GGSS1074 Rev 14.1 Gen Trfr Specification

8/18/2019 GGSS1074 Rev 14.1 Gen Trfr Specification

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@Eskom

Generation

GROUPORBU

GENERATION

REFERENCE

GGSS 1074

REVISION

14.1

DOCUMENT TYPE

Specification

DATE

February 2008

TITLE

SPECIFICATION FOR LARGE POWER GENERATOR

TRANSFORMERS IN POWER STATIONS

PAGE 1 OF

146

THIS DOCUMENT HAS BEEN SEEN AND ACCEPTED BY:

All Power Station Electrical Engineering Managers:

ll GEe Members

~

- --

LP or

AUTHORIZE,9...BV

~ . . . . . - 7 I l i A - : : : : : - - / - . . . . .

GJ C l 'OTpOrate

\ Consultant)

REVISION

DESCRIPTION OF REVISIONS AUTHORISED DATE

Extensive update

2

3

GIC and various other requirements added (Sept 2004

GIC Update section 4.1.2, schedules AB2.1 0 and section 4.30.2.1

G.J.C

February 2008

4

~ e c t i o n

4.11.2 added locating of blocks. Section 4.17 New paint specification included &

5

~ e c t i o n 4.33 Guarantee requirements added. '

6

~ n t a n k e d Current, Special OD cooling and Emergency cooling tests added to section

7 ~ 2 5 6

~ c h e d u l e

AB transferred to excel spreadsheet. Manufacturers design limit section added

8

AB.10)

pesign flux Density Definition changed (AB 8.8); Core Bolt design option removed; Core

PD

cooling requirement added; Heat Run DGA requirements added; Self Protection

lause added; Heat Run Gassing requirements added; Oil Quality test added; Assembled

9

ransport section added

Harold Moore recommendations added: Design review requirements added to section

4.24.2.2 (b); Iso-phase temperature section added to Schedule AB.25; Partial discharge

acceptance criteria lowered section 4.25.13.2 (a); Temperature rises for transformer metal

10

parts added to section 4.1.1.

Delivery delay statistic section added to schedule AB item AB.47; Transport section

11 updated.

Definition section 3 updated. Thermoplastic resin performance criteria added to section

12

4.1.1. Free Buckling design criteria added to section 4.2. Limited transient transfer option

added to Schedule AB.31.21

ap- Changer 20 overload requirement added to section 4.15.3.1 (a). Schedule AB item

Io-B.23.13.3 tap-changer overloading requirement added.

13

Permissible gas increase table

11

added to section 4.25.6; Loading diagram requirement

or manual added to section 4.26.1.2. Double trip contact Buccholz and 4 micro switch

emperature instrument requirements added to Schedule AB.

14

Nuts and Bolts section added 4.17.4.4; Auxiliary quality of supply text added to section

and Schedule AB, item AB.36 updated; Oil Sampling device Section 4.18.3 edited

o allow for different devices. Schedule AB, item AB.28.2 (Site tests) edited to include

~ d d i t i o n a l

tests. AB.31 edited to make provision for a

COCo

14.1

~ e t a l

parts temperature rise change; additional site tests; test bushings to allow for SFRA

ests while intransit included (4.9.1); packaging requirements for auxiliary items; tanks


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Table of Contents

CONTENTS PAGE

LIST OF TABLES ............................................................... ..................................................................... ....................IX

1. SCOPE ....................................................... ............................................................... ............................................. 10

2. NORMATIVE REFERENCES .................................................................... ....................................................... 10

3. DEFINITIONS.............................................................. .................................................................. ...................... 13

4. REQUIREMENTS...................................................... .................................................................... ...................... 13

4.1 R ATINGS AND OPERATING CONDITIONS ............................................................... ........................................... 13 4.1.1 Ambient Temperatures and Thermal Performance .............................................................. ........... 13 4.1.2 Geometrically Induced Currents.............................................................. ........................................... 14 4.1.3 Rated Power ............................................................... ................................................................ ........... 14 4.1.4 Current .............................................................. ............................................................... ...................... 14

4.1.4.1 Rated current .................... ...................... ....................... ....................... ...................... ..................... ..................... 14

4.1.5 Voltage .............................................................. ............................................................... ...................... 15 4.1.5.1 Rated voltage on principal tapping........ ....................... ....................... ....................... ..................... ..................... 15 4.1.5.2 Maximum continuous voltage on any tapping................................ ....................... ....................... ...................... .. 15 4.1.5.3 Maximum temporary overvoltage ...................... ....................... ....................... ....................... ....................... ...... 15 4.1.5.4 Overfluxing ...................... ...................... ....................... ...................... ....................... ..................... ..................... 15

4.1.6 Network frequency ............................................................... ................................................................ 15 4.1.7 Harmonics..................................................... ........................................................... .............................. 15

4.2 ABILITY TO WITHSTAND SHORT-CIRCUITS ............................................................ ........................................... 16 4.3 IMPEDANCE AND TOLERANCES ....................................................... ................................................................ 16

4.4 ACOUSTIC NOISE ........................................................ ............................................................... ...................... 16 4.5 INTERCHANGEABILITY .......................................................... ................................................................ ........... 17 4.6 CLEARANCES IN AIR ............................................................. ................................................................ ........... 17 4.7 PHYSICAL ARRANGEMENT ............................................................... ................................................................ 17

4.7.1 Bushings, cooler banks, conservator and maximum dimensions ................................................. 17 4.8 ERECTION........................................................ ................................................................ ................................ 18 4.8.1 General ............................................................. ............................................................... ...................... 18 4.8.2 Foundation tolerances and site details.............................................................. ................................ 19 4.8.3 Processing on site ................................................................ ................................................................ 19

4.8.4 Testing on site............................................................ ................................................................ ........... 20 4.8.5 Painting on site .......................................................... ................................................................ ........... 20

4.9 TRANSPORT ............................................................... ............................................................... ...................... 21 4.9.1 General conditions, blanking plates and gas filling .............................................................. ........... 21 4.9.2 Accelerometer limits............................................................. ................................................................ 22 4.9.3 Sea transport.............................................................. ................................................................ ........... 22 4.9.4 Road transport ........................................................... ................................................................ ........... 22


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4.10.6 Core cooling ............................................................... ................................................................ ........... 25 4.11 WINDINGS AND CONNECTIONS............................................................... ..................................................... 25

4.11.1 Connections ............................................................... ................................................................ ........... 25 4.11.2 Bracing of windings .............................................................. ................................................................ 26 4.11.3 Methods of making winding connections .......................................................... ................................ 26

4.11.3.1 Soldered and brazed connections... ...................... ....................... ...................... ....................... ...................... .. 26 4.11.3.2 Welded connections and joints in winding body............................ ....................... ........................ ................... 26 4.11.3.3 Bolted connections.................. ...................... ....................... ...................... ....................... ..................... .......... 26 4.11.3.4 Crimped connections and other methods .................... ........................ ....................... ....................... ............... 26

4.11.4 Winding terminations onto bushings....................................................... ........................................... 27 4.11.5 Insulation tests, fault and creepage levels for Bushings ................................................................ 27

