POWER SUPPLY FOR TRACTION
20100 Supply System
1. The single phase 50 Hz power for the electric traction is obtained from
220/132/110/66 kV Extra High Voltage 3-phase grid system through step down
single phase transformers. For this purpose duplicate feeders comprising
of only 2 phases are run from the nearest grid substation of the Supply
Authority to the traction substation. The brief description of the system
is given in Chapter 2 of Volume I. The 25 kV single phase conventional
system as adopted on Indian Railways has been described in that chapter. A
schematic diagram of the traction sub-station and feeding post indicating
the general feeding arrangement is indicated at Fig. 1.01.
Salient technical features of the 2x25kV Auto-Transformer (AT) feed system
are indicated in Chapter XI.
20101 Liaison with Power Supply Authorities
For ensuring continuity and reliability of power supply for traction it is
important that effective liaison is maintained between the officials of
Railway and Supply Authorities. Broadly action on the following lines be
a) A system of periodic meetings at different levels at mutually agreed
intervals needs to be evolved.
b) Reliability of supply involves also the maintenance of traction voltage
between 25kV and 27.5kV at the feeding posts and frequency between 48.5Hz
and 51.5 Hz. The serious repercussions on Railway traffic if the above
limits are not adhered to should be constantly impressed upon the Supply
c) The traction load should be treated as essential load and should not be
disconnected or reduced to meet supply system exigencies. This principle
has been accepted by most Supply Authorities and where this has not been
done, constant efforts should be made at the high level periodic meetings
to get this principle accepted.
d) Since the cumulative effect of frequent power supply interruptions,
even though of short duration at a time, can be very serious to Railway
working, a periodical review of such interruptions should be made at the
Divisional level and the cause of each interruption ascertained as far as
possible. The results of the review should be furnished to CEE to keep him
fully informed of the power supply position. This subject should also form
an important item for discussion at the periodic meetings with the Supply
e) Power Supply for electric traction should be governed by a specific
Agreement entered into by the Railway with the concerned Supply Authority
before the supply is actually taken. Where this has not been done already,
urgent action should be taken to have it finalized without delay.
f) When grid supply to any traction sub-station fails and consequently
emergency working has to be resorted to by extending the feed from
adjacent sub-stations, the maximum demand at these substations may go up.
Most Supply Authorities have agreed to ignore such temporary increase in
maximum demand for billing purposes. Where this has not yet been agreed
to, efforts should be continued to persuade the Supply Authorities to
accept this principle.
g) The present methodology of measuring maximum demand at each individual
sub-stations for the purpose of billing has been reviewed by the Central
Electricity Authority. It has been agreed that Railways should be charged
for traction power on the basis of simultaneous maximum demand recorded in
contiguous substations of the SEB serviced by the same grid transformers.
Modalities to implement the decision would have to be mutually settled
between SEB's and Railways, with cost of the equipment borne by Railways.
20102 Tariff for Traction
a) In Electric Traction the energy cost forms a substantial portion of the
total operating and maintenance cost. The tariffs charged by various state
Electricity Boards vary from a simple flat rate for the energy (charged by
some states like MSEB & GEB) to a very complex tariff structure covering a
variety of parameters (as indicated in the tariff charged by MPEB). The
implications of the various parameters should be studied carefully to keep
the energy cost to the minimum possible level.
b) Contract Demand for each sub-station should be stipulated in relation
to the expected actual Maximum Demand in such a manner that infructuous
payments by way of minimum guarantee on the one hand and penal charges for
exceeding the contract demand on the other, are avoided. Notice period for
altering Contract Demand should also be kept as low as possible in the
agreement, preferably 4 to 6 weeks.
c) In the tariff charged for electric traction, following are some of the
parameters that should be given careful consideration with a view to
keeping down the energy bill to the minimum:
i) Maximum demand charge RsAVA/month : Normally one feeder is "ON" for
feeding the traction load. If two sets of trivector meters are provided,
the higher of the two should be the MD to be charged. Caution may be
exercised to ensure that addition of both is not taken as MD in billing.
ii) Energy charge Paisa/kWh.
