FIELD OF INVENTION
The present invention relates to a cooling process for compact rectifier engaged in
traction converters adaptable to electric locomotives.
BACKGROUND OF THE INVENTION
In the existing process, the AC/DC transmission takes place by employing a rectifier for
conversion of single phase AC supply from catenary to generate DC supply to feed DC
motors mounted on the axle of locomotive. The rectifier needs a cooling effect by any
means during the process of operation. The cooling effect of the rectifier is performed
by means of a ducting through a fan driven by a motor. But the use of a single uniform
duct leads to improper utilization of available cooling air pressure. To overcome the
existing improper cooling effect, the present invention relates to new process of cooling
effect of the existing rectifier.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a cooling process for
compact rectifier engaged in traction converter adaptable to electric locomotives which
eliminates the disadvantages of existing process.
Another object of the present invention is to propose a cooling process for compact
rectifier engaged in traction converter adaptable to electric locomotives which causes
compact rectifier trouble free.
A further object of the present invention is to propose a cooling process for compact
rectifier engaged in traction converter adaptable to electric locomotives which utilizes
available cooling air more effectively and efficiently.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - A photo view of an assembly of rectifier for electric locomotive
Fig.2 - A photo view of fan assembly with mounting arrangement and adaptor duct
Fig.3 - A diagram of air flow path in the rectifier
Fig.4 - A top view of air flow path
Fig.5 - A diagram showing diode heat sink assembly
DETAILED DESCRIPTION OF INVENTION
In electric locomotive, single-phase rectifier is used to convert AC supply collected from
OHE catenary through step down transformer to DC supply for feeding DC series
motors mounted on axels. Each single-phase Rectifier Bridge consists of four diodes and
to meet current requirement as many bridges can be connected in parallel. Each diode
is connected on each side to either AC supply (phase/natural) or to DC supply
(Positive/negative) terminals. In power rectifiers diodes are normally fitted on heat
sinks for cooling purpose and heat sink-diode modules are fitted in a unique fashion in
cubicle (10) with proper connections with AC and DC bus bars. Cooling air is provided
by a blower (6) mounted at bottom of cubicle (10), which sucks air from top of rectifier
and exhaust at the bottom. The unconventional air path of cooling air is selected to
avoid flow of contaminated air to rectifier, which being heavier is accumulated at
bottom, hence despite hotter air enters into rectifier from top. Many designs of rectifiers
can be realized by adopting different layout of heat sinks, bus bars and cooling
arrangement. The proposed design of rectifier is shown in Fig.l. The proposed cooling
arrangement realized by unique layout and cooling duct is described briefly as under:
A. Cooling air path
The cooling air path of the developed rectifier is shown in Fig. 3 and 4. For the
clarity of path other components such as bus bars, capacitors, resistors; fuses
etc. are not shown. The cooling air enters from the top rectangular duct (11) in
Fig. 3, which is covered with a wire mesh to prevent foreign material in to
rectifier. From the top duct (11), air enters into the two duct (17,18) formed by
the diode heat sink (12) modules Fig.3. These ducts are connected to air guide
duct (13) Fig (3) of special shape, which is mounted at other end to f?n
assembly flange (14) Fig.3. Finally, air enters into the fan motor casing (14) and
exhausted at the bottom (15). Thus, it can be seen that air path is
unconventional in the sense that relatively hot air in entry in the rectifier for its
cooling. The main consideration for this arrangement is that contamination in the
air is much more at floor level and decrease as moves up. Thus this arrangement
prevents entry of contaminated air into the rectifier thereby prevent flashover
between heat sinks (19). Second point to be noted is mounting of fan (16)
assembly as shown in Fig. 3. The fan (16) is at the bottom. This is done for
proper air distribution as flow in casing of fan motor (14) will become laminar
otherwise it will become turbulent if fan (16) assembly is mounted with fan on
top. Air guide duct (13) ensures transition of airflow from circular fan casing (14)
into two rectangular air ducts.
