technical specification for oil-immersed distribution

Ministry Of Electricity and Renewable Energy وزارة الكهرباء والطاقة المتجددة

Egyptian Electricity Holding Company الشركة القابضة لكهرباء مصر

EDMS 08- 200- 1 EEHC DISTRIBUTION MATERIALS SPECIFICATION

Date: 21-05-2018

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EDMS 08-200-1

TECHNICAL SPECIFICATION

FOR

OIL-IMMERSED DISTRIBUTION TRANSFORMERS

(CONVENTIONAL & HERMETICALLY SEALED)

50 KVA up to 5000 KVA –22 / 0.4 KV

Issue: May-2018 / Rev- 1

اختياريةتوجد بنود (Optional items ) الطرح. بلق يعيجب تحديدها بواسطة شركة التوز




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CONTENTS

1 SCOPE 3

2 GENERAL SPECIFICATIONS 3

3 SERVICE CONDITIONS 4

4 VOLTAGE RATIO 4

5 VECTOR GROUP 4

6 RATED POWER 4

7 TAPPING RANGE 5

8 OVERLOAD CAPACITY 5

9 CAPABILITY OF WITHSTANDING SHORT CIRCUITS 5

10 LIMITS OF TEMPERATURE RISE 6

11 COOLING 6

12 INSULATION LEVEL 6

13 IMPEDANCE VOLTAGE 6

14 BUSHINGS 7

15 CORE 7

16 WINDINGS 8

17 TRANSFORMER OIL 8

18 OIL EXPANSION CONSERVATOR 9

19 TANK 9

20 ACCESSORIES 10

21 WHEELS 10

22 NAME PLATE 10

23 TRANSFORMER LOSSES 11

24 PENALTY AND REJECTION 12

25 TRANSFORMER TESTING 13

26 GUARANTEE TABLE : 15

27 MAX PERMITTED POWER LOSSES OF TRANSFORMERS (

at 95ºC ) : 16

GUARANTEE TABLE DISTRIBUTION TRANSFORMER 17




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1. SCOPE

This specification covers the supply of three (3) phase conventional or

hermetically sealed , two-winding oil immersed distribution transformers to be

installed indoor/outdoor.

2. GENERAL SPECIFICATIONS

The transformer shall be designed, for indoor installation with high voltage and

low voltage porcelain bushings provided with screwed stems and nuts with

washers. The tank shall be made of steel with bolted cover. Temperatures

between -5 ºC to 95ºC.

The transformers should comply with the latest edition of IEC publications

unless otherwise the specific requirements:

IEC 60076 for power transformer

Part 1 – General

Part 2 – Temperature rise

Part 3 – Insulation levels and dielectric tests

Part 4 – lightening impulse and switching impulse testing

Part 5 – Ability to withstand short circuit

IEC 60345 Loading guide for oil immersed power transformers

IEC 60137 For bushings

IEC 60214 For Tap Changer

IEC 60551 Determination of transformer and reactor sound levels.

IEC 60296 For new insulating oil transformer

EN 50464-4 Endurance test ( Tank Test For Hermetical Sealed Type ).




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3. SERVICE CONDITIONS

The transformers should be manufactured for the local service conditions as:-

Altitude less than 1000 meters

Max. ambient temperature 45ºC

Min. ambient temperature -5ºC

Relative humidity 10-100 %

4. VOLTAGE RATIO

The ratio of the transformers shall be 22000/400 v, + 0.5 % as a tolerance, 50 Hz

at no-load.

5. VECTOR GROUP

The winding connection group of the transformers shall be delta on the primary

side and star on the secondary side in accordance with the vector group Dyn11

as specified in IEC 60076.

6. RATED POWER

The transformer should be able to deliver for an unlimited period of time at the

main tapping of the tap changer, the maximum continuous power rating of

(50-63-100-160-200-300-400- 500-630-800-1000-1250-1500-1600-2000-2500-

3000-3500-4000-5000 K.V.A.) without exceeding the allowable temperature

rise limit .




