SPECIFICATION NO.

TI/SPC/PSI/CT/0515(05/2015) Page 1 of 27

TRACTION INSTALLATION DIRECTORATE

GOVERNMENT OF INDIA
MINISTRY OF RAILWAYS

TECHNICAL SPECIFICATION

FOR
CURRENT TRANSFORMERS

i. 220 kV, 200 - 100/5A

ii. 132 kV, 400 - 200/5A

iii. 110 kV, 400 - 200/5A

iv. 66 kV, 800 400/5A

for

RAILWAY AC TRACTION SUBSTATIONS

(MAY 2015)

SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015)

ISSUED BY

Traction Installation Directorate

R e s e ar c h De s i g n s & S t a n d ar d s O r g a n i s a t i on ,
M a n a k N ag ar ,
Lu c kn o w - 2 260 1 1 .
 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 2 of 27

SPECI FICATION : T E C H N I C A L S P E C I F I C A T I O N F O R
CURRENT TRANSFORMER FOR RAILWAY AC
TRACTION SUBSTATIONS.

SPECIFICATION No. TI/SPC/PSI/CT/0515(05/2015)

Amendment Amendment /Revision Total pages Date of

Number including drawings Issue

Prepared By Checked By Approved By

Signature
Date
Dsignation SSE(TR) DDTI(PSI) DTI(PSI)
 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 3 of 27

INDEX

ITEM HEADING PAGE

NO

1.0 Scope 4

2.0 Governing Specification 4

3.0 Service Conditions 5

4.0 Traction Power Supply System 5

5.0 Rating and other Particulars 6

6.0 Type & General Construction 8

7.0 Bushing and Terminal Arrangement 9

8.0 Parts Fittings and Accessories 10

9.0 Painting 10

10.0 Testing 10

11.0 Technical data and drawings 14

12.0 Spares 16

13.0 Erection Testing and Commissioning 16

14.0 Training of Indian Railways Engineers 16

15.0 Warranty 16

16.0 Packing and Shipment 17

APPENDIXES
APPENDIX- A General Arrangement at the Traction 18
Transformer at Traction Sub-station

APPENDIX- B Schematic Diagram showing the protection 19

scheme

APPENDIX- C Schedule of Guaranteed Performance, 20

Technical and Other Particulars

ANNEXURES
ANNEXURE- A Drawing & Details of Terminal Connectors 23

ANNEXURE- B Format for Title of Drawings 24

ANNEXURE- C Details of 132 kV CT to be used in Mumbai 25

 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 4 of 27

area

1.0 SCOPE
1.1 This specification applies to outdoor electrically exposed type Current
Transformer for a nominal system voltage of 220 kV or 132 kV or
110 kV or 66 kV for use in unattended Railway Traction Sub-station
in any part of India together with associated. Electrical/Electronic
measuring/indicating instrument and protective devices. It
supersedes Specification No. ETI/PSI/117(07/88),
ETI/PSI/102(08/87), ETI/PSI/40(08/83), ETI/PSI/22(09/82) and
ETI/PSI/55(09/79).
1 . 2 The Current Transformer shall be complete with all parts, fittings and
accessories including mounting frame work of steel, necessary for its
efficient operation. All such parts, fittings and accessories shall be
deemed to be within the scope of this Specification, whether
specifically mentioned herein or not. The Current Transformer shall
be of proven design.

2.0 GOVERNING SPECIFICATION:

2.1 Assistance has been derived from the following Standards,
specifications/codes of practices (latest version) in the preparation of
this specification.

S. Standards & Codes of Applicable Rules.

No. Practices
1. IS:5 1978 Colours for ready mixed paints and
(3rdRevisin) enamels.
2. IEC: 185-1966 Current Transformer.
3. IS:335-1983 Specification for new insulating oil
4. IS:1271-1958 Classification of insulating material for
electrical machinery and apparatus in
relation to their thermal stability in service.
5. IS:1570 (Pt.V) Specification of bolt, nut and spring
washer.
6. IS:1576-1967 Solid press-board for electrical purposes.
7. IS:2074-1979 Ready mixed paint, air drying red oxide
zinc chrome priming.
8. IS:2099-1985 Bushing for alternating voltages above
1000 volts.
9. IS:2705-1981 Specification for Current Transformers: -
PartI: General requirement.
PartII: Measuring Current Transformer.
Part-III: Protective Current Transformer.
10. IS:2932-1974 Enamel synthetic interior
(a) Under coating
(b) Finishing
11. IS:3024-1965 Electrical steel sheets (oriented with
amendment No. 1&2)
12. IS:4201-1988 Application guide for Current Transformer.
13 IS:4253 (Part-II)-1980 Cork and rubber.
14. IS:5561-1970 Electrical power connectors.
15. IS:11322-1955 Method for partial discharge measurement
 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 5 of 27

in in Instrument Transformers.
16 RDSOs Spec No. Steel and stainless steel fasteners.
ETI/OHE/18(04/84)
with correction Slip
No.6 (09/87)
17 RDSOs Spec No. Specification for hollow porcelain insulator
ETI/PSI/70(11/84) and bushings.

2.2 Any deviation from this specification proposed by the tenderer

calculated to improve upon the performance, utility and efficiency
of the equipment will be given due consideration, provided full
particulars of the deviation with justification thereof are furnished.
In such a case, the tenderer shall quote according to this
specification and the deviations, if any, proposed by him shall be
quoted as an alternative/alternatives. In case of any contradiction
between the provisions of the Indian Standards
Specification/Recommendation of IEC and this Specification the
letter shall prevail.

