WESTERN ELECTRICITY SUPPLY COMPANY OF ORISSA LIMITED
TECHNICAL SPECIFICATION
(DISTRIBUTION TRANSFORMER)
1.
NOTE:
This specification covers design, manufacture, testing and supply of Distribution
transformers as per details furnished.
2.
LOCATION:
The transformers may be installed outdoor anywhere in Western Orissa.
Elevations of the sites above mean sea level shall not exceed 1000 meter.
3.
SYSTEM DETAILS:
All systems are effectively earthed at the neutral points of the star connected
windings of the transformers.
4.
WEATHER CONDITIONS:
01.
The
The area is also subject to heavy monsoon rains 80 to 90% of the annual
precipitation being in the month of June to October.
Maximum Ambient temperature
Maximum Ambient temperature in shade
Maximum temperature of air in Sun
Maximum Humidity
Average rainfall per annum
Maximum Wind pressure.
Isoceraunic level
45°C
50°C
60°C
95°C
3.175 mm.
150 kg/m.sq.
50 days/year
02.
For the purpose of this specification the limits of ambient temperature shall be 40°C
average over a 24 hours period.
5.0
STANDARD:
01.
Transformers
conform to
requirements
ISS (All as
02.
In the event of a conflict between the above standards and the stipulation laid down
in the specification the later shall govern.
6.0
RATING AND GENERAL DATA FOR DISTRIBUTION TRANSFORMERS:
01.
covered by this specification shall, unless otherwise specified be built to
the latest Indian Electricity Rules, wherever applicable and the
of latest issue of ISS: 1180 and ISS 2026, CBIP Standards and other
per latest issues).
Core form, three phase oil immersed step down two winding distribution transformers
for outdoor installation in lighting area of outdoor type as stated.
02.
Rating: Please refer to Annexure -A.
03.
Number of Phase: Three.
04.
Frequency: Transformer shall be suitable for continuous operation with a frequency
variation of: 3% from normal 50 Hz without exceeding the specified temperature rise.
05.
Type of cooling: ONAN
06.
Voltage Ratio: Refer to Annexure - A.
07.
Vector Group Reference: Dyn11, unless otherwise stated.
08.
CONNECTION:
The primary (HV) winding shall be connected in delta and the secondary (LV)
winding star with vector group Dynll. The neutral of the secondary (LV) winding
shall be brought out to a separate insulated terminal.
For 10 KVA & 16 KVA Rated: Single Phase
The size (Cross Section) of the neutral connection conductors and jumpers must
be of same size as that of the phase connection conductors and jumpers and
shall be properly supported and insulated.
09.
Temperature Rise:
(a) For winding 50°C (measured by resistance) and for top (Measured by
thermometer) when tested in accordance with IS: 2026/1977.
10.
% Impedance: As per Annexure - A.
11.
Terminal Arrangement:
Bare on outdoor porcelain bushings for outdoor type transformers as per ISS j CBIP
specification and other relevant specification. The inner end of the bushing shall be
completely immersed in the oil. The bushing rods should be locked in position so
that twisting of leads is avoided during tightening of nuts of bushing rods.
12.
Tapchanging Switch:
Off circuit tap changing switch should be provided to transformers above 100 KVA
rating where switch position No.1 shall correspond to the maximum plus tapping. The
tap position No. should be of increasing order at clock-wise direction, the top
marking should be of engraved in nature. Provision shall be made for locking the
tap switch handle at each position. The locking arrangement shall be such that
padlock cannot be inserted unless required contacts corresponding to the tap position
are correctly connected with full contact pressure. Mechanical backstops should be
provided at the limiting tap position. The tap changing shall be effected by an
external three-phase gang operated switch. The Operation shaft shall be brought out
of the tank provided with a hand wheel so that it can be operated at standing
height from ground level and shall be easily accessible. The tap changer handle
should be fitted on the side wall of the transformer.
The supplier must provide all information to establish the quality, make and
type of tap changers to be used in the transformer with sectional drawings howing
the size, arrangement and functioning of the contacts and tap switch.
The sample of the tap switch used for different sizes of transformers and
voltage grades shall have to be approved before using them in transformers, if called
for.
13.
LEADS:
All leads of the windings, connection of the windings or their wires to one another,
to terminal bushings or to a tap changer shall be properly insulated and covered
with insulation sleeves. The soldering materials shall have higher melting temperature
above 300°C and preferably above 400°C for better thermal endurance and
mechanical strength. The tenderer shall specifically mention the method and materials
to be used by them for lead connections.