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7. TAPPING RANGE

The transformers should be equipped with 3 phase, 3 wires, and lockable

manual off load tap changer, on the high voltage winding. The tap changer

switch is mounted on the tank cover.

The voltage regulation shall be affected in seven steps having the following

sequences (referred to input voltage):-

Tap No 1 (+5 %)

Tap No 2 (+2.5 %)

Tap No 3 (0 %)

Tap No 4 (-2.5 %)

Tap No 5 (-5 %)

Tap No 6 (-7.5 %)

Tap No 7 (-10 %)

8. OVERLOAD CAPACITY

Permissible overload capacity 20 % for 1.5 hr ( without exceeding the

permissible heating ) or according to IEC 60354 (according to distribution Co.

requirement).

9. CAPABILITY OF WITHSTANDING SHORT CIRCUITS

Transformers should be capable of withstanding, without damage, the thermal

and mechanical effects of short circuits at the terminals for 3 sec. duration

(S.C. level of 22 KV network is 750 M.V.A).




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10. LIMITS OF TEMPERATURE RISE

The transformer shall be able to deliver its max. continuous ratings, without

exceeding the permissible temperature rise limits:-

Top oil level temperature rise 45ºK

Winding temperature rise measured by resistance method 55ºK

Hot spot 60 ºC

11. COOLING

Cooling is by natural circulation of oil internal to the transformer and by

external air i.e ONAN.

12. INSULATION LEVEL

The following test voltages shall be applicable to the transformers:-

a. High voltage :Impulse withstand voltages are 125 KV for indoor

145 KV for outdoor

b. Power frequency withstand voltage 50 KV./ 1 minute

c. Low voltage Power frequency withstand voltage 3 KV. /1 minute

13. IMPEDANCE VOLTAGE

The impedance at mid-tap shall be as follow :

4 % for transformers (50-63- 100-160-200-300-400-500-630 KVA ) at 95 ºC

5 % for transformers ( 800-1000-1250 KVA ) at 95 ºC

6 % for transformers ( 1500-1600-2000-2500 KVA ) at 95 ºC

7 % for transformers (3000- 3500-4000-5000 KVA ) at 95 ºC




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14. BUSHINGS

Bushings are of porcelain and generally comply with the requirement of

IEC 60137 publication . The minimum creepage distance shall not be less than

2 cm/ KV for indoor, 4 cm/KV for outdoor (as per…. EDC requirements).

The high voltage bushings shall be fitted with duplex arc gap set at 65 mm.

For transformers with rating from 500 KVA and higher, the low voltage

bushing should be provided with copper flags and for transformers with ratings

lower than 500 KVA, the low voltage bushing should be provided with suitable

copper bars or copper flag.

As option:

For outdoor transformer the surge arrestor (gap less than metal oxide) 10KA,

24KV max. continuous operating voltage 20KV ± 5% (leakage pass 4cm/kv at

least) should be installed with medium voltage bushing.

15. CORE

The core should be made of low loss steel lamination which are made of cold

rolled grain oriented, annealed, high permeability, non-ageing, silicon steel type

with thickness less than 0.3 mm for each lamination.

The lamination should be insulated with suitable varnish or paint, solid

insulation is not acceptable.

The core, framework, clamping arrangement & general structure should be

mechanically robust to withstand any shocks to which they may be subjected

during transport, installation, service & faults.

The core construction should provide efficient cooling of its internal parts.




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The core joints should be properly interleaved, precautions shall be taken to

keep the noise at the level of 48-56 db ,according to rated capacity and at

measured distance of 1(one)meter, at mid tap & no-load & eliminate vibration

in the core when loaded & to diminish harmonic voltage as far as possible

especially the third harmonics.

