Field of the invention:-
The invention relates to cooling of semiconductor devices in general and to cooling of
diodes for high power applications by water-cooled heat sinks in particular.
Background and prior art:-
As is commonly known, diodes are deployed for rectification of AC into DC. Depending
upon the application, the amount of rectified dc current can have a wide range. With
advancement of technology, diodes with high power rating have come into existence.
The amount of electrical power that a semiconductor diode can continuously handle is
very much dependent on the cooling that the device is provided with. With better
cooling, the same diode or a rectifier bridge can deliver more power. This is due to the
fact that semiconductors are very temperature sensitive. Semiconductor device
application has therefore seen a constant search for better cooling methods to achieve
improved operational characteristics and compactness. Diodes are provided with heat
sinks for dissipation of the heat generated.
As started, diodes used in high power applications (conversion) have their current rating
dependent on the heat dissipation capacity of their heat sinks. The diodes are typically
arranged in convenient sets or modules for easy assembly and maintenance. Forced air
cooling of such diode modules are known in the prior art, where the diodes are provided
with finned heat sinks. Due to the convenience of stacking and easy removal for
maintenance, the arrangement of providing diodes in modules is prevalent in the
industry universally. Forced air cooling of the modules suffices only for relatively low
power ratings of the modules. These modules are usually stacked vertically. For
increasing the current rating, forced water cooled diodes are also known in the prior art.
While forced water cooling gives much more effective heat dissipation characteristics
compared to forced air cooling resulting in higher current handling capability for the
diodes, it poses many difficulties in application. Consequently, a diode assembly with
forced water cooling is so designed presently that it is applicable to a specific
application, and cannot be called a modular design.
The present application seeks to overcome this drawback of the prior art.

Objects of the invention:-
An object of the invention is to provide water cooled diodes in a modular construction.
Another object of the invention is to provide water cooled diode modules which are
compact.
A further object of the invention is to provide water cooled diode modules which can be
conveniently stacked.
Yet another object of the invention is to provide quick replacement of water cooled
diode modules, reducing down time appreciably during servicing.
Another object of the invention is to facilitate easy testing of the diodes as a module.
Description of the invention:-
For high current applications it is necessary to configure a number of high current
diodes in parallel. The existing arrangement of stacking them in a vertical configuration
has limitations like providing electrical terminations, flexibility of connecting water
terminations and providing current sharing reactor in each path as in electrical scheme
Fig.l. The present invention eliminates the above problems by making compact size
modular unit of 2 diodes with all the required paraphernalia viz., water cooled heatsink,
reactors, in such a way that the convenience of stacking these modules for the required
rating can be easily achieved.
Brief description of the accompanying drawings :-
Fig. 1 shows the schematic of connection of the diodes in the diode module in
accordance with the invention.
Fig. 2 shows the assembly details of the diode module in accordance with the invention.
Fig. 3 shows details of end plate assembly of the diode module.
Fig. 4 shows the load compensatory arrangement.
Fig. 5 shows details of the high efficiency water cooled heat sink.

The invention will now be explained in its exemplary embodiment with the help of
accompanying drawings. There can however be many other embodiments of this
invention, which are all deemed covered by this description. Fig.1 shows electrical
scheme of module. Fig.2 shows the assembly details of the complete module in which 2
numbers presspack diodes (01) are sandwiched between two water cooled heat sinks-
(2) and one water cooled heat sink-cum-AC bus bars (02A) with insulating spacers
(3) on either side. The clamping force for the diodes is applied through 4 numbers of
special bolts (04) electrically isolated at one end with respect to the end plate type 1
(05), end plate 2 (06). An assembly of disc spring washers (07) along with a load
compensatory arrangement (08) is positioned between the end plates (05, 06) and the
heatsink assembly (02) to monitor and indicate the clamping force. The cooling water
tubes (09) connecting the heatsinks are terminated on quick disconnect couplings (10)
fixed on end plate. The reactors (11) are fitted on to the DC bus bars (12).
The quick release water coupling (10) facilitate easy connectivity of cooling water which
is used for removal of the heat generated by the diodes in operation. The cooling water
flows through AC busbar (02A) which also act as heat sinks. The temperature of the
heat sinks is monitored with thermal switches (not shown) whose terminals are brought
in to the terminal board (TB).
The switching action is done by presspack diodes (01). A plurality of the water cooled
diode modules (A) according to the invention are connected in parallel to achieve very
high operational current ratings of the order of 60,000 A. For parallel operation of the
modules, reactors (11) are required, which are pent of the diode module itself.
The unique features of this invention are:
a) Incorporation of clamping force indicating mechanism (16) in which the indicators
become free to move at the predetermined clamping load ensures the verification of
correctness of clamping force without disturbing the assembly. The details of this are
shown in fig.3. The functioning of this is as follows:

