Title of Invention

A NEW APPROACH FOR ASSEMBLING PERMANENT MAGNETS ON ROTOR OF A PERMANENT MAGNET GENERATOR USING MAGNETIC BOLTS AND FLUX BARRIER

Abstract

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 sfator (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.

Full Text

A new approach for assembling permanent magnets on rotor of a pilot exciter of a synchronous generator using magnetic bolts and flux barrier. FIELD OF INVENTION: This invention relates to an improved permanent magnet generator assembly. 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 magnei 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. 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. -1- 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 flux 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. -2- 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 fiat 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 barrler(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 fiat surface of the rotor sleeve (1) by using pole 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. ~"3 — 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 allow 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. -4- WE CLAIM 1. 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 sfator (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. -5- 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. 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 sfator (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.

Documents:

00802-kol-2005-claims.pdf

00802-kol-2005-description complete.pdf

00802-kol-2005-drawings.pdf

00802-kol-2005-form-1.pdf

00802-kol-2005-form-2.pdf

00802-kol-2005-form-3.pdf

802-KOL-2005-(19-11-2012)-ABSTRACT.pdf

802-KOL-2005-(19-11-2012)-AMANDED PAGES OF SPECIFICATION.pdf

802-KOL-2005-(19-11-2012)-CORRESPONDENCE.pdf

802-KOL-2005-(19-11-2012)-DESCRIPTION (COMPLETE).pdf

802-KOL-2005-(19-11-2012)-DRAWINGS.pdf

802-KOL-2005-(19-11-2012)-FORM-1.pdf

802-KOL-2005-(19-11-2012)-FORM-2.pdf

802-KOL-2005-(19-11-2012)-OTHERS.pdf

802-KOL-2005-(19-11-2012)-PA.pdf

802-KOL-2005-ABSTRACT.pdf

802-KOL-2005-CORRESPONDENCE-1.1.pdf

802-KOL-2005-CORRESPONDENCE.pdf

802-KOL-2005-DESCRIPTION (PROVISIONAL).pdf

802-KOL-2005-DRAWINGS.pdf

802-KOL-2005-EXAMINATION REPORT.pdf

802-KOL-2005-FORM 1.pdf

802-KOL-2005-FORM 18.pdf

802-KOL-2005-FORM 2.pdf

802-KOL-2005-FORM 3.pdf

802-KOL-2005-GPA.pdf

802-KOL-2005-SPECIFICATION.pdf