16. WINDINGS

The winding conductors should be made of the best quality, high conductivity

electrolytic copper, complying with the requirements of the IEC publication

max. flux density in the yoke should not be more than 1.6 tesla.

The windings shall be clamped effectively so that they withstand shocks and

vibrations during transport and forces produced by the most severe short circuit

currents as indicated in item “9” of this specification.

17. TRANSFORMER OIL

The oil shall be of the best quality mineral oil of high breakdown strength, low

viscosity, high resistance to oxidation and shall not deteriorate under all loading

conditions.

It is required to have the ability to mix with another oil type.

Kinematic viscosity less than 16.5 mm2/s at 40ºC

Flash point ºC (open). > 140

Pour point ºC < - 30

Total acidity > 0.03 mg KOH per g of oil

Dissipation factor at 90 ºC < 0.005




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Breakdown voltage, as delivered > 50 KV / 2.5 mm

(test method 7.12)- IEC 60296

(Specification of oil according to BS 148 , 1984 & IEC 60296 Latest edition ) .

يئة.بلوغير ضار با لخلطل لقابالمستخدم في المحول ن يكون الزيت يجب ا

18. OIL EXPANSION CONSERVATOR

It shall be made of sheet steel with an adequate capacity to allow for the extreme

changes in the oil level e.g. when the transformer is off circuited at 0ºC and

when the transformer is full loaded at 45ºC ambient.

The quantity of oil shall be plainly marked on the conservator.

The conservator is provided with oil level indicator (sight glass at low voltage

side), dehydrate breather with orange silica-gel, oil filling and drain plugs and a

connection pipe for connecting the oil to the transformer.

ىخفضعلى ان يزود المحىل التقليذي بمبيه للزيت واحية الجهذ الم

19. TANK

The transformer tank shall be made of best quality plate steel with bolted cover.

The tank shall be rigid enough to withstand the mechanical stresses due those

occurring during transformer lifting and transport, without deformation and also

due to effects of S.C. inside the transformer.

Radiators should be welded to the tank. The transformer should have sufficient expansion for oil breath

( hermetically sealed)




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20. ACCESSORIES

1- Drain plug complete with control tap

2- Welded lifting shackles

3- Tank earthing , M 10 stud with nut shall be used.

4- Dial thermometer.

In the case of using hermetically sealed transformers, the following shall be

installed:

Pressure Relief valve (PVR).

DGPT2 device.

The transformer tank can be hermetically sealed by means of a nitrogen cushion.

21. WHEELS

The enclosure base should be fitted with 4 wheels to facilitate moving of the

transformers during installation in two perpendicular directions.

22. NAME PLATE

Each transformer should be fitted with a name plate fitted in a visible position,

showing the information listed below. Entries on the plate should be indelibly

marked by etching or engraving:

a) Manufacturers serial number

b) Year of manufacture

c) Type: Conventional /Hermetically Sealed.

d) Number of phases

e) Rated power




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f) Rated frequency

g) Rated voltages

h) Rated currents

i) Vector group

j) Impedance voltage

k) Type of oil

l) Total weight

m) Weight of oil

n) Connection diagram

o) A table giving tapping voltages of the positions

23. TRANSFORMER LOSSES

The transformer should be designed for minimum losses, when comparing

between different tenders, the present worth value of the annual capitalized cost

of guaranteed losses in the transformers shall be added according to the

following formula :-

P. w = K x 8760 x C [Wi + ( LS.F) P2 Wcu ]

Where

K = Present worth factor (L.E)

K=( (1+i)N -1 / i (i+1)

N ( )

i: interest rate , N: number of years

C = Cost of KWH which can be assumed to be 1.40 L.E (according to the

max commercial cost of KWH and can be adjusted as EEHC update) LS.F = Loss factor for the load = 0.4 Wi = Iron (No load) losses in KW at rated voltage and main tapping




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Wload = Load losses in KW at full load and 95ºC at main tap

P = Peak load (P.U.) = 0.8

24. PENALTY AND REJECTION

24-1 Rejection of Material:

If during inspection tests at the works attended by the customer

representative engineer any material is found to be defective or not

manufactured according to the specifications agreed upon the customer

representative engineer have the right to reject such material if he is not

convinced that it can satisfactorily be repaired. In such case the contractor

shall be obliged to replace the defective material without being entitled to

any extra payment whatsoever or to any extension of time of completion of

contract.

