by
2
Sequence to follow
Introduction of Electric traction
25kv AC traction on IR
Present/future scenario on IR
Concern
Possible alternatives.
 2 x 25 kV a c system.
 Major components of 2 x 25 kV System.
 Experience of 2 x 25 kV system on IR.
 Comparison of two systems.
 Improvement in train operations.
 PROS & CONS OF 25 kV V/s 2 X 25 kV a.c. SYSTEM
 Financial evaluation
 Constraints in conversion of conventional 25kv system
 Conclusions & recommendations
3
Introduction of Electric traction
 World over electric traction was
experimented with d.c power supply
during initial days of electric traction.

The first system with 25 kV, 50 Hz,
a.c. power supply was introduced in
Germany and France.
4
Five ‘standard’ types of electrification systems emerged & can be
found across Europe: 750 V DC 3rd rail, 1.5 kV DC, 3 kV DC, 15 kV
16.7Hz AC and 25 kV 50Hz AC
Status on IR
S.No.
Voltage
Section
1
750 V DC
Kolkata Metro
2.
1500 V DC
Mumbai suburban area
3.
3000 V DC
Earlier used on Kolkota Suburban area & a
portion of E.Rly. but now changed to 25 kV a.c.
4.
2x25 KV AC
Bina-Katni-Bishrampur including Chirimiri
5.
25 kV AC
All other electrified sections except 1. to 3.
above.
5
25 kv Conventional OHE system (w/o BT & RC)
Return current goes back to TSS through rails and earth.
• 25 kv Conventional OHE system (with BT & RC)
Return current does not pass through the rails or earth but
through a separate return conductor.
Return conductor runs close & parallel to catenary wire, inductive
interference is reduced.
6
25 kv Conventional OHE system (w/o BT & RC)
7
25 kv Conventional OHE system (w/o BT & RC)
Return current goes back to TSS through rails and earth.
• 25 kv Conventional OHE system (with BT & RC)
Return current does not pass through the rails or earth but
through a separate return conductor.
Return conductor runs close & parallel to catenary wire, inductive
interference is reduced.
8
Booster Transformer Feeding System with Return
Conductor and Rail Joints)
9
• Introduction of CC +10 rake
• Introduction of 25 tone axle load stock
• Augmentation of automatic signaling in entire sections
• Increase in no. of trains in the feeding zone of TSSs.
• Increase in haulage capacity of trains
• Increase in speed of the trains.
10
Concern
Off late, Railways have been facing competition from road
sector for freight traffic and from airlines for passenger
traffic.
Further, higher GDP growth @8% and above is expected
in future.
Railways shall have to cater much more traffic, thus it has
become necessary to increase the speed, capacity and
hauling load of the train, for which power requirements for
running these trains shall also go up.
11
Possible alternatives
 Further reduction the spacing between Traction
substations – construction of new TSS at 15-20 km interval, Tr line
& bays, DJ operation constraints etc
 Increase in the capacity of the traction
transformer- from 13.5/21.6 MVA to 30 MVA, additional cost of
Approx. 1.5 crores.
 Parallel operation of transformers : construction cost
of third bay associated switch gears.
 2 x 25 kV a.c system:
higher tonnage freight trains &
higher speed passenger trains with minimum voltage drop can be hauled
12
2 x 25 kV a.c system
Principal of operation
Power is fed from the TSS at 50 kV and utilization is
achieved at 25 kV by providing Auto-Transformers
of adequate capacity and by providing one
additional conductor -- feeder Wire.
Provides +25 kV Voltage between OHE and rail and 25 kV voltage between Rail/earth and the Feeder
Wire.
Spacing & capacity of the AT’s depends upon
system design capacity requirements and tolerable
limits of the inductive interference levels and
normally varies from 10 to 15 kms interval
13
Fig 3
2x25 Kv OHE system (with Auto transformer )
14
2 x 25 kV a.c system
contd….
 The traction load is shared by both the
adjacent ATs in inverse proportion of
respective distances i.e. the AT nearer to
the Locomotive will share more load
than the other one.
15
SSP
Contact wire
SP
TSS
Rail
AT 1
AT 2
2x25 kV system
AT
feeder
AT 3
Location of train
----Share
of
trainload by AT1.
