FIELD OF THE INVENTION
The present invention relates to a rotating rectifier assembly of brushless
excitation system for Synchronous Machines. More particularly, the invention
relates to an improved and compact rotating rectifier assembly in a brushless
excitation system to minimize overall size, easy for dis-assembly and
maintenance.
BACKGROUND OF THE INVENTION
Brushless Exciter is an auxiliary machine used along with synchronous alternator
or motors to provide D.C. excitation power to the field winding carried by the
rotor of the motor or alternator as shown in Figure 1. Brushless exciter consists
of a stationary field winding carried by the exciter stator and has a rotating
armature which carries 3-phase armature winding. 3-phase voltage induced in
the exciter armature during rotation is rectified to direct current by a rotating
rectifier bridge. Normally the rectifier diodes are used as static devices.
Rotating rectifier diodes are of special type which can withstand rotational and
acceleration forces if mounted properly by using rotating support fixture. RC
snubber and varistors are used as protection devices against transient voltage
and sudden current change. Three phase winding terminals of rotor armature are
connected to respective A.C. rings, are connected to the rectifier bridge formed
by six diodes by using copper strips. The D.C. output from rectifier bridge will be

connected to D.C rings on the drive end side. D.C. output from D.C. rings is
connected to generator field winding through hollow shaft. These connections
have to make properly as all these components are rotating and experience
centrifugal force. The assembly of the electronic devices also needs special care.
Brushless Excitation Systems are now widely used for supplying direct current to
the field winding of the synchronous machine to make the system maintenance
free by eliminating slip rings and brush gear.
The rotating rectifier assembly comprises a rotor-spider assembly (1) and a
plurality of rectifier modules (2) as indicated in Figure 3. A rectifier module
comprises a diode-heat sink assembly and a snubber circuit are assembled
together. A set of a-resistor and capacitor are held by an L-shaped channel
known as snubber circuit or R-C assembly. Snubber circuit facilitates protection
'of diodes against destructive voltage surges during turn-off transient voltages.
A diode-heat sink assembly is disposed by means of hexagonal bolts on an
insulated base plate and snubber circuit is welded to the base plate to form a
rectifier module. The plurality of rectifier modules are bolted to the spider plates
of rotor spider. This entire assembly acts as single assembly, which provides
easy assembly and removal of the heat sinks, diodes and other devices for
mounting, inspection and repair.

Normally, this type of construction requires separate diode wheels and the
rectifier assembly which are difficult to manufacture due to numerous
components, connectors and supports which had to place on inside rim of the
wheels. Accordingly, there is a need for a simplified assembly which can
-withstand against rotating forces. In addition to above, the rotating rectifier
assembly must be capable to circulate air for heat dissipation of exciter as well
as rectifier assemblies, so as to eliminate requirement of a separate fan.
It is therefore an object of the invention is to propose an improved and compact
rotating rectifier assembly in a brushless excitation system to minimize overall
size, which requires less axial space, is inexpensive and can withstand rotating
forces.
Another object of the invention is to propose an improved and compact rotating
.rectifier assembly in a brushless excitation system to minimize overall size, which
eliminates the necessity of a separate fan for heat dissipation from rotating
exciter armature and diode assembly itself.
A still another object of the invention is to propose an improved and compact
rotating rectifier assembly in a brushless excitation system to minimize overall
size, in which diode assemblies and other devices are arranged and electrically
connected to rectify 3-phase A.C. voltage to D.C. voltage.
A further object of the invention is to propose an improved and compact rotating
-rectifier assembly in a brushless excitation system to minimize overall size, which

allows a simplified inspection procedure and maintenance as well as minimization
of difficulty in construction.
OBJECTS OF THE INVENTION
-It is therefore an object of an invention is to propose an improved and compact
rotating rectifier assembly in a brushless excitation system to minimize overall
size, easy for dis-assembly and maintenance, which requires less axial space,
inexpensive and can with stand against rotating forces.
Another object of the invention is to propose an improved and compact rotating
rectifier assembly in a brushless excitation system to minimize overall size, easy
for dis-assembly and maintenance, which eliminates the necessity of a separate
fan for heat dissipation from rotating exciter armature and diode assembly itself.
A still another object of the invention is to propose an improved and compact
rotating rectifier assembly in a brushless excitation system to minimize overall
size, easy for dis-assembly and maintenance, in which diode assemblies and
other devices are arranged and electrically connected to rectify 3-phase A.C.
voltage to D.C. voltage.
A further object of the invention is to propose an improved and compact rotating
rectifier assembly in a brushless excitation system to minimize overall size, easy
for dis-assembly and maintenance, which allows a simplified inspection
procedure and maintenance as well as minimisation of difficulty in construction.

SUMMARY OF THE INVENTION
In accordance with the present invention, the improved and compact rotating
rectifier assembly comprises a rotor spider assembly and a plurality of rectifier
modules. The rectifier modules are bolted to a spider plate of the spider
assembly at four locations.
Likewise, a total of six rectifier modules in an exemplary embodiment are bolted
and electrically connected to each spider plate of the rotor spider assembly to
form a complete rectifier bridge circuit as per technical requirement.
The rectifier circuit consists of at least six diodes assemblies with R, Y, B phases
of A.C. circuit connected at input side, and the DC terminals taken on output side
as shown in Figure 1. A snubber circuit is also connected across each diode
assembly for protection against transient over voltages.
Thus, a compact assembly is made which is relatively easy and inexpensive to
manufacturer, requires less axial space with improved heat dissipation.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is a schematic diagram showing brushless excitation system.
Figure 2 shows a vertical sectional view of a brushless exciter.

