FIELD OF INVENTION
The invention relates to an improved 3-phase rectifier device directly mountable
on an alternator adaptable to Diesel Electric Locomotives) having AC/DC
transmission.
BACKGROUND OF THE INVENTION
Diesel Electric Locomotives with AC/DC transmission employs a rectifier for
conversion of 3 phase AC supply produced by an alternator coupled with the
diesel engine to DC supply to feed DC motors mounted on the axle of the
locomotive. Generally, separately mounted rectifiers are used in the diesel
electric locomotives. The cooling air for the rectifier is provided either from a
mechanical blower driven by the engine or by a separate DC/AC motor driven
blowers. The rectifiers are mounted inside or outside of the control compartment
having stand-alone structure.
Such a typical structure of the rectifiers occupy a considerable floor area on the
locomotives and require additional cooling arrangement. The floor area on the
locomotive is very limited which house the essential equipment/items for
example, diesel engine, its accessories, fuel tank etc. Hence the floor space on
the locomotive is precious for designers. Further, for the cooling of the rectifiers
according to the existing system, an additional arrangement is required incurring
additional cost & power consumption-
OBJECTS OF THE INVENTION
Thus, an object of the present invention is to propose an improved 3-phase
rectifier device directly mountable on an alternator of a locomotive which
occupies no additional space on the floor of the locomotive.

Another object of the present invention is to propose an improved 3-pliase
rectifier device directly mountable on an alternator of a locomotive which uses
the cooling air produced by the fan of the alternator for self-cooling thereby
eliminating a separate arrangement for the cooling of the rectifier device.
Yet another object of the present invention is to propose an improved 3-phase
rectifier device directly mountable on an alternator of a locomotive which
provides flexible interconnections for connecting the alternator and the rectifier
in such a way that no mechanical stress is transferred on the alternator or on the
rectifier and the connections being contained inside, thus no external cable
connections are required for connections between the rectifier and the
alternator.
A further object of the present invention is to propose an improved 3-phase
rectifier device directly mountable on an alternator of a locomotive in which the
direct mounting arrangement of the rectifier on the alternator simultaneously
eliminates the possibility of affecting performance of the rectifier due to vibration
produced by the alternator.
A still further object of the present invention is to propose an improved 3-phase
rectifier device directly mountable on an alternator of a locomotive which
constitutes an integral part of the alternator.
An yet further object of the present invention is to propose an improved 3-phase
rectifier device directly mountable on an alternator of a locomotive which is less
costly and easy to maintain.

SUMMARY OF THE INVENTION
Accordingly there is provided an improved 3-phase rectifier device directly
mountable on an alternator adaptable to diesel electric locomotives, comprising:
atleast twelve heat sinks mounted with insulation bars on a base plate
configured identical to the profile of a stator casing of the alternator, the heat
sinks being allocated in a group of four to each of the 3-phase of the rectifier,
atleast three flat square base dkxJes having flexible lead mounted on each of the
heat sinks, a plurality of semkx)nductor fuse each having a micro-switch provkJed
in series to each of the dkxles for indication of a fuse-failure visual signal; a
plurality of capacitors and resistors disposed on the base plate; a themnal switch
for each of a heat sink group for activating the control circuit when temperature
of the heat sink exceeds a specified temperature; a plurality of insulatk)n sheets
covering each of the groups of the heat sink and extending upto a top cover of
the rectifier to form a duct for ftow of cooling air from the alternator. Thus, the
present invention proposes an improved three-phase rectifier device directly
mountable on an alternator of a Diesel Electric Locomotive used in Railways
application. The rectifier is designed on semicircular base plate to match the
profile of the alternator. The horizontal & vertkal members of MS angles are
used to raise structure over the base plate. The rectifier is fixed on the alternator
configured with a plurality of holes tapped in a casing of the alternator including
a shock absorber sheet. The cooling of the rectifier is achieved by a plurality of
fans mounted on a shaft of the alternator primarily meant for cpolinfl of the
alternator by fiowing air through an inlet opening in the casing of the alternator,
further foltowed through several ducts formed by a plurality of heat sinks of the
rectifier. Diodes are fixed on the heat sink in diamond shape using standard hard
wares through atleast two clear & two tapped holes. The AC terminations of the
rectifier are done with flexible copper bus bars projected from the altemator