100%
SHARE
OF
TRAIN
LOAD
BY
AT
_____ Share of
train load by AT2.
Share of
trainload by AT3.
0
L
L
16
Major components of 2x 25 kV System
Auto-Transformer
Scott-connected transformer
V-Connected Transformer
Capacitance - Resistance Devices
Series Capacitors
Fault locators
17
Experience of 2 x 25 kv system on IR
On IR 2x25 kv system was commissioned
in Bina-Katni-Anuppur-Bishrampur
including Chirimiri section in 1995-96.
This section falls in erstwhile S.E.Railway
of Indian Railway presently in Bilaspur
division of South Eastern Railway and
Jabalpur division of west Central Railway
18
Experience of 2 x 25 kv system on IR
contd….
 In the past 7 – 8 years, the system is being
loaded to only 22% of the designed capacity in
WCR portion.
 The system had been designed to cater for
running of 2 no. 9000-ton trains & 4 nos. 7500
tone trains, which probably has not happened.
 In SECR due to operational requirements, one
TSS i.e. Bishrampur has been closed down in Dec
1999 & the transformers of balance TSSs are
loaded to maximum 50-55 % of the total rated
capacity .
19
Experience of 2 x 25 kv system on IR
contd….
Thus, the system is highly underutilized at present and advantage of
2x25 kV system could not be availed
by IR. That is perhaps the reason
that this experiment could not continue
in other sections
20
COMPARISON OF TWO SYSTEMS
 Voltage profile of section :Due to less OHE current,OHE
voltage profile of the 2x25 kV system is better.
Harmonic: Since the fault levels are much higher on the 25
kV & 220 /132Kv side, there are less harmonics on the
system.
 Technology :The technology of 2x25 kV system is bit
complex due to the provision of equipment like; Scott
connected transformer, C-R device etc
Substation Spacing: : The substation spacing for 2x25 kV
system is 80 – 100 kms.as compared to approx. 40 – 60 kms
for conventional system.
21
IMPROVEMENTS ON TRAIN OPERATION
 2 x 25 kV system is highly suitable for highspeed corridors and high haulage capacity sections.
 Improved operational benefits for the drivers
due to less frequent opening/closing of breakers at
neutral sections.
 No arcing problems encountered at overlaps as in
the case of BT/RC system.
22
PROS & CONS OF 25 kV V/s 2 X 25 kV a.c. SYSTEM
MERITS OF THE SYSTEM
 Reduced infrastructure cost due to increased spacing between TSSs.
 reduced voltage droop & losses due to lower current in feeder circuit.
 Better voltage regulation even on heavier load current, thereby allowing
more traffic in the section.
No requirement of BT & RC throughout the section.
 Most suited for highly loaded sections i.e. where load is in the range of
9000 ton plus and also more suitable for high speed operations.
Technology for manufacturing most of the items already exists in the
country and therefore local availability is not an issue anymore
23
PROS & CONS OF 25 kV V/s 2 X 25 kV a.c. SYSTEM
DEMERITS OF THE SYSTEM
 Time required for maintenance including slewing of OHE is more
 Initial cost of 2x25 kV system as a whole is approx. 10-12% higher
than the conventional cost.
 C-R Panel failures have been reported by WCR due to HT bushing
bursting and burning of register elements, for which indigenous sources are
not available but can be developed once the demand is there.
 Losses are on higher side, in case the load on the system is less than
say 50% of the rated load.
24
Financial evaluation
In the present energy fuel scenario, when
electrification projects are yielding very high return
i.e. 20 – 40%, even with marginal higher cost of 2 x 25
kV a.c. system, this system would be financially viable.
Further,it will provide very high capacity for future
growth to implement heavy haul for quantum jump in
through put without any additional infrastructure.
25
FINANCIAL EVALUATION OF THE SYSTEM
The brief summary of salient
features of both the
sections
is givenCost/RKM
in the followingCost/TKM
table:
RKM
TKM
Total
Section
VijayawadaVSKP
(Conventional)
sanctioned/Ex
ecuted cost (
Rs. In Crs.)
