2.0
SPECIFIC REQUIREMENTS
The transformer shall generally comply with the following specific requirements:
2.1 The Transformers shall be natural air cooled.
2.2 Windings shall be totally encapsulated in suitable class F resin, which shall provide both
dielectric strength and mechanical stability for the windings. Resin shall be with high heat
dissipation rate or emissivity and it shall be stable when exposed to sunlight. Further, the
Bidder shall take care of absorption of energy due to sunrays as regards the temperature-rise.
2.3 The transformer LV side shall be connected to the switchgear through PVC Cables.
connections shall be through cables.
2.4
The HV
The insulation class for cast resin transformer shall be class F.
2.5 3 Nos. resistance winding temperature detectors/thermistors shall be provided. These
shall give alarm at 120 deg.C and give trip signal to trip the transformer incoming breaker
at 140 deg.C through RTDs/Thermistor and Temperature Surveillance protection arrangement.
2.6 The Transformer shall be provided with adequate no. of embedded
temperature detectors for remote indication in CRTs and necessary
indication instruments in local shall be provided.
2.7
The temperature detectors shall be wired through terminal box mounted on transformer
and from there shall be taken to the marshalling box.
2.8
Encapsulated winding shall be free of internal voids, surface irregularities etc. No
surface finishing of encapsulated winding shall be undertaken after the process of
encapsulation.
2.9 Epoxy moulded of specified rating Neutral CTs for Earth fault
protection shall be
provided.
2.10 Temperature rise of winding shall be limited to 70 deg.C over an ambient of 50 deg.C.
3.0
Enclosure
3.1
The encapsulated cast resin transformer shall be housed in naturally
entilated floor mounted cubicle with louvers backed by fine brass wire mesh. Degree of
protection for enclosure shall be at least IP 32.
3.2
Protective housing made of sheet steel of minimum 2 mm thick
conforming to IP32
shall be provided to prevent contact with live parts.
Enclosure shall have ventilating openings provided with wire mesh screens and shall be
supplied with suitable lifting lugs.
3.3
The enclosure shall be adequately reinforced to ensure rigidity so as to permit
transportation of transformer within enclosure.
3.4
Double leaf access with safety limit switch shall be provided with concealed hinge and
neoprene gaskets for easy access to HV links and also for withdrawal of core and coil assembly
if required.
3.5
Enclosure shall be provided with lifting lug and grounding terminals.
Further the enclosure door shall have locking provision.
3.6
Necessary cubicle illumination shall be provided in the enclosure.
4.0 Core and Coils
4.1 The transformers may be 3 phase core type. The core shall be built up with high grade,
non aging, low loss, high permeability grain oriented cold rolled silicon steel laminations
especially suitable for core material. Laminations shall be annealed in a non-oxidising
atmosphere to relieve stresses and restore the original magnetic properties of CRGO sheets
after the cutting and punching operations.
4.2 CRGO sheets shall be coated with Insulation varnish. Insulation shall be able to withstand
annealing temperature as high as 850 deg. C and will reduce eddy current to minimum.
4.3 The coils shall be manufactured from electrolytic copper conductor of high proof stress
with more numbers of radial supports and fully insulated for rated voltage. For encapsulated
design, HV & LV coils shall be separately encapsulated under vacuum in cast resin compound.
4.4 The insulating material shall conform to class F. Coils shall be so insulated that impulse
and power frequency voltage stresses are minimum and to withstand power frequency voltage
stresses and to withstand even the severest of temperature fluctuation.
4.5 Flux density at normal over voltage or frequency shall be such that under 10% overvoltage
condition it will not exceed 1.9 tesla.
4.6 Coil assembly shall be suitably supported between adjacent sections by insulating spacers
and barriers. Bracing and other insulation used in assembly of the winding shall be arranged
to ensure a free circulation of the air and to reduce the hot spot of the winding. Permanent
current carrying joints in winding and leads shall be brazed.
4.7 All leads from the windings to the terminal board and bushings shall be rigidly supported
to prevent injury from vibration or short circuit stresses. Guide tube shall be used where
practicable.
4.8 The core and coil assembly shall be securely fixed in position so that no shifting or
deformation occurs during movement of transformer under short circuit stresses, switching or
other transients.
4.9 The transformer with core coil assembly shall be provided with bi-directional flat type
rollers and clamps/accessories for fixing the transformer. The wheels shall facilitate the
movement of transformer for taking in/out of the cubicle.
