FIELD OF INVENTION
The present invention relates to a 3 pole off load switch (Reverser) of 1500 Amp
continuous current employed in traction application in high power electric loco.
BACKGROUND OF THE INVENTION
In the AC-DC electric locomotive, change in the direction of movement of locomotive is
achieved either by changing the direction of current in the armature or field. Later
technique is being adopted universally. To perform the above function a multi pole off
load switch (Reverser) depending upon the number of motor is required. The function
of off load switches (Reverser) has to carry the field current of the motors mounted on
the axle in addition to change the motor field connection in off load condition. Thus,
these switches shall have to be capable of carrying worst case current without
exceeding its temperature beyond specified limit. Development of high hauling capacity,
5000 HP, 25 KV, Electric Locomotive type WAG7 by railways necessitated requirement
of off load switches (Reverser) having current carrying capacity of 1500A DC.
At present two different designs of off load switch (Reverser) one of CLW design for
1500 Amp DC and another of BHEL design for 1000 Amp DC are available as shown in
Fig.l. CLW design consists of a drum (1) on periphery of which copper strips (2) are
lapped. Power finger moves over the copper strip (1). Complete assembly is mounted
between cylinder assembly (3) and end frame (10). As the copper is soft material,
contact pressure of the power finger is required to keep low to have less wear and tear
of surface of copper trip. Low contact pressure affect the thermal conductivity of the
contact and this design requires frequent maintenance.

BHEL design consists of a steel main shaft (5) on which DMC molding blocks (6) are
mounted over which power finger (7) moves. Lower end of the power finger is mounted
on bottom terminal bar (8) and upper end of the power finger is supported on the
contact blocks (9) mounted on top terminal bars (8) under desired pressure. Complete
assembly is mounted between cylinder assembly and end frame (4). Power finger
make/break contact with the contact blocks only during the time of making/breaking
only. In the middle of the make/break operation power finger does not make nay
contact with the contact block and move freely. Thus there is less wear and tear in the
contacts of power finger and contact blocks, thus higher contact pressure can be
achieved to have better thermal conductivity.
Due to above advantage of BHEL design over CLW design it has been decided to
choose the BHEL design. Present BHEL design of existing off load switches (Reverser)
type 30 RPS are available in two pole, four pole and six pole combination and have
current carrying capacity up to 1000 Amp. DC. At present four pole off load switches
(Reverser) are under service in AC Locomotives. It was decided to design the new three
pole off loaf switch (Reverser) with mounting dimension same as that of four pole off
load switch (Reverser) to have one to one interchangeability and its obvious merits.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a 3 pole off load switch (reverser)
of 1500 Amp continuous current employed in traction application in high power electric
loco which can be deployed as reverser.
Another object of the invention is to propose a 3 pole off load switch (reverser) of 1500
Amp continuous current employed in traction application in high power electric loco

