working of subway system

1. VIVEKANANDHA COLLEGE OF
ENGINEERING FOR WOMEN
[AUTONOMOUS]
DEPARTMENT OF ELECTRICAL AND
ELECTRONIC ENGINEERING
SUBWAY SYSTEM
PRESENTED
BY,
PAVITHRA.S

2. Contents:
† INTRODUCTION
† ROLE OF ELECTRICITY
† MOTOR
† FUTURE DEVELOPMENT

3. INTRODUCTION:
† In some subway systems, the trains themselves, known as
rolling stock, are extremely complex . which will contain
multiple computer systems.
† These systems will control everything from the interior
lights to navigation. The trains will even have the
capability to use brake heat to generate power.
† Usually, automated subways also include surveillance
systems, such as closed-circuit TV, to allow people to
monitor trains' progress and safety from a control room.
† Sensors also detect objects near the train or in doorways,
so people don't get caught between the doors or hurt
themselves trying to board the train before it departs

4. ROLE OF ELECTRICITY:
† Most existing subways, the trains, tunnel lights and
station equipment all run on electricity.
† Overhead wires or an electrified rail known as the third
rail supplies power to the trains.
† The third rail lies outside or between the subway tracks,
and a wheel, brush or sliding shoe carries the power
from the rail to the train's electric motor.
† In the New York City subway system, the third rail
carries 625 volts of electricity, and the original lines
required their own power plant to operate.
† A series of cables and substations carried the electricity
from the power plant to the third rail.

6. CONT.,
† Electrical power also controls the subway's ventilation
system.
† Many subway systems include numerous sections of
above-ground track and station entrances that are
open to the air.
† However, natural air circulation from these sources
isn't enough to keep the air in the tunnels breathable.
† Subways have an extensive series of fans and air
shafts that circulate fresh air.
† The amount of circulation required is immense - the
planned ventilation system to be included in the New
York City subway upgrade will move 600,000 cubic
feet of fresh air every minute.

7. MOTOR:
† The motor used in locomotives are called as traction
motors.
† Modern electronics allow AC motors to be controlled
effectively to improve both adhesion and traction.
† This type of motor is commonly called the Asynchronous
Motor and was often referred to as the squirrel cage motor
on account of its early design form
† A modern railway 3-phase traction motor is controlled by
feeding in three AC currents which interact to cause the
machine to turn.
† The three phases are most easily provided by an inverter
which supplies the three variable voltage, variable
frequency (VVVF) motor inputs.
† The variations of the voltage and frequency are controlled
electronically.

8. Schematic of 25kV traction control system with the 25kV fed into a transformer. A
secondary winding is taken off for the AC to DC converter, which produces a DC output
to pass to the motor converter, which then provides the controlled three phases to the
traction motors.

10. Cont.,
† Control of these systems is complex but it is all carried out by
microprocessors.
† The control of the voltage pulses and the frequency has to be
matched with the motor speed.
† The changes which occur during this process produce a set of
characteristic buzzing noises which sound like the "gear changing"
of a road vehicle
† the modern device, in the form of the IGBT, can handle thousands of
amps and it has appeared in traction applications.
† Its principle benefit is that it can switch a lot faster (three to four
times faster) than GTOs.
† This reduces the current required .The faster switching also reduces
the complex "gearing" and makes for a much smoother and more
even sounding acceleration buzz from under the train.
† With IGBTs, "gear changing" has gone

11. FUTURE DEVELOPMENT:
† The next development in electric motor design is the
permanent magnet motor.
† This is a 3-phase AC synchronous motor with the
usual squirrel cage construction replaced by magnets
fixed in the rotor.
† The motor requires a complex control system but it
can be up to 25% smaller than a conventional 3-phase
motor for the same power rating.
† The design also gives lower operating temperatures so
that rotor cooling isn't needed and the stator is a sealed
unit with integral liquid cooling.
† Development of motor design and the associated
control systems continues and it is certain that the
permanent magnet motor will be seen on more
railways in the future.

12. Thank you!!!