B. Heat sinks ducts
As explained earlier, single-phase rectifier uses basic bridge consists of four
diodes and to meet the current requirement as many bridges can be used in
parallel with proper heat sinks (13) and cooling arrangement. In the proposed
rectifier capsule type power diodes (20) are used Fig. 5 which are sandwiched
between heat sink (19,19) Fig.5 having typical designed fins for efficient cooling
and low pressure drop as shown in Fig.5. Two diode-heat sink (12) modules of
bridge for positive side and other two of negative side are mounted back to back
as having same potential to form two separate stacks. Similarly, diode heat sink
(12) modules of other bridges are mounted over each other to form two columns
(A,B) Fig.3. These columns are covered at sides by cover plate (21) Fig.3 and
from both front and rear by molded top covers (22) Fig.3. Thus, two ducts
(17,18) with minimum air leakage and modular design are formed in 28 (shown
in Fig.3). These ducts (17,18) are mounted at distance from each other +o
achieve electrical clearance between positive and negative terminals of rectifier.
All connection from diode heat sink (12) assembly is taken through flexible
copper connection through slots made for this purpose in insulation covers to AC
and DC sides. In Diode heat sink (12) assembly shown in Fig.5, it can be notices
at there is clear gap over diodes (20) and at centre of heat sink (19) for
clamping arrangement, these gaps are to be covered along with covers (23,24)
between columns of diode heat sink (12) assembly otherwise maximum air will
flow through then without causing any cooling. This is done by providing covers
(24) for heat sink Fig.4, diode covers (23) Fig. 4 and cover for airflow blocking
(25) Fig. 4. In this fashion, ducts (17,18) have been formed with minimum
leakages and utilize max potential of cooling air by forcing it through fins of heat
sinks (19). Thus, diode heat sink modules (12) Fig. 1 themselves have been used
to form air ducts.
C. Molded Air guide duct
For effective and efficient cooling of any equipment, most demanding task is to
ensure uniform air distribution over cross section. This task becomes further
difficult when air delivery cross section of cooling air system is different than that
of product to be cooled in geometrical shape. The proposed design falls into this
category as the cross section of a motor assembly (14) is circular and is to be
connected to rectangular ducts (26) of Fig.2 formed with electrically conducting
diode heat sink (12) modules. This technical challenge has been resolved by
designing a molded air guide duct (13) Fig.2 and Fig.3 with insulating material
having circular flange (27) at one end Fig.2 matching that of fan assembly (14)
and two rectangular opening (26) at other end Fig.2 match that of air duct
(17,18) formed with diode heat sink (12) assembly as shown in Fig.2 and 3.
Beside typical shape, many waffles have been provided inside the air guide duct
(13) Fig.2 to ensure uniform airflow in the rectangular ducts (26). The insulating
material has helped in providing required electrical insulation between electrically
conducting heat sinks (19) and fan motor assembly (14) at earth potential as
well as ease of molding. The air guide ducts (13) is bolted to air ducts (17, 18)
and body of rectifier at one end with proper air sealing at one end and other end
it is connected to flange of an motor assembly (14) without any hardware.
Basically, fan motor assembly (14) is pushed to air guide duct (13) with help of
special mounting arrangement (28) as shown in Fig. 2. Thus, air leakage at the
joint is totally eliminated irrespective of dimensional in accuracies in assemblies.
As explained above, an efficient and effective cooling system has been developed
which has resulted in reduction of air leakage from 20% to 5% level in complete
assembly thereby ensures efficient operation of rectifier at relatively lower
temperature.
WE CLAIM
1. A cooling process for compact rectifier engaged in traction converters adaptable
to electric locomotives comprises:
- a fan assembly (14) attached with a unique air guide duct (13) connected
to two rectangular duct (17,18) formed by the diode sink modules (2) and
having a wire mesh mounted top duct (11);
characterised in that cooling air transition from circular (27) to rectangular
duct (25) takes place through top duct towards air guide duct ensuring
contamination free better distribution and laminar in airflow creates
cooling effect of the rectifier.
2. The cooling process as claimed in claim 1, wherein duct (28) are formed around
stacks of diode heat sink module (12), cover plates (21), molded cover (23),
diode cover for heat sink and cover for airflow blocking (21) to achieve optimum
air sealing.
3. The cooling process as claimed in claim 1, wherein electrical isolation between
live parts such as diode heat sink assembly, bus bar etc. and motor fan assembly
is provided by unique moulded design of air guide duct of insulation material.

The present invention relates to a cooling process for compact rectifier engaged in
traction converters adaptable to electric locomotives comprises a fan assembly (14)
attached with a unique air guide duct (13) connected to two rectangular duct (17,18)
formed by the diode sink modules (2) and having a wire mesh mounted top duct (11)
characterised in that cooling air transition from circular (27) to rectangular duct (25)
takes place through top duct towards air guide duct ensuring contamination free better
distribution and laminar in airflow creates cooling effect of the rectifier.