FIELD OF INVENTION:
The invention relates to compact rectifiers for WAG7 locomotives in general and
to a compact rectifier for WAG7 locomotive with improved heat sink and layout
of diode heat sink assembly in particular.
BACKGROUND AND PRIOR ART:
Electric Locomotives, with AC/DC transmission of power, employ a rectifier for
conversion of single phase AC supply from catenary to generate DC supply to
feed DC motors mounted on the axles of locomotive. These rectifiers are of
compact configuration as they are accommodated on every electric locomotive,
where there is severe space restriction.
As these rectifiers are meant for WAG7 locomotives of the Indian Railways, they
must conform to the dimensions specified by Indian Railways. Therefore there is
severe restrictions in design of rectifier.
In the prior art, such compact rectifiers have complicated layout of the diode
heat sink assembly and bus bar arrangement. This leads to difficulty in
maintenance as well as connection of the various elements. Moreover, at times
electrical creepage distance has been compromised to achieve compactness.
These lead to increased failures due to flashover and result in increased
downtime.
The compact rectifier in accordance with the present invention seeks to
overcome the above mentioned drawbacks of prior art.
The proposed rectifier has been developed as per Indian Railways technical
specification which gives details of only the electrical performance parameters
and mechanical dimensions but gives full freedom to the designer with respect to
layout design and selection of components. Thus many other designs are
available meeting the specification but differing in the details.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a compact rectifier which meets Indian
Railways specification, but has better reliability and requires lesser maintenance.
Another object of the invention is to provide better layout of devices in which
placement of same phase diodes back-to-back eliminates the need of electrical
insulation between two adjacent heat sinks.
A further object of the invention is to provide improved connectors for current
collection from heat sinks so that flashovers due to loose connections is avoided.
Yet another object of the invention is to provide an improved layout which
provides easier access to the devices, thereby enabling easier maintenance and
achieving reduced down time.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. A shows the heat sink diode module.
Fig. B shows the inner heat sink.
Fig. C shows the outer heat sink.
Fig. D shows the plan view of the compact rectifier according to the invention.
Fig. E shows details of heat sink and RC panel assembly.
Fig. F shows shunt connection to diode heat sink assembly (isometric view).
The invention will now be described in detail with the help of an exemplary
embodiment, as depicted in the accompanying drawings. There can however be
other embodiments of the same invention, all of which are deemed covered by -
this specification.
DESCRIPTION OF THE INVENTION:
According to the present invention, a compact rectifier is proposed for electric
locomotives with AC/DC power transmission. Each arm of the rectifier has four
diodes. As seen in Fig. E, a compact module (2) has been designed which
consists of a diode (A2) mounted between two heat sinks (A1, A3), a molded
cover (E4) for the diode heat sink module snubber resistor (E6) and capacitor
(E5) and mounting arrangement for the same. Four such modules form one arm
of the rectifier. A simple arrangement of mounting of diode has been used (1)
fig A, wherein diode (A2) is mounted between two heat sinks (A1,A3). This
arrangement ensures proper contact of the diode and is sturdy. The shape of the
heat sink has been specially made so as to give maximum possible mechanical
clearance and electrical creepage in the compact space. Heat sink towards outer
side (A3) of the rectifier has a cutout essentially to facilitate connection of
flexible copper connection to the inner heat sink (Al).
As seen in Figs. B and C, length of the outer heat sink (A3) is lesser than that of
the inner heat sink (Al) and cutout on the other end, so that access to the inner
heat sink is available through the cutout on one side and from the open length
on the other side. The cutout and difference in the length of the two heat sinks
give the advantage that even after using flexible connections adequate electrical
clearance and creepage is available. Provision has been made for separate
mounting holes and electrical connections eliminating loosening of electrical
connection in vibration. This can be seen in isometric view in isometric view in
Fig F.
