TECHNICAL SPECIFICATIONS FOR ELECTRIC WORKS

Specification for ground mounted hermetically sealed,

oil filled distribution transformer

Group: Transformers/ Reactors

Subject: Oil filled Distribution transformers

0 JAN 2022 First Issue

Rev. Date Description/issued for

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 1 of: 23
 INDEX

TECHNICAL SPECIFICATIONS FOR ELECTRIC WORKS .................................................. 1

1 SCOPE.............................................................................................................................. 4
2 APPLICATION FIELD .................................................................................................. 4
3 REFERENCE DOCUMENTS ....................................................................................... 5
3.1 ADDC/AADC specifications ............................................................................................ 5
3.2 Reference standards........................................................................................................... 5
3.3 Regulation and law ............................................................................................................ 6
4 SERVICE CONDITIONS .............................................................................................. 6
5 TECHNICAL FEATURES AND RATINGS ................................................................ 7
5.1 Type of transformer ........................................................................................................... 7
5.2 Number of winding ........................................................................................................... 7
5.3 Number of phases .............................................................................................................. 7
5.4 Rated frequency................................................................................................................. 7
5.5 Cooling system .................................................................................................................. 7
5.6 Rated power....................................................................................................................... 7
5.7 Rated voltages ................................................................................................................... 7
5.8 Insulation level .................................................................................................................. 7
5.9 Voltage regulation ............................................................................................................. 7
5.10 Winding connection and phase displacement.................................................................... 8
5.11 Installation ......................................................................................................................... 8
5.12 Overload capability ........................................................................................................... 8
5.13 Over-excitation conditions ................................................................................................ 8
5.14 Losses ................................................................................................................................ 8
5.14.1 No-load currents and losses ............................................................................................... 8
5.14.2 Load losses and short circuit impedance ........................................................................... 9
5.15 Temperature rise .............................................................................................................. 10
5.16 Sound level ...................................................................................................................... 10
5.17 Capability to withstand short-circuit ............................................................................... 10
6 CONSTRUCTION AND DESIGN REQUIREMENTS ............................................. 11
6.1 Core and frame core ........................................................................................................ 11
6.2 Windings ......................................................................................................................... 11
6.3 Tank ................................................................................................................................. 11
6.4 Bushing............................................................................................................................ 12
6.5 Cable termination box ..................................................................................................... 13
6.6 Neutral current transformer (NCT) ................................................................................. 14
6.7 Cooling system ................................................................................................................ 14
6.8 Insulating oil .................................................................................................................... 15
6.8.1 Mineral oil ....................................................................................................................... 15
6.8.2 Natural ester oil ............................................................................................................... 15
6.9 De-energized tap changer ................................................................................................ 16
6.10 Accessories and auxiliary ................................................................................................ 16
6.11 Rating plate and other designation plate ......................................................................... 16

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 2 of: 23
 6.12 Protective painting........................................................................................................... 16
7 TESTS ............................................................................................................................ 17
7.1 Routine tests .................................................................................................................... 17
7.2 Type and special tests ...................................................................................................... 17
7.2.1 Temperature rise test ....................................................................................................... 17
7.2.2 Chopped wave lightning impulse test for the line terminals (LI) .................................... 17
7.2.3 Determination of sound level .......................................................................................... 18
7.2.4 Short-circuit withstand test .............................................................................................. 18
7.3 Site tests........................................................................................................................... 18
8 QUALITY AND CERTIFICATION ........................................................................... 19
8.1 Documentation supplied during the tender...................................................................... 19
8.2 Document to be supplied after the order ......................................................................... 19
8.2.1 Documentation for homologation, certification and approval (TCA) ............................. 20
8.2.2 Failure Mode and Effect Analysis report (FMEA) .......................................................... 21
9 DELIVERY, HANDLING AND LOGISTIC ISSUE ................................................. 22
9.1 Packaging and transportation .......................................................................................... 22
9.2 Installation and erection .................................................................................................. 22
9.3 Storage ............................................................................................................................. 22
10 EXCEPTIONS ............................................................................................................... 22
ANNEX A –FMEA .......................................................................................................................... 23