through the air inlet opening to prevent stress on the rectifier. The rectifier
doesn't occupy any additional space on the locomotive and also does not require
separate cooling arrangement.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 - Shows a nrKXinting arrangement of a rectifier device of the invention
on the alternator of a diesel electric locomotive.
Figure 2 - a block diagram showing the cooling arrangement of the rectifier
device of the invention.
Figure 3 - a circuit diagram of the rectifier device according to the invention.
Figure 4 - a block diagram showing the various components and
interconnectivity of tiie rectifier device according to the invention.
Figure 5 - a schematk: diagram of a construction phase of the rectifier device
illustrating mounting arrangement of the diodes on the heat sinks
according to the present Inventipp.
Figure 6 - a mounting arrangement of the rectifier devk:e including connection
arrangement of the rectifier device on the alternator according to the
invention.
Figure 7 - detailed arrangement of AC Bus bar connection of the rectifier device
according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
According to the present invention, a rectifier is proposed for diesel electric
locomotives with AC/DC power transmission. The rectifier shall be mounted on
the alternator and the rectifier is cooled by using the cooling air of the alternator.
The detail of the rectifier and its mounting arrangement is described below.
A. Mounting Arrangement
Figure 1 shows a base plate (1) of a rectifier ( R) is designed in the semicircular
shape to match the profile of a stator casing (SC) of an alternator (AL). A shock-
absorbing sheet (2) is employed between the rectifier ( R) and the alternator
(AL) to restrict impact of the vibration of the alternator (AL) on the rectifier ( R).
A plurality of mounting holes (3) are provided on both sides of the rectifier ( R)
and matching tapped holes (3) on the alternator (AL) casing (SC). The rectifier
(R) is mounted on the alternator (AL) by means of standard screws to ensure
proper fixing. The structure of the rectifier ( R) is raised over the base plate (1).
The structure comprises mild steel angles (4) vertically disposed to sustain the
vibration of the alternator (AL) and for proper load distribution of the rectifier
(R). The horizontal members (5) are provided to properly support the vertical
members (4) of the structure. The structure is designed in such a way that all
the three phases are spread over the periphery of the alternator (AL) and the
weight of the rectifier ( R) is equally distributed. In order to ensure stability of
the structure, all three phases of the diode modules are kept vertical to the
diameter of the alternator (AL).
B. Cooling Arrangement
The casing (SC) of the alternator (AL) for the diesel electric locomotive is
modified for providing cooling air for the rectifier (R). As shown in figure - 2, a
fan (6) is provided at one end of the alternator (AL) for providing the cooling air
to its stator & rotor winding. The fan (6) is mounted on the same shaft of the
alternator (AL) and the alternator (AL) is directly coupled with the diesel engine.
Hence the fan (6) gets driven by the diesel engine. At the other end of the
alternator (AL), inlet openings (7) are provided for entry of the atmospheric air,
which is sucked by the fan (6) and is exhausted through opening (8) in the
casing (SC) of the alternator (AL). TTie air inlet system of the alternator (AL) is
nfKxJified for cooling of the rectifier (R) in such a fashion that only cooling air
required for the rectlfter (R) is sucked through the rectifier (R) and the remaining
air is sucked directly via the inlet openings (8). The rectifier (R) is designed in
unique fashion so that cooling air Is sucked from the top through ducts (9)
formed by heat sinks of each of the three phases and is admitted to the
alternator (AL). The exhaust air of the rectifier (R) is mixed with the fresh air
sucked by the fan (6) through air inlet openings (8). The mixed air flows through
the alternator stator and rotor for ifs cooling and is exhausted at other end. The
temperature rise of the air at exhaust of the rectifier (R) is considerably low and
after mixing with fresh air, temperature further comes down and reaches slightly
above ambient temperature. Therefore cooling of the alternator (AL) is not
affected due to cooling of the rectifier (R). This cooling arrangement is unique.
C. Rectifier Design
The rectifier (R) is designed by using flat square base diodes (D). The rectifia^
(R) has six amis (A) and each ami (A) has atleast six dkxies (D) connected in
parallel. The rectifier (R) has been designed with N-1 capability i.e. the rectifier