24-2 Penalty And Rejection For Decreased Efficiency

The contractor should keep the No load losses and load losses and to be

within the guaranteed values, should the loss values, measured from the

works tests, exceed the allowable tolerances in the IEC or approved equal

standards, then the customer representative shall have the right to reject

the transformer with such losses.

However, the measured losses deviate from the guaranteed figures, but lie

within the allowable tolerances (10 % total losses ) , then the excess losses

shall be evaluated as per the following formula and the contractor shall be

penalized accordingly.

P.W = K x 8760 x C [dwi+ (LS.F) (p2) dwcu] LE




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Where:

P.W= present worth (L.E) of annual capitalized cost of losses at 11%

rate of interest over 20 years.

K = Present worth factor (L.E)

K=( (1+i)N -1 / i (i+1)

N ( )

i: interest rate , N: number of years

C = Cost of KWH= 1.40 L.E (liable to adjusted at the time of evaluation

of the penalty) LS.F = Loss factor for the load = 0.4 dwi = Excess losses in KW at rated voltage and main tapping

dwcu = Excess Load losses in KW at full load and 95ºC at main tapping.

P = Peak load (P.U.) = 0.8

No credit shall be given for any decrease in the value of loss(es) below

the guaranteed.

24-3 Replacement of Rejected Material And Equipment

If according to the above articles, any material or equipment is rejected,

the contractor shall be obliged to replace it without extra payment.

25. TRANSFORMER TESTING

Customer representative has the right to send its representative to attend any or

all of these tests. Testing dates shall be advised by the contractor to permit

witnessing by Customer representative (s) . test certificates shall be sent to

customer representative.




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A. Type Tests :

These tests shall be carried out on one transformer for each type in

accordance with the requirements of IEC standards for transformers, these

shall include the following:

1- Full wave lightning impulse voltage withstand test.

2- Temperature rise test.

3- Chemical oil tests.

B. Routine Tests :

These tests shall be applied on each transformer in accordance with the

requirements of IEC standards for transformers, these shall include the following

1- Measurement of d.c. winding resistance .(the allowable deviation in

the dc resistance value between phases should be less than 5% at high

voltage side and should be less than 10% at low voltage side)

2- Turns ratio and polarity check or vector-group symbol.

3- Measurement of impedance voltage

4- Measurement of load losses.

5- Measurement of No-load losses.

6- Induced over voltage withstand test .

7- Separate – source power frequency voltage withstand test.

8- Electrical oil tests.

9- Insulation tests between windings and earth and between winding

each other (absorption factor (R60/R15 > 1.3 )) .

R60: insulation resistance at 60 second.

R15: insulation resistance at 15 second.




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C. Special Tests :

Special tests shall be made in accordance with the requirements of IEC

standards for types of transformers those have not yet supplied or for

transformers those have delivered but their design is modified , these shall

include the following:

1- Short circuit test

2- Measurements of sound level test

26. GUARANTEE TABLE :

The attached guarantee table shall be duly completed, signed & submitted with

the offer




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27. MAX PERMITTED POWER LOSSES OF TRANSFORMERS ( at 95ºC ) :

% Z load losses (W) at

95ºC

No load losses

(W) at 400 V

Power

(KVA)

4 875 168 50

4 1260 224 63

4 1505 272 100

4 2170 384 160

4 2520 456 200

4 3815 576 300

4 4638 638 400

4 5460 700 500

4 6430 825 630

5 7700 1015 800

5 9450 1222 1000

5 11700 1500 1250

6 13860 1785 1500

6 14900 1950 1600

6 15750 2736 2000

6 16300 3400 2500

7 19750 3950 3000

7 22850 4075 3500

7 25950 4200 4000

7 31500 5000 5000

N.B.