5.0 Tappings
5.0.1 Off-circuit taps as specified shall be provided on the high voltage winding.
5.0.2 The transformer shall be capable of operation at its rated KVA on any tap provided the
voltage doesn't vary by more than +/- 10% of the rated voltage corresponding to the tap.
5.0.3 The winding including the tapping arrangement shall be designed to maintain
electromagnetic balance between HV and LV windings at voltage ratios.
5.1 Off circuit tap changer
The off circuit tap changing shall be effected by change of links. Arrangement shall be such
that the contacts are correctly engaged. A warning plate indicating that link shall be
operated only when the transformer is deenergised shall be provided.
6.0 Terminal arrangements
6.1 Terminals for cable connection shall be brought out through side wall mounted bushings to
a detachable cable end box with disconnect link.
6.2 Cable end box shall be self supporting, weatherproof, air filled type with sufficient
space inside for termination and connection of cables.
Cable end box shall be furnished complete with removable gland plate, double compression brass
glands, tinned copper lugs, armour clamps and necessary hardware.
6.3 In general, the arrangement shall be such as to permit removal of the transformer without
dismantling the bus duct/cable installation.
A separate L.V.neutral bushing shall be provided for connection to station ground mat(50 x 10
mm) GI flat.
6.6 Vector group forming links shall be provided.
7.0 Marshalling box
7.1 For each transformer, the marshalling box shall be of sheet steel IP52.
located directly on the outside face of the enclosure at suitable height.
The box shall be
7.2 All terminal blocks for cable connection shall be located in this box. The terminal blocks
shall be ELMEX or approved equal. It shall have stud type terminals, CT wiring with 2.5 mm2
wire and CT terminals will have provision for shorting the CTs.
7.3 The marshalling box shall be provided with removable cable gland plate with cable glands.
8.0 Wiring
8.1 All control, alarm and indication devices provided in the Transformer shall be wired upto
terminal blocks.
8.2 Wiring shall be done with PVC wires in conduit or PVC armoured cable. Minimum wire size
shall be 1.5 sq.mm copper. Not more than two wires shall be connected to a terminal 10% spare
terminals shall be provided.
9.0 Grounding
9.1 All metal parts of the transformer with the exception of individual core laminations, core
bolts, and clamping plates shall be maintained at fixed potential by earthing.
9.2 LV neutral shall be suitably earthed to two different neutral earth pits through separate
earth flats of suitable size with link.
9.3 Grounding bus shall be provided with two bolt drilling with GI bolts and nuts at each end
to receive 50 x 10 mm GI flats.
9.4 Two tinned copper earthing terminals shall be provided.
10.0 Painting
10.1 All steel surfaces shall be thoroughly cleaned by sand blasting or chemicals agents, as
required to produce a smooth surface free of scales, grease and rust.
10.2 The external surfaces after cleaning shall be given a coat of high quality redoxide or
yellow chromate primer followed by filler coats.
10.3 The transformer coil assembly shall be finished with two coats of post office red colour
synthetic enamel paint.
10.4 The enclosure shall be finished with two coats of synthetic enamel paint shade 631 of IS
5.
10.5 If it is considered necessary, the transformer may be given a further coating at site.
The Bidder shall therefore indicate the type and quality of the paint with full specification
for this purpose.
11.0 TESTS & TEST REPORTS
11.1 All routine tests shall be carried out at manufacturer's works in presence of Purchaser
or his representatives.
11.2 Type test certificates for similar equipment supplied by the Bidder shall be submitted.
In case type test certificates for similar equipment is not available, the same shall be
conducted in presence of Purchaser's or his representative if purchaser so desires. However
Heat Run Test shall be conducted.
12.0 TECHNICAL REQUIREMENTS
The service transformers shall comply with the particulars indicated below:
SPECIFICATION REQUIREMENTS
1.0 Transformer applications Service Transformer
2.0 Type and make Indoors, two winding, 3 phase, encapsulated dry type cast resin insulated
step down.