( R) will work at full capacity even in case one diode (D) has failed in each arm
(A) . This is very important feature from operation point of view of the
locomotive. The locomotive will keep on running at full capacity even after failure
of one diode (D) in each arm (A). Without this feature, on failure of single diode
locomotive will have come to stand still resulting in blocking the traffic on the
line till another locomotive is arranged. As shown in figure -3, the feature has
been implemented by providing a semiconductor fuse (F) in series of each diode
(D). For indication of the fuse failure to the driver a visual signal is provided in
the driver cab. Separate indication is provided for each fuse at the rectifier. A
micro switch (10) is mounted on each fuse (F), which operates in the event of
fuse failure resulting in glow of the indication at the rectifier ( R) as well as in the
driver cab.
As shown in figure 4, the three diodes (D) are mounted on each of a plurality of
12 heat sinks made of aluminum extrusion. The 12 heat sinks (11) are arranged
in 3 groups each having four heat sinks (11). Thus each phase of the rectifier (R)
has four heat sinks (11). The heat sinks (11) are mounted with insulation bars
(16) on the structure (1). Two heat sinks (11) are disposed face to face in each
phase and are at same potential electrically to prevent tracking between the heat
sinks (11). The flat base diodes (D) with pigtail (17) ensure that no stress of the
vibration is transferred to the diode (D). The flexible lead (17) of the diodes
(pigtail) is connected to the dc bus bar (15) through the fuse (F) (23), which are
mounted on the bus bars (15). The bus bars (15) are mounted on the structure
with the help of insulation arrangement. The design of the rectifier (R) is shown
in figure 4 in detail. The capacitors (13) and resistors (14) for the protection of
the diode (D) during switching of the alternator (AL) are mounted suitably on the
structure. Three thermal switches (12) are mounted, one each for each group of
the heat sinks (11). Thermal switch (12) operates, whenever temperature of the
heat sink (11) exceeds

specified temperature and in turn activates the control circuit to cut off the
supply from the rectifier (R). Thus, protection against overload & over
temperature is provided. The heat sinks (11) of each group i.e. phase of rectifier
(R) Is closed from both side by the insulation sheets to form a duct for flow of
the cooling air. This arrangenient results in effective utilization of the available
air for rectifier cooling. The ducts of the cooling air are extended up to top
covers of the rectifier (R). In the top cover of the rectifier, proper size slots are
provided for fiow of inlet air into the rectifier (R) and to restrict entry of the
foreign n^terial in to the rectifier (R). The rectifier (R) is covered from all sides
with insulation as per eiectricai requirement to prevent leakage of the exhaust air
of the rectifier (R) to atmosphere. Therefore, the air sucked through the rectifier
(R) is guided to fiow through the alternator. The all four heat sinks (11) of the
each phase are jointed together at the bottom by copper bus bars (18) to form
the AC terminal for each phase. Therefore, up to the bottom heat sinks (11) are
utilized for flow of the AC current.
D. Electrical ConneclJon & Diode Mounting Arrangement
Each of the dkxies (D) is mounted being disposed in a diamond shape with two
tapped holes (19) and two clear holes (20). The diode (D) is mounted on the
heat sink (11) with standard screws. The screws (21) are welded on the strip at
back of the heat sink (11), so that the screws (21) need not be hekJ by spanner
at this end. Therefore, the dkxle (D) can be removed from the front Itself. This
arrangement ensures proper contact of the diode (D) and is sturdy. The detail is
shown in figure 5.
The electrical connectkMis of the heat sink (11) with the bus bars (15) and with
input/output cables are critical for reliable design of the rectifier (R). The
connections shall be mechanically strong with proper contacts and mechanically
sturdy. Any loose connection will lead to bad contact leading to excessive