4.12 OIL............................................................... ................................................................ ................................ 27 4.12.1 Type and quality ........................................................ ................................................................ ........... 27 4.12.2 Dielectric strength...................................................... ................................................................ ........... 28 4.12.3 Moisture content ........................................................ ................................................................ ........... 28

4.12.3.1 Insulation test blocks for moisture measurement ...................... ....................... ...................... ........................ .. 28 4.12.4 Oil-filling / impregnation under vacuum ............................................................. ................................ 28 4.12.5 Preparation for storage ........................................................ ................................................................ 29 4.12.6 Preservation system............................................................. ................................................................ 29 4.12.7 PCB content ............................................................... ................................................................ ........... 29 4.12.8 Contact with bare copper ............................................................... ..................................................... 29

4.13 M AIN TERMINALS .............................................................. ................................................................ ........... 29 4.13.1 Position of open terminals.............................................................. ..................................................... 29

4.13.1.1 HV and LV terminals...... ....................... ...................... ....................... ...................... ..................... .................. 29 4.13.2 Terminal markings ................................................................ ................................................................ 31 4.13.3 Bushings ........................................................... ............................................................... ...................... 31

4.13.3.1 Terminals ..................... ...................... ....................... ...................... ....................... ..................... ..................... 31 4.13.3.2 Short-time current ...................... ...................... ....................... ...................... ...................... ....................... ...... 31 4.13.3.3 Insulation levels and creepage distances...... ....................... ...................... ....................... ...................... .......... 31 4.13.3.4 Bushing types......... ...................... ....................... ...................... ....................... ................... ....................... ...... 32

4.13.3.5 Minimum insulation, spacing and terminals for bushings on transformers of 5 MVA and above ................... 32 4.13.3.6 Gauge glasses.............. ....................... ...................... ....................... ...................... ...................... ..................... 32 4.13.3.7 Test tappings ...................... ....................... ...................... ....................... ...................... ...................... .............. 32 4.13.3.8 Safe mounting height ...................... ...................... ....................... ...................... ..................... ....................... .. 33 4.13.3.9 Mechanical forces ....................... ...................... ....................... ...................... ..................... ....................... ...... 33 4.13.3.10 Oil filling plugs.................... ....................... ...................... ....................... ...................... .................... .............. 33 4.13.3.11 Oil sampling..................... ....................... ...................... ....................... ...................... ..................... ................. 33 4.13.3.12 Gaskets................ ...................... ..................... ...................... ...................... ...................... ....................... ......... 33 4.13.3.13 Tests.................... ...................... ...................... ..................... ...................... ...................... ....................... ......... 33

4.13.4 Cable sealing boxes and disconnecting chambers.............................................................. ........... 33

4.13.4.1 General............... ...................... ....................... ...................... ....................... .................... ...................... .......... 33 4.13.4.2 Construction of cable-box shells ...................... ...................... ....................... ...................... ....................... ...... 33 4.13.4.3 Filling orifice ................... ...................... ...................... ...................... ...................... ....................... ................. 34 4.13.4.4 Independent mounting.............................. ...................... ....................... ...................... ....................... .............. 34 4.13.4.5 Cable-entry and connections ..................... ....................... ...................... ....................... ...................... ............. 34 4.13.4.6 Armour cable clamps ...................... ....................... ...................... ....................... .................... ...................... ... 34 4.13.4.7 Single-core cables and cables with insulated sheaths................. ....................... ....................... ...................... .. 34 4 13 4 8 Oil t l l d b th 35


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4.14.6.2 Secondary connection wiring and termination........ ...................... ....................... ...................... ...................... 37 4.14.7 Protective current transformers ............................................................... ........................................... 37

4.14.7.1 Type ................... ....................... ...................... ....................... ...................... .................... ...................... .......... 37 4.14.7.2 Ratio........... ....................... ...................... ....................... ...................... ..................... ...................... ................. 37 4.14.7.3 Turns compensation .................... ...................... ....................... ...................... ...................... ...................... ...... 37 4.14.7.4 Required data .................... ...................... ....................... ...................... ....................... .................... ................. 37 4.14.7.5 Designation ..................... ...................... ....................... ...................... ....................... ...................... ................. 38 4.14.7.6 Current transformers for delta-connected windings ..................... ....................... ....................... ...................... 38 4.14.7.7 Winding temperature indication for delta windings... ....................... ....................... ....................... ................. 38 4.14.7.8 Type and accessibility............. ...................... ....................... ...................... ....................... ..................... .......... 38

4.14.8 Data for rating and diagram plates ......................................................... ........................................... 38 4.14.8.1 Terminal markings.................... ....................... ...................... ....................... ...................... ....................... ...... 39

4.15 VOLTAGE VARIATION AND CONTROL ...................................................... ..................................................... 42 4.15.1 Tapping ranges .......................................................... ................................................................ ........... 42 4.15.2 Off-circuit tapping switch ................................................................ ..................................................... 42 4.15.3 On-load tap changing equipment ............................................................ ........................................... 42

4.15.3.1 Ratings ..................... ...................... ....................... ...................... ....................... ..................... ....................... .. 42 4.15.3.2 Design of the tap-changer ...................... ....................... ...................... ....................... .................... .................. 43 4.15.3.3 Driving mechanism, control and indicating equipment........................ ....................... ....................... .............. 44 4.15.3.4 Mechanical tap position indicators....................... ....................... ...................... ....................... ...................... .. 47 4.15.3.5 Maximum and minimum tap position indicators................... ....................... ....................... ...................... ....... 47 4.15.3.6 Operation counters .................... ....................... ...................... ....................... ...................... ....................... ...... 48 4.15.3.7 Drawings and technical data ................... ....................... ...................... ....................... ........................ ............. 48 4.15.3.8 Tap position numbering ...................... ....................... ...................... ....................... .................... ..................... 48 4.15.3.9 Alarm, control and tripping contacts............ ....................... ...................... ....................... ...................... .......... 48 4.15.3.10 Standard on-load tap changer control schemes: minimum requirements for driving mechanisms:.................. 50

4.16 AUXILIARY SUPPLIES, TERMINAL BOXES, WIRING AND CABLING ...................................................... ........... 54 4.16.1 Auxiliary Supplies ...................................................... ................................................................ ........... 54 4.16.2 Terminal boxes .......................................................... ................................................................ ........... 54

4.16.2.1 Terminal boxes and covers............................ ...................... ....................... ...................... ...................... .......... 54 4.16.2.2 Venting and draining........................ ...................... ....................... ...................... .................... ....................... .. 54

4.16.2.3 Earthing terminal................................ ....................... ...................... ....................... ..................... ..................... 54 4.16.2.4 Spare terminals.......................... ....................... ....................... ...................... ...................... ....................... ...... 54 4.16.2.5 Incoming auxiliary circuits ....................... ....................... ....................... ....................... ..................... ............. 55 4.16.2.6 Provision for outgoing cables...................... ....................... ....................... ....................... ...................... .......... 55 4.16.2.7 Contactors ..................... ...................... ....................... ...................... ....................... .................... ..................... 55

