Regarding AC electrification system in AC Locomotives

1. GANDHINAGAR INSTITUTE OF TECHNOLOGY
Branch: Electrical
Subject: Utilization of Electrical Energy and Traction
(2160907)
Topic: AC Electrification System
PREPARED BY: Darshil Shah (140120109050)
GUIDED BY: Prof. Rahish Silavat

2. INDEX
 Introduction
 Types of AC electrification system
 Single phase AC system
 Three phase AC system
 Composite system
 Single phase to Three phase or Kando System
 Single phase to Direct Current system
 Conclusion
 References

4. INTRODUCTION
 Electrification technique is very much vast application to ensure the better efficiency and reliability
of the Traction system. By applying this Electrification system there are no any kinds of pollution
and any kind of unnecessary maintenance is required.
 A Railway Electrification System supplies electric power to railway trains and trams without an
on-board prime mover or local fuel supply. Selection of an electrification system is based on
economics of energy supply, maintenance, and capital cost compared to the revenue obtained for
freight and passenger traffic.
 Different systems are used for urban and intercity areas; some electric locomotives can switch to
different supply voltages to allow flexibility in operation.
 So, according to this here topic can also bifurcate in further classifications:
1. DC Electrification system 2. AC Electrification system
Single phase System Three phase System

5. TYPES OF AC ELECTRIFICATION
SYSTEM
1. Single phase AC system
2. Three phase AC system
3. Composite system
4. Single phase to Three phase system
5. Single phase to DC system

6. SINGLE PHASE AC SYSTEM
 In this system, AC series motors are used for getting necessary motive power. The voltage employed
for distribution network is 15,000 to 25,000 volts at 6 (2/3) or 25 Hz, which is stepped down on the
locomotive to a low voltage (300 to 400 V) suitable for supplying to single phase AC series motors
by means of a stepdown transformer carried on locomotive.
 The distribution network may be fed directly, at high voltage, from generating station when the
extent of electrification is within a radius of about 30 km from the generating station. For longer
distances the economic voltage for the power transmission system is higher than that desirable for
traction system, and therefore, transformer substations are employed for feeding the distribution
network.
 Low frequency operation of overhead transmission line is reduced the line reactance and hence the
voltage drop directly.
 If, electric supply is taken from industrial frequency network, which is usually the case, substations
in addition to transformers have necessarily the frequency converter to convert 3- phase, 50 Hz into
single phase 6 (2/3) or 25 Hz as required. AC system is invariably adopted for mainline service
where the cost of overhead structure is more important and rapid acceleration and retardation is not
so important as for suburban railways.

7. THREE PHASE AC SYSTEM
 In this system, 3 phase Induction motors operating at 3000 to 3600 volts and normal frequency
6 (2/3) Hz are employed for getting the required motive power. The three phase induction
motors are simple and robust in construction and have high operating efficiency & property of
automatic regenerative braking without requiring any additional equipment.
 The substations receives power from high voltage transmission line at power frequency & step
down the voltage & change the frequency. Since, two trolley wires per track are necessary, the
line voltage of the distribution system has to be limited to values below the highest voltage
used for single phase railways, and as the 3 phase induction motors can be built economically
for operation at moderately high voltage, the line voltage is usually chosen so that the motors
may be supplied directly from trolley wires.
 This system employed in hilly areas, where output power required is high & regeneration on
large scale is possible.
 Disadvantage is two overhead contact wires and constant speed characteristic of induction
motors this system is no longer likely to be adopted.

8. COMPOSITE SYSTEM
 Efforts have been made to combine the advantages of DC/AC and 3 phase/1 phase system and
composite system have been evolved.
 The single phase AC system is preferable for the view point of distribution and contact wire
system. It can be converted either three phase AC or DC at low voltage in locomotives. At
present there are two composite systems are used:
1. Single phase to Three phase system (Kando system)
2. Single phase AC to DC system

9. COMPOSITE SYSTEM
Single phase to Three phase system
Single phase to DC system

10. SINGLE PHASE TO THREE PHASE
SYSTEM
 In this system, single phase high voltage AC system is employed for distribution purpose and
three phase induction motors for getting the necessary motive power in order to have the
advantage of low cost of single phase overhead distribution system together with desirable
characteristics of 3 phase Induction motors.
 The voltage used for distribution network is 15000 volts at 50 Hz. Locomotive carries a phase
converter for converting single phase to three phase supply at relatively low frequency.
 It is convenient to use for some railway tractions.

