FIELP OF INVENTION
The present invention relates to development of electro pneumatic contactor
with higher current carrying capacity for traction application.
BACKGROUND OF THE INVENTION
The Electro-pneumatic contactors are used in traction application for switching
electric power to motors mounted on the axle to achieve optimum performance
of the Locomotive. Thus, these contactors are manufactured to have the
capability of carrying worst case current without exceeding its temperature
beyond a specified limit. Development of high hauling capacity, 5000 HP, 25 KV,
Electric Locomotive type WAG7 by railways necessitated requirement of motors
switching contactors having current carrying capacity of 1500A DC. Existing
contactor type 22PC has current carrying capacity of only 1050 Amp DC.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an electro-pneumatic
contactor having current carrying capacity of 1500 Amp for traction control of
5000HP, 25KV electric motors for traction application.
Another object of the present invention is to propose an electro-pneumatic
contactor having current carrying capacity of 1500 amp for traction control of
5000HP, 25KV electric motors for traction application, which maintains the
overall size and mounting dimension identical to the prior art contactors.
A still another object of the present invention is to propose an electro-pneumatic
contactor having current carrying capacity of 1500 amp for traction control of
5000HP, 25 KV electric motors for traction application, which uses a substantially
large number of components of the existing contactors, which allows restricting
the cost including an effective inventory control.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1- A Line diagram of an electric locomotive showing an electro-pneumatic
(EP) contactor
Fig. 2- A photo view of an assembly of a 1500 A EP contactor for electric
locomotive according to the invention.
Fig. 3- A diagram of cylinder assembly with moving contact of the EP-contactor
according to the invention.
Fig. 4- A diagram of blowout coil assembly with fixed contact of the EP-contactor
according to the invention.
DETAILED DESCRIPTION OF INVENTION
Fig. 1 shows a single line diagram of a typical electric locomotive. The current is
collected from a 25KV OHE catenary through a pantograph (1), a transformer (3)
to step down to 1000 V, a plurality of rectifiers (4) to convert the A.C. supply to
DC supply for feeding to a plurality of DC series motors (6) mounted on axels.
The locomotive has at least two bogies one on each end. In each bogie, three
motors (6) are fitted through a control gear arrangement for achieving the
required circuit topology and speed. The motors (6) are connected to DC supply
via a plurality of electro-pneumatic contactors L1-L6 (5) to make the connection
as and when required and disconnect from the supply when necessary, or for
protection during occurrence of fault. Thus, these line contactors carries full load
as well as fault current of the motor and has to be suitably rated. The speed of
the locomotive is controlled by varying the terminal voltage with the help of a tap
changer (10) connected at primary side of the transformer (3). When the voltage
reaches at its maximum value, the speed is further increased by diverting field
current partially through a plurality of resistors (8). The resistors FR1-6 (8)
across the field windings (9) are connected through a plurality of field shunting
contactors FS1-6 (7) and are switched off and on as per requirement.
A. Basic Operation
Normally a contactor in a circuit is used for switching of current on load, thus it
has to be capable of breaking the circuit at load, making the circuit, and carrying
the current continuously at rated value without exceeding temperature rise
limits. Fig.-2 shows a complete contactor type 22PC with & without arc chute.
The contactor operates when pressurized air enters into a cylinder (11), through
a magnet valve (12), which operates under 110 Volt DC signal and allows entry
of air into the cylinder (11) on application of electric supply. Upward entry of air
into a push piston rod assy (13) of the cylinder (11) resulting in a movement of a
moving contact assy (14) upward till the moving contact assembly (14) makes a
strong contact with a fixed contact assy (15). Thus, electrical contact is made.
The current is collected through a current collecting shunt (17) at the moving
contact and through a blowout coil (16) at the fixed contact end. As long as air
pressure is maintained in the cylinder (11), electrical contact remains in closed
position, which opens on switching off the supply to the magnet valve (12)
resulting in release of air pressure from the air cylinder (11) and hence, the
moving contact assy (14) returns to its original position. When the contacts open
at load, a big arc is produced, which needs to be properly extinguished. The
blow out coil (16), which carries load current, produces magnet field in
conjunction with the cheeks (19) of an arc chute (18). This magnetic field with
current flowing in the blowout coil (16) produces an electromotive force, which
pushes the arc into the arc chute (18), where it gets divided in multiple parts and
finally gets extinguished. The current flow in the electric path can be switched by
applying electric supply to the magnet valve, which pushes pressurized air in the
cylinder, thus current flow is controlled by Electro Pneumatically driven
contactor.
B. Redesign of Components of Current path
As explained above, the current path can be made or brake electro
pneumatically by the contactor. The current path mainly consists of the fixed
contact, the blowout coil assembly, the moving contact, and the cylinder
assembly shown in fig 3 and 4 respectively. The current carrying capacity
depends upon the cross sectional area of the current collecting shunt (17)
and moving contact assy (14) including the blowout coil and fixed contact
assy. But only increase of cross section is not enough, the effect of this on
the contact pressure, temperature rise, arc extinction and pneumatic pressure
is to be taken into consideration. Further, the constraint of maintaining
overall size and interchangeability of the new components with the existing
component have been solved. The components of the current path as
described above has been redesigned suitably meeting all of the above
constraints to meet the current capacity of 1500 Amp. The contactor fitted
with modified current carrying components has been tested at 1500 Amp and
temperature of components was found well within the specified limits.
Thus a new and innovative electro-pneumatic contactor type 22PC has been
developed for 1500 Amp continuous current carrying capacity with minimum
changes in design and keeping overall size and component level
interchangeability of more than 90% components of the existing design.
KEY FEATURES
We Claim:
1. An improved electro pneumatic contactor for traction control of an electric
motor of 5000HP and 25 KV in a locomotive , the improvement is
characterized in that the moving contact assembly (14), the current
collecting flexible shunt (17), the blowout coil assembly (16), and the
Fixed contact assembly (15) are reconfigured to be compatable with the
existing components of the electro pneumatic contactor to achieve a
current carrying capacity of the contactor to 1500 Amp.
2. The contactor as claimed in claim 1, wherein the Overall size and
mounting arrangement is kept identical to the existing contactor.

An improved electro pneumatic contactor for traction control of an electric motor
of 5000HP and 25 KV in a locomotive , the improvement is characterized in that
the moving contact assembly (14), the current collecting flexible shunt (17), the
blowout coil assembly (16), and the Fixed contact assembly (15) are
reconfigured to be compatable with the existing components of the electro
pneumatic contactor to achieve a current carrying capacity of the contactor to
1500 Amp.