4.16.3 Wiring ................................................................ ................................................................ ..................... 55 4.16.3.1 Insulation................................... ....................... ...................... ....................... ....................... ...................... ...... 55 4.16.3.2 Insulation test voltage ................... ....................... ...................... ....................... ...................... ....................... .. 55 4.16.3.3 Type of conductor ..................... ...................... ...................... ...................... ...................... ...................... ......... 55 4.16.3.4 Protection of external wiring.................... ....................... ....................... ....................... ..................... .............. 55

4.16.3.5 Fixing of wiring ....................... ...................... ....................... ...................... ..................... ...................... .......... 55 4.16.3.6 Termination of wiring ..................... ...................... ....................... ...................... ..................... ....................... .. 55 4.16.3.7 Identification of wiring ...................... ....................... ...................... ....................... ..................... ..................... 56

4.16.4 Auxiliary cabling......................................................... ................................................................ ........... 56 4.16.4.1 Cabling by the Contractor ...................... ...................... ...................... ...................... ...................... ................. 56 4.16.4.2 Cabling by the Employer ...................... ...................... ...................... ..................... ...................... ..................... 56 4.16.4.3 Identification of fuses........................ ....................... ...................... ....................... ...................... ..................... 57

4 16 5 Secondary terminals 57


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4.17.3.2 Requirements ................... ...................... ...................... ...................... ...................... ....................... ................. 61 4.17.4 Tank construction ...................................................... ................................................................ ........... 67

4.17.4.1 Shape...................... ...................... ...................... ...................... ..................... ....................... ....................... ..... 67 4.17.4.2 Cooling corrugations....................... ....................... ...................... ....................... .................... ....................... .. 67 4.17.4.3 Guides for core and winding assembly ..................... ...................... ...................... ...................... ..................... 67 4.17.4.4 Bolts and Nuts........... ...................... ....................... ...................... ....................... .................... ....................... .. 67

4.17.5 Tank strength and oil tightness ............................................................... ........................................... 68 4.17.5.1 Rigidity ....................... ...................... ....................... ...................... ....................... ...................... ..................... 68 4.17.5.2 Internal pressure and vacuum........................... ....................... ...................... ....................... ....................... ..... 68

4.17.6 Magnetic flux effects ............................................................ ................................................................ 68 4.17.7 Underbase ........................................................ ............................................................... ...................... 68 4.17.8 Jacking pads .............................................................. ................................................................ ........... 69

4.17.9 Lifting lugs......................................................... ............................................................... ...................... 70 4.17.10 Pressure relief devices ............................................................... ..................................................... 70 4.17.11 Provisions for earthing ................................................................ ..................................................... 71 4.17.12 Main tank covers .............................................................. ................................................................ 72

4.17.12.1 Shape...................... ...................... ...................... ...................... ..................... ....................... ....................... ..... 72 4.17.12.2 Lifting ...................... ....................... ...................... ....................... ...................... ..................... ....................... .. 72 4.17.12.3 Support................ ...................... ...................... ...................... ...................... ..................... ....................... ......... 72 4.17.12.4 Gas venting ..................... ...................... ....................... ....................... ...................... ...................... ................. 72 4.17.12.5 Vacuum connection.................................. ...................... ....................... ...................... ....................... .............. 72 4.17.12.6 Cover identification.................................... ...................... ...................... ...................... ....................... ............. 73 4.17.12.7 Thermometer pockets....................... ...................... ...................... ...................... ..................... ....................... .. 73 4.17.12.8 Currents flowing in tank cover and bushing turrets ....................... ...................... ....................... ..................... 73

4.17.13 Welding of cover ............................................................... ................................................................ 73 4.17.14 Gaskets: Types, material, re-tightening and welding ....................................................... ........... 73

4.17.14.1 General............... ...................... ....................... ...................... ....................... .................... ...................... .......... 73 4.17.14.2 Attachments to the transformer tank .................... ....................... ...................... ....................... ...................... .. 74 4.17.14.3 Pipe joints........................... ....................... ....................... ...................... ...................... ....................... ............. 74 4.17.14.4 Drilling of pipe flanges ..................... ....................... ...................... ....................... ...................... ..................... 74

4.17.15 Access openings and covers............................................................... ........................................... 74

4.17.15.1 Handles ..................... ...................... ....................... ...................... ....................... .................... ....................... .. 74 4.17.15.2 Lifting lugs............ ....................... ...................... ....................... ...................... ..................... ...................... ...... 74 4.18 V ALVES AND OIL SAMPLING DEVICES ............................................................... ........................................... 74

4.18.1 Isolating valves .......................................................... ................................................................ ........... 74 4.18.2 Filtering and drain valves ............................................................... ..................................................... 75 4.18.3 Oil sampling devices ............................................................ ................................................................ 75 4.18.4 Strength and oil tightness............................................................... ..................................................... 76 4.18.5 Valve stem seals........................................................ ................................................................ ........... 77 4.18.6 Locking and Padlocking....................................................... ................................................................ 77

4.18.7 Blanking plates........................................................... ................................................................ ........... 77 4.18.8 Valve function plate .............................................................. ................................................................ 77 4.18.9 Valve position indication ...................................................... ................................................................ 77 4.18.10 Labelling of oil sampling devices......................................................... ........................................... 77

4.19 OIL CONSERVATOR TANK AND CONNECTIONS ............................................................ ................................ 78 4.19.1 Capacity ............................................................ ............................................................... ...................... 78 4.19.2 Strength and colour .............................................................. ................................................................ 78


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4.20.7 Oil tightness and strength .............................................................. ..................................................... 81 4.20.8 Electrical connections, terminals and terminal box .............................................................. ........... 81

4.20.9 Devices for the protection of relay contacts ................................................................ ..................... 81 4.20.10 Type and routine testing ............................................................. ..................................................... 82 4.20.11 Assembly, operating and maintenance instructions......................................................... ........... 82 4.20.12 Floats............................................................. ............................................................... ...................... 82

4.21 DEHYDRATING BREATHERS......................................................... ................................................................ 84 4.21.1 General ............................................................. ............................................................... ...................... 84 4.21.2 Type of breather ........................................................ ................................................................ ........... 84 4.21.3 Breather proportions ............................................................ ................................................................ 84 4.21.4 Diffusion of air through the desiccant ................................................................ ................................ 84

4.21.5 Air intake during starting of oil circulating pumps ....................................................... ..................... 84 4.21.6 Containing of the silica gel charge .......................................................... ........................................... 84 4.21.7 Visual inspection of the desiccant ........................................................... ........................................... 85 4.21.8 Seals....................................................... ................................................................ ................................ 85 4.21.9 Castings ............................................................ ............................................................... ...................... 85 4.21.10 Corrosion proofing............................................................ ................................................................ 85 4.21.11 Mounting and pipework connections ............................................................. ................................ 85

4.22 OIL LEVEL INDICATORS, ALARM AND SIGNALLING DEVICES ............................................................. ........... 86 4.22.1 General ............................................................. ............................................................... ...................... 86

