A THREE-PHASE GENERATOR HAVING NO WINDING

Abstract: When generating three-phase fifty cycles current by means of a generator with a rotor having no winding there are several ways of carrying out such a generator for which the three-phase properties are obtained thereby that the number of rotor poles is larger or smaller than the number of stator poles. For fifty cycles such a generator will achieve rather low speed and will have a higher consumption of material than a generator for high speed. The invention is based as a two-pole stator and a two-pole rotor, allowing the highest possible speed of rotation in relation to the frequency. The principle can be utilized for all even number of poles, (2, 4, 6, 8 ...). According to one embodiment of the invention the generator has five slots per pole of the stator, implying six stator teeth per pole with a tooth pitch or slot pitch of 60 electrical degrees. One of the phases, e.g. B<u2>u-S<u2>u, consists of one coil having the coil pitch equal to the pole pitch and being located in the most central slots (3, 9) in each stator pole, while each one of the two other phases, B<u1>u-S<u1>u and B<u3>u-S<u3>u, consists of two series-connected coils having a coil pitch that is equal to half a pole pitch, each one of said series-connected coils being located in two slots (1, 4; 7, 10 and 2, 5; 8, 11, respectively) in one pole.

Description: 1 A three-phase generator having no winding The present invention relates to a three-phase generator having no winding, according to the accompanying patent claims The invention is based on a generator having a laminated rotor and laminated stator poles of dynamo sheet. The number of rotor poles is equal to the number of stator poles and is an even number p = 2, 4, " 8 ... . Around each stator pole a magnetizing coil is concentrically arranged. Each stator pole fase is provided with five slots of even pitch in which the AC winding is located. When, for example, it is desired to utilize a generator that is direct-coupled to a motor shaft and is driven by an internal combustion engine and is generating a current of fifty cycles, or in general , when it is desired to utilize a high number of revolutions at fifty cycles and at a minimum weight of the generator, it is necessary to use the lowest possible number of rotor poles: 2, 4, 6. A generator accord¬ ing to the Swedish patent specification 7506491 (correspond- ning to the U.S. patent specification 4,075,521) is limited to a rel atively low maximum number of revolutions at fifty cycles, because the three-phase system is based on a number of rotor poles p + 1 and a number of phases q = p/2. Such a generator has a maximally possible number of revolutions at fifty cycles that is n = 50-60/(6-1) = 600. The solution of the problem to design a generator having but a few poles and a rotor having no winding and giving a symmetrical three-phase current and having a low noice level , will be described in the following. Fig. 1 illustrates a two-pole. embodiment,- Fig. 3 a four- -pole embodiment and Fig. 4 a six-pole embodiment of the three-phase generator according to the invention. Fig. 2 illustrates the summation of the induced slot voltages for forming a symmetrical three-phase system. In these generators, where the rotor pole width is equal to half the stator pole pitch, and where the rotor pole pitch is equal to the stator pole pitch, the stator pole pitch is 360 electrical degrees. The slots in each stator pole are arranged to have an even pitch and a number of five, implying that the number of stator- teeth per pole is equal to six, and that a tooth pitch comprises 360/6.= 60 electrical degrees. In the most central slots of each pair of poles coils having- coil pitch (long coil pitch) equal to the pole pitch are provided. In the remaining slots of each pole, coils having a coil pitch (short coil pitch) equal to half the pole pithc are provided. One of the phases consists of only coils having a long coil pitch, said coils being connected in series. The two remaining phases each one consists of series- -connected equally positioned coils having a short coil pitch. The coil terminals B. , B 2 , B 3 as well as ' the terminals S , S 2 , S, will then be situated at a distance of two coils equal to 120 electrical degrees from each other. The number of . "long" coils will be equal to half the number of the poles, while the number of "short" coils will be twice the number of the poles. Thus, in the two-pole generator according to Fig. 1, one phase will consist of only one coil having a long coil pitch, while each one of the two remaining phases will consist of two ceries-connected coils having a short coil pitch. It might, at a cursory glance, appear to be strange that this geometrically unsymmetrical circuit diagram will give rise to a symmetrical three-phase voltage. However, in the "long" coil influenced by a flux changing its direction, a voltage will be induced having the same magnitude as the voltage across the two series-connected coils in one of the remaining phases wherein the flux is varying between a zero and a maximum value. A better way of illustrating how the - voltages are generated is given by the vector diagram in Fig. 2 wherein the slot voltages in the three phase are added to give a symmetrical three-phase system. The relationship n = f-60/p revolutions per minute gives for f = 50 cycles per second the speed of rotation 1500 for the two-pole generator, 750 for the four-pole generator and 500 for the six-pole generator.

Claims: of 360/6 = 60 electrical degrees, and that in the most central slots (3,9) of each pair of stator poles the coil sides of series-connected coils having the coil pitch equal to the pole pitch are provided and constitute one phase, and remaining slots (1 ,4 and 2,5 and 7,10 and 8,11) ui iπiπg equal ly suuaceα co constitute the third phase, the .. phase terminal (B, ,B 2 ,B 3 ) and the second phase terminal (S- j jS-jS.,), respectively, will be situated two coil pitches from each other and thus mutually displaced by 120 electrical degrees. 2. A three-phase generator according to claim 1 , in which the number of slots in each stator pole is a multiple of 5, and 24 po es n t e rotor. 4. A three-phase generator according to claim 3, which the number of slots per pole is diverging from a multiple of 5, or has a somewhat varying pitch if a special shape of the curve of the voltage is desired, or in order to suppress not desired harmonics if skewing or bevelling of the rotor poles is not a cufficient remedy. OMPI

Inventors: NORDEBO K
Applicants: NORDEBO K
Application year: 1979
Main classification: H02K19
IPC codes: H02K19