14.
Conductors: Aluminum or Copper as indicated in Annexure-A.
7.0
TANK:
01.
Tank wall must be fabricated from tested quality of mild steel sheets of thickness
minimum 3.15 mm for transformers above 10 KVA and upto 250 KV A and
minimum 4 mm for the next higher ratings. Top and bottom plate of the tank must
be of minimum 5 mm. thick. It should be shaped so as to make welding to a
minimum. All welding shall be done electrically and relieved of welding stresses. All
seams shall be double welded (both outside & inside of tank) for absolute oil
tightness. The tank wall shall be formed by stiffeners of structural steel for general
rigidity and to dampen transformer noise. It shall also withstand partial vacuum as
per latest CBIP manual against standard atmospheric pressure. Maximum Tolerance
on the negative side of the steel sheets shall be 0.15 mm. Tank design shall be
such that the core and coil assembly can be tanked or detanked freely and easily
without dismantling LV bushing etc. The top cover plate should be slightly sloped
towards HV side for non-accumulation of rain water / transformer oil.
Inside wall of the tank and the M.S. Channel shall be painted with varnish
or with hot oil resistance paint.
Stiffener shall be continuously welded on the tank wall. Upto 100 KV A stiffener &
top flange are to be of MS flats. Above 100 KV A the stiffener & top flange are to
be of MS angles only, not MS flats.
02.
The tank cover shall be bolted on to flanged rim of the tank with a weather proof,
hot oil resistant, resilient gasket in between for oil tightness. If the gasket is
compressible, metallic strips shall be provided to prevent over compression of the
gasket. Access and inspection holes blanked with oil tight gasket sealed cover plate
shall be provided for working on the connection of the lead of windings, the bottom
terminals of bushings and the off load tap switch. Bushing turrets, cover of access
holes, covers for pockets of thermometers and other devices shall be designed to
prevent any ingress of rain water into the tank and the tank cover as a whole shall
shed off all rain water.
All the gaskets including Gasket used between tap cover and tank flange shall be of
neoprene rubberised cork sheet RC 70-C and shall be provided with watertight
compound between the tank flange of the gasket. Top cover gasket & HV bushing
gasket should be of minimum 6 mm thick. The gaskets should be of either Grind
beck / Gujarat cork / Bharat corrob / Talbros / Cortica /any reputed make. A
sample of piece of gasket of sizes 100 X 100 mm which quality is to be used
should be sent along with the tender.
G.I Nuts, bolts, flat washers, spring washers shall be used and suitably spaced to
press the tank cover. Following minimum clearance between top yoke and tank cover
are to be maintained:
a) Height of oil level from top yoke to top cover shall not be less than 100
mm for 11KV & 150mm for 33KV. The thermometer pocket (Dimensions as
per ISS) should be placed nearer to the top core towards LV side and
should have provision for fixing stem type oil temperature indicator for all
KVA rating jobs.
b) Transformers fitted with off load tap changer shall maintain minimum
clearance of 25 mm. for 11 KV and 50 mm. for 33 KV from any live part
of the tap changer to top yoke. Height of oil level from live part of tap
changer to top cover shall not be less than 80 mm for 11KV & 130mm for
33KV.
03.
The conservator shall be provided with oil level indicator, drain plug & oil filling
hole with cover. Conservator pipe shall be welded on the top cover and should
be projected at least 20 mm inside the bottom of conservator so as to create a
sump for collection of impurities. The minimum oil level should be above the top
of the HV bushing.
The conservator oil level indicating portion (which contains oil) should be
painted in White colour. The indicating portion of the glass should be of minimum
15mm width. The glass should be of transparent & non-sticky type so that the
oil level can be easily seen from a distance of 8 meters.
Inspection cover has to be provided on the top cover for ratings of above
250 KVA. The inspection cover shall be suitably elevated from the level of the
top cover to prevent ingress of water into the tank. Air release plug has to be
provided on inspection cover.
04.
PRESSURE TEST:
The tank shall be fixed with a dummy cover with all fittings including bushings in
position and shall be subject to air pressure of 35 Kpa above atmosphere for 30
minutes. The permanent deflection of flat plate after pressure has been released shall
not exceed the values given below:
Length of plate
Upto 750 mm.