4.22.2 Range of indication............................................................... ................................................................ 86 4.22.3 Graduation of indicator ........................................................ ................................................................ 86 4.22.4 Direct reading indicator ........................................................ ................................................................ 86 4.22.5 Dial-type indicator ...................................................... ................................................................ ........... 86 4.22.6 Gaskets ........................................................ ........................................................... ............................... 87 4.22.7 Mounting ........................................................... ............................................................... ...................... 87 4.22.8 Low and high level alarms.............................................................. ..................................................... 87

4.23 COOLING ARRANGEMENTS.......................................................... ................................................................ 87 4.23.1 Type of cooling required...................................................... ................................................................ 87

4.23.2 Hot oil connection point ....................................................... ................................................................ 87 4.23.3 Electrostatic Charging Tendency (ECT) ........................................................... ................................ 87 4.23.4 Oil temperature measurement and settings ................................................................ ..................... 88 4.23.5 Winding temperature measurement and settings....................................................... ..................... 88 4.23.6 Constructional details........................................................... ................................................................ 89 4.23.7 Detachable radiators............................................................ ................................................................ 89 4.23.8 Galvanised radiators ............................................................ ................................................................ 89 4.23.9 Separately mounted cooler banks .......................................................... ........................................... 89 4.23.10 Forced cooling (OF, OD, AF) ............................................................... ........................................... 90

4.23.10.1 Cooler control and settings........................... ....................... ....................... ....................... ..................... .......... 90 4.23.10.2 Cooler control equipment......... ...................... ...................... ..................... ...................... ....................... .......... 90 4.23.10.3 Oil pumps................... ...................... ....................... ...................... ....................... ................... ....................... .. 92 4.23.10.4 Fans...... ...................... ....................... ...................... ....................... ...................... ................... ....................... .. 92 4.23.10.5 Motors........ ....................... ...................... ....................... ...................... ....................... .................... ................. 92 4.23.10.6 Maintenance.................... ...................... ....................... ...................... ....................... ...................... ................. 93

4.24 QUALITY AND DESIGN REVIEW REQUIREMENTS .......................................................... ................................ 94 4 24 1 Quality 94


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4.25.7.3 Tests circuit arrangement and currents........................ ....................... ....................... ..................... ................ 111 4.25.7.4 Application of currents......................... ....................... ...................... ....................... ....................... ............... 112 4.25.7.5 Test results and conclusions....................... ...................... ....................... ...................... ...................... ........... 112

4.25.8 Impedance and load loss measurement ........................................................... .............................. 112 4.25.8.1 Impedance........... ....................... ...................... ....................... ...................... ....................... ....................... ... 112 4.25.8.2 Load losses............... ...................... ....................... ...................... ....................... ...................... ...................... 112

4.25.9 Acoustic noise level measurement ......................................................... ......................................... 113 4.25.9.1 Method... ....................... ...................... ....................... ...................... ....................... ..................... .................. 113 4.25.9.2 Records ................... ....................... ...................... ....................... ...................... ....................... ...................... 113

4.25.10 Magnetising harmonic current measurement ..................................................... ........................ 113 4.25.10.1 Transformers to be tested.................... ...................... ....................... ...................... ..................... ................... 113 4.25.10.2 Records ................... ....................... ...................... ....................... ...................... ....................... ...................... 113

4.25.11 No-load loss and current measurements .................................................. .................................. 113 4.25.11.1 Method... ....................... ...................... ....................... ...................... ....................... ..................... .................. 113 4.25.11.2 Records ................... ....................... ...................... ....................... ...................... ....................... ...................... 113

4.25.12 Core assembly dielectric and earthing continuity tests .......................................................... ... 114 4.25.12.1 Method... ....................... ...................... ....................... ...................... ....................... ..................... .................. 114 4.25.12.2 Records ................... ....................... ...................... ....................... ...................... ....................... ...................... 114

4.25.13 Power frequency voltage withstand tests ........................................................... ........................ 114 4.25.13.1 Separate source voltage withstand tests ...................... ....................... ....................... ..................... ................ 114 4.25.13.2 Induced AC voltage tests ....................... ...................... ....................... ...................... ...................... ............... 115

4.25.14 Lightning and chopped impulse voltage withstand tests ....................................................... ... 115 4.25.14.1 Methods and procedures .................... ...................... ....................... ...................... ...................... ................... 115 4.25.14.2 Tests required............. ....................... ...................... ....................... ...................... ........................ .................. 115 4.25.14.3 Test apparatus .................... ...................... ....................... ...................... ....................... ....................... ........... 116 4.25.14.4 Choice of tapping position ..................... ....................... ...................... ....................... ..................... ............... 116 4.25.14.5 Impulse voltage levels................ ....................... ...................... ....................... ..................... ........................ ... 116 4.25.14.6 Application of voltage impulses........................... ....................... ....................... ....................... ..................... 116 4.25.14.7 Records ................... ....................... ...................... ....................... ...................... ....................... ...................... 116

4.25.15 Dielectric loss angle test............................................................. ................................................... 117 4.25.15.1 Measurement required.......................... ....................... ...................... ....................... ....................... ............... 117 4.25.15.2 Acceptance criteria.................. ...................... ....................... ...................... ....................... ...................... ....... 117 4.25.15.3 Records ................... ....................... ...................... ....................... ...................... ....................... ...................... 117

4.25.16 Bushing tests.......................................................... ................................................................ ......... 117 4.25.16.1 Tests and records........................ ...................... ....................... ...................... ....................... ....................... ... 117 4.25.16.2 Cantilever loads for leak tests ....................... ...................... ....................... ...................... ....................... ....... 118 4.25.16.3 Type tests ...................... ...................... ....................... ...................... ....................... ..................... .................. 118 4.25.16.4 Routine tests........... ....................... ...................... ....................... ...................... ........................ ...................... 118

4.25.17 Testing of current transformers ........................................................... ......................................... 119 4.25.17.1 General............... ...................... ....................... ...................... ....................... .................... ........................ ...... 119 4.25.17.2 Insulation test levels............. ...................... ....................... ...................... ....................... ..................... ........... 119

4.25.17.3 Type tests ...................... ...................... ....................... ...................... ....................... ..................... .................. 119 4.25.17.4 Routine tests........... ....................... ...................... ....................... ...................... ........................ ...................... 119 4.25.17.5 Test certificates ...................... ...................... ....................... ...................... ....................... ....................... ....... 120

4.25.18 On-load tap changer tests .......................................................... ................................................... 120 4.25.18.1 General............... ...................... ....................... ...................... ....................... .................... ........................ ...... 120 4.25.18.2 Type tests ...................... ...................... ....................... ...................... ....................... ..................... .................. 120 4.25.18.3 Routine tests........... ....................... ...................... ....................... ...................... ........................ ...................... 121

4 25 19 Transformer tanks tests 122


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4.29 R ATING AND DIAGRAM PLATES............................................................... ................................................... 128 4.29.1 General ............................................................. ............................................................... .................... 128 4.29.2

Materials and methods of marking.......................................................... ......................................... 128

4.29.3 Mounting ........................................................... ............................................................... .................... 129 4.29.4 Information to be displayed ............................................................ ................................................... 129

4.30 ADJUDICATION OF TENDERS ....................................................... .............................................................. 129 4.30.1 Failure rates, reliability and manufacturing experience of Contractor ........................................ 129