iii) Fuel Adjustment Charge (FAC) accounting for the variations in cost
of fuel and calorific value compared to stipulated basis figures. This
charge should be realistic and should be periodically verified with the
iv) Penalty for low power factor: The penal charge is prescribed as an
extra amount leviable in Rs/ kVA of Maximum Demand if power factor falls
below a specified value. SEBs usually insist on consumer providing PF
correcting equipment and do not permit power factor lower than a
v) Billing Demand is usually a certain percentage of contract demand or
the actual MD whichever is higher.
vi) Excess over Contract Demand and corresponding units of energy are
usually charged at higher tariff (excluding FAC). Even if the excess MD is
for a short period of just 15 min., proportionate units for the entire
month are charged at penal rate. One of the SEBs does computation of
excess energy as under:
Excess Energy = TU (1-CD/MD),
where TU = Total Energy
MD = Maximum Demand
CD = Contract Demand
The Contract demand therefore, has to be carefully determined, and
reviewed periodically and if necessary modified to avoid penal charges.
vii) Minimum Guarantee
Usually, the agreement with SEB stipulate a percentage return of 15 to 20%
on the capital cost invested by the SEB for giving the connection, as
minimum guarantee. This is generally met by the pattern of energy
consumption in traction. However, minimum guarantee in some cases is
specified in terms of guaranteed average load factor (say 30%). This ties
up the Contract Demand with the units consumed.
If a few heavy trains operate in a section raising the Maximum Demand
high, the average load factor may not reach 30% unless adequate frequency
of passenger trains also forms part of the traffic pattern. Here, if
contract demand is too high, 30% load factor is difficult to achieve while
if contract demand is too low, exceeding it and attracting penal changes
becomes a possibility. Careful balance between the two conflicting
requirements has, therefore, to be struck.
viii) Harmonic Voltage Distortion
The consumer is required to carry out Harmonic Analysis under full load
conditions. It is stipulated that the individual harmonic voltage
distortion (Vn) and total harmonic voltage distortion (Vt) at the point of
supply shall not exceed 1% and 3% respectively.
V - RMS value of fundamental voltage.
Vn - RMS value of harmonic voltage of order "n", expressed as percentage
of RMS value of the fundamental and shall be calculated using the
d) The tariff charged for traction should be reviewed periodically with
the SEB. It should be ensured that the rates do not exceed those charged
in EHV tariff of the SEB applicable to other consumers.
20103 Monthly Meter Readings
a) In earlier Railway Electrification installations, only one set of
meters owned by the Supply Authorities has been installed to meter the
traction load. In later installations, a second set of meters is being
provided on the sub-station switchboard at Railways cost. Where only one
set of meters belonging to the supply authority is installed yearly
testing of the meter should be carried out. If its accuracy is in doubt at
any point of time, the Railway is entitled to ask for testing and
certification of the meter. Where a second set of meters has been provided
at Railways cost, the figures for billing purposes should ordinarily be
based on the average readings of the two sets of meters, unless
specifically provided for otherwise in the Agreement. The exact procedure
covering these aspects should be embodied in the Agreement with the Supply
b) The monthly meter readings should be taken on an agreed date each month
jointly by representatives of the Supply Authority and the Railway. The
meter card as well as the printornaxigraph chart reading showing the
maximum demand for the month should be initialled by representatives of
both parties. Only readings jointly recorded as above should be accepted
for billing purposes.
c) When visiting the grid sub-stations for taking meter readings, the
supervisory official concerned will also obtain additional information
such as daily maximum demand for traction, power factor, load factor,
variation of voltage, changes in the system of interconnection, which have
a bearing on power supply for traction. Suggestions for suitable changes
in the Supply Authority's network may be made at appropriate level and if
necessary concrete proposals initiated for making power supply 100%
20104 Scrutiny of Bills
a) The Supply Authorities bills should be carefully scrutinized in the
Divisional office with reference to the
Agreement and the tariff. A time schedule should be laid down jointly with
the Accounts Department for scrutiny and passing of the bill so as to take advantage of the
rebate admissible, if any, for prompt
payment. Penal charges levied, if any, should be carefully scrutinized and
appropriate remedial measures
taken to prevent recurrence. If the minimum charge payable is in excess of
the amount warranted by the actual energy consumption, this fact should be
promptly brought to the notice of CEE as well as the operating Department
to take special steps to arrange for movement of additional traffic, to
the extent possible, in the affected section, including diversion from
b) Detailed instructions should be issued locally, jointly with the
Accounts Department, listing the items to be checked prior to passing the
bills from the Supply Authorities. An illustrative list is given below:
i) Arithmetical accuracy.