751 to 1250 mm.
Deflection.
5 mm.
6 mm.
05.
If required, the manufacturers should submit pressure test certificate for the
transformer tanks at least for cash batch either conducted by them or by their
fabricators, for which order is placed with them & the edges (both inside &
outside) of the transformer tanks should be double welded electrically & scrupulously
as per the specifIcation.
8.0
CORE:
01.
The magnetic core shall be build of very low loss silicon steel preferably cold rolled
grain oriented steel.
02.
The materials used for insulating the sheets shall have high interlamination resistance
and rust inhibiting property. It shall not be deteriorated by from hottest operating
temperature and clamped pressure of the core of disintegrates due to mechanical
modes of core vibration. It shall not have the least tendency to absorb moisture or
to react with the dissolved particles in the insulating oil thus accelerating sludge
formation.
03.
The assembled core shall be securely clamped in the lines and in the uniform
pressures so as to minimize the noise from the core.
The tie rod & core bolt should be made of MS Bright rods. Upto 100KVA
the rod dia should not be less than 12 mm & above 100KVA the rod dia should
not be less than 16 mm.
04.
The core clamping frame shall be provided with lifting eyes for the purposes of
tanking and untanking the active part of the transformers. The whole core shall be
electrically connected by copper strip of adequate section to the core frame at two
points for being eventually earthed through the tank to drain off electrostatic potential
that may be build up.
Core clamp structure should be of MS channels only. Upto 100 KVA ISMC
75X40 mm, for 250 & 315 KVA ISMC 100X50 mm, & for 500 KVA & above
ISMC 125X65 mm are to be used.
Core base (Foot plate) should be of ISMC 75X40 mm for all KVA ratings
& should be properly bolted to the core clamp.
05.
The supporting frame work of the cores shall be so designed so as to avoid the
presence of pockets which would prevent complete emptying of the tank through the
drain valve or cause trapping of air during filling.
06.
Adequate provision shall be made to prevent movement of the core and winding
relative to the tank during transport installation or while in service.
07.
The cores shall conform to:
IS: 3024 = 1965 Electrical sheet steel. &
IS: 649= 1983 method of test of steel sheet.
08.
Flux density at normal voltage & frequency shall
the cores should be annealed rust free, of same
M3jM4 or better grade should be used. Suppliers
certificate, Purchase Order copy, received challans
time of inspection call definitely.
09.
Over flux in the core shall be limited to 12.5% to ensure that in the event of over
voltage to the extent of 12.5%, the core does not get saturated.
10.
Maximum No-load current in terms of % full load current (without any positive
tolerance at normal supply frequency (+j- 3% tolerance) should be as follows:
KVA
25
63
100
250
315
500
At 100 % Voltage
3.5
3.0
2.5
2.0
1.9
1.7
not be more than 1.65 tesla. All
grade & same thickness. Cores of
should give the manufacturer's test
j bill copy of core supplier at the
At 112.5% voltage
7.0
6.0
5.0
4.0
3.8
3.4
630
1.7
3.4
11.
Tenderer should give the core details like Grade, Bmax, Core dia, Core Window
height, Core limb center, Step widths & stacks, Core lamination factor & stack
factor, Core weight.
Usually core lamination factor for M3 grade 0.23 mm thick core is 94.5% &
for M4 grade 0.27 mm thick core is 95%.
12.
The No-load loss is to be given by design calculation showing the amount of stray
loss & active core loss.
13.
Joint in the core limb or core yoke is not acceptable. However joint of core limb to
core yoke should be of Mitred joint at an angle of 45° only. Rectangular joint of
limb to yoke is not acceptable.
9.0
WINDING:
01.
Transformer shall be provided with the requisite number of windings and shall be
designed to withstand the electromechanical stress exerted under short circuit
conditions as per ISS: 2026: 1977.
Class "A" insulation shall be used. Paper insulation shall be of best quality. Wooden
supports, if used, shall be well seasoned and compatible with hot transformer oil.
02.
The insulation level of the windings shall be as follows:
Voltage
11000
33000
Impulse Voltage
(KV peak)
433
Short duration power
frequency voltage (KV)
--75
170
28
70
3
03.
The winding shall be so designed to reduce to a minimum the out of balance forces
in the transformer at all voltage ratios.
04.