4.30.1.1 Population .................... ...................... ...................... ...................... ...................... ........................ .................. 130 4.30.1.2 Factory Failure.................... ....................... ....................... ...................... ....................... ..................... ........... 130 4.30.1.3 Factory failure rate...................... ...................... ....................... ...................... ...................... ....................... ... 130 4.30.1.4 In service failure .................... ....................... ...................... ....................... ...................... ....................... ....... 130 4.30.1.5 In service failure rate..................... ....................... ...................... ....................... ....................... ...................... 130

4.30.2 No-load and Full-load loss evaluation (Not applicable to rewinds) ............................................. 130 4.30.3 Special too Active part Design Items to be Reviewed During the Tender Evaluation .............131

4.30.3.1 General Coil Layout................ ...................... ....................... ...................... ....................... ...................... ....... 131 4.30.3.2 Losses............................ ...................... ...................... ...................... ...................... ....................... .................. 132 4.30.3.3 Core Design .................... ...................... ....................... ...................... ....................... ....................... .............. 132 4.30.3.4 LV Winding/s Design ...................... ...................... ....................... ...................... .................... ....................... 132 4.30.3.5 HV Winding/s Design... ....................... ...................... ....................... ...................... .................... ................... 132 4.30.3.6 Tapping Winding Design ...................... ....................... ....................... ...................... ...................... ............... 132 4.30.3.7 Main Insulation Design..... ...................... ....................... ...................... ....................... .................... ............... 132 4.30.3.8 Electromagnetic Forces During Short Circuit Conditions...... ....................... ....................... ..................... ..... 132 4.30.3.9 Winding Hot Spot Gradient.................................. ....................... ...................... ....................... ...................... 133

4.31 SPECIAL TOOLS AND EQUIPMENT........................................................... ................................................... 133 4.32 TRAINING OF EMPLOYER’S STAFF .......................................................... ................................................... 133 4.33 GUARANTEE REQUIREMENTS...................................................... .............................................................. 134

5. APPENDIX A (DETAIL PAINT COATING SPECIFICATIONS (SECTION 4.17) ........................................ 136

6. SCHEDULE AB. (SCHEDULE B TO BE COMPLETED BY TENDERERS) ................................................ 147


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List of Figures

Figure 1 — Position of terminals for system transformers (Top view of transformer) ................................... 30 Figure 2 — Current transformer terminal markings ................................................................ ............................ 40 Figure 3 — Control circuits for three-phase OLTC motor drives ............................................................... ....... 50 Figure 4 — Control circuits for single-phase OLTC motor drives .............................................................. ....... 51 Figure 5 — Common circuits for OLTC control ............................................................ ....................................... 52 Figure 6 — General arrangement of terminal block ................................................................ ............................ 59 Figure 7 — General arrangement of type 'E' terminal block............................................................. ................. 60 Figure 8 — Arrangement of jacking pads ............................................................ ................................................. 70 Figure 9 — Oil sampling flange interfaces ............................................................... ....................................... 76 Figure 10 — Buchholz relay outline drawing and sizes.......................................................... ............................ 83 Figure 11: Preferred cooler stop circuit................................................................ ................................................. 93

List of Tables

Table 1 — Maximum overall dimensions for YNd1-connected transformers having ratings up to andincluding 20 MVA ........................................................... ............................................................... .................. 18

Table 2 — Dimensions of air-side bushing terminals ............................................................. ............................ 31 Table 3 — Minimum thickness of mild steel plate for cable box shells ............................................................ 34 Table 4 — In-built current transformers (Class "X" specification core details) ............................................... 41 Table 5 — Contact state at each tap position ............................................................... ....................................... 53 Table 6 — Detailed Coating specifications.......................................................... ................................................. 62 Table 7 — Peak of valley profiles .............................................................. ............................................................ 66 Table 8 — Minimum thickness of transformer tank base plates — mild steel ................................................ 68 Table 9 — Jacking pads......................................................... ............................................................... .................. 69 Table 10 — Gas and oil actuated relays oil flow rates for closure of surge contacts .................................... 80 Table 11 — Permissible gases in oil increases during testing .................................................... .................... 108 Table 12 — Maximum cantilever forces on bushing terminals.................................................... .................... 118 Table 13 — Maximum permanent deflection of steel tank panels between stiffeners................................. 122


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1. Scope

This Specification applies to power station oil-filled transformers for both rewind and new transformers,having a winding operating at or above 11 kV, and a rating above 2,5 MVA. When a transformer isrefurbished the relevant sections of the specification applicable, are those that have relevance only onthe new and replaced parts of the refurbished transformer.

2. Normative references

The following standards are part of this specification and are to be read in conjunction with thisdocument. The latest revision on the date of enquiry applies. Note that where a conflict arises betweenany of the other references and specifications mentioned in this document the IEC documentation hasprecedence. The requirements of this Specification (GGS 1074) take precedence over the requirementsof normative references and other specifications mentioned in this document.

Specification Description

IEC 60060(All Parts)

High-voltage test techniques.

IEC 60076 Power transformers.

IEC 60085 Thermal evaluation and classification of electrical insulation.

IEC 60137 Insulating bushings for alternating voltages above 1 000 V.

IEC 60542 Application guide for on-load tap changers.

IEC 60947-1 Degrees of protection of enclosures for low-voltage switchgear and controlgear.

IEC 60156 Insulating liquids - Determination of the breakdown voltage at power frequency.

IEC 60044

(All Parts)Current transformers.

IEC 60214-1 On-load tap-changers.

IEC 60255-21-3 Electrical relays.

IEC 60270 Partial discharge measurements.


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BS EN 13601 Copper for electrical purposes - rod and bar.

BS 1706 Electroplated coatings of zinc & cadmium on iron and steel.

BS 1872 Electroplated coatings of tin.

BS 2562 Specification for cable boxes for transformers and reactors.

BS 3382 Electroplated coatings and threaded components.

BS 3523 Granular desiccant silica gel impregnated with cobalt chloride.

BS 3571 General recommendations for manual inert gas metal arc welding Part 1: MIGwelding of aluminium and aluminium alloys.

BS 4360 Specification for weldable structural steels.

BS 4504 Circular flanges for pipes valves and fittings (PN designated).

BS EN 1011 Arc welding of carbon and carbon manganese steels.

DIN EN 1092-1 Flanges Slip-on type for Brazing or Welding; Nominal pressure 10 max.

DIN EN 1092-1 Welding neck flanges; nominal pressure 6 (max).

BS EN 50035,50045, 50022 Assembly rails

ISO:9001Quality systems - Model for quality assurance in design development productioninstallation servicing.

EN 10240, ISO1461

Hot-dip (galvanised) zinc coatings (other than on continuously zinc coated sheetand wire).

SABS 0111-1 Engineering Drawing - Part 1: General Principals

SABS 1507-6Electric cables with extruded solid dielectric insulation for fixed installations(300/500 V to 1900/3300 V).