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 3 of: 23
 1 SCOPE
The scope of this specification is to provide the technical requirements for the design,
manufacturing, inspection, factory tests, packing, shipping, delivery to site, installation and
commissioning for oil immersed, hermetically sealed, ground mounted distribution transformers
to be used in the distribution networks of ADDC/AADC.
2 APPLICATION FIELD
This specification refers to the lists of, three phases, hermetically sealed, oil immersed distribution
ground mounted transformers mentioned in Table 1 that can be used for indoor or outdoor
installation.
Table 1- List of ground mounted distribution transformers
Rated voltage HV winding
ADDC/AADC Rated Type of
(kV) voltage variation Connection
type code power Cooling tap Installation
range symbol
(kVA) HV LV changer
(N. step x %)
OGM-0500-11 500
OGM-0630-11 630
OGM-1000-11 1000 Indoor/
ONAN 11 ± 2 x 2.5% DETC Dyn11
OGM-1250-11 1250 outdoor
OGM-1500-11 1500
OGM-2000-11 2000
OGM-0500-22 500
OGM-0630-22 630 0.415
OGM-1000-22 1000
Indoor/
OGM-1250-22 1250 ONAN 22 ± 2 x 2.5% DETC Dyn11
outdoor
OGM-1500-22 1500
OGM-2000-22 2000
OGM-2500-22 2500
OGM-1000-33 1000 Indoor/
ONAN 33 ± 2 x 2.5 % DETC Dyn11
OGM-1500-33 1500 outdoor

The supply limit, if not otherwise prescribed, will be the following:

• high voltage side: the HV bushing with the relevant terminal box and the structure to fix the cable
of the 11 kV, 22 kV or 33 kV systems
• low voltage side: the LV bushing with the relevant terminal box and the structure to fix the cable
of the 0.415 kV system
• terminal board of the marshalling box applied to the transformer walls, for the connection of power
and signalling cables.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 4 of: 23
 3 REFERENCE DOCUMENTS
The list of the reference documents is indicated in the following paragraphs.
In case of discrepancy between these specifications and any of the applicable Codes and Standards,
the following order of precedence shall apply:
1) ADDC/AADC specifications
2) applicable reference standards
3) other documents.
The Bidder shall note that compliance with the provision of these specifications does not relieve
him from his responsibility to supply the equipment and accessories of proper design, electrically
and mechanically suited to meet the operating guarantees at the specified service conditions.
3.1 ADDC/AADC specifications
Table 2- List of ADDC/AADC specifications
S-GEN-SER S-GEN-ID
S-GEN-NET S-CPS-MV-LV-PROT
S-GEN-COR

3.2 Reference standards

The last edition of the standards mentioned in Table 4 that shall be take in consideration.
Table 3- List of standards
Standard Description
IEC 60076-1 Power transformers – Part 1: General
IEC 60076-2 Power transformers – Part 2: Temperature rise for liquid-immersed transformers
IEC 60076-3 Power transformers – Part 3: Insulation levels, dielectric tests and external clearances in air
IEC 60076-5 Power transformers – Part 5: Ability to withstand short circuit
IEC 60076-7 Power transformers – Part 7: Loading guide for oil-immersed power transformers
IEC 60076-10 Power transformers - Part 10: Determination of sound levels
IEC 60076-10-1 Power transformers - Part 10-1: Determination of sound levels – Application Guide
IEC 60076-13 Power transformers – Part 13: Self-protected liquid-filled transformers
IEC 60076-18 Power transformers – Part 18: Measurement of frequency response
IEC 60076-22 Power transformer and reactor fittings - SERIES
IEC 60076-22-1 Power transformer and reactor fittings - Protective devices
IEC 60076-22-2 Power transformer and reactor fittings – Removable radiators
IEC 60076-22-7 Power transformer and reactor fittings – Accessories and fittings
IEC 60616 Terminal and tapping markings for power transformers
IEC 61869-1 Instrument transformers – Part 1: General requirements
IEC 61869-2 Instrument transformers – Part 2: Additional requirements for current transformers
IEC 60137 Insulated bushings for alternating voltages above 1 000 V
IEC 60296 Fluids for electrotechnical applications – Unused mineral insulating oils for transformers and
switchgear
IEC 60422 Mineral insulating oils in electrical equipment – Supervision and maintenance guidance
IEC 60599 Mineral oil impregnated in electrical equipment in service – Guide to the interpretation of dissolved
and free gases analysis