The end plate (06) is assembled with 2 disc springs (07) along with spacers
(03),(13) and clamped with a bolt (14) and nut (15) with the indicator strip (16)
at the outside end of end plate. The disc spring unit is pre-compressed to the
required clamping force using any loading arrangement and the nut (15) is
tightened in this condition and locked to the screw using a quick setting
adhesive.
The indicator strip will be clamped and will not move till the disc spring unit is
compressed to the pre-loaded condition. When the clamping force is slightly in
excess of this force, the indicating strip will become free to move sideways. This
would indicate correct clamping force.
b) Load compensatory arrangement assembly (08) shown in Fig.4 does the
function of keeping the diode, heat sink interface contact pressure to a value
of approximately 20 Kgs during the process of replacement of a defective
diode from the assembly.
The mechanism consists of compression spring (18) assembled with a plunger
(19) inside the FRP housing (20). The plunger has a circular groove on its
periphery at the distance of 6 mm from the bottom seating of the plunger.
This groove (21) is marked with coloured paint so that the movement of the
plunger can be seen while reducing clamping force.

c) The high efficiency water cooled heat sinks (02) shown in Fig.5 are made of
drawn copper flat has 2 water connections terminations (22) & (23) threaded with
3/8 "BSP thread. A flat seating at the end of threading provides seating for the water
sealing gasket. These ports connect to 2 water plenums on either side of heatsink
and these water chambers (24) & (25) are connected by a number of small holes
made in row along the flat surfaces of heatsink so that heat conducted to the surface
of heatsink can be effectively taken out by the water in circulation through (26)
these small holes. Two holes with guide bushes (27) provide alignment between
heatsinks of the assembly. The heat sink surface electroless nickel coating for
providing proper interface between diode surface and heat sink and better corrosion
resistance.

WE CLAIM:
1. A water cooled diode module (A) comprising:
- two presspack diodes (01) sandwiched between two water cooled heat sinks (02) and
one water cooled heat sink cum Ac busbar (02A) at the center
with insulating spacers (03) on either side, the diodes being clamped with
four bolts (04) between end plates (05,06),
- an assembly of disc spring washers (07) alongwith a load compensatory
arrangement (08) and clamping force indicating mechanism (16) being positioned
between end plates (05,06) and two heat sink (02) and heat sink-cum-AC busbars
(02A),
- two DC busbars (12) with reactors (11) mounted on them and
- quick disconnect couplings (10) connected to cooling water pipes (09),
characterized in that a plurality of such diode modules can be connected in parallel to
achieve very high current operation.

2. A water cooled diode module (A) as claimed in claim 1, wherein clamping force
indicating mechanism (16) indicate correct clamping force.
3. A water cooled diode module (A) as claimed in claim 1, wherein load compensatory
arrangement assembly (08) ensures correct pressure of the diode/ heat sink interface
during replacement of defective diode.
4. A water cooled diode module (A) as claimed in claim 1, wherein the high efficiency
water cooled heat sinks (02A) also act as AC busbars.

5. A water cooled diode module (A) as claimed in claim 1, wherein the connection of
the cooling water is provided easily through quick release coupling (10) connected to
cooling water tubes (09).

ABSTRACT

WATER COOLED DIODE MODULE
1. A water cooled diode module (A) comprising:
- two presspack diodes (01) sandwiched between two water cooled heat sinks (02) and
one water cooled heat sink cum Ac busbar (02A) at the center with insulating spacers
(03) on either side, the diodes being clamped with four bolts (04) between end plates
(05,06),
- an assembly of disc spring washers (07) alongwith a load compensatory arrangement
(08) and clamping force indicating mechanism (16) being positioned between end
plates (05,06) and heat sink assembly (02),
- two DC busbars (12) with reactors (11) mounted on them and
- quick disconnect couplings (10) connected to cooling water pipes (09),
characterized in that a plurality of such diode modules can be connected in parallel to
achieve very high current operation.