Figure 3 shows a rotating rectifier assembly.
Figure 4 shows an isometric view of a rectifier module.
DETAILED DESCRIPTION OF THE INVENTION
Figure 3 shows a rotor spider assembly (1), and a rectifier module (2). The rotor
spider assembly (1) comprises a Spider hub (3), a Spider rib (4), a Spider plate
(5) and a Support rib (6).
Figure 4 shows a rectifier module (2) which comprises a Base plate (7), an
Insulation sheet (8), a L-shaped Channel (9), a Resistor (10), a capacitor (11), a
Heat sink (12), a Diode (13), a Diode connecting stud (14), an Allen Screw (15).
A connection is made between the heat sink to the base plate through an
'hexagonal bolt (16) with insulation bush. Another connection is made between
the base plate to the spider plate through another hexagonal bolt (17).
The rotor spider comprises at least two spider-hubs (3), at least six spider-ribs
(4), and at least six spider-plates (5). The spider-hub (3) is a hollow cylindrical
part, both kept at a distance apart and several keyways are provided in order to
engage the shaft in it thus avoiding a single large hub with higher weight.
On the outer portion, the hub supports the spider-ribs. This is a flange type
structure, which is welded perpendicular to the hub outer surface at a position
near to the centre of the hub outer surfaces. Apart from this, other spider-ribs

are welded at 60 degree with respect to each-other, taking vertical rib as a
reference. At the top of the spider- ribs, key-ways are provided along its length
to hold the armature core and arrest it against electromagnetic forces and
rotation.
The spider-plates (5) are welded to the ribs (4) hexagonally. These plates are
rectangular in shape having four threaded holes on each plate in order to bolt
the rectifier module. On top surface of each spider plate, a support rib (6) is
provided in order to support armature core.
A complete rotor spider is made up of high strength steel (EN material), so that it
can withstand the weight of armature core along with the windings and also the
mechanical forces during rotation. It has to withstand against the torque
transmission from armature to shaft.
The rectifier module (1) comprises of a diode-heat sink assembly and snubber
circuit mounted on base plate. An insulation sheet (8) is sandwiched as electrical
insulation.
Disc shaped diodes (13) of required current capacity are bolted to a heat sink
(12) with adequate contact pressure by means of at least four Allen screws (15).
The heat-sink (10) is made up of aluminium, which is electrically and thermally
conducting material capable of acting as a heat-sink, preferably having fins to
increase the radiating surface and heat dissipating ability. The force applied to

diodes (13) is sufficient to provide electrical contact at run-away speed condition
but not to exceed the minimum force which could cause the mechanical damage
to the diodes. At four corners of the heat-sink, the threaded holes are provided
to mount the heat-sink assembly on the base plate through hexagonal bolts (16)
with insulation bush.
A Resistor-Capacitor (R-C) Assembly in which a resistor (10) and a Capacitor (11)
are held by L-shaped bracket (9) and bracket is welded to the base plate (7).
Thus, the R-C assembly and diode heat-sink assembly are assembled on base
plate which forms a compact assembly or a module. Thus module can be readily
handled and assembled to the spider plate by means of hexagonal bolts (17).
Thus, it forms the integrated rotating rectifier assembly as shown in Figure 2. If
desired, these assemblies can be disassembled at any time for maintenance and
inspection purpose.

WE CLAIM :
1. In a brushless Excitation System, a rotating rectifier assembly
comprising:
a rotor spider assembly mounted on a shaft, a plurality of a rectifier
modules disposed on a periphery of the spider plates of the spider
assembly, a rectifier module comprises a diode heat-sink assembly
and a R-C assembly to form a compact module which can be easily
assembled and removed from the rotor spider.
2. The rotating rectifier assembly as claimed in claim 1, wherein the
spider assembly has six spider-ribs welded around an outer periphery
maintaining 60 degree with respect to each other, the spider ribs
maintained at a distance apart which engages the shaft by means of
key ways.
3. The rotating rectifier assembly as claimed in claim 2, where in the six
spider-plates are welded between two spider-ribs forming a hexagon,
and wherein each spider-plate having four threaded holes for disposing
a rectifier module.

4. The rotating rectifier assembly as claimed in claim 1, comprising a
rectangular arm disposed in the middle over top surface of the plate to
support an armature core.
5. The rotating rectifier assembly as claimed in claim 1, where in the
rectifier modules are supported to the inner potion of the spider plate
by means of hexagonal bolts and where in at least six pairs of disc
type diodes with two anti- in parallel diodes are disposed on each heat
sink by means of alien screws on each spider-plate.
6. The rotating rectifier assembly as claimed in claim 5, wherein a resistor
and a capacitor is mounted on an L-shaped channel which is welded
on a base plate on each of the spider-plate.
7. The rotating rectifier assembly as claimed in claim 1, wherein the disc
shaped diodes are disposed on the heat sink which is electrically and
thermally connected therewith and wherein the heat sink is engaged to
a base member separated by an insulated sheet.