3.0 Applicable standard IS:2026/IS 11171/ IEC: 60076/ IEC: 60726/IS 6600
4.0
5.0
6.0
7.0
8.0
Full load rating :
KVA 250
Rating no load voltage : HV/LV KV 6.6/0.420 KV
Rated frequency :
Hz 50
Winding connection of different windings and vector group :
System earthing
(a) HV(b) LV
Dyn11
Medium resistance : Solidly
9.0 Type of tap changer off circuit/on load : Off load
10.0 Tappings range and number of steps : +/- 10% in steps of 2.5%
11.0 Type of voltage variation (CFVV/ VFVV/CbVV): CFVV
12.0 Overfluxing capability :110% continuous
13.0 Winding insulation type
HV : Uniform
LV : Uniform
Impulse withstand voltage of winding HV/LV (kVp) : 60/20
14.0 Power frequency withstand voltage of winding HV/LV KV/rms : 20./3
15.1 Applicable standard for bushing : IS 2099
15.2 Clearance in air between phases(minimum) mm
HV -120 (P-P)
100 (P-E)
LV - 25.4 (P-P) 19.0 (P-E)
15.3 Creepage distance mm/kV : 25
16.0 Temp. rise above 50 deg.C Deg. C
(a) In winding by resistance : 70
(b) On enclosure by thermometer : 20
17.0 Parallel operation of transformer : Not applicable
18.0 SYSTEM FAULT LEVEL
40KA Sym. AT 6600V :
19.0 PERCENTAGE IMPEDANCE
HV
MV
LV
%
%
%
DATA SHEET
To be furnished by the bidder
A Guaranteed Data
Dry type (capacity wise)
5.0%
50kA Sym. AT 400V
1.0 Rating
a) Rated kVA :
b) Temperature rise above 50 deg c ambient for Dry type
i. For winding over ambient of 50oC :
ii. For core :
2.0 Losses
a) No. load loss at rated voltage and frequency :
b) Load-loss at rated current and at 75oC :
3.0 Impedance at rated current frequency at 75oC, % :
4.0 Zero sequence impedance, % :
5.0 Efficiency at 75oC and 0.8 p.f. lag, % :
a) At 100% load :
b) At 75% load :
c) At 50% load :
6.0 Regulation at full load and at 75oC :
a) At u.p.f :
b) At 0.8 p.f. lag, % :
7.0 Clearance :
Min. clearance in mm : HV LV
a) Between phases in air
b) Between phase and ground in air
8.0 Guaranteed overall dimensions, mm :
a) Length
b) Breadth
c) Height :
9.0 Guaranteed weights, kg. :
a) Core and coil
b) Total weight
B General Details
1.0 Name of Manufacturer :
2.0 a) Service - whether indoor ;
b) Type - core or shell :
3.0 Reference standard :
4.0 Type of cooling :
5.0 Rating
a) Rated kVA :
b) Rated current, amp (rms)
HV :
LV :
c) Rated voltage, kV
HV :
LV :
d) Number of phases :
e) Rated frequency, c/s :
f) Transformer capable of withstanding 125% rated voltage for 1 minute and 140% rated voltage
for 5 sec.? : YES / NO
6.0 Temperature rise above 50 deg c ambient for dry type
i) For winding over ambient of 50 deg c
7.0 ii) For core
Hot spot temperature in winding limited to ,
deg c.
8.0 a) Windings
i. No. of windings per phase :
ii. Insulation class :
b) Connections
i. High voltage :
ii. Low voltage :
iii. Vector group reference (in accordance with IS:2026) :
c) Terminal arrangement
i. HV :
ii. LV :
d) Winding insulation category
i. HV : Uniform / Non-uniform
ii. LV : Uniform / Non-uniform
e) Insulation level as per IS:2026 (Part-III) or IEC-76-3 :
9.0 Type of tap changer :
10.0 Taps
a) Capacity :
b) Steps and range :
c) Tapping provided on HV side? : YES / NO
11.0 Losses
a) No-load loss at rated voltage and frequency :
b) Load loss at rated current and at 75oC :
12.0 a) Impedance at rated current frequency and at 75oC, % :
b) Reactance at rated current and frequency, % :
c) Resistance at rated current and at 75oC :
d) Zero sequence impedance, % :
e) Zero sequence capacitance of
i. L.V. Winding, micro farad / phase :
ii. HV winding, micro farad / phase :
f) Air core reactance :
g) Knee-point voltage :
13.0 Efficiency at 75oC and 0.8 p.f lag, :
a) At 100% load :
b) At 75% load :
c) At 50% load :
14.0 a) Load and power factor at which maximum efficiency occurs, % full load :
b) Maximum efficiency, % :
15.0 Regulation at full load and at 75oC
a) At unity power factor, % :
b) At 0.80 power factor lagging, % :
16.0. No load current referred to HV and 50 Hz
% rated current
a) At 90% rated voltage :
b) At 100% rated voltage :
c) At 110% rated voltage :
d) At 125% rated voltage :
17.1 Approximate maximum flux density, web/m2
a) At 90% rated voltage, 50 Hz :
b) At 100% rated voltage, 50 Hz :
c) At 110% rated voltage, 50 Hz :
d) At 125% rated voltage, 50 Hz :
e) At 140% rated voltage, 50 Hz :
17.2 Following particulars shall be provided for the worst condition of simultaneous
occurrence of 110% rated voltage and 95% rated frequency.