3.0 SERVICE CONDITIONS:

3.1 The Current Transformer is intended for use in humid tropical
climate in any part of India with the following atmospheric
conditions:
1. Maximum ambient temperature of 45C
air in the shed
2. Minimum temperature air in the 0 C
shed
3. Maximum relative humidity 100%
4. Maximum wind pressure 200 kg/m2
5. Number of thunderstorm days per 85 days (Approx.)
annum
6. Maximum no of dust storm 35 days
days/annum
7. Average annual rainfall 1750 to 6250 mm.
8. Altitude Not exceeding 1000 m

3.2 The Current Transformer shall be subjected to vibrations on account

of trains running on nearby railway tracks. The amplitude of these
vibrations which occur with rapidly varying time period in the range of 15 to
70 ms lies in the range of 30 to 150 microns at present with the
instantaneous peak going up to 350 microns.

4.0 TRACTION POWER SUPPLY SYSTEM:

4.1 General scheme: The single phase, 50 Hz power supply for Railway
Traction at 25 kV is obtained from 220kV/132kV/110kV/66kV three phase
grid system through a step down single phase Traction Power Transformer,
The primary winding of which is connected to two phases of the three
phase effectively earthed transmission line network of the of the State
Electricity Board. In order to reduce the impedance on the three-phase grid
system, the two phases of three-phase transmission line are tapped in a
cyclic order for feeding the successive substations. The distance between
adjacent Sub-stations is normally 40 km and 80 km depending upon the
density of traffic, gradients in the section, etc.
 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 6 of 27

4.1.1 One terminal of the 25 kV secondary winding of the Traction

Transformer is connected to the Overhead Equipment (OHE) and the other
equipment is solidly earthed and connected to the appropriate running rails.
The load current flow through the OHE to the locomotives and returns
through the rail(s) and earth to the Sub-station. Where Booster
transformers and Return conductors are used the Return current flows
through these and partly through the earth in the vicinity of the Sub-
station. Approximately midway between two adjacent Sub-stations, a dead
zone known as the Neutral Section or Phase Break is provided to
separate the different phases. The power to the OHE on one side of the
sub-station is controlled by a feeder circuit breaker while that for each track
is controlled by an interrupter. In case of a fault on the OHE, the feeder
circuit breaker isolates it. The incoming 220/132/110/66 kV supply voltage
may vary between 10% to -12.5% as per I.E. Rule No. 54. A schematic
diagram No. ETI/PSI/702-1 MOD D showing the general arrangement at
the Traction Transformer at the Traction Sub-station is at Appendix-A.
4.2 The Current Transformer shall be on the Primary side of the single
phase Traction Power Transformer for use with the following
Electrical/Electronic measuring/indicating instruments/meters and
protective devices/Relays: -
a) Instantaneous Overcurrent Relay,
b) Inverse Definite Minimum Time Lag Over Current Relay,
c) Restricted Earth Fault Relay.
A panel/Digital type indicating Ammeters will also be connected to these
Current Transformers.
4.3 Operation of any of the protective devices/relays which serve as the
backup protective system for that on the 25 kV side of the Traction Power
Transformer shall trip the circuit breaker on the primary side of the
Transformer. A schematic diagram showing the protection scheme is at
Appendix B.
5.0 RATING AND OTHER PARTICULARS
5.1(a) For other tan Mumbai area: The rating and other particulars of the
Current Transformer shall be as follows:-
i)Type: Single phase, oil filled natural
air cooled, One core for other
than Mumbai area.
ii) No. of windings: Primary Two
Secondary - One
iii) System voltage:

a. Nominal system voltage, kV 220 132 110 66

b. Highest system voltage, kV 245 145 123 72.5
iv) Rated primary/secondary Currents:
a. Nominal system voltage, kV 220 132 110 66
b. Highest system voltage, kV 245 145 123 72.5
c. Primary Current, Amp. 200- 400- 400- 800-
100 200 200 400
d. Secondary Current, Amp. 5 5 5 5
v. Rated Frequency, Hz 50 Hz, +/- 3%
vi Class of Insulation A
vii Rated Burden 30 VA
 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 7 of 27

viii Accuracy Class Other than Mumbai area -

5P to IS: 2705-1981(Part-
III)
ix Accuracy limit factor 15

x. Rated short time current:

Nominal Transformation Short time Short time current
system ratio current rating rating (Dynamic)
voltage, kV (thermal) for kA.
one second, kA
220 200-100/5 31.5 78.75
132 400-200/5 31.5 78.75
110 400-200/5 31.5 78.75
66 800-400/5 31.5 78.75

xi. Rated Insulation Level:

a. Nominal system voltage, 220 132 110 66
kV
b. Rated one minute power 460 275 230 140
frequency withstand
voltage, kV(rms)
c. Impulse withstand 1050 650 550 325
voltage (1.2/50 micro,
sec. wave shape),
kV (peak)
xii. Terminal Bushing:
a. Nominal system voltage, 220 132 110 66
kV
b. Rated current, Amps. 800 800 800 800
c. Minimum creepage 6125 3625 2075 1813
distance, mm
xiii. Temperature rise: See clause 10.1.2
xiv. Rated overload: 150% of full load for 15 minutes.
xv. Secondary winding resistance at 75 0C (Max.) 0.3 Ohms.