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 5 of: 23
 Standard Description
IEC 61181 Mineral oil-filled electrical equipment – Application of dissolved gas analysis (DGA) to factory
tests on electrical equipment
IEC 62535 Insulating liquids - Test method for detection of potentially corrosive Sulphur in used and unused
insulating oil
IEC 61198 Mineral insulating oils - Methods for the determination of 2-furfural and related compounds
IEC 60815 Guide for selection and dimensioning of high-voltage insulators for polluted conditions
IEC 60214-1 Tap-Changers – Part 1: Performance requirements and test methods
IEC 60214-2 Tap-Changers – Part 2: Application guide
IEC 61462 Composite hollow insulators – Pressurized and unpressurized insulators for use in electrical
equipment with rated voltage greater than 1000 V – Definitions, test methods, acceptance criteria
and design recommendations
IEC 62155 Hollow pressurized and unpressurized ceramic and glass insulators for use in electrical equipment
with rated voltage greater than 1000 V
IEC 60529 Degree of protections provided by enclosures (IP Code)
IEC 60947-7-2 Low-voltage switchgear and control gear – Part 7-2: Ancillary equipment –Protective conductor
terminal blocks for copper conductors
IEC 60417-2 Graphical symbols for use on equipment - Part 2: Symbol originals
EN 50386 Bushings up to 1 kV and from 250 A to 5 kA, for liquid filled transformers
Selection and dimensioning of high-voltage insulators intended for use in polluted conditions – Part
IEC/TS 60815-1
1: Definitions, information and general principles
ISO 2178 Non-magnetic coatings on magnetic substrates – Measurement of coating thickness –Magnetic
method
ISO 2808 Paints and varnishes – Determination of film thickness
ISO 2409 Paints and varnishes – Cross-cut test
ISO 12944 series Paints and varnishes - Corrosion protection of steel structures by protective paint systems
ISO 19840 Paints and varnishes - Corrosion protection of steel structures by protective paint systems -
Measurement of, and acceptance criteria for, the thickness of dry films on rough surfaces
ISO 8501 Preparation of steel substrates before application of paints and related products - Visual assessment
of surface cleanliness
ISO 4628-3 Paints and varnishes – Assessment of degree of rusting
EN 1977 Copper and copper alloys - Copper drawing stock (wire rod)
EN 50387 Busbar bushings up to 1 kV and from 1,25 kA to 5 kA, for liquid filled transformers
3.3 Regulation and law
During the creation of this specification no known regulations or laws were available related to
transformers.

4 SERVICE CONDITIONS
The service conditions are specified in S-GEN-SER, in case something is not or not properly
specified regarding the service conditions, the IEC 60076-1 shall be taken into account.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 6 of: 23
 5 TECHNICAL FEATURES AND RATINGS
In these paragraphs the technical features and the transformer ratings are described
5.1 Type of transformer
This specification is applicable for oil immersed transformers, three-phase, hermetically sealed,
ground mounted.
5.2 Number of winding
The number of winding is two.
The winding with the highest rated voltage is identify with the acronym HV while the winding
with the lowest rated voltage is identify with LV.
5.3 Number of phases
The number of phases is three
5.4 Rated frequency
The rated frequency is 50 Hz.
5.5 Cooling system
The cooling system of the transformer is ONAN.
5.6 Rated power
The values of the rated power are reported in Table 1 and Table 2.
5.7 Rated voltages
The rated voltages for HV winding are 11 kV, 22 kV and 33 kV.
The rated voltage for LV winding is 0.415 kV.
5.8 Insulation level
All windings shall be manufactured with uniform insulation.
The insulation level of the transformer windings shall be as specified in Table 4.
Table 4- Winding insulation level
Highest Line terminal AC Full wave
Rated voltage Ur voltage for withstand voltage lightning
Winding
(kV) equipment - AV impulse - LI
Um (kV) (kV) (kV)
33 36 70 170
HV 22 24 50 125
11 12 28 75
LV 0.415 1.1 3 -
5.9 Voltage regulation
The voltage regulation is on HV winding, the regulation tapping range is for all considered
transformers ± 2 x 2.5% of the rated voltage.
Client: ADDC/ AADC
STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 7 of: 23
 5.10 Winding connection and phase displacement
The transformers shall be Dyn11.
5.11 Installation
The transformer shall be suitable for indoor and outdoor installation.
5.12 Overload capability
The transformer shall be manufacturer to withstand the overload specified in According to IEC
60076-7.
The transformer accessories (bushings, cable-end, connections, tap-changer) shall be able to
withstand a current up to 1.2 times the rated currents without any restrictions as per IEC60137.
5.13 Over-excitation conditions
The transformer shall be able to operate in the over excitation conditions specified in IEC 60076-
1. Moreover, the transformer shall be able to operate at no-load with a magnetic flux in the core
up to 1.1 times the rated magnetic flux.
5.14 Losses
No positive tolerance is accepted for the specified losses. TAQA/ADDC/AADC reserve the right
to conduct no load and load losses measurements on a random selection of the supplied
transformers. Depending on the outcome, a single transformer or a complete batch can be rejected.
Disciplinary such as disqualification as pre-qualified supplier will be considered depending on
how big the deviation is and how many objects are exceeding the maximum allowed value. For
special cases TAQA/ADDC/AADC can order 11/.415 kV transformers with higher losses. The
selection for these transformers will be made in the corresponding data sheet selecting “low loss”
or “normal loss” option.
5.14.1 No-load currents and losses
The transformers shall respect the maximum values of the no-load current and no-load loss
specified in Table 5 and Table 6 for low loss transformers.
Table 5 - No-load current values at rated voltage
Power No-load current
(kVA) (%)
500
≤2
630
1000
≤ 1.7
1250
1500
≤ 1.5
2000
2500 ≤ 1.4