a) Maximum flux density :
b) Temperature rise :
c) Period of allowable operation under the above worst condition :
18.0 Maximum current density, amps/cm2
a) HV winding :
b) LV winding :
19.0 Clearance
Minimum clearances in mm : HV LV
a) Between phases
i. In air :
b) Between phase and ground
i. In air :
20.0 Withstand time without injury for
a) Three phase dead short circuit at terminal with rated voltage maintained on the other
side, sec. :
b) Single phase short circuit at terminal with rated voltage maintained on the other side,
sec.
21.0 Insulation strength
a) One minute power frequency test kV rms :
i. H.V :
ii. L.V :
iii. L.V Neutral :
b) Impulse withstand voltage, kV :
i. H.V :
ii. L.V :
iii. L.V Neutral :
22.0 Tap-changer
a) Tap-changer operable at standing height from ground? : Yes / No
b) Provided with :
i. Tap position indicators? : Yes / No
c) All contacts silver plated? : Yes / No
23.0 Enclosure details (for dry type transformer)
a) Material :
b) Thickness :
c) Degree of protection :
24.0 Details of core material
a) Core lamination material :
b) Thickness of lamination, mm
c) Insulation of lamination :
d) Core bolt withstand voltage for 1 minute, kV :
25.0 Insulation material
a) Turn insulation, HV :
b) Turn insulation, LV :
c) Insulation core to LV :
d) Insulation, HV to LV :
26.0 Details of bushings
: HV LV LV Neutral
a) Make :
b) Type :
c) Voltage class, kV :
d) Creepage distance, mm
e) Free space required at top for bushing removal, mm :
f) Weight of bushing, kg :
g) Applicable standard :
h) Minimum clearance in air
i. Phase to phase, mm :
ii. Phase to earth, mm :
iii. Phase to neutral, mm :
i) Impulse withstand voltage, kV (peak) :
j) Power frequency withstand voltage , kV (rms) :
27.0 Marshalling box
a) Weather proof : Yes / No
b) Degree of protection :
28.0 Terminal blocks
a) Make
:
b) 10% spare terminals furnished? : Yes / No
29.0 Wiring
a) Cable type :
b) Voltage grade, Volt :
c) Conductor size
i. Current circuits, mm2 :
ii. Other circuits, mm2 :
30.0 Tests
a) Routine test as per IS : 2026 :
31.0 Accessories
Each transformer furnished with fittings and accessories : Yes / No
32.0 Approximate overall dimensions, mm
a) Length :
b) Breadth :
c) Height :
33.0 Approximate weights, kg
a) Core and coil :
b) Total weight :
34.0 Shipping data
a) Weight of the heaviest package, kg :
b) Dimension of the largest package (LxBxH), mm :
35.0 Rollers
a) Quantity :
b) Whether bi-directional : Yes / No
c) Gauge :
d) Whether lockable in both the positions ; Yes / No
36.0 Bushing Current Transformer(s)
a) Make :
b) Type : Yes / No
c) Quantity :
d) Voltage :
e) Current ratio :
f) Burden & accuracy class :
g) Internal resistance at 75oC :
h) Knee-point voltage :
i) Short-time withstand current in amps. And duration in secs. :
j) Thermal current rating :
k) Dynamic current rating :
l) Applicable standard :
37.0 Accessories furnished (list should be seriatim as of Technical Specification
a) :
b) :
c) :
38.0 Termination Arrangement
a) Details of HV cable termination arrangement furnished? : Yes / No
b) Details of LV cable termination arrangement furnished? : Yes / No
39.0 Drawing & data are furnished with the bid? : Yes / No
40.0 List of special maintenance tools and accessories :
SIGNATURE OF BIDDER
NAME
COMPANY SEAL DESIGNATION
NAME & ADDRESS OF COMPANY
DATE