US1988039A

US1988039A - Generator armature

Info

Publication number: US1988039A
Application number: US623205A
Authority: US
Inventors: Grob Hugo
Original assignee: Individual
Current assignee: Individual
Priority date: 1931-07-13
Filing date: 1932-07-18
Publication date: 1935-01-15
Anticipated expiration: 1952-01-15

Description

Jan. 15, 1935. H. GROB 1,988,039

GENERATOR ARMATURE Filed July 18, 19:52

V H. Gro

IN VEN TOR.

A TTORNEYS.

Patented Jan. 15, 1935 UNITED STATES GENERATOR ARMATURE Hugo Grob, Berlin, Germany Application July 18, 1932, Serial No. 623,205 In Germany July 13, 1931 1 Claim.

This invention relates to high-speed direct current generators and has for its object to provide means for removing or at least diminishing the undesired influence of the remanent magnetism 5 of the iron parts of the generator,

In all direct current generators the influence of the remanent magnetism of the iron parts entails the disadvantage that the voltage supplied by the generator when starting is too low and reaches its regular value only once the generator is working under full load whereby, due to the effect of the compound winding, the full excita tion has become effective. This drawback must be avoided as far as possible in generators which are intended for supplying a uniform voltage which is independent of the load.

This undesired effect of the remanent magnetism can be diminished, as known, by inserting an additional magnetic resistance into the magnetic circle. This additional resistance necessitates a corresponding increase of the exciting ampere-turns in relation to the magnetomotiveforce of which the magnetomotive force of the remanent magnetism falls to insignificance.

The said additional resistance can be placed either in the air-gap, in the yoke of the generator, or in the teeth of the armature. As will be seen from the following the first named two places, however, are not adapted to produce the desired effect. If the additional magnetic resistance is produced by an increase of the air-gap between the armature and the pole-shoes, the self-excitation of the generator becomes difiicult; if the additional resistance is placed in the casing by diminishing the cross sectional area of the yoke the remanent magnetism of the generator increases because in consequence of the diminishing of the cross sectional area of the yoke the restricted part of the yoke becomes saturated to a higher degree. Besides, the restriction has to be machined very exactly, because even a slight unintentional further reduction of this cross section causes the magnetic resistance to increase rapidly.

If, however, the additional resistance is provided in the armature teeth, these drawbacks are Wholly overcome. Due to the permanent reversal of magnetism during the revolution of the armature no increase of the remanence will occur and also the self-excitation of the generator is not affected.

For a suflicient suppression of the undesired efiect of the remanence the additionally inserted magnetic resistance must have a certain value. In high-speed direct current generators, to which the present invention relates principally, for instance, in generators which are driven by steam turbines, the radial length of the slots is rather short, because only a relatively small volume of copper is necessary for the armature winding. In consequence thereof the teeth are also rather short and if the additional magnetic resistance is produced by diminishing the cross section of the teeth, this will necessitate a high saturation, the exact value of which, owing to the great influence of even a small deviation of the dimensions or of the magnetic quality of the iron, is very difiicult to attain.

The object of the present invention is a shape of the slots of the armature of a high-speed direct current generator which gives the armature teeth such a length that it is possible to place into the same the additional magnetic resistance without being compelled neither to too high a saturation nor to an extreme accuracy in the dimensions. This attained by enlarging the slot space in radial direction toward the centre of the armature, this space then becoming considerably larger than is necessary for placing the armature winding. As then the restricted part of the magnetic circle is longer, the saturation of this part necessary to produce the additional magnetic resistance need not be so high, and therefore admits a more exact calculation. Besides, inaccuracies in the dimensions or in the magnetic quality of the iron do not influence the saturation to a great extent.

In the accompanying drawing the figure is a diagrammatic view of an example of the slot construction according to this invention.

A is the armature plate with the slots B. These slots are made deeper than is necessary for placing the winding C in order to make sure that the tooth-length a is sufiicient to produce the required additional magnetic resistance. The slotspace not occupied by the winding C is filled up with insulating material E or with another nonmagnetic material.

By the enlargement of the slots, the iron-losses in the teeth are somewhat increased. As, however, the tooth-iron-volume is rather small in high-speed generators, these losses are only of little account; they can, moreover, easily be compensated by increasing the crossection of the winding for which there is sufficient space seeing that the slot space is designed considerably larger.

For better commutation the armature conductors usually are arranged as near as possible to the armature-surface.

To recapitulate the invention: In high-speed direct current generators it is advantageous, unless special conditions have to be considered, to make the slots as small as possible, just sufficient for placing the winding in order to attain a free and strong magnetic flux. The present invention, however, demonstrates that by increasing the slots it is possible to avoid the disadvantages of the remanent magnetism without affecting the self-excitation. The idea of the invention is to enlarge the slots just enough for keeping down the efiect of the remanence sufiiciently, but not more, so that the required number of ampereturns and the additional tooth-iron-losses do not become too high.

It is acknowledged that it has been known heretofore to provide a small space around the conductors for insulation purposes or for mechanical reasons; e. g. for facilitating the embedding of the winding.

The invention may also be used in the case of alternating current generators provided with a direct current collector, the purpose of which is the excitation of the generator.

I claim:

Means for reducing the remanent magnetism of a high speed direct current compound generator comprising a slotted armature having conductors arranged in the slots, the armature teeth being proportioned to produce a magnetic reluctance sufficient to effect the desired reduction in remanent magnetism, the slots being thereby enlarged beyond the necessary size and a member of 20 non-magnetic material for filling the excess slot space.

HUGO GROB.