IEC 60815 Guide for the selection of insulators in respect of polluted conditions


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Rev 4 (1998)

IEC 60068-3-3(1991)

Environmental testing - Part 3: Guidance. Seismic test methods for equipment

ISO 10816-1(1995)

Mechanical Vibration – Evaluation Of Machine Vibration By Measurements OnNon-Rotating Parts

NRS 002 (2000),

2nd ed Graphical Symbols For Electrical Diagrams

SABS 0142(2003)

The Wiring of Premises – Part 1: Low-Voltage Installations

ASTM E376. Coating thickness by magnetic field or eddy current electro-magnetic testmethods

BS EN 22063 Metallic and other inorganic coatings. Thermal spraying. Zinc, aluminium andtheir alloys.

ISO 8501-1. Preparation of steel substrates before application of paints and related products – Visual assessment

SIS 055900 Pictorial surface preparation standard for painted steel surfaces

SABS SM

772:1978 / SANS5772.

Profile of blast-cleaned steel surfaces for painting (determined by micrometer

profile gauge).

SABS SM 769:1978 / SANS5769.

Cleanliness of blast-cleaned steel surfaces for painting.

SABS 1091 National Colour Standards for Paint.

SABS ISO 1461 Hot-dip galvanised coating on fabricated iron and steel articles – Specificationand test methods.

SABS ISO 2808:1999 / SANS2808

Paints and Varnishes: Determination of film thicknesses.


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IEC 60156 Insulating liquids – Determining of the breakdown at power frequency-testmethod.

ASTM D2240 Accelerated aging of insulating liquids.

IEC 61181 Impregnated insulating materials - Application of dissolved gas analysis (DGA)to factory tests on electrical equipment

The following schedules form part of this Specification.

Schedule AB: Particulars of the Employer's requirements and guarantees and technical particulars.

3. Definitions

In addition to the definitions below the definitions in IEC 60076-1 also apply.

CTC : Continuous Transposed Copper

Thermallyupgraded Paper :

Transformer insulation paper that has a DP of no less than 200 after being exposed toa temperature of 110°C for 150 000hrs

4. Requirements

4.1 Ratings and operating conditions

4.1.1 Ambient Temperatures and Thermal Performance

This Specification gives detailed requirements for transformers for use under the general conditionsspecified in Schedule AB, item AB.2.

Due to the higher prevailing ambient temperatures, winding temperature and top oil temperature rises willnot exceed the temperature limits as specified in Schedule AB, item AB2. In this respect, thetemperature limits differ from those specified in IEC 60076-2.

The temperature rise limits applicable are as follows:

• Oil Temp rise: (IEC Top Oil Temp Rise) (IEC Ambient Temp Corrections) (Employers Safety


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Thermoplastic resins used in CTC and other winding structures are to be able to withstand thermaltransients conditions brought about by short circuits and other transient phenomena.

4.1.2 Geometrically Induced Currents

This section is applicable to transformers where the Neutral of the transformer is Earthed and if GIC(Geomagnetically Induced Current) compatibility is specified in Schedule AB, item AB2.10.

Under the following operating conditions:

Continuous Maximum System Voltage,

Nominal System Frequency, Continuous Maximum Load, With a tap position such that the maximum number of turns are between the HV terminals and

Neutral, And a GIC induced DC Current of a magnitude, stipulated in Schedule AB, item AB2.10. Flowing

simultaneously through each phase between the HV and Neutral terminals.

When the above mentioned conditions are met and the specified quasi-DC current is sustained for a

period as specified in Schedule AB, item AB2.10, the following applies:

• The transformer must not be damaged. Some thermal ageing of the transformer is allowable,provided the overall specified life span is not shortened.

• Produce dangerous gas or activate the Buchholz trip or alarm circuit.,

• The Winding and Oil Temperature trips or alarms must not be activated.

During the presence of the quasi-DC currents. Special consideration must be given to effects such asvibration increases, increased magnetic forces as well as hot spot temperature rises.

The effect of GIC currents on the transformer design must be quantified and the mitigation techniquesused by the Contractor must be highlighted and submitted to the Employer as stipulated in Schedule AB,Item AB2.10. The Contractor includes a description of the intended design to be applied in the tenderdocumentation.

During the high-level initial design review phase, the Contractor presents the results of his studies of theGIC impact on his design and illustrates that the transformer withstands the criteria specified in thisdocument and Schedules AB, itemAB2.10 to the Employer for his approval.

4.1.3 Rated Power

The values of rated power specified in Schedule AB, item AB.19 are the continuous ratings in MVA atwhich each of the windings of the transformer can operate on the principal tapping at a voltage equal tothe appropriate nominal system voltage Un. The design ensures that the transformer operates undernormal conditions without exceeding the temperature rise limits specified in this Specification


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4.1.5 Voltage

4.1.5.1 Rated vol tage on principal tapping

The rated voltage of each winding of the transformer on the principal tapping is to be as specified inSchedule AB, item AB.21 and, unless otherwise specified, corresponds to the system nominal voltage,Un.

4.1.5.2 Maximum continuous voltage on any tapping

Regardless of the actual location of the tappings in the HV winding, the rated voltage of the HV windingon any tapping is assumed to be equal to the rated voltage on the LV winding multiplied by the voltageratio on that tapping.

4.1.5.3 Maximum temporary overvoltage

Under switching conditions, the power frequency line voltage may exceed the maximum system voltage(Um). The transformers are designed to withstand the following overvoltages without harm unless

otherwise specified in Schedule AB, item AB.22.3

(a) 1.05 Um for 5 minutes;

(b) 1.25 Um for 5 seconds;

(c) 1.5 Um for 1 second; and

(d) 1.7 Um for 0.25 seconds.

Also see the additional requirement to comply with IEC 60076-3, statement in Schedule AB, item AB.22.4

4.1.5.4 Overfluxing

Within the prescribed maximum equipment voltage (Um) the transformer is able to operate continuously

without damage at an overflux value as stated in IEC 60076-1, sec (4.4), unless otherwise stated in

Schedule AB, item AB.7.7. Refer to Schedule AB, item AB.7.7 for the maximum overflux percentageand time duration.

4.1.6 Network frequency

The transformer is designed for a rated frequency of 50 Hz and a frequency deviation in the following


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4.2 Ability to withstand short-circuits

Notwithstanding the overcurrent limits tabulated in IEC 60076-5, the transformer is capable ofwithstanding the thermal, mechanical and other effects of the following faults for the duration of the faultper incident. The fault duration is the larger of the time values given in Schedule AB, item AB.12. If thefault clearing times given in Schedule AB, item AB.12 are smaller than 2s, the fault duration is to betaken as 2s.

a) A three-phase bolted fault on any set of terminals assuming the fault level(s) on the remaining sets ofterminals is that given in Schedule AB, item AB.9.

For the purpose of guarantees, design and possible tests, the supply system is represented by voltagesources having the appropriate values of MAXIMUM system voltages, Um. This supply system is

connected to the transformer through impedances having values such that the in feed in kA from thevoltage sources to a three-phase fault on any of the transformer terminals is equal to the fault currentlevels given in Schedule AB, item AB.9. Furthermore, it is assumed that the unit will be on the tapposition associated with the minimum impedance. The number of faults the transformer is subjected to isunlimited.

