FIELD OF THE INVENTION
The present invention generally relates to electrical machines and in particular to
Permanent Magnet Generators (PMG). More particularly, the present invention
relates to a method for assembling the magnetized rotor and stator core of a
PMG in a device and to obtain output sinusoidal terminal voltage by the PMG.
BACKGROUND OF THE INVENTION
The conventional Generators are excited by field winding. The Permanent
Magnet Generator (PMG) is excited by magnets mounted on rotor and it requires
neither winding nor slip ring & brush gear. In conventional Machines, air gap flux
can be controlled but in the PM Machines, the flux cannot be controlled as
generation of the flux is from Permanent Magnets. Once the magnets are
inserted into the rotor, the flux is constant.
In the PM Generators, high energy magnets are inserted into the rotor. The
shape of the output of the terminal voltage of PMG depends on the shape of the
magnet. Accordingly, it is very difficult to obtain a sinusoidal voltage output.
Further, the conventional method for assembling a magnetized rotor and a stator
cannot be used for high rated PMGs because the magnetized rotor gets attracted
to the stator core making it quite difficult to align the rotor during insertion of
the rotor into the stator core. Thus, the prior art assembly method if adapted in
the assembly of PMGs, a suitable guide is to be fabricated and used during the
assembly to maintain uniform air-gap.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method for assembling a
magnetized rotor into a stator core of high rated permanent magnet generators
(PMGs) which eliminates the disadvantages of the prior art.
Another object of the invention is to propose a method for assembling a
magnetized rotor into a stator core of high rated permanent magnet generators
(PMGs) which is enabled to generate pure sinusoidal output of the terminal
voltage of PMG.
SUMMARY OF THE INVENTION
According to the invention, the magnet size and shape is optimized to minimize
leakage flux, enhance energy efficiency, and generate a pure sinusoidal output
of terminal voltage of the PMG. To optimize the shape of the magnet, a
computer-implemented analysis has been carried out several times with different
variations in the magnet dimensions of which three analyses plots are shown in
Figure 1, Figure 2 and Figure 3. As the conventional method for assembling the
magnetized rotor into the stator core cannot be used for high rated PMGs, a
Screw jack shaft device shown in Figure 4 is used to assemble the magnetized
rotor into the stator core. This device of Figure 4 allows to maintain an uniform
air gap and easy assembly of the magnetized rotor and stator core.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The advantages of the present invention will become apparent from the following
detailed description of embodiments with reference to the accompanying
drawings, in which :
Figure 1 (a) is a flux plot of a PMG with rectangular Magnets of width 72.6mm,
height 16mm and radius 211.5mm.
Figure 1 (b) shows terminal phase voltages of the PMG with rectangular Magnets
of width 72.6mm, height 16mm and radius 211.5mm.
Figure 1 (c) shows air gap flux density of the PMG with rectangular Magnets of
width 72.6mm, height 16mm and radius 211.5mm.
Figure 2 (a) shows flux plot of the PMG with rectangular Magnets of width
72.6mm, height 16mm and radius 211.5mm with resi glass bandaging used in it.
Figure 2 (b) shows air gap flux density of the PMG with rectangular Magnets of
width 72.6mm, height 16mm and radius 211.5mm with resi glass bandaging
used in it.
Figure 2 (c) shows terminal phase voltages of the PMG with rectangular Magnets
of width 72.6mm, height 16mm and radius 211.5mm with resi glass bandaging
used in it.
Figure 3 (a) shows flux plot of the PMG with trapezoidal Magnets of width
72.6mm, height 16mm and radius 211.5mm with resi glass bandaging used in it.
Figure 3 (b) shows air gap flux density of the PMG with trapezoidal Magnets of
width 72.6mm, height 16mm and radius 211.5mm with resi glass bandaging
used in it.
Figure 3 (c) shows terminal phase voltages of the PMG with trapezoidal Magnets
of width 72.6mm, height 16mm and radius 211.5mm with resi glass bandaging
used in it.