The winding shall also be designed such that all coils assembles of identical voltage
rating shall be interchangeable and repairing of the winding can be made readily
without special equipments.
05.
BRACING ON WINDINGS:
(1)
The windings and connections of all transformers shall be braced to withstand
shocks, which may occur during transport or due to switching short circuit and other
transient conditions during service.
(2)
Coil clamping rings, if provided, shall be of steel or of suitable insulating material.
Axially laminated material other than bakelised paper shall not be used.
06.
WINDINGAND CLEARANCE INSIDE THE TANK:
CONSTRUCTION:
The winding shall be assembled on the core co-axially for magnetic balance and
symmetrically for electrically balance. Liberal ducts shall be provided for oil circulation
and lowering hot spot temperature in the winding. Spacers, wedges shall be robust,
hard insulation and so fitted in the winding that they will neither move, nor permit
any relative movement of any part of the winding during normal service and under a
terminal short circuit, not mechanically injure any insulation in the windings.
i) The transformer shall have separate HV and LV windings made of
electrical grade hard drawn Aluminium or Copper wires as specified conforming to
relevant ISS of latest edition.
ii) The maximum current density of Windings without any positive tolerance in
amp/sq.mm taking account of deduction of strip conductor's corner radius chamfering
as per IS are as follows:
.
HV winding
LV winding
For Aluminium winding
1.40
1.55
For Copper winding
2.90
3.20
iii) The Designed maximum SC current density of Windings without any
positive tolerance in amp / sq.mm taking account of deduction of strip conductor's
corner radius chamfering as per IS"are as follows:
HV Winding
LV Winding
For Aluminium winding
31.0
34.0
For Copper winding
55.0
62.0
iv) The resistance variation of phases should be limited to 7% only.
below.
v) The details of insulation covering of the LV and HV conductors are tabled
VOLTAGE RATIO
11/0.433 KV
KVA
LV
HV
25
63
100
250
315
500
DPC,AL
DPC,AL
DPC,AL
TPC,AL
TPC,Cu
TPC,Cu
DPC/SE(Medium)AL
DPC,AL
DPC,AL
DPC,AL
DPC,Cu
DPC,Cu
vi) No. of HV coils per phase/ or limb shall not be less than the following:
Voltage
Ratio(KV)
11/0.433
No. of HV Coils KVA Wise.
25 KVA 63 KVA 100 KVA 250 KVA 315 KVA
4
4
4
4
4
500 KV A
4
The recommended minimum size of S.E. AL Conductor to be used in the HV
side of the 25 KVA transformer is 21 SWG (0.5189 sq.mm.). The quality of
enamel in the S.E. wires to be used is to be ensured. Similarly qualities of
insulating materials are also to be ensured. The method of ensuring- the above
qualities may be stated.
vii) Minimum clearance between HV coils/or sections should be 6.4 mm and at tap
break the minimum clearance should be 15 mm including 3.0 mm insulating ring.
viii) Minimum interphase clearance (HV to HV) with 3mm (2X1.5 mm thick)
phase barriers should be 10 mm upto voltage class of 12 KV.
For 36 KV class transformers, the interphase clearance should not be less
than 20 mm with 6 mm (2X3 mm thick) phase barrier. The phase barrier should
cover the MS tie rods.
ix) The minimum end clearance (HV to earth) should be 22 mm upto voltage
grade 12 KV and should be 60 mm for voltage class 36 KV.
x) The end insulation at both ends shall include upto 36 KV grade windings:
class at the
windings.
(a) 3 mm thick yoke insulation over windings of the phases.
(b) 6 mm common block for 12KV & 10 mm common block for 36KV
top and bottom for circulation of oil in the vertical ducts in LV and HV
xi) The minimum radial clearance in windings will be as follows:
(a) Between core and LV winding 3.5 mm including cotton tape, 10 mm.
insulating paper wrap to cover the core limb & 3 mm oil duct runner
between the paper wrap & the LV coil.
(b) Between LV winding and HV winding 10 mm including 1.0 mm thick HV
cylinder placed between the oil duct runners, Where LV winding is 433 V
grade and HV winding 12 KV grade.