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 8 of: 23
 Table 6- Maximum value of no-load loss at rated voltage in function of the rated power for low
loss transformers
Rated power No-load loss (W)
(kVA) Um ≤ 24 kV Um = 36 kV
500 510 -
630 600
1000 770 885
1250 950 -
1500 1150 1325
2000 1450
-
2500 1750
For special cases the no-load losses mentioned in table 7 will be applicable:
Table 7 Maximum value of no-load loss at rated voltage in function of the rated power for
normal loss transformers
Rated power No-load loss (W)
(kVA) Um = 12 kV
500 600
630 1000
1000 1700
1250 1800
1500 2300
2000 2600
5.14.2 Load losses and short circuit impedance
The transformers shall respect the maximum values of the load losses and short circuit impedance,
referred at 75°C, with tap correspondent at rated voltage, as specified in Table 8.
Table 8- Guaranteed values of load loss and short circuit impedance for low loss transformers
Rated power Load loss (W) Short circuit
(kVA) Um ≤ 24 kV Um = 36 kV impedance (%)
500 4000 4.0
630 5000 4.0
1000 8000 8800 5.0
1250 10000 - 5.0
1500 12000 13200 6.0
2000 16000 7.0
-
2500 19000 8.5
In the data sheet, the manufacturer shall declare the value of the load losses at taps correspondent
at rated voltage and the extremes of the regulation range.
For special cases the load losses mentioned in table 9 will be applicable:

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 9 of: 23
 Table 9 Guaranteed values of load loss and short circuit impedance for for normal loss
transformers
Rated power Load loss (W) Short circuit
(kVA) Um = 12 kV impedance (%)
500 4800 4.0
630 5500 4.0
1000 7000 5.0
1250 8000 5.0
1500 9000 6.0
2000 17000 7.0
5.15 Temperature rise
The temperature rise of the core, oil and windings are specified in Table 10.
Table 10- Values of temperature rise
Temperature rise
Top oil 50 K
Average winding 55 K
Winding hot spot 68 K
5.16 Sound level
The transformers shall respect the values of the sound power level specified in Table 11 at rated
voltage and rated frequency.
Table 11- Values of sound power level
Sound power
Rated power
level
(kVA)
(dBA)
500 53
630 54
1000 56
1250 59
1500 60
2000 61
2500 63
5.17 Capability to withstand short-circuit
The transformers shall be able to withstand the short circuit test in compliance with IEC 60076-5.
If the test is not prescribed, the Manufacture shall prepare a technical report where the calculation
of the forces and stresses on the actual transformer are compared with those of a similar
transformer that passed the short circuit test, following the indication of IEC 60076-5.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 10 of: 23
 6 CONSTRUCTION AND DESIGN REQUIREMENTS

6.1 Core and frame core

The magnetic core shall be manufactured with grain-oriented cold laminated magnetic strips or
wrapped type with amorphous material.
If threaded rods are installed inside to the core, them shall be insulated for 1.5 kVdc against the
core and frame.
6.2 Windings
Although the preferred conductor material for the winding will be aluminium, for certain cases the
utility can decide to use copper conductor windings. The choice will be made in the data sheet D-
TRD-GMO.
For Aluminium winding, the windings shall be made with aluminium conductors (with the
minimum content of aluminium not less than 99.5 %). Copper conductor windings shall be
concentric type made with electrolytic copper conductors of a high conductivity.
The insulation paper used to cover the conductors and the insulation material shall in class A
(according to IEC 60085). Enamelled insulated conductors shall be complying with IEC 60317.
6.3 Tank
The transformer tank shall be hermetically sealed type, completely filled with oil, with upper
flange and bolted cover.
The cooling system shall be made with corrugated sheet steel welded to the tank.
The cooling fins shall be welded with round stiffening rods to prevent vibration during operation
of the transformers.
The gaskets shall be made in material oil resistant and capable to withstand the thermal stress that
can occur during the operation. All gaskets shall be of closed design (without open ends) and shall
be of one piece only.
Rubber gaskets used for flange connections of the various oil compartments shall be laid in grooves
or groove-equivalent retainers on both sides of the gasket throughout the total length. Gaskets of
neoprene and/or such material which can be easily damaged by over-pressing (e.g. any kind of
impregnated/bonded cork) are not acceptable. Use of hemp as gasket material is also prohibited.
Lifting lugs shall be provided on the cover as well as rigid traverses under the bottom as a mounting
base. Bi-directional wheels with blocking facilities shall be provided.
The electrical continuity shall be guaranteed between cover and tank by suitable earthing
conductor.
The top cover of tank shall be designed in such a way that the MV bushings shall be
replaceable without removing or opening the top cover.
Two earthing terminals, completely made of stainless steel, shall be provided and installed
diagonally at the bottom of the transformer tank (according to type B2 of IEC 60076-22-7).