5.1(b) For ABT Metering: The rating and other particulars of the
Current Transformer shall be as follows:-
i)Type: Single phase, oil filled natural
air cooled, One core
for ABT Metering.
ii) No. of windings: Primary Two
Secondary - One
iii) System voltage:

a. Nominal system voltage, kV 220 132 110 66

b. Highest system voltage, kV 245 145 123 72.5
iv) Rated primary/secondary Currents:

a. Nominal system voltage, kV 220 132 110 66

 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 8 of 27

b. Highest system voltage, kV 245 145 123 72.5

c. Primary Current, Amp. 200- 400- 400- 800-
100 200 200 400
d. Secondary Current, Amp. 1 1 1 1
v. Rated Frequency, Hz 50 Hz, +/- 3%
vi Class of Insulation A
vii Rated Burden 30 VA
viii Accuracy Class For ABT Metering 0.2S
to IS: 2705-1981(Part-III)

x. Rated short time current:

Nominal Transformation Short time Short time current
system ratio current rating rating (Dynamic)
voltage, kV (thermal) for kA.
one second, kA
220 200-100/5 31.5 78.75
132 400-200/5 31.5 78.75
110 400-200/5 31.5 78.75
66 800-400/5 31.5 78.75

xi. Rated Insulation Level:

a. Nominal system voltage, 220 132 110 66
kV
b. Rated one minute power 460 275 230 140
frequency withstand
voltage, kV(rms)
c. Impulse withstand 1050 650 550 325
voltage (1.2/50 micro,
sec. wave shape),
kV (peak)
xii. Terminal Bushing:
a. Nominal system voltage, 220 132 110 66
kV
b. Rated current, Amps. 800 800 800 800
c. Minimum creepage 6125 3625 2075 1813
distance, mm
xiii. Temperature rise: See clause 10.1.2
xiv. Rated overload: 150% of full load for 15 minutes.
xv. Secondary winding resistance at 75 0C (Max.) 0.3 Ohms
5.1(c) For Mumbai area: The rating and other particulars of the
Current Transformer shall be as refer Annexure -C:-

6.0 TYPE AND GENERAL CONSTRUCTION:

6.1 The current Transformer shall be suitable for mounting on
steel structures embedded in concrete foundations close to the circuit
breakers.
6.2 The Current Transformer shall be of sealed type either filled
with inert gas or provided with metallic bellows above the cooling and
insulating oil. In case of inert gas filling, a pressure relief device shall be
provided.
 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 9 of 27

6.3 The core shall be built up of high permeability Cold Rolled

Grain Oriented (CRGO) silicon steel laminations conforming to IS: 3024, the
laminations being coated on both sides with suitable insulations capable of
withstanding stress relief annealing.
6.4 Class A insulation immersed in oil shall be used. The Current
Transformer shall be supplied complete with insulating oil conforming to
IS:335 required for first filling.
6.5 The current transformer shall have a Single Core with wound
primary. The primary winding shall be split in two sections insulated from
each other and connected to terminals P1, P2, C1 & C2. It shall be possible
to change the transformation ratio by connecting C1 with C2 for series
configuration or P1 with C1 & P2 with C2 for parallel configuration. For
connecting these terminals in series or parallel configuration, suitable links
of adequate section made of copper flat shall be provided. The nuts and
checknuts used for connecting these links shall be made of copper. Only
copper conductor shall be used for primary and secondary windings.
6.5.1 Normally no joints in the winding shall be allowed. Joints if
unavoidable shall be brazed with high silver alloy grade Ba Cu Ag6 of IS:
2927-1975 or electrically butt-welded.
6.6 The secondary terminals of the Current Transformer shall be
housed in a weather proof terminal box of mild steel of thickness not less
than 1.6mm. The connection/disconnection of external cable to/from the
terminals shall be easy and convenient.
The cables shall be of 4 sq. mm, sections 2 core PVC insulated and PVC
sheathed and their entry into the terminal box shall be through proper
cable glands fitted on the bottom of the terminal box. The cable glands
shall be supplied with the Current Transformer.
6.6.1 Facilities for shortcircuiting the secondary terminal shall be
provided within the terminal box. The Current Transformer shall be
provided with a standard IOA test winding.
6.7 All the bolted mechanical and electrical connections in the
Current Transformer will be tightened properly to prevent loosening in
service due to vibrations.

7.0 BUSHING AND TERMINAL ARRANGEMENT:

7.1 Out door type bushing shall conform to IS: 5621.The basic
insulation level shall have the appropriate value as given in clause 5.1(xi)
of this specification. The porcelain housing shall be capable of withstanding
all electrical and mechanical stresses that might be produced during the
operation of the Current Transformer under normal and short-circuit
conditions.
7.2 The profile of porcelain shed shall be simple and free from the
ribs on the underside so as to avoid accumulation of dust and pollutants
and permit easy cleaning. The porcelain housing shall be of single piece
construction i.e. without joint in the porcelain body. The material of
clamping rings/ flanges used shall conform to MCI Grade BM-340 of IS:
2108 or to SGCI Grade: 400/12 of IS:1865 or to Aluminium alloy
Grade:4450 of IS:617. The mass of Zinc coating shall not be less that 1000
gm/mm2.
 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 10 of 27

7.3 Porcelain housing/support insulator used shall have creepage

distance as given in Clause 5.1(xii)-C.
7.4 The bushing/housing terminal shall be provided with rigid type
connectors as per Research Designs & Standards Organisation (RDSO)
drawing No. ETI/PSI/11010 in Annexure A suitable for connecting to
ZEBRA 28.62 mm ACSR conductor. The connector shall conform to IS:
5561 and its design shall be such so as to be connected to the equipment
terminal pad with a minimum of four 12 mm dia bolts, nuts and lock nuts
which shall all be of stainless steel conforming to IS: 1570(Pt. V) Grade 04
Cr. 17 Ni 12 Mo2. Each of these bolts shall also have a flat washer and
spring washer.
7.5 The connectors and porcelain housing shall be procured only
from approved manufacturers.