which will have less wear and tear in the contact of Power finger and contact blocks so
that higher contact pressure is achieved to have better thermal conductivity.
A further object of the invention is to propose a 3 pole off load switch (reverser) of
1500 Amp continuous current employed in traction application in high power electric
loco which is capable of carrying 1500 Amp through design change of current carrying
components only.
A still further object of the invention is to propose a 3 pole off load switch (reverser) of
1500 Amp continuous current employed in traction application in high power electric
loco which enables utilization of most of components of existing design resulting a
better spare management.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - A photo view of assemblies of CLW and BHEL design 1000 A off load switch
(Reverser)
Fig.2 - A Line diagram of electric locomotive showing off load switch (Reverser)
Fig.3 - A diagram of side view of complete assembly of 1500 A off load switch
(Reverser)
Fig.4 - A diagram of front view of complete assembly of 1500 A off load switch
(Reverser)
Fig.5 - A diagram of cylinder assembly
Fig.6 - A diagram of power finger and power contacts
DETAILED DESCRIPTION OF THE INVENTION
Single line diagram of typical electric locomotive is shown in Fig.2. The current is
collected from 25KV OHE catenary through pantograph (11), step down to 1000 V by
transformer (13) and converted by rectifiers (14) to DC supply for feeding DC series
motors (16) mounted on axels. The locomotive has two bogies one on each end. In
each bogies, three motors are fitted through control gear for achieving required circuit
topology and speed. The motors are connected to DC supply through electro-pneumatic
contactors Ll-16 (15). Direction of the locomotive is controlled by changing the
direction of the current in the traction motor field by changing the connection of filed
through contact of the off load switch (Reverser) in off load condition. To achieve
above, both ends of the series field (19) of the motors (16) are connected through
contacts J11-J13 and J21-J23 (17) of the off load switch (Reverser). Contacts of the off
load switch are required to carry full load as well as fault current of the motor and has
to be suitably rated.
A. Functional description
The off load switch (Reverser) is used in the motor circuit of locomotive as
shown in the Figure 3. It has to carry the motor field current continuously at
rated value without exceeding temperature rise limits and is used to change the
motor field connection in off load condition so as to change the direction of
movement of locomotive. Connections of only one pole are shown in the Figure
3. When locomotive is running in one direction, the flow of current in the circuit
is shown in 3 (a). Current flows from positive of the rectifier to armature A1-AA1
of motor, contact 1-4 of off load switch (Reverser), field F1-FF1 of motor, contact
5-2 of off load switch (Reverser) and then to the negative of the rectifier. When
the off load switch (Reverser) is operated its power fingers change their position
as shown in 3(b). Now flow of current will be from positive of the power supply
to armature A1-AA1 of motor, contact 1-3-5 of off load switch (Reverser), field
FF1-F1 of motor, contact 4-2 of off load switch (Reverser) and then to the
negative of the rectifier thus reversing the direction of flow of current in the field.
B. Operating Mechanism
Complete assembly of 3-pole off load switch is shown in Figure 4. It consists of
cylinder assembly (Figure 5), end frame (4) and main shaft and terminal bar
assembly (Figure 6). Main shaft and terminal bars are mounted between cylinder
assembly (Figure 5) and end frame (4). Molding blocks (6) depending upon the
number of poles are mounted on the steel main shaft (5). Each molding block (6)
have two semicircular grooves and inserts (20) are molded inside the each
molding block (6). Power finger assembly consisting of power finger (7) and
terminal block (21) is tightened on the bottom terminal bar. Two semicircular
rivet and socket (22) are riveted at the middle of the each power finger
assembly. Semicircular rivets of the power finger assembly rests on the
semicircular grooves provided on the DMC molding blocks (6). Power fingers are
secured by spring locating plate (23), spring (24) and spring guide (25) mounted
on inserts of DMC molding blocks and is in contact with contact blocks (9)
mounted on the top terminal bars (8). Thus power fingers move smoothly.
Cylinder assembly consists of cylinder (26), rack (27), pinion (28) and two
magnet valves (29). Piston gaco washers (30) are fitted on both side of rack
which moves inside of cylinder (26). Rack (27) has teeth on its upper side, which
are engaged with the teeth of pinion (28). Pinion (28) have two rollers (31) fitted
over it. Operating lever (32) is mounted on steel main shaft (5) and inside
portion of operating lever (32) moves on these rollers (31). When either of the
magnet valves (29) is energized with 110 Volt DC signal pressurized air enters
through any one of the two magnet valves. Entry of air in to the cylinder pushes
rack (31) to one or other side which rotate pinion (28). Rotation of pinion results
into movement of operating lever (32) which in turn rotates the steel main shaft
(5) which finally result into movement of power finger assembly.
C. New design of three pole off load switch
New design of three pole off load switch (Reverser) has been designed
maintaining same overall size, mounting dimension and interchangeability of
component with existing four pole design. As explained in previous clause,
current of the fields of individual motors are to be carried continuously by
individual pole of the off load switch (Reverser). The current carrying capacity
depends upon the cross sectional area of the current carrying parts, lay out and
spacing of the current carrying parts. To keep the interchangeability of
component of new design with existing design, same components of the existing
four pole design have been used to the extent possible. Spacing between the
heat dissipating components have been increased suitably to achieve better
cooling and maintain the temperature rise well within the limits. The new design
of the off load switch (Reverser) has been tested at 1500 Amp and temperature
rise of the components was found well within the specified limits.
Thus a new design of three pole off load switch (Reverser) has been developed
for 1500 Amp continuous current carrying capacity with minimum changes in the
existing four pole design and keeping overall size, mounting dimension and
component level interchangeability with more than 85% components of existing
four pole design. All the drawback of CLW design has been taken care and
advantages of BHEL design has been retained in the new three pole design.
KEY FEATURES

