| Title of Invention | A BRUSHLESS EXCITER CAPABLE OF PROVIDING INITIAL EXCITATION POWER DURING FIELD FLASHING FOR BLACK START OPERATION OF BRUSHLESS SYNCHRONOUS GENERATORS |
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| Abstract | A brushless exciter capable of providing initial excitation power during field flushing enabling black start operation of brushless synchronous generators comprising a plurality of stator poles (2) having pole surface; at least one d.c. field winding (3) for excitation; a three phase armature winding (6) covering, the rotor (1); a trapezoidal groove is configured on the pole surfaces in which a plurality of trapezoidal shaped permanent magnet (8) being fixedly disposed, and in that the magnets (8) disposed north and south locations on alternate stator poles (2) producing a magnetic flux in the air gap on providing a d.c. field winding (3) which causes the armature winding (6) to generate sufficient voltage to provide the initial excitation power to the exciter. |
| Full Text | Filed of Invention The invention relates to the area of brushless exciter used for brushless synchronous generators for obtaining self excitation during black start operation of the generator. The hvention in particular relates to a brushless exciter capable of providing self-excitation power during field flashing enabling black start operation of brushless synchronous generators. Background of the Invention The brushless exciter is an electrical machne and is used to excite the generator field whdhg. The brushless exciter of present art generally has wound field coils as stater winding and three-phase rotor winding. When a d.c supply is given to this stator windhg, a magnetic field is set up h the air-gap. The three-phase rotor whding will accordingly have three-phase induced voltages because of mechanical rotation. These three-phase voltages are converted to d.c. by a three-phase rotating diode bridge and fed to the field winding of the generator. The exciter can generate output only when the field windings are excited by d.c current through the static regulator. The excitation power is normally obtained from a permanent magnet generator (PMG), a station auxiliary supply or a station battery. In the absence of PMG, auxiliary supply or station battery, it is not possible to excite the exciter field windhg and h turn the man generator can not be excited for producing electrical power. Sometimes, the residual magnetism available in the silicon steel stampings (used to make excier poles) can create initial magnetisation or excier field flashing. If the machine is not used for long time, the residual magnetism is lost and it will not be possble to carry out field flashing via the automatic voltage regulator in order to have black start operation of generator. The patient GB1415376 dated 26.11.1975 discloses an arrangement of magnets on a cylindrical structure including a separate machine oiher than the brushless exciter to effect self exclation. Objects of Invention It is therefore an object of the invention to propose a brushless exciter capable of providing self-excitation power during field flashhg enablhg black start operation of brush less synchronous generators. Another object of the invention is to propose a brushless exciter capable of providing self-excitation power during field flashing enabling black start operation of brushless synchronous generators which will make the generator more reliable and can be started any time without the availability of auxiliary supply or station battery. Summary of the Invention Accordingly there is provided a brushless exciter capable of providing initial excitation power during field flushing enablhg black start operation of brushless synchronous generators comprising a plurality of stator poles having pole surface; atteast one d.c. field winding for excitation; a three phase armature winding covering the rotor. A trapezoidal groove is configured on the pole surfaces in which a plurality of trapezoidal shaped permanent magnets being fixedly disposed. The magnets disposed north and south locations on albernabe stator poles produce a magnetic flux in the air gap on providing a d.c field winding which causes the armature winding to generate sufficient voltage to provide the initia exclation power to the exciter. The proposed brush less exciter with self excitation has field coils as stator winding and three-phase armature winding. When a d.c supply is given to this stater winding, a magnetic field is set up in the air-gap. The rotor has three phase armature winding. The embedded magnets produces flux, which passes through the rotor and armature winding without any d.c supply being given to the stater winding/field cols. The initial excitation power is obtained from the flux produced by embedded magnet. The developed brush less exciter has also been loaded to check the demagnetisation effect of the armature current. The exciter field winding is excited with d.c field current and it has resulted h increased output (excitation power for the generator). The reversal of filed current has reduced the initial excitation obtained by the embedded magnet and zero excitation level can also be achieved to obtain smooth control. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig. 1 shows a schematic diagram of a brush less exciter. Fig. 2 shows the brushless exciter construction without self excitation. Fig.3 shows the constructional details of a brushless exciter with embedded magnets for self excitation according to the present invention. DETAILED DESCRIPTION OF A PREFFERED EMBODIMENT OF THE INVENTION The brushless exciter, an electrical machine, is used to excite the generator field winding (Schematic diagram shown in Fig.1). When a d.c supply is given to its stator winding (3), a magnetic field is set up in the air-gap. The three-phase rotor winding will have three-phase induced voltages because of mechanical rotation. These three-phase voltages are converted to d.c. by a three-phase rotating diode bridge (9) and fed to the field winding (3) of the generator. The exciter can generate output only when the field windings (3) are excited by d.c current The excitation power is normally obtained from a permanent magnet generator (10), station auxiliary supply (11) or station battery (12). In the absence of PMG (10) or auxiliary supply (11), it is not possble to excite the exciter field winding (3) and in turn the main generator can not be excited for producing electrical power. Sometimes the residual magnetism available in the silicon steel stampings of exciter stater poles (item 2) is used to create initial magnetisation or exciter field flashing. If the machine is not used for long time the residual magnetism is lost and it will not be possible to carry out field flashing vla the automatic voltage regulator/ static regulator. The proposed brush less exciter with self excitation has salient stator poles made of silicon steel stampings (item 2) and has d.c. filed winding (3) for excitation. A trapezoidal groove is milled on the pole surface and trapezoidal size of permanent magnet (8) is pasted in the groove. The thickness and size of the magnet is decided based on the initial voltage required from the exciter armature winding (6). These trapezoidal magnets (8) form alternate north and south poles. During black start operation, the magnets (8) (north and south on alternate poles) will produce flux in the air-gap and the exciter armature winding (6) will generate sufficient voltage (about 5-10 %) to start the initial excitation and energising the automatic voltage regulator (11)/static regulator (12) . As the generator rotates and reaches full speed the AVR (11) will supply d.c excitation to the exciter field winding (3) from the station auxiliary supply (11) in addition to the field generated by the magnets (8). As the generator rotates and reaches full speed, the AVR (11) will supply d.c excitation to the exciter field winding (3) to produce main flux in addition to the generated by the permanent magnets (both the fields aiding each other). This will avoid loss of excitation because of increase in the exciter field current during voltage build-up after field flashing. ln case there is requirement to reduce the excitation power to zero value, the exciter field colls current has to be reversed in order to counter the filed/flux produced by the magnet pieces embedded in the stator poles. WE-CLAIM: 1. A brushless exciter capable of providing initial excitation power during field flushing enabling black start operation of brushless synchronous generators comprising: - a plurality of stator poles (2) having pole surface; - atleast one d.c. field winding (3) for excitation; - a three phase armature winding (6) covering the rotor(1); characterized in that a trapezoidal groove is configured on the pole surfaces in which a plurality of trapezoidal shaped permanent magnet (8) being fixedly disposed, and in that the magnets (8) disposed north and south locations on alternate stator poles (2) producing a magnetic flux in the air gap on providing a d.c field winding (3) which causes the armature winding (6) to generate sufficient voltage to provide the initial excitation power to the exciter. 2. A brushless exciter capable of providing initial excitation power during field flushing enabling black start operation of brushless synchronous generators as substantially described herein and illustrated with reference to the accompanying drawings. |
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00989-kol-2005-description complete.pdf
989-KOL-2005-CANCELLED PAGES.pdf
989-kol-2005-correspondence-1.1.pdf
989-KOL-2005-CORRESPONDENCE-1.2.pdf
989-kol-2005-correspondence.pdf
989-KOL-2005-DESCRIPTION (COMPLETE).pdf
989-kol-2005-examination report.pdf
989-kol-2005-granted-abstract.pdf
989-kol-2005-granted-claims.pdf
989-kol-2005-granted-description (complete).pdf
989-kol-2005-granted-drawings.pdf
989-kol-2005-granted-form 1.pdf
989-kol-2005-granted-form 2.pdf
989-kol-2005-granted-specification.pdf
989-KOL-2005-REPLY TO EXAMINATION REPORT.pdf
989-kol-2005-reply to examination report1.1.pdf
| Patent Number | 251184 | |||||||||
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| Indian Patent Application Number | 989/KOL/2005 | |||||||||
| PG Journal Number | 09/2012 | |||||||||
| Publication Date | 02-Mar-2012 | |||||||||
| Grant Date | 29-Feb-2012 | |||||||||
| Date of Filing | 31-Oct-2005 | |||||||||
| Name of Patentee | BHARAT HEAVY ELECTRICALS LIMITED | |||||||||
| Applicant Address | REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJBLOCK 3RD FLOOR. KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA | |||||||||
Inventors:
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| PCT International Classification Number | H03L 5/00 | |||||||||
| PCT International Application Number | N/A | |||||||||
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