(c) Between LV winding and HV winding of 36 KV grade~ 19 mm
including 2.0 mm thick HV cylinder placed between the oil duct runners.
xii)
3.0 mm oil duct runner for cooling is to be provided radialy between the layers in
the LV coil for transformer rating 250 KVA & above.
xiii)
1 no. of transposition has to be done when the no. of conductors for LV coil is
more than two (2) nos.
xiv)
Minimum clearance between tank wall and HV windings / Live parts:
(a) Where the HV winding is 12 KV class, clearance: 25 mm. No additional
insulating
barrier shall be used in between.
(b) Where the HV winding is 36 KV class clearance: 60 mm.
The dimension in respect of ducts and clearance in windings shall hold good for the
assembled windings and core prior to application of pressure for permanent shrinkage
of coils. The changes in dimensions in finished condition shall remain within 15%
(fifteen percent).
xv)
All the insulating pressboards should be of either "TYPE-D" grade or Precompressed grade. The make should be of Raman / Senapathy / Any reputed
manufaturer's. A sample piece of pressboard of sizes 100 X100 mm which quality is
to be used should be sent along with the tender.
07.
(i) The stacks of windings shall receive adequate shrinkage treatment before final
assembly. Adjustable devices shall be provided for taking up any possible shrinkage
of coils in service.
(ii) Meggering of the core-coil assembly for improvement of Insulation Resistance
should be done by putting the core-coil assembly inside the furnace, and not
adopting the method of shorting the LV side & giving 3-phase supply to the HV
side.
(iii) The insulation resistance at 30°C should be maintained at least 1000MQ. The
PI value should be maintained at least 1.25.
08.
Conformation to IS standards relating to conductors and insulation.
The following Indian standards specification shall govern the quality of conductor,
covering insulation such as enamel, paper and insulating boards.
(1) IS: 2067 - 1975: Wrought Aluminium Wire for electrical purposes.
(2) IS: 4800 - 1968: Enameled round winding wire.
(3) IS L 7404 (Pt- I & II) 1974: For paper covered copper conductor (round
and rectangle)
(4) IS: 1397 - 1967: Kraft paper
(5) IS: 335 - 1983: New Insulating Oil.
(6) IS: 1576 - 1967
IEC: B-2.1}
IEC: B - 3.1}
Solid press Board for electrical
IEC: B - 4.3}
purposes.
10.
BUSHING:
The bushings shall conform to IS: 2099 - 1962 (Latest): Bushing for Alternating
voltages above 1000 volts. The dimensions of bushings shall conform to IS: 3347.
The clearance in air between live and conductive parts and live conductive
part to earthed structures shall be as follows:
Clearance
--------------------------------------------------------------------------------------------------------------Nominal
System
Voltage
KV rms.
--------0.433
11
33
Test Voltage
Impulse
KVR
Phase to
phase
(mm)
Phase to
earth
(mm)
Arcing
Horn
Gap.
-------------75
170
---------85*
280**
350
--------40
140
320
-------------85
220
* Except for upto 25 KVA transformer for which clearance will be 75 mm minimum
as per ISS.
** Up to 100 KVA rating the clearance will be minimum 255 mm.
10.0
Cooling Arrangement:
01. The transformer shall be suitable for loading of 100% continuous maximum rating with
'ON' cooling without exceeding the thermal limit.
02.
The transformer shall be fitted with cooling tubes bent and welded to tank or
radiators consisting of a series of separate circular or ERW Elliptical tubes of Sec57, or a pressed steel plate assembly formed into Elliptical oil channels, welded at
their top and bottom to the tank. In case of Pressed Steel Radiator no joints in
between the radiator fins connecting pipe assembly is accepted.
03.
The radiator tubes shall be seamless, made of CRCA sheet having a maximum
wall thickness of 1.5mm and a clean bright internal surface free from rust. They
shall be suitably branched to protect them from mechanical shocks normally met
in transportation and to damp the modes of vibration transmitted by the active
part of the transformer in service.
04.
The manufacturer will have to provide wall surface area of tank & radiator cooling
tubes separately as part of the guaranteed technical particulars. They have to give
the oil temperature rise calculation with radiator size & pieces provided along with
the cooling chart of the radiator of the same manufacturer are to be used.
11.0
PAINTING:
11.01 The surface to be painted shall be made free from all rust and mill scale or foreign
adhering mater of grease and all external rough surface cavities by shot blasting or
other approved method.
11.02 All steel surfaces in contact with insulating oil as far as accessible shall be painted
with
heat resistant, oil insulable, insulating varnish or paint.