7.6 For equipment earthing, the steel supporting frame shall be

provided with two earthing terminals of adequate capacity to carry the
rated shot-circuit current safely. The earthing terminal shall be connected
to 50mm x 8 mm MS flat. The earthing terminal shall be provided with 17.5
+0.5mm dia. hole for fixing the earthing flat 0.4
7.7 The approved source of porcelain housings are as under:
(i) M/s Aditya Birla Insulator, Hallol & Rishra.
(ii) M/s Insulators & Electricals Co. Mandideep, Bhopal.
(iii) M/s Modern Insulators Ltd., Abu Road,
(iv) M/s WSI, Chennai.
8.0 PARTS FITTINGS & ACCESSORIES:
8.1 Apart from the parts, fittings & accessories specifically detailed in the
foregoing clauses, the following shall be supplied with each Current
Transformer.
(i) Rating plate with diagram of connections and terminal
markings.
(ii) Weatherproof terminal box.
(iii) Lifting lugs.
(iv) Pressure Release Device.
(v) Nitrogen gas filling valve and oil filling port.
(vi) Oil level gauge of prismatic glass.
(vii) Adjustable arcing horns.
(viii) Cable Gland (Brass Nickel plated).

9.0 PAINTING
9.1 All the steel surfaces which are in contact with insulating oil
shall be painted with heat resistant oil insoluble insulating warmish. All
steel surfaces exposed to weather shall be given on primer coat of zinc
chromate and two coats of gray paint to shade No. 631 of IS: 5. One coat
of additional paint shall be given at site by the manufacturer.

9.2 Fasteners.
All fasteners of 12 mm diameter and less exposed to atmosphere
shall be stainless steel and those above 12 mm diameter shall be preferably
 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 11 of 27

be of stainless steel or of mild hot dip galvanized to RDSOs specification

No. TI/SPC/OHE/FASTNERS/0120(03/2013).
10.0 TESTING
10.1 Once a purchase order is placed for supply of a Current Transformer
the designs and drawings shall be furnished to the purchaser/ Director
General (Traction Installation), Reseach Designs and Standards
Organisation, [DG(TI), RDSO] Lucknow, as the case may be, within the
period stipulated in the order. Only after all the designs and drawings have
been approved for prototype tests and a written advice given to that
affect, shall be successful tenderer/manufactuer take up manufacture of the
prototype of the transformer. It is to be clearly understood that any change
or modification required by the above authorities to be done in the
prototype shall be done expeditiously, not withstand approval having
already been given for the designs and drawings. Such change or
modification shall be incorporated in the drawings as indicated in clause
14.4.
(ii) Prior to giving a call to the purchaser/DG(TI), RDSO, Lucknow, for
inspection and testing of the prototype, the successful tenderer/
manufacturer shall submit a detailed test schedule consisting of schematic
circuit diagrams for each of the tests and the number of days required to
complete all the tests at one stretch. Once the schedule is approved, the
tests shall invariably be done accordingly. However, during the process of
type testing or even later, the purchaser reserves the right to conduct any
additional test(s), besides those specified herein, on any equipment/ items
so as to test the equipment/item to his satisfaction or for gaining additional
information and knowledge. In case any dispute or disagreement arises
between the successful tenderer/manufactuerer and representative of the
purchaser/DG(TI) RDSO, Lucknow, during the process of testing as regards
the procedure for type tests and/or the interpretation and acceptability of
the results of type tests, it shall be brought to the notice of the
purchaser/DG(TI), RDSO, Lucknow as the case may be, whose decision
shall be final and binding. Only after the prototype transformer is
completed and ready in each and every respect, shall the successful
tenderer/manufacturer give the actual call for the inspection and testing
with at least 15 days notice for the purpose.
iii) In the event of the tests not being carried through the completion at
the one stretch for any reason attributable to the successful tenderer/
manufacturer and it is required for the representative of the
purchaser/Director General (Traction Installation), Research Designs &
Standard Organisation, [DG(TI) RDSO], Lucknow, to go again or more
number of times to the works of the successful tenderer/manufacturer or
other place(s) for continuing and/or completing the tests on the
prototype(s) of the equipment, the successful tenderer/manufacturer shall
reimburse to the purchaser/DG(TI), RDSO, Lucknow, the costs for the
representative having to visit the works or other place(s) for the tests more
than once. The costs as claimed by the purchaser/DG(TI), RDSO, Lucknow,
shall be paid through a demand draft to the concerned Accounts Officer of
the Purchaser/DG(TI), RDSO, Lucknow, as shall be advised to the
successful tenderer/manufacturer.
iv) The following type tests shall be carried out on the prototype current
transformer art the works of the successful tenderer/ manufacturer or at
the reputed testing laboratory in the presence of the representative of the
 SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 12 of 27

Purchaser/DG(TI), RDSO, Lcuknow, in accordance with the relevant

specifications and as modified or amplified as under:
10.1.1 Visual inspections: It shall comprises
(a) Checking of the layout, terminal markings, mounting
arrangement, labeling and any other items.
(b) Quality of painting and anti-rust treatment.
(c) Quality of workmanship and finish as well as provision of all
parts, fittings and accessories.
10.1.2 TEMPERATURE-RISE TEST:
This test shall be carried out on the Current Transformer for
the higher rating fitted with approved terminal connector for fullload and
for overload specified in clause 5.1(xiv). The temperature rise under
specified overload shall not exceed the following values.:
(a) Winding : 500C (Temperature rise measurement
by the resistance method).
(b) Insulating oil : 400C (temperature rise measurement by
thermometer)
(c) Terminal connector : 400C (temperature rise measurement
by thermometer)
The above values are with reference to an ambient temperature of
450C.
10.1.3 Impulse Voltage Test:
The lightening impulse voltage withstand test shall be done on the
primary windings with test voltages specified in clause 5.1(xi).