Note: That if no fault level(s) are specified in Schedule AB, item AB.9. or if explicitly so stated inSchedule AB, Item AB.9 the transformer(s) is be designed to be Self-protected. Self-protected impliesthat the transformer is connected to an infinite bus when short circuited with no additional networkimpedance in circuit limit the fault current(s).

The Employer reserves the rights to apply a short circuit test to one transformer of any batch on site orelsewhere where convenient, before taking over the batch, in order to prove the short circuit strength ofthe windings. Such tests follow the guidelines laid down in IEC 60076-5 and subsection 4.25.7 of thisSpecification.

In the absence of such tests the Contractor demonstrates with acceptable design calculations that thetransformer meets the requirements for short circuit strength. Transformer inner windings are always tobe designed for Free Buckling under short circuit conditions.

Generator transformers are capable of developing 3-phase short circuit on the LV-terminals in spite ofstatement 3.2.5 in IEC60076-5.

4.3 Impedance and tolerances

The leakage impedance of the transformer of the main power windings at 75 ºC and 50 Hz lies within the

limits as specified in Schedule AB, item AB.35.1.1 and AB.35.2. This permissible range of impedancegiven includes all manufacturing tolerances. The impedances and impedance ranges refer to the nominal

impedance of the transformer Therefore the impedance on any tapping is the impedance in Ω as viewed


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The transformer is designed to meet the dBA sound pressure noise level specified in Schedule AB, item AB.27.

4.5 Interchangeability

All transformers of a specific rating and ratio ordered under the same Contract are identical andinterchangeable with one another at short notice. Where replacement transformers are ordered for anexisting power station, the Contractor attempts in the design and choice of parts to enhanceinterchangeability. No alterations to control circuits are permissible for this purpose. All parts of thetransformer are made accurately to dimensions so that any corresponding parts will fit into place without

the need for adjustments.

See also 4.7.1 “Bushings, cooler banks, conservator and maximum dimensions” and Schedule AB, item AB.4.5.

Also see interchangeability requirements for transformers intended to be used as a replacement toexisting transformers. The Contractor pays special attention in his design to ensure maximuminterchangeability between the supplied transformer and others as indicated in Schedule AB, item 4.5.Issues to address are:

(a) Interface between signals and the power plant such as tap changer, temperature indications, tripsand alarms, pressure relief alarms and trips, Buchholz alarm and trips.

(b) Outer dimensions and clearances.

(c) Plinth loading.

(d) Power and earth terminations.

(e) LV busbar interface and

(f) Cooling ventilation direction matching.

4.6 Clearances in air

When assembled with the connections as in service, electrical clearances in air are adequate towithstand the assigned impulse withstand test voltages. This is to be demonstrated by the impulsevoltage type tests specified in Schedule AB, item AB.22.5, item AB.22.6 and item AB.22.7 during theperformance of which all relevant fittings are in position as for service conditions.

Care is taken to ensure that fittings are located such that there is no interference with the external


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dimensions

Unless otherwise specified, the physical arrangement is such that:

a) the high-voltage and low-voltage bushings are approximately parallel to the major axis of thetransformer;

b) for three-winding transformers the low-voltage bushings are approximately parallel to the minoraxis of the transformer and on the right-hand end when viewed from the HV side, and on the endopposite to the oil conservator;

c) separately mounted cooler banks, if provided, is to be located to permit the unobstructedwithdrawal of the transformer in the direction of the minor axis; and

d) the maximum overall dimensions (excluding surge arresters) for YNd1-connected transformershaving a highest voltage rating of 132 kV and below and ratings up to and including 20 MVA arelimited as detailed in Table 1 below:

Table 1 — Maximum overall dimensions for YNd1-connected transformers having ratings

up to and including 20 MVA

HV rating, Un(kV)

HEIGHT(mm)

LENGTH(mm)

WIDTH(mm)

132

88

66

44

4 800

4 800

4 800

4 800

7 600

6 600

6 600

6 200

4 300

4 300

4 300

4 300

Note:1) The HV bushings must as far as possible be symmetrically arranged about the overalltransverse centre line of the transformer

2) The above dimensions exclude surge arresters and their mounting brackets

4.8 Erection

4.8.1 General

ff f f


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4.8.2 Foundation tolerances and site details

Foundations provided by the Employer are levelled to within a tolerance of ± 3 mm in 3 m in all directions.Newly constructed pedestal foundations for separate cooler bank arrangements are 15 mm lower thanthe main transformer plinth to facilitate line-up of cooler pipes by using spacers. Except for newstations, the new transformers will have to fit the existing foundations, thereby imposing sizerestrictions on the manufacturers.

See also 4.16.4.1 with regard to cable trenches.

4.8.3 Processing on site

Erection includes filtering of oil and any drying-out and testing and checking procedures which arenecessary to ensure that the transformer is ready for operation before handing over, together with theprovision of the necessary materials, apparatus and instruments for these processes.


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4.8.4 Testing on site

The testing and checking procedures includes verification of:

(a) all voltage ratios on all phases;

(b) vector group;

(c) three-phase 380 V magnetising currents and short circuit test with impedance measurements on alltaps;

(d) winding and core megger test (minimum 1,5 kV);

(e) functional test for all alarm and trip contacts;

(f) CT polarities, function and insulation;

(g) fan and oil pump directions and operation of starting and overload protection relays;

(h) control/power cabling insulation (minimum 1 kV);

(i) correct operation and indication of tap changers;

(j) winding and bushing tan delta (< 0.4%) tests with Doble M4000;

(k) correct operation of monitoring equipment; and

(l) correct position of all valves in the oil circuits.

(m) Frequency Response Analysis Technique (FRA)

(n) moisture content test (Method to be approved by Employer )

(o) HV and LV winding resistance test

(p) Core and core clamp insulation

(q) Tap changer continuity

The results of the above tests are to be documented, signed off as part of the quality process andincluded in the transformer manuals.

All equipment provided for erection is removed from site when erection is completed and the site cleanedof any debris and oil spillage.


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4.9 Transport

4.9.1 General condit ions, blanking plates and gas fil ling

It is the Contractor’s responsibility to make all arrangements for transport with the appropriate authorities.

The Employer only accepts delivery from the Contractor on site. It is the Contractor's responsibility to co-ordinate the arrangements for all stages of the transport of the transformer from the Contractor's Works tosite, including transport-shipping where necessary, unless otherwise stated in Schedule AB, Item AB.1.

Where off-loading is required, all apparatus, materials and packages are to be addressed to theContractor , who takes delivery of the same at site.

The dimensions of the transformer are to be such that when packed for transport, it will comply with therequirements of the loading and clearance restrictions for the approved route.

All metal blanking plates and covers which are specifically required to transport the particular transformer,is considered part of the transformer and are handed over to the Employer after completion of erection. A

listing of all these items and relevant drawings is to be included in the manuals, to enable the Employer tohave the plates manufactured if required. The dimensions and quantity of each item required fortransport must be indicated on the drawings.

