FIELD OF INVENTION
The present invention relates to "a permanent magnet generator with magnets mounted
on the rotor sleeve by deploying magnetic bolts and flux barrier".
BACKGROUND OF THE INVENTION
Permanent Magnet Generator (PMG) is a rotating electrical machine with permanent
magnets mounted on rotor to establish the field flux. The PMG when used to excite the brushless
exciter of an industrial generator is called as pilot exciter. The PMG can also be used as wind
generators. The PMGs are normally manufactured using ALNICO magnets and these magnets are
mounted by using special high strength non-magnetic bolts with mechanical strength of 770
N/mm2. The non-magnetic bolts offer a very high reluctance path for the flux produced by the
magnet and also provides the mechanical locking for the rotating cylindrical magnet. The size of
the bolts increases with increase in size and weight of magnets. The availability of such higher
size non-magnetic bolts with high mechanical strength is sometimes difficult and requires very
costly process/involved technology to manufacture.
In the present invention, the permanent magnets are mounted on the rotor using
magnetic bolts and flux barrier. The cylindrical shaped flux barrier created from SS 316 material
and high mechanical strength magnetic bolts are easily available for various sizes at a lower price
where as very costly technological process is to be followed for making high strength non-
magnetic bolts. The flux barrier being used in the present invention prevents the leakage of flux
through the magnetic bolt due to which the air gap flux increases. Thus the mechanical locking
for the rotating permanent magnets is being provided by using high strength magnetic bolts and
flux barrier without compromising with the required output voltage of the permanent magnet
generator.
OBJECTS OF THE INVENTION
An object of this invention is to propose an improved permanent magnet generator assembly.
Another object of this invention is to propose an improved permanent magnet generator
assembly using high tensile magnetic bolts.
Further object of this invention is to propose an improved permanent magnet generator assembly
which is highly cost effective.

Still further object of this invention is to propose an improved permanent magnet
generator assembly which is superior in mechanical strength and offers more
reliability.
STATEMENT OF INVENTION:
According to this invention there is provided a permanent magnet generator for
synchronous generator, comprising:
a rotor (8) having a sleeve (1), the sleeve (1) constitutes atleast one flat surface
configured thereon a plurality of tapped holes (9);
a stator (10) wound with three phase fractional slot winding(12);
a plurality of magnets (4) mounted on the atleast one flat surface of the sleeve
(1) by means of corresponding number of pole shoes (5) and bolts (6),
characterized in that:
atleast one flux barrier (7) is provided being interposed in the pole shoe (5) so as
to reduce the fiux leakage, and in that:
the bolts (6) comprise high strength magnetic bolts.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. 1 shows PMG rotor with magnet assembly and stator.
Fig. 2 shows the magnetic bolts.
Fig. 3 shows flux barrier.

DETAILED DESCRIPTION OF THE INVENTION:
The permanent magnet generator has been built with magnets mounted on the
rotor sleeve by using magnetic bolts and 3 mm thick flux barrier and tested
successfully. The PMG has a 3-phase stator and permanent magnet rotor,
wherein the magnets are mounted on the rotor sleeve having flat surfaces equal
to number of poles on the outer diameter. The cylindrical magnets are mounted
by using the magnetic bolts (6) along with pole shoes (5) and flux barrier (7). The
cylindrical shaped Flux barrier(7) created from SS316 material and normal high
strength magnetic bolts (6) are easily available as ready stock item for various
sizes at a lower price, The number of turns in the PMG stator can be adjusted to
avoid the use of step-up transformer at a later stage.
Permanent Magnet Generator (PMG) is a rotating electrical machine with
permanent magnets assembled on the rotor having flat milled surfaces and
tapped hole to mount the magnets along with pole shoes. This will eliminate the
costly high strength non-magnetic bolts. In the present inventions a pilot exciter
has been developed using the proposed magnet assembly by use of normal high
strength magnetic bolts. The high strength magnetic bolts are generally available
in the market as standard item where as very costly technological process is to
be followed for making high strength non-magnetic bolts.
The developed PMG in Fig. 1 consists of a rotor (8) made with EN 24 material
having flat surfaces with tapped holes (9) for mounting magnets (4). The stator
(10) is wound with three phase fractional slot winding (12). The cylindrical
magnets (4) are mounted on the flat surface of the rotor sleeve (1) by using poie
shoe (5)., magnetic bolts (6) (Fig. 2) and non-magnetic SS316 (ASTM-A-276) flux
barrier (7) (Fig.3). The flux barrier (7) used restricts the leakage flux (which can
increase due to use of magnetic bolts) and enhances the main flux. The high
strength EN grade magnetic bolts (6) (Fig. 2) are more reliable mechanically
(with mechanical strength of 930 N/mm2) and does not require complex process
for manufacturing.