10.1.4 Short-time current test:

The short time thermal (rms) and dynamic (peak) current withstand
tests shall be done to verify the ability of the Current Transformer and the
terminal connectors fitted there to withstand the rated short-time current
specified in clause 5.1(x). The Current Transformer shall be deemed to
have passed the test if the conditions laid down in clause 7.6.3 of IS: 2705
(Pt. I) are satisfied.
10.1.5 Excitation test and plotting of magnetizing characteristics curves.
The curve shall be drawn at least up to that point, where an increase
of 100% in voltage results in an increase of 50% in current.

10.2 TYPE TEST ON ACCESSORIES:

10.2.1 Porcelain Bushing
The following tests shall be carried out on prototype unit of 52 kV or
72.5 kV or 123 kV or 145 kV or 245 kV (as the case may be) class bushings
in accordance with IS: 2099 and IS: 5621.
(i) Dry power-frequency withstand voltage test.
(ii) Wet power-frequency withstand voltage test.
(iii) Dry-lightening impulse voltage withstand test.
(iv) Thermal stability test.
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 13 of 27

(v) Temperature-rise test.

(vi) Thermal short time current withstand test.
(vii) Dynamic current withstand test.
(viii) Cantilever load withstand test.
(ix) Measurement of partial discharge quantity (as per IS:6209)
(x) Tightness test at flange or other fixing devices.
(xi) Temperature cycle test.

10.2.2 Test on terminal connectors:

The terminal connector shall be from the approved supplier of
RDSO. In case these are not from the approved suppliers of RDSO,
the following tests shall be carried out:
(i) Visual inspections and verification of dimensions.
(ii) Tensile test.
(iii) Resistance Test.
(iv) Temperature-rise test at normal and specified overload.
(v) Short- time current test.
(vi) Chemical analysis of materials used.
10.3 In addition to the above tests, all routine tests detailed in
clause 10.7 shall be carried out on the test unit.
10.4 If the prototype of a Current Transformer conforming to this
Specification has been approved for earlier supplies to Indian
Railways, the testing of prototype again may be waived provided that
no change in the design or material(s) used have been made.
10.5 Manufacturers type test certificates in respect of the tests
carried out on (a) porcelain housing and (b) terminal connector, as
per relevant IEC recommendations/IS specifications shall be
submitted by the successful tenderer for approval.
10.6 The tenderer may quote separately his charges for conducting
short-time current (thermal) and dynamic current withstand tests
described in clause 10.1.4, hereof. No charges shall be payable for
any other type and routine/acceptance test.

10.7 Routine tests/Acceptance tests.

Every Current Transformer shall be subject to the following
tests at the manufacturers works as per IS: 2705 (Pt.I) and IS:
4322.

10.7.1 Verification of Terminal markings and polarity.

10.7.2 High voltage power-frequency tests on primary winding.
The windings shall be subject to the following tests voltages:
a. Nominal system 220 132 110 66
voltage, kV
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 14 of 27

b. Voltage to be 460 275 230 140

applied between
winding & earth,
kV (rms)
c. Voltage to be 2 2 2 2
applied between
two sections of
primary winding,
kV (rms)

10.7.3 High voltage power-frequency withstand test on the

secondary winding: 3 kV (rms) for one minute.

10.7.4 ACCURACY TESTS:

The accuracy test shall comprise the following:-
a) Current error & phase displacement at the rated primary
current.
b) Composite error at rated accuracy limits primary current.
10.7.5 Measurement of insulation resistance between primary
winding and secondary winding with a 2500 V Megger; and that
between secondary winding & earth with a 500 V Megger.

10.7.6 Measurement of secondary winding resistance and its

computation at 750C.
10.7.7 Measurement of partial discharge of windings.
10.8 Only after clear written approval of the results of the tests on
the prototype unit is communicated by RDSO/purchaser to the
manufacturer, shall be taken up bulk manufacture of the ordered
Current Transformers which shall be strictly with the same material
and process as adopted for the prototype. In no circumstances shall
material, other than those approved in the designs/drawings and /or
the prototype, be used for bulk manufacture on the plea that they
had been obtained prior to the approval of the prototype.
11.0 TECHNICAL DATA AND DRAWINGS:
11.1 The information furnished in Schedule of Guaranteed
Performance, Technical & other particulars (Appendix C) shall be
complete in all respects. If there is entry like shall be furnished later
or blanks are left against any item, the tenderer is not likely to be
considered such as omissions causes delay in finalising the tender.
Evidence in the form of type test reports for basic insulation level,
i.e. rated impulse withstand voltage test, rated power frequency
(wet) withstand test, rated power frequency (dry) withstand test,
temperature rise test and short time current withstand test on the
current transformer offered shall be furnished.
11.2 The tenderer shall specifically indicate in a statement attached
with his offer, his compliance with each clause and sub-clause of this
specification. A separate statement shall be attached with the offer
indicating reference to the clauses where the tenderer deviates
therefrom together with detailed remarks/justification. If either the
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 15 of 27