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 11 of: 23
 Figure 1 – Type B2 earthing terminal of the tank

6.4 Bushing
The insulators that shall be installed on the transformers shall be in accordance with IEC 60137
and IEC/TS 60815. The bushing shall be with housing in ceramic they shall be in brown colour
and compliant with IEC 62155.
The dimension of the MV bushing shall be in accordance with the EN 50180. The dimension of
the LV busbar shall be in accordance with EN 50387.
All metallic parts used to fix the bushings such as but not limited to bolts, nuts and washers shall
be made from stainless material, resistant to corrosion.
All the bushings shall not have any spark gap shaft.
The ratings of the bushings in function of the winding rated voltage and the power of the
transformers are specified in Table 12 and Table 13.
Table 12 – HV bushing ratings
Winding rated voltage kV 11 22 33
Highest voltage for equipment (Um) kV 12 24 36
Type Non-condenser Non-condenser Non-condenser
AC withstand voltage (wet) kV 28 50 70
Lightning impulse withstand voltage kV 75 125 170
Cantilever withstand load N Class II Class II Class II
Creepage insulating Distance mm ≥ 192 ≥ 384 ≥ 720
Mounting angle with respect to the vertical ° > 30 > 30 > 30
Rated current A 250 (1)
Note: (1) Value suitable for all rating power

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 12 of: 23
 Table 13 – LV bushing or 4 pole monoblocks rating
Rated Rated Insulation level
Type of Reference
Installation power current
bushing Um AC LI standard
(kVA) (A)
500 Busbar 1250
630 Busbar 1250
1000 Busbar 2000
Ground EN 50387
1250 Busbar 2500 1.1 3 -
mounted
1500 Busbar 3150
2000 Busbar 4000
2500 Busbar 5000
The arrangement of the bushing shall the following:
• The HV bushing shall be installed vertically on the cover, along the longer side of the tank.
• The LV bushing shall be installed on the opposite side, vertically on the cover.
Both the HV and LV side are protected by means of a cable box.
The porcelain of the HV bushing shall be removable without open the cover.
The marking of the terminals (HV, LV and earthing) must be fixed, indelible and identify each
terminal unambiguously (see Figure 2).

B Y R

b y r n

Figure 2 – Identification of the terminals

6.5 Cable termination box

The cable boxes that shall be installed to protect the HV bushings, LV and neutral bushing, and
shall have a protection class IP54 and insulation levels comply with the related bushings.
The cable boxes shall be made with suitable cable gland (of non-magnetic material) for
connections of cables with outdoor sealing ends and with all necessary fittings, lugs of specific
size, glands, clamp bonding strap(s), cable bushing supports, etc.
In the HV cable box, a grounding studs with bolts and washers of stainless steel for earthing of the
cable sheaths shall be provided.
The cable boxes shall be designed with the cables entrance located in the bottom side and with
suitable bars where to fix the cables and in the bottom part of the transformer a relevant cable
supports, of non-magnetic material, shall be provided.
In one side of the cable box a plate easily removable shall be provided to allow access to the
transformer terminal.
Each cable termination box shall be equipped with 2 numbers of thermal imaging windows,
positioned in such a way that all bushings and connections can be monitored without removing the
cable termination box cover.
Client: ADDC/ AADC
STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 13 of: 23
 The LV cable box and the relevant neutral terminal bar shall be designed to considering the
presence of the neutral conductors and the earthing conductor.
The Table 14 provides the requirements of the cross section, and the number of cables per phase
for the LV cable termination box.
Table 14 – Characteristics of the cables for LV cable box
Rated Phase terminals Neutral terminal Section on the
power No. of cables No. of cables cable
kVA No. No. mm2
500 1 1 +PE 630
630 2 1+ PE 630
1000 2 1+PE 630
1250 3 2+PE 630
1500 3 2 +PE 630
2000 4 3+PE 630
2500 5 3+PE 630
Note: PE protective earthing conductor
6.6 Neutral current transformer (NCT)
If required as per datasheet, a current transformer for protection purpose must be provided.
The NCT parameter shall be as follows for ADDC:
• For transformers up to and including 1000kVA : 1000/1A/5P20/10VA
• For transformers above 1000kVA : 2000/1A/5P20/10VA
The NCT parameter shall be as follows for AADC:
PTR Rating NCT
500 900/1
630 1200/1
1000 1800/1
1500 2700/1
2000 3600/1
6.7 Cooling system
The cooling system of the transformers shall be ONAN, made by fins installed on the tank walls.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 14 of: 23
 6.8 Insulating oil

