FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
AC generator
INVENTOR
Pawar Dilip Uttam, Crompton Greaves Ltd, LT Motors Division (M3), A-6/2 MIDC, Ahmednagar 414 001, Maharashtra, India, an Indian national
APPLICANTS
CROMPTON GREAVES LIMITED, CG House, Dr Annie Besant Road, Worli, Mumbai 400030, Maharashtra, India, an Indian company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to an AC generator.
BACKGROUND OF THE INVENTION
An AC generator comprises a wound stator associated with a rotor which is energized by a direct current and rotated by a prime mover relative to the stator for generation of output current in the windings of the stator. The stator comprises two sets of windings namely a main winding or high voltage winding and an auxiliary winding or low voltage winding for each phase of the generator and the rotor comprises a single winding namely field winding. The AC generator further comprises a compounding excitation (CE) transformer which comprises two windings namely a load winding and a compounding winding corresponding to each phase of the generator. The main winding of each phase is connected to the corresponding load winding of the CE transformer and the auxiliary winding of each phase is connected to the corresponding compounding winding of the CE transformer. The compounding winding of the CE transformer corresponding to each phase of the generator is also connected to the field winding of the rotor through a rectifier. The electrical load is connected to the load winding(s) of the transformer. The output voltage generated in the main winding(s) of the stator is given to the load through the load winding(s) of the CE transformer. The voltage generated in the auxiliary winding(s) of the stator is given to the rectifier through the compounding winding(s) of the CE transformer which regulates the magnitude of the output voltage depending upon the load requirements. The rectifier converts the current into direct current and supplies it to the field winding of the transformer for its energisation. The main winding and auxiliary winding of the stator are composed of a number of coils (wraps) of conductors (filaments) wound together. The coils of the main winding and auxiliary winding are inserted in the stator slots of the stator. The conductors of the main winding and the auxiliary winding are insulated from each other using insulating material such as fibre glass, paper or wire enamle. The insulating material adds to the cost of the AC generator. Even though the main winding and auxiliary winding are not electrically connected, they


have to be wound in such a manner that the polarities of the main winding and auxiliary winding match so as to get the desired voltage regulation. The matching of polarities is cumbersome and time consuming because of the multiple number of conductors of the main winding and auxiliary winding. Also, any mismatch of the polarities of the main winding and auxiliary winding will not give the desired voltage regulation. The assembly time of the AC generator increases due to the matching of polarities involved in the winding of the main winding and auxiliary winding. In order that the output voltage of the generator is not distorted it should be free from 3r harmonics. This can be achieved by maintaining the distance between the two sides of each coil of the main winding as 2/3rd of the full pitch distance. The distance between the two sides of a coil of the main winding is called the pitch distance. In order to maintain the pitch distance of the coils of the main winding as 2/3rd of the full pitch distance it is necessary to accommodate one side of two coils of the phase(s) in one stator slot. As both the main winding and auxiliary winding are inserted in each stator slot, it becomes very difficult to accommodate one side of each of two coils of the phase(s) of the main winding in the same slot because of space constraint in the stator slot. Also if one side of each of two coils of the phase(s ) of the main winding is inserted in a stator slot along with the auxiliary winding, identification of conductors and connection of the conductors become difficult because of the large number of conductors. As a result it is impractical to maintain the pitch distance of the coils of the main winding at 2/3rd of the full pitch distance. This gives rise to 3rd harmonics in the output voltage of the generator and distortion of the output voltage of the generator.
OBJECTS OF INVENTION
An object of the invention is to provide an AC generator, which eliminates the auxiliary
winding and is economical.
Another object of the invention is to provide an AC generator, which allows the pitch distance between the coils of the main winding to be maintained at 2/3rd of the full pitch distance.


Another object of the invention is to provide an AC generator, which generates an output voltage free from 3rd harmonics.
Another object of the invention is to provide an AC generator, which ensures desired voltage regulation.
Another object of the invention is to provide an AC generator, which is simple in construction and reduces the assembly time.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided an AC generator comprising stator and rotor, the stator comprising a main winding for each phase of the generator, the main winding comprising a plurality of coils made of conductors wound together and inserted in the stator slots such that one side of each of the two coils are accommodated in the same stator slot, the main winding of each phase being connected to the corresponding load winding of a compounding excitation transformer, the main winding of each phase being provided with at least one tap at a predetermined location which is connected to the corresponding compounding winding of the compounding excitation transformer, the compounding winding corresponding to each phase of the generator being connected to the fielding winding of the rotor through a rectifier, the rotor being further connected to a prime mover.
The following is a detailed description of the invention with reference to the accompanying drawing, in which:
Fig 1 is an electrical diagram of a 3-phase AC generator according to an embodiment of the invention;
Fig 2 is a crosssectional view of the wound stator and rotor assembly of the AC generator of Fig 1; and