heating, which can result in melting of the contact. In this design sturdiness of
the connections are very important as the rectifier (R) is mounted on the
alternator (AL), which is rotating and is coupled to a diesel engine resulting in a
lot of vibration. Therefore, connections need to be designed in such a way that
no mechanical stress due to vibration is transferred on connection joints or on
the device and shall remain sturdy. In this design, the pigtails (17) are connected
to the DC bus bars (15) through the fuses (F) with proper hardware, hence no
mechanical stress can be transferred to the diodes (D) and out going cables of
load are connected at both side with a solid copper bus bar (15). The cross
section of the copper bus bars (15) is selected according to the current flow. The
outgoing DC terminals cross section is large, which reduces progressively at
other end. The heat sinks (11) are mounted on the structure as shown in figure
6.
The 3 Phase AC connections are concealed between the rectifier (R) and the
alternator (AL) and are not available outside. To prevent the transfer of
mechanical stress from the alternator (AL) to the rectifier (R), the solid bus bars
(22) from the alternator (AL) are projected through opening in the casing (SC) of
the alternator (AL) for each phase. At the rectifier end, all four heat sinks (11)
are connected together with the solid bus bars (18) and prQper hard wares to
ensure sturdy connections. The each phase connection is connected to th^
alternator (AL) with flexible copper connection (24) to alternator bus t>ars with
proper hard wares. Detail is shown in figure 7 the flexible copper connection (24)
is made of the thin copper sheets clamped together to avail flexibility and
sturdiness. Due to the flexibility of the copper connecttons, mechanical stress
generated in the alternator Is prevented from transferring to the rectifier.
We Claim:
1. An improved 3-phase rectifier device directly mountable on an alternator
adaptable to diesel electric locomotives which comprises at least twelve
heat sinks (11) mounted with insulation bars (15,16) on a base plate (1)
configured identical to the profile of a stator casing (SC) of the alternator
(AL), the heat sinks (11) allocated in a group of four to each of the 3-
phase of the rectifier; at least three flat square base diodes (D) having
flexible lead (17) are mounted on each of the heat sinks (11); a plurality
of semiconductor fuse (F) each having a micro-switch (10) provided in
series to each of the diodes (D) for indication of a fuse-failure visual
signal; a plurality of capacitors (13) and resistors (14) disposed on the
base plate (1) forming the electrical circuit of the device; a thermal switch
(12) provided for each of the heat sink group (11) which activates the
control circuit when temperature of the heat sink (11) exceeds a specified
temperature; and a plurality of insulation sheets covering each of the
groups of the heat sink (11) provided which extend upto a top cover of
the rectifier (R ) to form a duct (9) for flow of cooling air from the
alternator (AL).
2. The rectifier as claimed in claim 1, wherein the diodes (D) are mounted in
a diamond shape on the heat sink (11) being frontally removable.
3. The rectifier as claimed in claim 1, wherein the flexible lead (17) of the
diodes (D) are connected to the bus bar (15) through the fuses (F) to
avoid transfer of mechanical stress to the diodes (D) and wherein the
outgoing load cables connecting the alternator (AL) are connected with
atleast one solid copper bus bar (15).
4. The rectifier as claimed in any of the preceding claims, wherein a plurality
of solid bus bars (22) from the alternator (AL) are projected through
opening in the stator casing (SC) for each phase preventing transfer of
mechanical stress from the alternator (AL) to the rectifier (R ), and
wherein each of the phase connections is connected to the alternator (AL)
with flexible bus bar connectors (24).
5. An improved 3-phase rectifier device directly mountable on an alternator
adaptable to Diesel Electric Locomotives having AC/DC transmission as
herein substantially described and illustrated with reference to the
accompanying drawings.

The invention relates to an improved 3-phase rectifier device directly mountable
on an alternator adaptable to diesel electric locomotives which comprises at least
twelve heat sinks (11) mounted with insulation bars (15,16) on a base plate (1)
configured identical to the profile of a stator casing (SC) of the alternator (AL).
The heat sinks (11) are allocated in a group of four to each of the 3-phase of the
rectifier. At least three flat square base diodes (D) having flexible lead (17) are
mounted on each of the heat sinks (11). A plurality of semiconductor fuse (F)
each having a micro-switch (10) is provided in series to each of the diodes (D)
for indication of a fuse-failure visual signal. A plurality of capacitors (13) and
resistors (14) are disposed on the base plate (1) forming the electrical circuit of
the device. A thermal switch (12) for each of the heat sink group (11) is provided
which activates the control circuit when temperature of the heat sink (11)
exceeds a specified temperature. A plurality of insulation sheets covering each of
the groups of the heat sink (11) is provided which extend upto a top cover of the
rectifier (R) to form a duct (9) for flow of cooling air from the alternator (AL).