statement of compliance or statement of deviation is not attached

with the offer, it is not likely to be considered. If there are no
deviations, a NIL statement shall be attached.
11.3 The tenderer shall furnish the following drawings as per Indian
Railways standards in sizes of 210mm x 297 mm or any integral
multiplies thereof. A format of the title sheet is attached at Appendix
D.
a) Outline general arrangement giving the overall
dimensions of current transformer.
b) Internal arrangement of Current Transformer including
crosssectional views.
11.4 The tenderer shall also furnish the following information
along with his offer-
a) Excitation characteristic curve.
b) Manufacturers test certificates of :-
(i) Winding wire (ii) Oil seal/gaskets (iii) insulating oil
(iv) pressure release device.
c) The tenderer shall furnish the detailed calculation and basis
in support of the minimum knee point voltage.
For calculations purpose the lead resistance may be
presumed as 0.4 ohms.
11.5 The successful tenderer shall be required to submit for
approval the following detailed dimensioned drawings as
per Indian Railways standard in Annexure B (Title of
Drawing) in sizes of 210mm x297mm or any integral
multiples thereof-
a) General outlines drawings showing mounting
arrangement, relative position of primary and secondary
terminals, CT earthing and position of various parts, fittings
and accessories.
b) Cross-sectional view along with its internal details.
c) Porcelain housing/bushing including its clamping
arrangement.
d) Name and rating plate with the diagram of connections
(both in English and Hindi).
e) Details of primary terminals and links used for changing
the transformation ratio.
f) Secondary terminals and terminal box.
g) Details of metallic bellow, if provided as well as its
operation.
h) Detailed part drawings for:-
(i) Oil level gauge(ii) Nitrogen Gas filling valve(iii) Pressure
release device(iv) Cable gland (v) Terminal connector (vi)
Earthing terminals and (vii) Oil draining pipe with plug.
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 16 of 27

11.6 After approval, six copies of approved drawings along with

two sets of reproducible prints shall be supplied to each
consignee(s). Besides, two copies of drawings along with
one set of reproducible prints shall be supplied to the
Director General (Traction Installation), Research Designs &
Standards Organisation, Lucknow (India).
11.7 The successful tenderer shall supply five copies of the
instruction/maintenance manual for the Current
Transformer to each consignee(s) and two copies to the
Director General (Traction Installation), Research Designs
and Standards Organisation, Lucknow (India).
12.0 SPARES:
The tenderer shall furnish along with his offer a list of spare
(with cost) recommended by him for maintenance of
Current Transformer for a period of two year.
13.0 ERECTION TESTING AND COMMISSIONING:
13.1 The transformer shall be erected by the purchaser under
the supervision of a competent engineer of the successful
tenderer/manufacturer/supplier. The Current Transformer
shall be subjected to the specified proving/pre-
commissioning tests by the Railwayss Engineer at site and
with which the successful tenderer/supplier/ manufacturer
shall also be fully associated. For this purpose, prior
intimation regarding the date and location of tests shall be
given by the purchaser to the supplier/
manufacturer/successful tenderer.
14.0 TRAINING OF INDIAN RAILWAYS ENGINEERS
14.1 The offer shall include the training of two Engineers of the
Indian Railways free of cost at the manufacturers in India
or abroad and at the maintenance depots/workshop on a
railway system or other public utility where Current
Transformers of similar/identical design are in operation.
The total duration of training for each engineer shall be for
12 weeks of which approximately 6 weeks will be at
manufacturers works and 6 weeks on Railway system or
other public utility. The cost of travel to the country of the
manufacturer and back will be borne by the Indian
Railways. Other details shall be settled at the time of
finalizing the contract of the purchase order.
15.0 WARRANTY:
15.1 Each Current Transformer supplied against a purchase
order/contract in which this specification is quoted,
irrespective of origin (imported or indigenous), shall be
guaranteed for trouble-free and satisfactory performance
for a period of 24 months from the date of supply of or 18
months from the date of commissioning at the sub-station
on Indian Railways, whichever period is shorter. Details of
warranty clause, the extant of responsibility and other
relevant aspects shall be included in the purchase order or
contract. The tenderer shall furnish detailed terms and
conditions in this regard in his offer.
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 17 of 27

The successful tenderer shall make necessary

arrangements for closely monitoring the performance of the
Current Transformer through periodical (preferably once in
two months during the warranty period) visits to the sub-
station for on the spot detailed observations. Arrangement
shall also be made for spare parts to be kept readily
available with the manufacturer/supplier/ successful
tenderer to meet exigencies warranting replacement so as
to put back the Current Transformer in service without
unduly long interruption of traction power supply.

16.0 PACKING AND SHIPMENT:

16.1 The Current Transformer shall be transported from the
manufacturers works to the destination by rail, road or sea
as determined in the contract/purchase order. The parts,
fittings and accessories which are liable to damage during
transit shall be separately packaged/crated and dispatched
so as to reach destination along with the Transformer
tanks. Any opening crated on the Current Transformer tank
by the removal of any parts, fittings and accessories shall
be closed by suitable blanking plates.
A general packing list, for the various components of each
Current Transformer shall be furnished. The packing has to
be done properly so that no damage may be done during
transit.

APPENDIX A
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 18 of 27

APPENDIX B

Schematic Diagram Showing the Protection Scheme:

SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 19 of 27

SUB-SECTOR SUB-SECTOR SUB-SECTOR

SECTOR
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 20 of 27

APPENDIX-C
SCHEDULE OF GUARANTEED PERFORMANCE, TECHNICAL AND
OTHER PARTICULARS.