Fig 3 is an electrical diagram of a single phase AC generator according to an embodiment of the invention.
As illustrated in Figs 1 and 2 of the accompanying drawings, the three phase AC generator 1 comprises a stator 2 and rotor 3 whose shaft is marked 3a. The stator comprises a main winding for each of the three phases of the generator marked R, Y and B. The main winding for each phase comprises a plurality of coils made of conductors wound together and inserted in the stator slots 2a such that one side (not marked) of each of two coils of the generator is accommodated in the same stator slot. The sides of the coils corresponding to the phases of the generator in the stator slots are represented by R, Y, B. Rl, Yl and Bl are the load windings and R2, Y2 and B2 are the compounding winding of a compounding excitation (CE) transformer 5 corresponding to each phase of the generator. The main winding of each phase is connected to the corresponding load winding Rl, Yl and Bl of the CE transformer. The main winding of each phase is provided with one tap marked T at a predetermined location which is connected to the corresponding compounding winding of the CE transformer. The compounding winding corresponding to each phase of the generator is connected to the field winding 3b of the rotor through a rectifier 6. The shaft of the rotor is connected to a prime mover (not shown). The AC generator functions in known manner. The tap(s) in each phase of the main winding supplies the alternating voltage generated in the stator windings to the compounding winding of the CE transformer. The compounding winding provides the required regulation to the voltage to the rectifier for conversion into direct current and energisation of the field winding of the rotor.
Fig 3 of the accompanying drawings illustrates a single phase AC generator la. The main winding for the single phase of the generator is marked S. The load winding and compounding winding of the CE transformer corresponding to the single phase of the generator are marked L & C, respectively. The main winding is provided with one tap T which is connected to the compounding winding of the CE transformer. The single phase AC generator functions in the same manner as the three phase.


The main winding(s) of the AC generator may comprise more than one tap.
According to the invention as the auxiliary winding(s) of the stator is/are eliminated. Therefore the insulation between the main winding(s) and auxiliary winding(s) is eliminated. Elimination of the auxiliary winding(s) and insulation renders the AC generator economical. As the auxiliary winding(s) is/are eliminated possibility of mismatch between the polarities of the main winding and auxiliary winding does not occur. Therefore, desired voltage regulation is achieved in the generator. Matching of polarities of the main winding and auxiliary winding match need not be carried out as the auxiliary winding(s) is/are eliminated. Assembly time of the generator is therefore reduced. As the auxiliary winding(s) is/are eliminated it is possible to accommodate one side of each of the two coils in each slot thereby maintaining the distance between the coils of the main winding at 2/3rd of the full pitch distance. Therefore, 3rd harmonics are not present in the output voltage of the generator and the output voltage is not distorted.


We Claim
1. An AC generator comprising stator and rotor, the stator comprising a main winding for each phase of the generator, the main winding comprising a plurality of coils made of conductors wound together and inserted in the stator slots such that one side of each of the two coils are accommodated in the same stator slot, the main winding of each phase being connected to the corresponding load winding of a compounding excitation transformer, the main winding of each phase being provided with at least one tap at a predetermined location which is connected to the corresponding compounding winding of the compounding excitation transformer, the compounding winding corresponding to each phase of the generator being connected to the fielding winding of the rotor through a rectifier, the rotor being further connected to a prime mover.
2. The AC generator as claimed in claim 1, which is a single phase or three phase generator.




ABSTRACT
An AC generator (1) comprising a stator (2) and rotor (3). The stator comprises a
main winding (R, Y, B) for each phase of the generator. The main winding
comprises a plurality of coils made of conductors wound together and inserted in
the stator slots (2a) such that one side (not marked) of each of the two coils are
accommodated in the same stator slot. The main winding of each phase is
connected to the corresponding load winding (R2, Y2, B2) of a compounding
excitation transformer (5). The main winding of each phase is provided with at
least one tap (T) at a predetermined location which is connected to the
corresponding compounding winding (Rl, Yl, Bl) of the compounding
excitation transformer. The compounding winding corresponding to each phase of
the generator is connected to the fielding winding (3b) of the rotor through a
rectifier (6). The rotor is further connected to a prime mover (not shown) (Figs 1
and 2).