There is no limitation for the size of magnetic bolts however higher sizes of non-
magnetic bolts with high strength are available against order at a very high price.
The rotor along with the shaft is assembled along with the stator having three
phase winding as shown in Fig. 1.
The flux barrier (7) provided inside the counter sunk hole (11) of the pole shoe
(5) is electromagnetically optimized in thickness/size so as to aliow the maximum
size of magnetic bolts (6) that can be used without affecting the main flux path to
a great extent, it has been found that a 3 mm to 4 mm thick flux barrier (7) is
quite good enough to allow magnetic bolts (6) to be used in stead of non-
magnetic bolts.
The voltage generated by using the magnetic bolts (6) with 3 mm flux barrier is
180 volts for a standard machine which drops to 165 volts when loaded. This
power along with step-up transformer in the automatic voltage regulator cubicle is
enough to excite the field winding of brushless exciter for industrial generators.
The Flux barrier (7) is made of non-magnetic stainless steel material (SS 316
grade/ASTM-A-276) so as to reduce the leakage flux. In the absence of this flux
barrier (7), the voltage generated by PMG by using magnetic bolts (6) will be
much lower (since the leakage flux will be very high because of magnetic bolts
without flux barrier), which is not enough for the excitation of field winding of
brushless exciter of the generator.

WE CLAIM
1. A permanent magnet generator with magnets mounted on the rotor
sleeve by deploying magnetic bolts and flux barrier, the said generator
comprising;
a rotor (8) having a sleeve (1), the sleeve (1) constitutes atleast one flat
surface configured thereon a plurality of tapped holes (9);
a stator (10) wound with three phase fractional slot winding (12);
a plurality of magnets (4) mounted on the at least one flat surface of the
sleeve (1) by means of corresponding number of pole shoes (5) and bolts
(6), characterized in that:
at least one flux barrier (7) is provided being interposed in the pole shoe
(5) so as to reduce the flux leakage, and in that:
the bolts (6) comprise high strength magnetic bolts.
2. The generator as claimed in claim 1, wherein the flux barrier (7)
comprises non-magnetic stainless steel material.
3. The generator as claimed in claim 1, wherein the pole shoe (5) is provided
with a counter sunk hole (11).
4. An improved permanent magnet assembly such as herein described.

ABSTRACT

A PERMANENT MAGNET GENERATOR WITH MAGNETS MOUNTED ON
THE ROTOR SLEEVE BY DEPLOYING MAGNETIC BOLTS AND FLUX
BARRIER
A permanent magnet generator for synchronous generator, comprising: a rotor
(8) having a sleeve (1), the sleeve (1) constitutes atleast one flat surface
configured thereon a plurality of tapped holes (9); a stator (10) wound with
three phase fractional slot winding (12); a plurality of magnets (4) mounted on
the at least one flat surface of the sleeve (1) by means of corresponding number
of pole shoes (5) and bolts (6), characterized in that: at least one flux barrier (7)
is provided being interposed in the pole shoe (5) so as to reduce the flux
leakage, and in that: the bolts (6) comprise high strength magnetic bolts.