6.8.1 Mineral oil

The insulating liquid shall be obtained from naphthenic based mineral oil and shall be compliant
to IEC 60296 designation TVAI.
The names of the additives (antioxidant and passivating) present in the oil shall be specified as
well as the concentration.
The oil shall not contain PCB.
The requirements are those defined by IEC 60296 standard with the modifications given in the
following:
• Viscosity at 40°C ≤ 9.5 mm2/s
• Typical value of oil Dielectrical Dissipation Factor at 90° ≤ 0.001 mm2/s
• Flash point ≥ 135°C
For the corrosive sulphur requirement, the oil shall fulfil the test method prescribed in ASTM D
1275, method B, and the IEC 62535.
During the normal operating condition, the oil shall not develop a formation of stray gassing and
the oil shall respect the limits specified in IEC 60296.
The manufacturer shall ensure that the oil complies with the required requirements and provide
the relative certification for oil used for filling the transformers.
TAQA/ADDC/AADC reserves the right to carry out oil tests at any time of supply.
The oil Supplier and the oil type shall be both clearly indicated in the rating plate and/or in the
manual.
6.8.2 Natural ester oil
The natural ester liquid shall be in accordance with the standard IEC 62770.
In relation to corrosive sulphur, the insulating oil supplied in addition to what is already requested
from standard IEC 60296 (test according to DIN 51353 and IEC 62535) must also pass the
additional test ASTM D1275-15 (Standard Test Method for Corrosive Sulphur in Electrical
Insulating Liquids).
The natural ester under normal operating conditions must not give rise to abnormal gas
development, known as stray gassing measured at 120° C under the test conditions defined in the
CIGRE Brochure 296. For this purpose, the following must not be exceeded:
• The values of 70, 200 and 25 ppm of H2 respectively at 16, 164 and 164 + 16 hours
• The values of 200, 500 and 50 ppm of C2H6 respectively at 16, 164 and 164 + 16 hours.
The fluid can be classified according to fire-point K1, K2 or K3 type in compliance with the
standard IEC 61039.
All parts of the transformer that are or may come into contact with the fluid must be compatible
with the type of fluid used.
It is forbidden to use fluids with characteristics such as to make them classified as dangerous
substances.
The Manufacturer must guarantee the compliance of the fluid with the required requirements and
provide the relative certification for the filling batch used during the factory acceptance test.
The oil used to fill the transformer before the test shall be of the same vegetable ester (brand and
type) that will be used for the final filling of the transformer on site.
Client: ADDC/ AADC
STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 15 of: 23
 6.9 De-energized tap changer
The transformer shall be supplied with de-energized tap changer (DETC), in conformity with IEC
60214.
The tap changer shall be manually operated and installed in a position that can be replaced without
draining the oil below the core level.
The operation range of the tap changer is specified in Table 1.
The position 1 shall correspond at the maximum voltage, position 3 at rated voltage and 5 at
minimum voltage of HV winding.
The tap changer shall be installed on the cover, equipped with a device that show the position of
tap and it shall be lockable.
Tap changers shall have been type tested by a recognised independent testing authority. Only
designs which have been type tested in accordance with the relevant IEC standards will be
accepted.
6.10 Accessories and auxiliary
Table 15 provides a list of the accessories that shall be installed
Table 15 – Accessories for ground mounted transformers
No. Accessories
Dial type thermometer for top oil temperature with radial type main and maximum pointer, two
adjustable contacts for oil temperature alarm and trip (at 95oC and 105oC).
1 Thermometers shall be of protection category IP55 and shall be provided with sight glasses of
polycarbonate or laminated security glass.
Spring-loaded pressure relief device with pin-type operation indicator and trip contact in metal
1 housing of protection class IP55.
Oil level indicator mounted in a corner of the tank. A device combined with the protection device
for monitoring of oil leakage and gas formation with trip contact, e.g. a suitable gas detector relay
1 with sight glass, is also acceptable. In such a case the device shall be installed directly above core-
coil assembly as above.
6.11 Rating plate and other designation plate
One rating plates shall be provided, according to the following indications, and shall be fixed on
appropriate supports on the longer sides of the transformers.
The rating plate shall be made of polished stainless steel and shall contain the information
according to IEC 60076-1, with a plan view of the transformer giving the correct physical
relationship of the terminals.
All terminals shall be identified with a marking plate of stainless steel engraved and shall be
permanently fixed.
6.12 Protective painting
The requirements of protective painting are stated in the specification S-GEN-COR.
Colour code is RAL 7032.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 16 of: 23
 7 TESTS
All required tests must be in accordance with S-GEN-TEST.
Each year, during the supply of the transformers, TAQA/ADDC/AADC reserves the right to select
from the Manufacture premises some transformers, that have passed the routine test, to be sent to
an accredited laboratory to repeat some routine, type or special tests.
If the test will fail all the cost (transportation and tests etc.) will be pay by the Manufacturer and
the supply will be stopped until the non-conformity is solved.
The test shall be performed in accordance with IEC 60076-series, if not otherwise specified.
7.1 Routine tests
The following routine tests shall be performed in each transformer:
• Check of the correspondence with approved prototype.
• Measurement of voltage ratio and check of phase displacement (IEC 60076-1).
• Measurement of winding resistance in all taps (IEC 60076-1).
• Measurement of no-load loss and no-load current at rated voltage (IEC 60076-1).
• Measurement of short-circuit impedance and load loss at principal tap position at rated voltage at
75 °C.
• Dielectric routine test (IEC 60076-3):
o Applied voltage test.
o Induced voltage withstand test.
• Leak testing with pressure (tightness test). The test shall be performed with pressure of 1.3 time
the maximum value measured during the temperature rise (∆P) on the prototype. The pressure shall
be maintained for 8 hours and no leakage shall be detected.
• Measurement of d.c insulation resistance (R15, R60) between each winding to earth and between
windings at 2.5 kVdc for LV windings and 5 kVdc for the HV windings.
• Check and verification of the functionalities of accessories.
• Check of external coating (ISO 2178 and ISO 2409 or as specified)
7.2 Type and special tests
The following type and special tests shall be performed on prototype, TAQA/ADDC/AADC could
request the repetition of some tests on the other units.
7.2.1 Temperature rise test
The temperature rise test shall be performed following the indication of the std. IEC 60076-2.
During the temperature rise test, a device to measure the overpressure inside to the tank shall be
installed. The maximum value measured during the heating of the transformer (∆P) shall be used
during the leakage test (see clause 7.1- .
7.2.2 Chopped wave lightning impulse test for the line terminals (LI)
The test shall be performed according to the indication of IEC 60076-3 on HV and LV terminal.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 17 of: 23
 7.2.3 Determination of sound level
The test shall be performed according to the indication of IEC 60076-10 supply the transformer at
rated voltage.
7.2.4 Short-circuit withstand test
The test shall be performed according to the indication of IEC 60076-5.
7.3 Site tests
No site tests are applicable.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 18 of: 23
 8 QUALITY AND CERTIFICATION