11. SINGLE PHASE TO DIRECT
CURRENT SYSTEM
 In this system, the advantage of two system are combined together by employing high voltage
AC 1 phase system for overhead distribution system is obtained together with desirable
characteristics of DC series motors.
 Basically this system is adopted on 25 kV and 50 Hz. It consist numerous advantages over
DC system as enumerated below:
 The line current for given demand of power is reduced on account of high system voltage. It
causes reduction in cross-section of overhead conductor which leads to a savings in cost of
supporting structures & their foundations being lighter in weight & simpler. The weight of
copper require for track km for the 1500 V DC system is 3700 kg and for 3000 V DC system
is 3300 kg whereas for AC system is 1600 kg.
 On account of high voltage substations are spaced at longer distances (50 to 80 km) whereas
the substations are spaced at 12 to 30 km in case of 3000 V DC system and 5 to 12 km in case
of 1500 V DC system. It affects substantial savings in capital and expenditure on traction
substation & transmission line on account to reduce no. of S.S. and reliability.

12. SINGLE PHASE TO DIRECT
CURRENT SYSTEM (cont…)
 A very special feature of the AC locomotive In comparison with the DC locomotives is the
greater amount of adhesion obtained with AC locomotives. In case of AC rectifier locomotives
employing DC traction motors, coefficient of adhesion is obtained as much as 45% against the
value of 27% in case of DC locomotives.
 The greater adhesion is obtained because of possibility of connecting all DC series motors in
parallel permanently and controlling their speed by varying the voltage across each motor.
 The starting efficiency is high of AC locomotive than DC locomotives as in case of AC supply
voltage for starting reduced by means of ON load tap changer installed either primary or
secondary side of transformer where in case of DC it is obtained by starting Resistance.
 There are some drawbacks with AC locomotives such as unbalanced imposed on power supply
and interference with neighboring communication lines. It can be minimized by taking suitable
precautions as:

13. SINGLE PHASE TO DIRECT
CURRENT SYSTEM (cont…)
 Taking of supply for the traction substations at very high voltages (110 or 132 kV) and
from a supply system having high capacity.
 Balancing of traction load equally on all the three phases which is possible by connecting
different traction substations across different phase in rotations.
 Employing Scott-T connection to three/two phase transformer in traction substation.
 Replacing open aerial communication lines by lead or aluminium sheathed underground
cables and earthing the sheathing of cables at regular intervals.
 Provide isolations to transformers and keep voltage upto 60V under operating conditions.

14. COMPARISION OF AC 1- PHASE, 3- PHASE
SYSTEM & COMPOSITE SYSTEM
Single phase AC system Three phase AC system Composite system
Single phase AC supply is
required
Three phase AC supply is
required
Transformation is required
High starting torque Less starting torque Less starting torque
AC Series motor is used 3 phase Asynchronous motor is
used
First use of DC motor and then
use of 3 phase Induction Motor
2500-5000 V from Generating
station to Receiving station
3000-3600 V from Generating
station to Receiving station
15000 V for single phase to
three phase conversion
High efficiency Less efficiency Moderate efficiency
It is used for small (50-80 km)
distances
for hilly areas for long distances

15. REFERENCE
 www.Wikipedia.com/three-phase-traction-system
 www.electronics-hub.com/electrical-traction
 www.elprocus.com/what-is-an-electric-locomotive-systems-and-their-types-in-india

16. CONCLUSION
 According to the AC electrification system, we are come to know that AC motors are good
and efficient to handle the constant speed at longer distance, also according to previous
methods 1 phase AC Induction motors are efficient for the traction for AC Locomotives.

17. THANK YOU FOR LISTENING