11.03
All steel surfaces exposed to weather shall be given a primary coat of Zinc
chromate and two coats of dark admiralty gray paints.
11.04
All paints shall be carefully selected to withstand tropical heat and extrimitics of
weather.
The paint shall not scale off or wrinkle or be removed by abrasion due to
normal handling.
11.05 All nuts and bolts used in the transformer for external fittings shall be galvanized or
zinc
passivated.
11.06 All nuts and bolts used in the transformer for internal fittings i.e. in oil shall be
painted.
12.0
01.
TEST & INSPECTION (AS PER ISS):
Routine Test:
All transformers shall be subjected to routine tests at the manufacturer's works. The
following tests are to be carried out.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
Measurement of winding resistance by Kelvin / Wheat stone's Bridge.
Ratio, polarity and vector group.
Load loss & Impedance voltage.
No-load loss & No-load current at normal & 112.5 % over voltage.
Insulation resistance & PI value by motorised megger.
Induced over voltage withstand.
Separate source voltage withstand.
Oil BDV test.
Temperature rise test - will be conducted on one transformer for every lot
offered for inspection. As per amendment No.2, October, 1984 to IS 2026
(Part-2) - 1977, the temperature rise test for transformers having tap
changer will be performed on the lowest tap at appropriate current relating to
the said tapping (with losses fed corresponding to minimum voltage tapping).
(j) Oil leakage test-Pressure test at 0.8 kg/ sq. cm. will be conducted on one
transformer for every lot offered for inspection.
02.
TYPE TESTS:
The supplier should produce the type test reports of the above KVA ratings done
earlier within last 5 years for any design.
(a) Dynamic short circuit withstand test.
(b) Impulse voltage withstand test.
(c) Temperature rise test if any.
03.
The transformers to be manufactured and supplied should have identical design and
drawings as that of approved design and drawings. Approved drawings are to be
submitted before commencement of supply.
04.
Performance under External Short Circuit conditions and limit of temperaturense.
All transformers shall be capable of withstanding, without damage, the thermal and
mechanical effects of a short circuit at the terminals of any or all windings for 2
secs. The temperature in the windings after 2 secs of over current must not exceed
200°C for AL and 250°C for CD windings.
05.
The Board may also make a testing arrangement for carrying out short circuit tests
with duration not exceeding 2 secs. For Distribution Transformer up to 100 KVA in a
suitable place. The transformer subjected to such test shall be examined for
temperature rise within specified limit and for any damage or displacement of any
parts within the transformer.
The transformer so tested shall not exhibit more than 2 percent variation in
percentage reactance after the short circuit test from the original measured value
before testing according to clause No.11.5.4 of IS 2026 (part-I), 1977.
The selection of transformer for such test shall be carried out at the discretion of
the Board from any lot of Transformers of same capacities offered for inspection and
testing before delivery.
06.
Inspection:
The transformer may be stage inspected at the factory of the manufacturer. The
manufacturer shall intimate in advance in writing to the purchaser about the stages of
manufacture & subsequent readiness of the transformers to enable him to carry out
stage inspection, final inspection and testing of the finished transformers.
The stage inspection will be carried out at the discretion of the purchaser
during the process of manufacturing of the transformers. The manufacturer need not
stop the process of production because of programme of stage inspection of the
Purchaser.
of:
While offering for final inspection the following point should invariably be taken care
(i)
Nameplates should be welded / reveted on the tanks of the
transformer. SL No. of the transformer should be welded to the main tank
wall before inspection.
(ii)
The bolts connecting the top cover of the transformer with the tank at
the two opposite corners are to be provided with holes at their lower
portions which would go beyond nuts so that the transformers may be
sealed by inserting sealing wire in these holes.
07.
The purchaser has got the right to have further tests carried out at any place
including the testing at supplier's end, which may include cut-open test, winding
resistance test, etc.
14.0
Contract Drawings:
The General outline drawing giving details of dimensions and fittings should be
submitted for each type of transformer. 15.0 Over-load Capacity:
15.0
Overload Capacity
Each transformer shall be capable of carrying sustained overload as stated in ISS.
16.0
Transformer Oil:
The oil shall be as specified in IS: 335- 1993 and it shall be free from moisture
and have uniform quality throughout. It shall be capable of withstanding BDV of
60KV at 2.5 mm gap moisture contain 5ppm. The transformer oil used should be
new transformer oil of Apar/ Savita/Raj or any reputed brand. Reclamation oil should
not be used.