ii) Meter readings shown on the bill tally with those received earlier
from the subordinates.
iii) The tariff applied is in terms of the agreement.
iv) The method of computation of the maximum demand for billing purposes
is in accordance with the agreement and that temporary increase in maximum
demand on account of emergency feeding has not been taken into account
where this principle has been accepted.
v) The time allowed for payment is in accordance with the agreement,
There is no duplication in billing.
vii) The payee as provided for in the agreement is clearly indicated. The
full particulars of the payee should be advised to the Accounts Branch to
enable that Branch to issue cheques accordingly.
viii) Each new bill should be analyzed and compared with earlier bill and
the reasons for any significant departures investigated.
In case of any dispute/discrepancy, the payment be made "under protest".
20105 Power Factor Improvement
a) Provision of power factor improvement capacitors at 25 kV bus of
traction substations should be planned giving priority to substations (i)
which feed large marshalling yards and (ii) where penalty for low power
factor and / or exceeding maximum demand has been stipulated in the
b) The average monthly power factor is calculated as ratio of kWh and kVAh
over a month. Care should be taken to make sure that it does not go
'leading' while P.F. correcting equipment is used and is kept near unity.
Switched capacitor be used where load variations are wide.
c) The Guidelines issued by RDSO in respect of selection of the kVAr
rating should be kept in view at the time of planning.
20106 Shut-Downs of Traction Supply to be Pre-Planned
a) At all grid sub-stations and traction sub-stations owned by the
railways, duplicate EHV feeders are available. Most of the sub-stations
also have two sets of traction power transformers and associated
switchgear. Maintenance of equipment and transmission lines should not,
therefore, necessitate total shut-down of EHV and 25 kV supply at a
sub-station. It should be arranged with the Supply Authorities that on the
rare occasions when such shut-down becomes inescapable, notice should be
given well in advance to Sr. DEE/DEE(TrD) stating the reasons for the
shut-down and the anticipated duration. Such shut-downs should be arranged
by Sr.DEE/DEE(TrD) in consultation with the Operating Department which may
have to re-schedule trains and take a other measures as necessary.
b) A double circuit set of transmission lines from the Grid Sub-station
are run to give supply to traction sub-station. Therefore, maintenance of
the transmission line does not necessiates total shut-down of
the systems. However, all such shut-downs should be planned well in
advance giving the reasons for the shut-down and anticipated duration.
20107 Operating Instructions for Grid Sub-Stations
Detailed operating instructions mutually agreed to between the Supply
Authorities and the Railway should be made out for each grid sub-station
as well as traction sub-station owned by the Railway and should be issued
to TPC as well as operators at grid stations. These instructions should
contain the following details:
a) Procedure for carrying out switching operations at the sub-station.
b) Procedure for interchange of message of pre-planned or emergency
c) Procedure to be followed in case of failure of supply and information
to be conveyed by grid sub-station operator regarding duration of failure
and anticipated time of restoration to enable emergency working to be
d) Records to be maintained by grid sub-station operator and TPC regarding
emergency feed arrangements.
e) List of office and residential telephone numbers of important grid and
railway officials to be contacted in an emergency.
f) Mutual assistance to be rendered for transmission of important messages
in the event of telephone failures at the grid sub-stations or RCC.
20108 Statistical Data Regarding Energy Consumption
In the divisional office, a register should be maintained to record
month-wise the following particulars in regard to energy consumption at
each supply point :-
a) Energy consumption (kWh)
b) Maximum demand (kVA)
c) Average power factor (kWh / kVAh)
d) Monthly average load factor (per cent)
e) Payment for energy
f) Payment for maximum demand
g) Payment towards meter rent
h) Payment of fuel surcharges, if any
i) Payment for P.F. surcharge/penal charge
j) Payment of covering the minimum guarantee load, if any
k) Other payments, if any
l) Total amount of bill under all heads
i) Average total cost per kWh
A consolidated statement giving the above details for all supply points
should be furnished by Sr. DEEfTrD) to CEE each month by a stipulated
date. CEE will in turn furnish a monthly statement in the prescribed
proforma to the Railway Board and Research Design and Standards