Figure 4 is a screw jack shaft device according to the invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to the invention, and in order to optimize the shape of the magnet
computer-implemented analysis has been carried out several times with different
variations in the magnet dimensions. In the present invention, the shaped
magnets 101, 201 and 301 as shown in figures Figure 1, Figure 2 and Figure 3
respectively are optimally designed to minimize the leakage flux and to generate
a sinusoidal output of terminal voltage of the PMG. The harmonic content of the
terminal phase voltage 302 as shown in Figure 3 is less compared to that of the
terminal phase voltages 102 and 202 as shown in Figure 1 and Figure 2
respectively.
High energy NdFeB Magnets are inserted into the rotor. As the rating of the PMG
increases, the quantity and size of magnets increase and handling a magnet and
insertion of the magnet into the rotor becomes very difficult. An innovative
device has been configured and used while inserting magnets into the rotor.
Similarly once all the magnets are inserted into the rotor, the magnetized rotor
402 is inserted into the stator core 406 as shown in Figure 4. For guiding the
magnetized rotor 402 into the stator core 406 during assembly, a Screw jack
shaft device as shown in Figure 4 is used according to the invention. A pair of
screw jack threaded shafts 405 is aligned on either side of the PMG rotor shaft
403 and rotated for advancing the rotor 402 into the stator core 406. The Screw
jack threaded shaft 405 is provided with a pointed rod 407 as shown in Figure 4
which is attachable to the ends of the rotor. As the total weight of the rotor
rests on the pointed rod 407, the jack pair is enabled to cater that load. A jack
shaft holder 404 is fixed to the base for mechanical stability. Initially , end shield
408 is fixed at one end of the stator frame. As the shaft advances towards, the
bearing assembly rest on a step provided in the end shield 408. End shield on
the other side is fixed after maintaining an uniform air gap.
WE CLAIM:
1. An improved process for inserting a magnetized rotor shaft (403) into a
stator core (406) of a permanent magnet generator (PMGs), comprising
the steps of:
- inserting a plurality of high energy magnets into the rotor shaft (403), the
quantity and size of the magnets-being optimized depending on the
capacity of the PMG;
- providing a screw jack shaft device having a pair of jack threaded shafts
(405), a pointed rod member (407) attachable to the rotor shafts (403 , a
jack shaft holder (404) fixable to a base, and at least two end shields
(408) each provided with a step;
- a stator core (406) for insertably accommodating the magnetized rotor
shaft (403);
wherein the pair of screw jack threaded shaft (405) is aligned on each side of
the rotor shaft (403) and rotated by the pointed rod member (407) to
advance the rotor into the stator core, wherein the bearing assembly of the
PMG upon advancement of the rotor towards the stator core rest on the step
of a first of said at least two end shields which is fixed on the stator frame,
and wherein a second end shield at the opposite end is fixed to the stator
frame after maintaining an uniform gap.
2. The process as claimed in claim 1, wherein the terminal voltage of the PMG
generates a sinusoidal wave form.

ABSTRACT
The invention relates to an improved process for inserting a magnetized rotor
shaft (403) into a stator core (406) of a permanent magnet generator
(PMGs), comprising the steps of inserting a plurality of high energy magnets
into the rotor shaft (403), the quantity and size of the magnets-being
optimized depending on the capacity of the PMG; providing a screw jack shaft
device having a pair of jack threaded shafts (405), a pointed rod member
(407) attachable to the rotor shafts (403), a jack shaft holder (404) fixable
to a base, and at least two end shields (408) each provided with a step, a
stator core (406) for insertably accommodating the magnetized rotor shaft
(403); wherein the pair of screw jack threaded shaft (405) is aligned on each
side of the rotor shaft (403) and rotated by the pointed rod member
(407) to advance the rotor into the stator core, wherein the bearing assembly
of the PMG upon advancement of the rotor towards the stator core rest on
the step of a first of said at least two end shields which is fixed on the stator
frame, and wherein a second end shield at the opposite end is fixed to the
stator frame after maintaining an uniform gap.