8.1 Documentation supplied during the tender

The technical documentations to be produced by the Supplier for the economical offer shall contain
the following items:
• The data sheet D-TRD-GMO filled.
• Preliminary general arrangement of the transformer with the main dimension and with detail of the
cable box.
• List of the transformer manufactured, with the same ratings of that requested in the offer, in the
last 5 years.
• Data sheet of all accessories installed (e.g. bushings, tap changer, thermometer etc.)
• Painting procedure.
• List of deviation from tender specification
8.2 Document to be supplied after the order
The technical documentation to be produced by the Supplier after the order shall contain the
following items:
• The technical data D-TRD-GMO sheet filled with the design values.
• Drawing of:
o rating plate.
o outline drawing with part list.
o transport drawing.
o auxiliary circuit of control and cabinet layout.
• Technical report to demonstrate the capability of the transformer to withstand the short circuit (see
clause 5.17) if the short circuit withstand test is not prescribed.
• Painting procedure approved by ADDC/AADC
• Manufacturing and test quality plan
• Type test certificate of the accessories installed (tap changer, bushing, control cabinet etc.)
• Routine test certificate of each component of the transformer (core, winding material, insulation
material accessories etc.)
• Auxiliary wiring drawing (if applicable).
• Factory tests procedure
• Test schedules for factory tests
• Commissioning test procedure and report
• Factory test report (to be submitted after witness tests)
• Operation and maintenance manual including test reports witnesses by ADDC/AADC or their
representative.
• Data sheet of all accessories installed (e.g. bushings, tap changer, Buchholz relay, thermometer