Where the supply of oil is included in the Contract and where transport weight limitations permit, thetransformers is to be transported with sufficient oil to cover the core and windings during all transport andstorage conditions. The tank is sealed for transport to prevent any breathing. Alternatively, where theabove method is not applicable, the transformer and all other turrets/tanks containing insulation materiale.g. the HV exit lead to the bushings, are maintained continuously under positive pressure of dry air or

nitrogen of at least 10 kPa during transport and storage until final installation. The pressure and thetemperature at the time of filling are documented as part of the quality system. A pressure gauge,suitably protected is fitted to each transformer and pressurized part to facilitate checking of gas pressureduring transit and on site. If another gas like Nitrogen is used appropriate safety labelling is provided.

The transformer is fitted with test bushings in the low voltage and high voltage blanking plates. Thesebushings are connected to the windings via internal leads. This will provide for the transformer to besubjected to Sweep Frequency Response Analysis tests without assembly. Prior to loading of thetransformer at the factory for transport while in a transport ready state (ie. under dry air pressure, with test

bushings fitted, without oil and high voltage or low voltage bushings installed) an SFRA test is performedand at additional points while in transit as set out in GGS 1384. Ensure that the requirements of GGS1384 are met and adhered to.

The total duration that the unit is filled with dry gas is limited to three months where after the transformermust be appropriately processed and filled with oil as for service.


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4.9.2 Accelerometer limits

An accelerometer is attached to the top of each transformer with a rating more than 40 MVA and/orprimary voltage of above 132 kV for the duration of the transport process. The accelerometer iscontinuously recording the acceleration of the transformer in three directions perpendicular to each otherand of which the main direction is in the direction of transport.

The recorder starts recording before lifting in Works, and continues until the unit is in its final position.The traces are inspected as part of the quality process.

The acceleration limit in any direction is 1g. The Employer is notified if this limit is exceeded.

Also see GGS 1384 for requirements.

4.9.3 Sea transport

The Contractor makes the necessary arrangements for suitable slings apparatus to be available for off-loading at the quay-side and may make use of the equipment provided under the Contract, on thecondition that it is handed over to the Employer in good order. Also see GGS 1384 for requirements.

4.9.4 Road transport

The transport arrangements includes any necessary extensions and/or improvements to road routes,bridges, and civil works, and also the assurance that any abnormal loads comprising the transformers,their transporters, ancillary apparatus and plant and equipment required for erection passes withoutobstruction throughout the selected route.

In order to facilitate transport of the new transformers, the Contractor must ensure that the customarytransport-brackets for beam-trailer transport are supplied and fitted to each transformer.

The requirements for locating these transport-brackets on the transformers are as follows:

Transformers > 350 - 450ton transport mass.Minimum of 4 brackets spaced between 6,0 - 8,0m centres longitudinally.Height from transformer base to bearing surface of transport-bracket3,8m (adjustable through 200mm up and down).

Transformers > 210 - 350ton t ransport mass .Minimum of 4 brackets spaced between 6,0 - 8,0m centres longitudinally.Height from transformer base to bearing surface of transport-bracket3,6m (adjustable through 200mm up and down).

Transformers > 150 - 210ton t ransport mass


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The Contractor is to supply a procedure for transporting the transformer in this way and indicates clearlyall limitations associated with an Assembled transport. This procedure is part of the manual supplied bythe Contractor.

4.9.6 Packaging requirements for auxi liary items

1. Eskom needs all the auxiliary items to transportable without the use of abnormal transport. Forthis, the accessories should be packaged within the following maximum parameters:

• L - 12,0m x W - 2,5m x H - 2,7m ; mass -


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4.10.3.2 Core clamping structure

The core clamping structure is earthed to the tank structure at one point only, through a removableexternal link suitably situated, and protected to allow testing after installation of the transformer.

The bottom core clamping structure is in electrical contact with the top core clamping structure throughthe tie bars, by way of the tank, or by means of a connection placed on the same side and end of the coreas the removable core earthing link.

If a copper earthing connection is used between the core clamping structure and the tank, it is flexible,(e.g. laminated, stranded or braided), tinned at the ends, and located on the same side and end of the

core clamping structure as the removable core earthing link.

Care is taken to ensure that the contact resistance between mechanical members that form part of anyintentional current paths, be it circulating or to earth, is not detrimentally affected by any painting.

It is ensured that no sparking which may upset the Dissolved Gas Analysis (DGA) monitoring of thetransformer occurs between bolted mechanical members during inrush or other transient conditions.

A drawing detailing the specifics of the earthing design is required as part of the manuals.

4.10.3.3 Cross-sectional area of earthing connections

Core earthing connections do not have a smaller cross-sectional area than 80 mm², with the exception ofthe connections inserted between laminations which may be reduced to a cross-sectional area of20 mm², where they are clamped between the laminations.

4.10.4 Mechanical construction

4.10.4.1 Lock nuts

The core and core clamping structure are of adequate strength to withstand, without damage, thestresses that are endured during handling, transportation, installation and service.

All nuts are effectively locked by means of locking plates, standard machined lock nuts or other approvedmeans. Pining of bolt-ends and/or threads alone or the use of tempered pressed steel nuts is not

acceptable. Gluing or other approved means is used to fix nuts and bolts of insulating material.

4.10.4.2 Mechanical supports

Where the core and winding assembly is attached to the transformer cover plate, it is neverthelesssupported by the tank bottom. Hand holes are provided in the attachment to the cover plate, for


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Unless otherwise approved in writing, continuous (no joints) vertical tie rods or plates are providedbetween the top and bottom core clamping structures.

Where transformers are ordered to replace existing transformers, unless otherwise specified, the jackingpoints on the main tank of the replacement transformer must align with the jacking points of the oldtransformer. If this can not be achieved, the Employer must be notified of this during the design stage, sothat the existing plinth can be assessed and modified if required.

The design of the transformer must be such that during transport, lifting or moving of the main tank or inthe fully assembled-oil filled state, the transformer can be supported with, or rested on at least twoseparate and parallel placed beams, rails or pedestal stacks, at any point along the base plate of thetransformer (equal distances from the center of gravity) without causing any damage to the transformer.This is important in order to maintain flexibility of use with the various methods of transportation andexisting rail systems on site. Any limitations with regards to lifting the transformer and supporting it withbeams, jacks and rails must be specified by the Contractor on the transportation drawings.

The Contractor must design the transformer to be safely transported with the Employer’s means oftransportation. At the design review stage, the Contractor will request the details for this transportationmethods and equipment e.g. dimensions and capabilities of the beam trailers.

4.10.4.4 Core cleaning

Only edge burs caused by the cutting of the core lamination plates may be removed by high speedgrinding. Any other damage to the core must be reported to the Contractor. The repair of such damage tothe core is to be discussed and the remedial action to be taken is to be agreed upon.

4.10.5 No-load losses and current

All core, shunts and construction parts are designed to withstand the fluxing conditions resulting from thecontinuous and temporary over voltage conditions as well as frequency deviations, as specified.

The no-load losses and the no-load current of each transformer are measured as specified in 4.25.11, aswell as at an agreed over flux condition to demonstrate compliance with this specification.

4.10.6 Core cooling

The transformer core in addition to the windings is to b

GGSS1074 Rev 14.1 Gen Trfr Specification

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Transcript of GGSS1074 Rev 14.1 Gen Trfr Specification