k) Reference list with particular emphasis on units of similar design and rating.

6.5.2 The following shall be submitted within one month of the Award of Contract.

(a) A complete set of final dimensioned drawings for the transformer including details of bushings, LV terminal box, etc.

(b) Pamphlets describing the bushings and auxiliary equipment such as Buchholz relays, dial thermometers, etc.

(c) Detailed schedule, listing all temperature protection/alarm devices.

(d) Detailed dimensioned drawings to enable NIE Networks to design and construct the required foundations for the transformer.

6.5.3 Record folders

With delivery of the transformer, the Supplier shall supply three bound record folders of the technical particulars relating to it. Each folder shall contain the following information:-

(a) Technical data.

(b) Test Certificates.

(c) General descriptions.

(d) Operation and maintenance instructions.

(e) Main drawings.

(f) Pamphlets describing auxiliary equipment such as Buchholz relay, etc.

(g) The O & M manuals shall also be sent on a CD in portable document format (pdf).

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6.2 Assembly, Operation and Maintenance Instructions

6.2.1 The transformer shall be installed on a foundation prepared by NIE Networks in strict accordance with drawings provided by the Supplier.

6.2.2 The transport to site and placing on foundations, which the Contract includes, shall be carried out by the Supplier's skilled staff, or by NIE Networks under the Contractors Supervision.

6.2.3 Site staff shall observe NIE Networks’ safety rules at all times.

6.2.4 All equipment used for oil-handling shall be, to NIE Networks' satisfaction, certified free from PCB.

6.2.5 The Supplier shall fully inform himself of all the requirements and available facilities in regard to transport, route planning, loading/unloading, etc. An outline transport plan shall be submitted with tender. One month prior to shipping the Contractor shall submit his transport plan to NIE Networks.

6.2.6 All transport accessories shall become the property of Northern Ireland Electricity Networks Ltd.

7 Quality Assurance

7.1 Quality System and Inspection

The successful Tenderer shall submit a detailed programme covering the design, manufacture and testing of the transformer within one month of receipt of NIE Networks’s official order.

He shall subsequently submit reports as requested by NIE Networks outlining progress and if necessary explaining deviations from programme. NIE Networks shall have the right, subject to prior arrangement, to inspect progress on the order at the Supplier's works.

8 Delivery and Service

8.1 Packing, Despatch and Delivery

Accessories shall be packed in non-returnable cases or crates with protection against damage by water, transport and outdoor storage. Each case shall have a detailed packing note and be clearly marked on the adjacent sides and top with NIE Networks' order number, transformer serial number and gross weight. Certain packing materials such as straw, peat-moss litter, grain, etc., are prohibited by Government regulation. Goods packed in prohibited material will be refused.

8.2 Spare Parts

The Supplier shall give an assurance that spare parts will continue to be available throughout the life of the transformer. A comprehensive list of recommended spare parts shall be included in the attached schedule.

The spare parts recommended shall be clearly identified on drawings which shall be included with the Tender. Spare parts shall be delivered suitably packed and treated for long periods in storage. Each packing shall be clearly and indelibly marked with its contents including a designation number corresponding to the spare parts list in the maintenance instruction.

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9 Schedule of Requirements

SCHEDULE A

(to be completed by Purchaser)

General particulars of definite work

1

2

3

4

5

6

7

8

Section(s) for purposes of payments and taking over

Site of Station

Number of Units required

Continuous maximum rating kVA

Rated higher voltage between phases kV

Rated lower voltage between phases V

Zero sequence impedance using low and high impedance earthing transformers

HV termination details:

State whether outdoor bushings or cable box option

NIE Networks’ Serial No.(s)

A

Various

Substations

16

200

33

400

Either option 2.7.1, 2.7.2 or 2.7.3 to be supplied

cable box

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SCHEDULE B


Commencement date and dates of readiness for inspection, testing, delivery, access to site and completion of definite work

Commencement Date

1

2

3

4

5

Section(s) for purposes of payment(s) and taking over

Site of Station

Times from Commencement Date:

Within which detailed drawings shall be submitted for approval

Calendar Months

Within which the material shall be ready for inspection and testing

Calendar Months

Within which the Contractor will require access to the site

Calendar Months

Within which the material shall be delivered to site

Calendar Months

Within which the works shall be completed, tested and ready for continuous use

Calendar Months

A

Various Substations

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SCHEDULE C


Access facilities to the site

1

2

3

4

5

6

7

8

Section

Site of Station

Ordnance Survey Grid Reference (O.S. NORTHERN IRELAND 1:50000 Sheet )

Whether direct road access is available to site

Approximate distance from the site to the

nearest road

Whether transport by rail is required

Whether there is a railway siding near

to the site

Whether there are any known transport

restrictions in the immediate locality of

site

A

Various Substations

Yes

Adjacent

No

No

None

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SCHEDULE D

(to be completed by Supplier)

Guaranteed rated values and characteristics

Manufacturer ................................................................................................

1. Maximum continuous ratings in kVA

ONAN ..............................................

Can the transformer, bushings and connections be safely overloaded in

accordance with latest edition of BS IEC 60076-7? .......................................

Rated short-time (30 sec) current through the neutral of the HV windings is not less than 750A?

…………………………………

2. Losses in kW

No-Load Loss ..........................................

Load-Loss at 75C ..........................................

3. Impedance voltage, no-load ratio and nominal current

IMPEDANCE NO-LOAD RATIO NOMINAL

VOLTAGE % (..../ kV) CURRENT

.................. .................. ...................

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4. Zero sequence impedance

SHORT OPEN

CIRCUIT CIRCUIT

Zero sequence impedance in ohms

HV Winding ............... ...............

LV Winding ............... ...............

Value of neutral earthing resistor (NER) ohms ………...

5. Core

Maximum permissible overfluxing expressed as a percentage of rated volts/Hz, on any tap.

NO-LOAD FULL-LOAD

Continuously ................. ..................

For 1 minute ................. ..................

For 10 seconds ................. ..................

6. Noise level

Guaranteed noise levels according to BS EN 60076-10 ..................................dB(A)

7. Oil

Supplier and type ...................................

Specification ...................................

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Method of delivery to site ...................................

Is an oxidation inhibitor

recommended? ...................................

Recommended concentration ...................................

8. Bushings

HV LV NEUTRAL

Manufacturer ......... ......... .........

Type Number ......... ......... .........

Creepage distance to earth ......... ......... .........

Electrical clearance to earth ......... ......... .........

Current Rating (Amps) ......... .......... …......

Cantilever operating load (kN) ......... .......... …......

9. Impulse tests

Are the standard wave-shapes obtainable

on all terminals? .........................................

If not, what wave-shapes are to be

expected? ........................................

10. Pressure relief devices

Maker/Type ...............................

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Number off ...............................

11. Short circuit withstand capability

HV for 3 seconds ..............................................................

HV for 30 seconds ..............................................................

LV for 3 seconds ..............................................................

12. Weights

Core and windings .............................kg

Oil in the complete transformer .............................kg

Complete transformer ready for service .............................kg

Transport unit .............................kg

13. Details of surface treatment

...........................................................

...........................................................

...........................................................

...........................................................

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...........................................................

14. Transport dimensions

Transport unit length .............................mm

Transport unit width .............................mm

Transport unit height .............................mm

15. Overall dimensions

Length overall .............................mm

Width overall .............................mm

Height overall .............................mm

Signed: ..............................................

For and on behalf of:

Date:

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SCHEDULE E


Prices and delivery

*State currency

*Firm Price

transformers each rated 200 kVA complete

with oil etc. in accordance with this Specification

and including all routine tests specified. ...........

Cost including transport, delivery, and

placing on prepared foundation and

supervision of assembly and testing on site. ...........

Extra cost of providing all appropriate

staff, cranes, etc. required for

assembly and site testing of two

transformers ...........

Extra cost of type test on one unit ...........

Tender valid until ...........

Signed : ..............................................

For and on behalf of : ................................

Date : ................................................

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SCHEDULE F


Price schedule of recommended spare parts

* State currency

Quantity Description *Total

Price

Signed : ..............................................


Date : ................................................

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SCHEDULE G


Schedule of deviations from specification

Signed : ..............................................


Date : ................................................

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200-25v4-33kv earthing transformers for use with 1 - nie

Documents