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 19 of: 23
 8.2.1 Documentation for homologation, certification and approval (TCA)
The Supplier, for each transformer type code to be subjected to homologation, certification or
approval procedure, shall make available a complete documentation containing calculations,
drawings, schemas, pictures of the HV and MV side, internal and external, descriptions, list of
characteristics, performances, assembling, maintenance and operational norms and whatever
necessary for the complete acknowledgment of the transformer.
All the final technical documentation shall be delivered in electronic form.
Not reserved documentation is the documentation issued by the Manufacturer that allows to
verify, directly or indirectly, the compliance of the transformer with the prescription of this
specification. The Manufacturer authorizes the diffusion and the reproduction of this
documentation within the ADDC/AADC.
It shall contain at least:
• List of all the documents, including the list of the reserved documentation (type B).
• List of the Suppliers of the main components and parts.
• Manual of the transport, installation, operation and maintenance.
• Drawing of the rating plates.
• Overall drawings and relevant details of both the completely assembled transformer (as in
operation) and of the transformer transportation.
• Drawing of the auxiliary circuits.
• Test reports of the transformer.
• Test reports and certifications of the subcomponents and materials used.
• External pictures.
• Calculation of the capability to withstand the short circuit (in case of the test is not performed).
• The data requested in the form D-TRD-GMO updated and validated after the homologation,
• certification or approval process.
Together with each transformer supplied (compliant to the relevant approved type), the Supplier
shall deliver
The documentation considered reserved, of which the Supplier does not authorize the diffusion,
used to completely identify the design and the manufacturing of the transformer. It shall include
all the elements required in this specification and the documentation of the origins of the materials
not reported in “not-reserved documentation”. Such documentation will be overviewed by the
ADDC/AADC representatives or by the certification body during the homologation or certification
and will be archived by the Supplier.
For the identification of the prototype the manufacture shall prepare a report where the design of
the transformer is described, with particular reference at the construction solution adopted.
Moreover, a detail photographic documentation shall be prepared with the following phases of the
construction:
• core assembled
• active part before the installation in the tank
• transformer completely assembled.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 20 of: 23
 8.2.2 Failure Mode and Effect Analysis report (FMEA)
The Manufacturer shall prepare a Failure Mode and Effects Analysis report (FMEA), see annex
A. The FMEA is an essential information to ADDC/AADC to assess the possible causes of
malfunctioning, damages or faults, the relative probability of its occurrence and their consequences
using a rational method that considers the potential modes of failure, their effects and their critical
aspects.
The scope of this analysis is to identify the fundamental causes of possible failures or
malfunctioning of the referred asset installed on ADDC/AADC network system and therefore to
intervene with condition monitoring, preventive and corrective actions according to the probability
of the failure and the severity of its effects occurring.
In analysing the failures or malfunctioning of the subsystems, the most likely failure modes, with
the relating possible causes, the resulting effects on the rest of the system and the checks in place
(for prevention or failure mode detection) are listed and recorded in the specific FMEA worksheet.
The analysis is applied on the main possible faults or malfunctioning of the asset/equipment and
shall be performed according to the criteria defined in IEC 60812:2006 “Analysis techniques for
system reliability – Procedure for failure mode and effects analysis (FMEA)” on the basis of
available data.
The proposed table to record the failure modes and its analysis is given in below which is based
on FMEA to present the knowledge while supplying the asset. It is mandatory that all the
manufacturers shall submit the FMEA to ADDC/AADC for the supplied materials included under
this specification.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 21 of: 23
 9 DELIVERY, HANDLING AND LOGISTIC ISSUE

9.1 Packaging and transportation

The Supplier shall be responsible for all delivery procedures and provisions for storing the
transformers.
The transport environment class according to EN 60721-3-2 is:
• 2K12 / 2B2 / 2C2 / 2S5 / 2M5.
9.2 Installation and erection
Not applicable for distribution transformer.
9.3 Storage
The transformer shall be suitable to be stored outdoor.
The storage environment class according to IEC 60721-3-1 is:
• 1K26 / 1B2 / 1C2 / 1S13 / 1M11.

10 EXCEPTIONS
Possible exceptions to the present prescriptions, concerning the adoption of technical and/or
manufacturing aspects different from the ones prescribed in the present GS, can be evaluated by
TAQA/ADDC/AADC.
In such a case, TAQA/ADDC/AADC will take into account the opportunity to require additional
tests with regard to the technical/manufacturing proposed solutions.
Such exceptions can be approved by TAQA/ADDC/AADC.

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 22 of: 23
 ANNEX A –FMEA
Example of structure for FMEA analysis.

Failure Failure Failure Maintenance Task

Component Frequency
Mode Effects Cause / Actions

(This will help

ADDC/AADC in (This will help ADDC/AADC for PM / CM)
condition monitoring)

Client: ADDC/ AADC

STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: GROUND MOUNTED HERMETICALLY SEALED OIL FILLED DISTRIBUTION TRANSFORMER
DOCUMENT NO: S-TRD-GMO_01 Rev: 0-2022 Sheet: 23 of: 23