S. Description Unit of
No. measurement
1. Name of the manufacturer
2. Country of origin
3. Standard governing specification
4. Manufacturers type designation
5. (a) Nominal system voltage kV
(b) Highest system voltage kV
6. (a) Rated primary current Amp
(b) Rated secondary current Amp
(c) Rated transformation ratio
7 Rated burden VA
8 Accuracy class
9 Rated accuracy limit factor
10 Current error at rated primary current Percent
11 Phase displacement at rated primary Minutes
current
12 Complete error at rated accuracy limit percent
primary current
13 Rated short-time current and duration
(a) Thermal (Ith) kA (RMS)for one
sec.
kA (peak)
(b) Dynamic (Idyn)
14 Temperaturerise of the windings
(by resistance method) over an ambient
temperature of 45 0C 0
C
(a) At rated current
(b) At 100% overload for 5 minutes 0
C
15. Partial discharge level pC
16. Particulars windings
a) Primary winding
i) Type
ii) No. of turns
iii) Current density at rated Amp/mm2
current
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 21 of 27

iv) Size of conductor

v) Class of insulation
b) Secondary windings:
i) Type
ii) No. of turns
iii) Current density at rated
current
Amp/mm2
iv) Size of conductor
v) Class of insulation
vi) Resistance computed to 75 0C
vii) Insulating material used
Ohm
c) Rated insulation levels:
i) One minute power frequency
kV (rms)
withstand voltage
ii) Inter-section withstand
voltage of primary windings. kV (rms)
iii) Impulse withstand voltage kV (peak)
17 Particulars of core:
i) Type
ii) Flux density.
a) At rated primary current Tesla
b) At 15 times rated primary current Tesla
iii) Thickness of steel laminations mm
iv) Whether CRGO steel stampings are
used ?
v) Knee point e.m.f.
vi) Exciting current to knee point
18. Particulars of porcelain housing/bushing:
(i) Specification to which it conforms
(ii) Name of manufacturer
(iii) Power frequency withstand voltage
for one minute.
(a) Dry
kV (rms)
(b) Wet
kV (rms)
iv) Dry lightning impulse withstand
kV (peak)
voltage, 1.2/50 micro-second
wave shape.
v) Visible power frequency discharge kV (rms)
voltage.
vi) Creepage distance in air
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 22 of 27

a. Protected mm
b. Total mm
vii) Weight of porcelain housing Kgs.
/bushing
19 Overall dimensions:
i) Length mm
ii) Width mm
iii) Height mm
20 Weights:
(i) Total weight of copper used
a) Primary winding Kgs.
b) Secondary winding Kgs.
(ii) Weight of core Kgs.
(iii)(a) Quantity of insulating oil Liter
b) Weight of insulating oil Kgs.
iv) Total weight Kgs.
21 Particulars of terminal connector:
(i) Name of manufacturer
(ii) Rated current Amp.
(iii) Temperature rise above an
ambient temperature of 45 0C
a) At rated current
b) At 150 percent of rated current for
15 minutes.
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 23 of 27

ANNEXURE- A
Details of Terminal Connector:
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 24 of 27

ANNEXURE- B
Format of Title Drawing:
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 25 of 27

ANNEXURE- C

1.0 SCOPE
This part of specification cover design, manufacture, testing,
inspection, packing and supply of 145 kV class outdoor,
Current Transformer with CT ratio of 1200-800-400/5A to the
Specification given below to be used in Mumbai area on 110
kV side at Traction Sub-station with 30 MVA Transformers and
required to be operated in parallel with adjacent Traction Sub-
stations.
2.0 RATING AND OTHER PARTICULARS:
i) Type Single phase, oil filled natural
air cooled outdoor.
ii) No. of cores 4
iii) System voltage
a) Nominal system 132
voltage , kV
b) Highest system
145
voltage, kV
iv) Rated
primary/secondary
currents
a) Primary current,
Amp 1200
b) Secondary 5
current, Amp
v) CT ratio 1200-800-400/5A
vi) Rated frequency 50 Hz,+/-3%
vii) Class of insulation A
viii) a) Short time 40
current rating
(thermal) for 3
second, kA
b) Short circuit 40
withstand current
(3 sec.), kA
c) Short time
current rating 100
(dynamic), kA
(peak)
ix) Rated insulation level
a) One minute 50 275
Hz withstand
voltage/induced
over-voltage, kV
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 26 of 27

(rms)
b) Impulse 650
withstand
voltage, positive
and negative
polarity (1.2/50
microseconds
wave), kV (peak)
x) Minimum creepage 4495
distance of insulator
(31 mm/kV), mm
xi) Temperature rise 50 0C over an ambient temp.
Maximum temperature 50 0C
rise of windings
immersed in oil
xii) Rated Overload 150% of full load for 15
minutes
xiii) Rated Burden & Class Core-1 Core- Core-2&4
of Accuracy of different 3
cores
Protection R met Protection
Burden in VA 40 40 -
Accuracy Class 5P20 0.2 PS
Instrument Security - <5 -
factor
Knee point voltage - - >750V
Iex (max) at Vk/2 - - <100 mA
Rct (max) - - <1.0 Ohm
at max.
tap.