Diode heat sink module assembly (D1) is so arranged that no electrical clearance
is required between adjacent diode heat sink modules placed back to back, as
they are on the same phase of the input AC supply. A unique mounting
arrangement for the fuses (D3) electrically in series with individual diodes has
been made so as to utilize the space essentially required for electromechanical
clearance between the two phases, best not seen in the plan view of the rectifier
in figure D. The fuses (D3) have been mounted on the AC bus bar (D4) and
connected to the diodes on the diode heat sink modules through flexible copper
braided shunts (D5). The AC bus bars are placed between two arms of the
rectifier electrically connected to the same phase. DC bus bar (D3) has been
placed on either side of the diode modules. Connections to the DC bus bar have
also been made through flexible copper braided shunts (D6).
The electrical connections of the heat sink with bus bars and with input/output
cables are critical for reliable operation of the rectifier. Any loose connection will
lead to bad contact and to excessive heating, which can result in melting of the
contact. Flexible copper connections (D5, D6) made of thin copper braids
clamped together to avail flexibility and sturdiness have been used. The
connections are mechanically strong with flexible copper braids giving proper
contact and mechanical strength.
In the present invention, a unique arrangement of heat sink diode module
assemblies has been adapted with placement of same potential heat sinks
adjacently. New layout made is such that the same potential heat sinks and bus
bars are placed in close proximity. This is best seen in Fig. D. This arrangement
eliminates use of electrical insulation between them as used in prior art. This is
of special importance in a compact rectifier in order to give reliable field service
as there is no chance of electric flashover due to creepage.
We claim;
1. Compact rectifier for WAG7 locomotive with improved heat sink and layout
of diode heat sink assembly and bus bars, the rectifier having four compact
diode heat sink modules (1) in each arm of the rectifier, fuses D3 being mounted
on the AC bus bar (D4) and connected in series with individual diodes on diode
heat sink module (1), said AC bus bars being placed between two arms of the
rectifier and electrically connected to the same phase, DC bus bars (D2) being
placed on either side of the said diode heat sink modules and connections to
both AC and DC bus bars being made with flexible copper braided shunts (D5,
D6),
characterized in that in the improved layout same potential heat sinks and bus
bars are placed in close proximity, thereby eliminating electrical insulation and
reducing electric flashover due to creepage.
2. A compact rectifier as claimed in claim 1, wherein required electrical
clearance between flexible shunt mounting screw (F3) on outer heat sink (A2)
and inner heat sink (Al) is ensured without employing any screw below the
shunt, whereby inner heat sink (Al) is tightened by three screws.
3. A compact rectifier as claimed in claims 1 and 2, wherein the length of the
outer heat sink (A3) is lesser than that of the inner heat sink (Al) at one end
and at the other end a cut is provided, so that access to the mounting screw of
inner heat sink is available from the front open length facilitating replacement of
module in situ condition.
4. A compact rectifier as claimed in claim 1, wherein the copper shunts (D5,
D6) are made with flexible copper braids to ensure proper contact without
transferring mechanical stresses to the modules, thereby ensuring proper contact
of diodes heat sinks to bus bars.
5. A compact rectifier as claimed in claim 1, wherein the rectifier comprises
a heat sink and RC panel assembly (2) which has the corresponding snubber
capacitor (E5) and snubber resistor (E6) constructed in modular form for making
module level replacements possible.
6. A compact rectifier as claimed in claim 1, wherein unique layout of the
rectifier heat sinks (A1, A2), bus bars (D2, D4) and fuses (D3) completely
eliminates need of any insulation material between heat sinks.

Compact rectifier for WAG7 locomotive with improved heat sink and layout of
diode heat sink assembly and bus bars, the rectifier having four compact diode
heat sink modules (1) in each arm of the rectifier, fuses D3 being mounted on
the AC bus bar (D4) and connected in series with individual diodes on diode heat
sink module (1), said AC bus bars being placed between two arms of the rectifier
and electrically connected to the same phase, DC bus bars (D2) being placed on
either side of the said diode heat sink modules and connections to both AC and
DC bus bars being made with flexible copper braided shunts (D5, D6),
characterized in that in the improved layout same potential heat sinks and bus
bars are placed in close proximity, thereby eliminating electrical insulation and
reducing electric flashover due to creepage.