202.74
Bina-Katni
(2x25
kv 201.18
system)
366
268
905
702
0.55
0.75
0.22
0.29
Basis
Completio
n report.
2x25 Kv
system
costlier
by
28%
Completio
n report
Higher cost is due to the fact that at the time of installation & commissioning of 2x25 kv
system, all the equipments of 2 x 25 kV a.c. system were imported & system was designed
for 9000 tone trains instead of 4730 tone for conventional system
26
Comparative cost/TKM for various electrification projects (Cost
in Crs. Of Rs.)
Sanctio
ned
cost
Electric
al cost
234.62
160.00
41.00
288
729
VL-Trichi 91.69
50.00
20.00
178
LINWadi
67.00
22.00
161
Section
MGSZFR
Average
87.37
PSI
cost
RK
M
TK TK
M M/
RK
M
Cost/TKM
Railway
Board
sanction
Total
Electri
cal
PSI
2.5
0.32
0.22
.06
21.7.06
284
1.6
0.32
0.18
.07
07.7.06
333
2.1
0.26
0.20
.07
23.8.06
.07
27
COST COMPARISON OF CONVENTIONAL & 2X25KV AT SYSTEM
FOR 100 RKM SECTION (as on 2006)
S.N
Items
25
kV
conventional
system
2 x 25
kV
AT
System
1
TSS **
344.74
899.00
2
SP
21.12
3
SSP
4
10 km Transmission Line per
TSS @Rs 24lacs per km &
bay cost as Rs. 80 lacs
5
PSI erection charges (40 %
of PSI equipments)
6
OHE cost (with 10% BT RC for
conventional OHE, as per unit
estimate
of
CORE/Allahabad.
Feeder wire cost added for 2x25
kv system)
7
**
***
conventional
system (3TSS, 3
SP, 4 SSP)
2 x 25 kV AT System
(1TSS, 1 SP, 4 SSP)
1034.22
899.00
113.53
63.36
113.53
16.44
112.24
65.76
448.96
320.00
320.00
960.00
320.00
465.34
584.60
3799.20
4176.00
Total
6387.9
6542.1
Total cost per TKM
9.1
9.3 (2.4 % higher)
15.83
17.40
PSI cost for conventional system taken as per CORE unit estimate.
Two sets, three single-phase v connected transformer considered.
28
FINANCIAL EVALUATION OF THE SYSTEM
IR has saved Rs.17,000 crores due to
electrification during the period 2000-01 to
2005-06, as per the published figures of
Annual Statistical Statement.
With this level of savings, we should not
hesitate to spend a little higher on 2 x 25 kV
system as compared to conventional 25 kV
system at this stage only.
It is being commonly considered by other
countries world over.
29
Constraints in conversion of conventional 25kv system
2x25 kv system appears to be only alternative to
meet the future load requirements especially in heavy
density traffic routes.
However, converting the existing 25 kv conventional
system to 2x25 Kv system has is not very easy,it has its
Constraints in conversion of conventional 25kv system to 2x25 kv system:
own constraints
• Super structures needs to be attached to mast to run
feeder wire, for which power block shall be required.
• Feeder wire needs to be erected above the centenary
wire & it will not be possible to strung the wire by using
wire trains, in fact this work will have to be carried out
manually.
Huge power block shall be required to execute this work.
30
It is for the above reasons
that, most of the Railways world
over go in for 2x25kv in the initial
stage itself even though the traffic
density is less at that time but
expected to increase in future.
It is for the above reasons that, most of the Railways world over go in for 2x25kv in the initial stage itself even though the traffic
density is less at that time but expected to increase latter on.
31
Conclusions & recommendations
• It’s the high time that a feasibility-cum-commercial study is
carried out for all the high density routes, where power supply
systems are nearing saturation, to arrive at a best possible
system instead of implementing the adhoc measures by adding
additional substations in the system.
•A comparative study be undertaken for 2x25 kV system vis-àvis the conventional/BT-RC system and if 2x25 kV system
proves to be cheaper, this can be straightway implemented.
• Keeping in view the future scenario of load and traffic level, it
is worth to adopt the 2x25kv system at initial stage itself,
especially wherein 30tonne axle load trains are expected to run
in automatic signaling territory .
32
33