17.0
(i) The outdoor apparatus including bushing insulations shall be designed so as to
avoid
pocket in which water can collect.
(ii) All mechanism shall be so as to prevent sticking due to rusher correction.
(iii) All apparatus shall be designed to minimise the risk or accidental short circuit
caused by animals & birds.
18.0
Intemal Earthing Arrangement:
All metal parts of the transformer with the exception of the individual core
laminations, core bolts and associated damping plate shall be maintained at same
fixed potential and core should be earthed at two points by copper foil.
19.0
ISS.
Anything not covered by this specification will be as per relevant REC Specification /
20.0
FITTINGS AND ACCESSORIES:
1. Two earthing terminals of M12 size.
2. Oil level gauge indicating three positions of oil marked as follows
Minimum at
5°C
Normal at
30°C
Maximum at
95°C
3. Lifting lugs
4. Rating, diagram and terminal marking plate of AL etched.
5. Transparent type silicagel breather with aluminium end cover & oil cup. 250gram
silicagel capacity for transformer rating up to 100KVA. 500gram silicagel capacity
for transformer rating above 100KV A & up to 630KVA.
6. Drain cum sampling valve as per REC upto 100KVA rating & 1" Wheel valve
above 100KVA.
7. Filter valve 3/4" size upto 100KVA & 1" size for above 100 KVA.
8. Platform mounting arrangement as per ISS up to 100KVA rating.
9. HV bushing with arcing homo
10. LV bushing for phase & neutral.
11. Bi-metallic connector for both HV & LV as per REC specification. For 1000
ampere rating brass palm connector as per ISS has to be supplied.
12. Filling hole having P-1 1/4" thread on conservator.
13. Thermometer pocket as per ISS.
14. Air release plug.
15. Conservator with fittings.
16. Off circuit tap switch for 250KVA & above.
17. Cast iron roller for 250KVA & above.
18. Explosenvent with air release plug for 250KV A & above.
19. Inspection cover with air release plug for above 250KV A.
20. Stem type oil temperature indicator for 250KV A & above.
21. SL No. of the transformer welded on the tank.
21.0
To facilitate testing, arrangements should be made for carrying out Heat Run
Tests of
two transformers of different capacities simultaneously.
ANNEXURE=A
1.
TECHNICAL SPECIFICATION
Loss Figures & % impedance
As per Standards
Losses Required to bid
No load
Loss in
Watts
(3)
Load Loss
No load
Load Loss
Percentage
KVA Rating Voltage Ratio.
at 75°C in
Loss in
at 75°C in
Impedance
Watts
Watts
Watts
(1)
(2)
(4)
(5)
(6)
(7)
10 KVA
11/0.250 KV
4.5%
50
200
16 KVA
11/0.250 KV
80
475
4.5%
65
250
63 KV A
11/0.433 KV
180
1235
4.5%
180
1235
100 KVA
11/0.433 KV
260
1760
4.5%
260
1760
250 KVA
11/0.433 KV
540
3700
5%
540
3700
500 KVA
11/0.433 KV
950
6500
5%
950
6500
No load loss and load loss figures as mentioned above are without any positive tolerance.
Tolerance in respect of percentage Impedance will be as per ISS-2026-1977
N.B : - Bidding is required primarily for the losses mentioned in Col.6 & Col.7
2.
Tappings:
+2.5% to -7.5% in steps of 2.5% for 250 KVA & above.
Off circuit tap changing switch should be provided on HV side Switch position No.1 shall
correspond to the maximum plus tapping. The tap position No. should be increasing
order in clock-wise direction. Provision for locking of the tapping switch should be made.
The tap marking should be of engraved in nature. The position of the tap changer
should be in the opposite side of the Thermometer packet.
3.
Winding Materials: Aluminium - Up to & including 250 KVA Rating
Copper - Above 250 KVA Rating
4.
Limits of temperature rise: (When tested as per IS: 2026- 1977 (part-II) latest)
40°C/50°C for top oil and winding respectively.
SPECIAL INSTRUCTIONS TO TENDERER
1. Warranty for the ‘Distribution Transformers’ shall be quoted for “30
months from supply or 24 months from commissioning, whichever is
earlier”.
2. We provide herewith a blank format as GTP-I, II & III for your quoting
which may be followed. Any deviation may be indicated for our
appraisal.