motors traction
TRANSCRIPT
31101 Introduction
Some of the recent technological innovations introduced by Foreign Railways are discussed
below. Advantages offered by these innovations in respect of operating performance and
maintainability have also been indicated. With a view to use developed technology of 3-
phase drive system on Indian Railways, import of 3-phase drive system locomotives with
technology transfer for subsequent indigenous manufacture is on hand.
31102 Conversion Equipment
1. With the availability of thyristor of higher power handling capability use of tap changer is
being eliminated making the equipment entirely static. This will not only reduce attention
required but also enhance reliability. Other very important benefit achieved by the thyristors
is the capability they offer to control individually the supply to each motor permitting full
utilization of the adhesion existing between the wheels and the rails.
2. Indian Railways have imported 12 locomotives from Japan and six from Sweden with this
technology (WAG 6 series). Earlier a few experimental thyristor units were also fitted in
existing locomotives, some of them with indigenous know-how. Indian Railways have also
imported 25 sets of thyristor control traction equipment for fitment on 25 kV ac MG EMUs
from UK. These are being fitted on 25 kV ac MG EMU coaches at ICF, Madras. Seven such
thyristor controlled EMU rakes are presently in operation on MG Section of Southern
Railway.
31103 Controls
With the advent of solid state devices in general, and microprocessors in particular, more
and more sophistication has become possible. Other things remaining the same, with step
less control and consequent non-pulsating torque offered by such controls, higher average
tractive effort can be achieved . The solid state control is fast acting and methods are now
available to detect incipient slip and take corrective action before the slippage becomes
uncontrollable and curative action is called for by reducing the tractive effort applied. Thus
the locomotives can be made to develop tractive efforts to very high levels of adhesion co-
efficient.
31104 Drive
1. One of the severe restrictions imposed on the capability of electric locomotives is the dc
series motor. These motors have limitations on their use because of windings on the rotor
and assembly of commutators, making it vulnerable against centrifugal forces and
requirements of satisfactory commutation. The 3-phase asynchronous motor with a bar
rotor does not have the surface speed limitations. The useful portion of its speed torque
characteristics is only near its synchronous speed. This useful portion can be spread over a
wide range by varying the synchronous speed through frequency control.
2. With the advent of Gate Turn Off (GTO) thyristors problems associated with conversion of
dc into multiphase ac system have been eliminated and use of 3-phase synchronous /
asynchronous motor has become feasible. "Variable Voltage and Variable Frequency" (VWF)
control has been developed and use of induction motors as traction drives has been tried
successfully on the different railway systems. With induction machines a maximum surface
speed of 100 m /s is achievable and an rpm level of 4500 has been accepted in the railway
systems in Europe. This considerably increases the output power of the traction motor for
the same size. This state of art technology has yet to arrive in our country.
3. Typical power circuit along with brief details of locomotive fitted with asynchronous
motors is shown in Fig. 11.01.
31105 Power Rating
1. Necessity for increasing the throughput resulted in the design of BOX "N" wagons. With
these wagons, a trailing load of 47001 has been optimized. Further improvements are under
consideration which may result in a maximum trailing load of 51001 on the existing loop
lengths. Also efforts are on hand to increase the maximum speed of these stock to 100
km/h. For trailing loads of 4700 t, a 6000 HP locomotive with 45 t starting effort was taken
as an optimum. Once the trailing load is increased to 5100 t and the speed potential to 100
km/h, the horsepower requirements further go up to 8000 with a starting tractive effort of
501. Indian Railways will require a 8000 HP loco to meet the increasing throughputs of
freight traffic.
31106 Other Developments on Hand
1. Indigenous development of multiplexing and locotrol for use on long passenger and
heavy-hauled goods trains.
2. Indigenous development of on board power factor correction equipment for improving
power factor of locomotive.
3. Indigenous development of fault diagnostics for locomotive.