It is necessary to add a valve with a tap to each transformer to get an oil specimen

for testing.




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GUARANTEE TABLE

DISTRIBUTION TRANSFORMER

22 / 0.4 KV

1- Manufacturer

2- Type

3- Standard specification

4- Rated output at 45ºC ambient ( KVA )

5- Method of cooling

6- Oil type

7- System of connection

8- Material of insulation

HV winding ـ

LV winding ـ

Major insulation ـ

9- Material of core and its cross-section area ( mm² )

10- Max. core flux density at full load ( tesla )

11- Turns ratio

12- No load losses (watts )

13- load losses at full load current and 95ºC winding temperature (watts)

14- Resistance per phase at 95ºC For primary ( ohms )

For secondary (ohms )

15- Cross-sectional area of cu windings For primary ( mm² )

For secondary ( mm² )




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16- Permissible symmetrical S.C current at L.V side terminals for 2 sec (KA)

17- Primary voltage at normal tapping (volts )

18- Corresponding secondary voltage at

No load (volts ) ـ

Full load at 1 p .f. at 95ºC (volts ) ـ

Full load at 0.8 p.f. at 95ºC (volts ) ـ

( % ) Regulation at 1 p.f. at 95ºC ـ

( % ) Regulation at 0.8 p.f .at 95ºC ـ

19- Permissible overload duration without change of specified temp. rise

according to IEC 60354

yes [ ]

no [ ]

20- Full load current at LV side (Amps )

Full load current at HV side (Amps ) ـ

No load current at LV side (Amps ) ـ

21- Impedance voltage ( % )

22- Efficiency at normal ratio and 95ºC ( % )

( % ) At 100% rated output 1 p.f ـ

( % ) At 100% rated output 0.8 p.f ـ

( % ) At 75 % rated output 1 p.f ـ

( % ) At 75 % rated output 0.8 p.f ـ

( % ) At 50 % rated output 1.p.f ـ

( % ) At 50% rated output 0.8 P.F ـ

( % ) At 25 % rated output 1 p.f ـ




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( % ) At 25 % rated output 0.8 p.f ـ

23- Temperature rise at rated output above 45°C ambient temperature

A- At oil top level (°C )

B- Winding temperature (°C )

C- Core temperature (°C )

24- Tapping switch (on H.V. Side)

No. of steps ـ

( % ) Value of the step ـ

25- Medium voltage insulators

Length of leakage ( mm ) ـ

Arc gap (mm) ـ

26- Means for firmly bracing of trans . Winding to avoid loosening

them due to S.C

27- Transformers shall be complete with all accessories in tendered

specifications [Customer Spec ]

yes [ ]

no [ ]

28- Transformers shall be manufactured according to standards

mentioned in tendered spec. and will satisfy all requirements in

tender specifications

yes [ ]

no [ ]

29- Tender specifications are attached with our offer and each page is

signed by us

yes [ ]

no [ ]

30- Overall dimensions (Length x Width x Height ) ( mm x mm x

mm )




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31- Total weight of trans. With oil (kgm

)

Weight of oil (kgm )

32- Noise level ( db )

33- Colour of silica gel

I/we guarantee the correctness of above data for transformers we are offering to

Customer Company For Distributing Electricity.

Date: / / Signature of tenderer

N / B:

1- No offers shall be considered unless attached with both above guarantee table

dully completed and signed for each size of trans. and also our tendered

specifications with all pages signed by tenderer.

2- Tenderer shall sign “√” in front of yes or no in the above guarantee table.

technical specification for oil-immersed distribution

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