WE CLAIM
1. A 3 pole off load switch (Reverser) (C) of 1500 ampere continuous current
employed in traction application in high power electric loco comprising:
a cylinder assembly (A);
an end frame (4);
a main shaft and a terminal bar assembly (3) mounted between cylinder
assembly (A) and end frame (4);
a plurality of molding blocks (6) being mounted on the steel main shaft (5);
each molding block (6) having two semicircular grooves and inserts (20) molded
inside each molding block (6);
a plurality of power finger assembly having power finger (7) and terminal block
(21) tightened on the bottom terminal bar;
a plurality of semicircular rivet and socket (22) riveted at the middle of each
power finger assembly;
the said power fingers secured by spring locating plate (23), spring (24) and
spring guide (25) disposed in contact with contact blocks (9) mounted on top
terminal bars (8);
wherein the cylinder assembly comprising of cylinder (26), rack (27), pinion (28),
magnet valve (29), piston gaco washer (30), roller (31) and operating lever (32);
characterized in that,
either of the magnet valves (29) is energized with 110 volt DC signal for allowing
pressurized air to enter into the cylinder through any one of the two magnet
valves when the said cylinder pushes the rack (31) for rotating the pinion (28)
resulting a movement of operating lever (32) for rotating the steel main shaft (5)
for the movement of power finger assembly.
2. The 3 pole off load switch (reverser) as claimed in claim 1, wherein the main
shaft and terminal bar assembly comprises of main shaft (5), DMC moulding

block (6), power finger (7), terminal bar (8), contact block (9), insert (20),
terminal block (21), rivet and sacket (22), spring locating plate (23), spring (24)
and spring guide (25).
3. The 3 pole off load switch (reverser) as claimed in claim 1, wherein semicircular
rivets of the power finger assembly rests on the semicircular grooves provided on
the DMC molding blocks (6).

A 3 pole off load switch (Reverser) (C) of 1500 ampere continuous current employed in
traction application in high power electric loco consists of a cylinder assembly (A)and
end frame (4), a main shaft and a terminal bar assembly (3) mounted between cylinder
assembly (A) and end frame (4). A plurality of molding blocks (6) are mounted on the
steel main shaft (5). Each molding block (6) has two semicircular grooves and inserts
(20) molded inside each molding block (6). A plurality of power finger assembly having
power finger (7) and terminal block (21) is tightened on the bottom terminal bar.The
power fingers are secured by spring locating plate (23), spring (24) and spring guide
(25) mounted on inserts of DMC molding blocks (6) and are in contact with contact
blocks (9) mounted on top terminal bars (8). The cylinder assembly comprises of
cylinder (26), rack (27), pinion (28), magnet valve (29), piston gaco washer (30), roller
(31) and operating lever (32). The magnet valve is energized with 110 volt DC signal
for allowing pressurized air to enter into the cylinder through any one of the two
magnet valves when the said cylinder pushes the rack (31) for rotating the pinion (28)
resulting a movement of operating lever (32) for rotating the steel main shaft (5) for
the movement of power finger assembly.