2.1
a) multi ratio specified shall be obtained by taps on
secondary side.
b) The values specified above for metering & protection
core shall be met for the lowest tap. (except) Rct and
knee point voltage for PS core which is at the highest
tap).
c) P1 and P2 markings to be permanently riveted.
d) CT shall be of dead tank design.
e) Power factor terminal (test tap) shall be provided inside the
secondary terminal box.
f) The disposition of various CT cores and detailed drawings
along with SOGP shall be furnished for RDSOs approval
before manufacture is taken up.
3.0 Construction:
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 27 of 27

The current transformers shall be hermitically sealed. They

shall be suitable for upright mounting on steel structures.
They shall be provided with Nitrogen cushions/stainless
steel bellows. CTs shall be suitable for hot line washing.
The Current Transformer winding shall be housed in a
galvanized tank suitable for outdoor duty. Earthing
arrangement shall be provided for CT tank.
3.1 Tank Fabrication
The tank shall be fabricated from tested quality low carbon
steel suitable for welding and of adequate thickness. The
tank shall be designed to withstand mechanical shocks
during transportation, vacuum filling of oil and continuous
internal pressure over normal hydrostatic pressure of oil
and short circuit forces.
The construction of the tank shall be designed to prevent
ingress of water into or leakage of oil from the tank. All
bolted connections shall be fitted with weather proof, hot
oil resistant gasket in between (Butile Nitrile/Neoprene
Rubber), for complete oil tightness. If gasket is
compressible, metallic stops shall be provided to prevent
over compression.
Tank fabrication drawings shall be submitted for approval
before the manufacturing is taken up.
3.2 SPECIAL CONSTRUCTION NOTE:
After the internal elements such as primary & secondary
windings are sealed in the tank with porcelain shell, the
assembled CTs shall be subjected to vacuum & heat
treatment and finally filled with degasified oil in vacuum.
4.0 General
4.1 Current Transformers shall be provided with unthreaded
stud terminals at top for connections to 110 kV, 50 mm
OD aluminium busbar. The primary current terminals shall
be of tinned copper.
4.2 The current transfer area of the terminals shall be
adequate to meet the temperature rise requirements as
per IEC: 44-1/IS: 2705 for CTs. The cross-section area of
the terminal shall be indicated in the drawings.
4.3 Mechanical load test on primary terminals: Test reports
are to be submitted as per IEC 44-1.
4.4 The Burdens specified for different cores refer exclusively
to connected burden and should exclude the bleeder
resistance if any. Current transformers guaranteed
burdens and accuracy class are to be intended as
simultaneous for all cores.
4.5 CTs shall be provided with a capacitance test tap in the HV
lead to enable future monitoring of conditions of HV
insulation.
4.6 Earthing terminals shall be provided in the secondary
junction box for earthing of secondary winding of CT.
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 28 of 27

4.7 The alignment and centre line of CT primary terminals

shall be correct so as to avoid bending of connections.
4.8 The CT secondary terminal box shall be of GI (IP 55) and
shall be provided with collar to prevent entry of moisture &
good neoprene gaskets designed to prevent entry of
foreign particles. Junction box shall be sufficiently large to
connect 1100 V upgrade, 4C x 6 sq. mm cables through
cable glands for all the secondary cores.
4.9 CT secondary terminals shall be terminated to stud type
non disconnecting terminal blocks inside the terminal box.
CT secondary terminals shall be provided with lock nuts.
4.10 All ferrous parts exposed to atmosphere including main
tank, secondary terminal box & top metallic should be hot
dip galvanized.
4.11 The current transformer shall be supplied complete with
insulating oil conforming to IS: 12463 and Railway
requirements. The insulating oil shall be procured from the
manufacturers approved by RDSO. The successful
tenderer/manufacturer shall submit test certificates as per
IS: 12463 for oil.
4.12 The tenderer shall furnish their compliance or otherwise
against each clause/sub-clause of the technical
specification. If the tenderer wishes to deviate from the
provision of any clause/sub-clause, he shall furnish the full
details with justification for such deviations.
4.13 Detailed drawings of CT along with SOGP shall be
furnished for RDSOs approval before manufacture is taken
up.
4.14 The CT shall be used for following additional protective
devices/relays.
i) Fibre optic line differential protection
ii) Directional over current relay.
iii) LBBU relay (LBB- breaker failure relay)
iv) Bus bar differential low impedance type protection
relay
v) Energy metering
5.0 The following Type and Routine Tests as per IEC:44-1, IS:270-
5 and RDSO specification No. ETI/PSI/117(07/88) with A&C
slip No. 1 to 6 shall be conducted on the Current Transformer
required for Mumbai area under DC-AC conversion.
5.1 Type Tests
1. Visual inspection
2. Temperature rise test
3. Impulse voltage test
4. Short time current test
SPECIFICATION NO. TI/SPC/PSI/CT/0515(05/2015) Page 29 of 27

5. Excitation test and plotting of magnetizing

characteristic curves.
6. Radio interference test
7. Seismic withstand test.
8. Thermal stability test.
9. Thermal co-efficient test i.e. Measurement of tan delta
as a function of temperature.
10. The CTs shall be subjected to special i.e. Multiple
chopped impulse test on primary winding as per clause 6.3 (C)
and Annexure - (B) of IEC 60044-1 in order to evaluate the
ageing characteristics of the CT insulation. This test is to be
done to assess the CT performance in service to withstand the
high frequency over voltage generated due to closing and
opening operations of isolators.
5.2 Routine Tests
1. Dimensional check
2. Verification of terminal marking and polarity
3. Power frequency voltage withstand test on primary winding.
4. Power frequency voltage withstand test on secondary
winding.
5. Accuracy tests.
a) Current error and phase displacement at the rated
primary current.
b) Composite error at rated accuracy limit primary current.
6. Measurement of knee point voltage, exciting current
and ISF test (only for metering core).
7. Measurement of winding resistance test.
8. Insulation resistance measurement test.
9. Inter turn over-voltage test.
10. Partial discharge test (PI) value shall be less than
5pC).
11. Capacitance and tan delta value measurement than
delta value should be less than .5%
12. Oil leakage test.