Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-04-19
2001-06-26
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S216055, C310S216055, C310S201000, C310S203000, C310S208000, C310S216006, C310S267000, C310S270000
Reexamination Certificate
active
06252328
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of electrical machines, in particular generators having amortisseur bars.
2. Discussion of Background
Amortisseur windings (“amortisseur bars”) are used in the rotors of electrical machines for various reasons. The arrangement and function of such amortisseur bars are explained, for example, in publications U.S. Pat. No. 4,453,101, U.S. Pat. No. 5,122,698 or U.S. Pat. No. 5,606,211. In this case, the amortisseur bars may be arranged in the winding slots between the winding bars and the locking wedges, as shown in U.S. Pat. No. 5,122,698. However, they may also be designed as locking wedges of winding slots, as shown in U.S. Pat. No. 5,606,211. The amortisseur bars are electrically connected to one another at their ends by amortisseur rings or amortisseur segments slipped over the rotor.
A specific use of the amortisseur bars relates to the pole zones of rotors. In the pole zones, in which there are no winding bars, special slots having a small depth are provided for accommodating the amortisseur bars, which are inserted or pushed into said slots (U.S. Pat. No. 4,363,986). So that the amortisseur bars are securely held in the slots by the centrifugal forces occurring at the high rotational speeds during operation, special provisions have to be made. This may be achieved by locking wedges pushed into the slots above the amortisseur bars (U.S. Pat. No. 5,122,698). However, this may also be achieved by retaining rings shrunk onto the rotor (U.S. Pat. No. 4,363,986). Finally, however, it is also possible to design the amortisseur bars themselves like locking wedges (U.S. Pat. No. 5,606,211).
In all cases, it has to be taken into account that the amortisseur bars must be pushed over a relatively large rotor length into the slots and secured there. In order not to make it unnecessarily difficult to push in the amortisseur bars during fitting, sufficient clearance is provided between the amortisseur bars or locking wedges and the slots. On the one hand, the result of this is that the amortisseur bars, at low rotational speeds or when the machine is stopped, only rest loosely in the slots provided for this purpose and tend to rattle. On the other hand, however, the result of this, in particular, is also that, at low rotational speeds or when the machine is stopped, the electrical contact between the ends of the amortisseur bars and the amortisseur rings or segments above them, but also between the amortisseur bars and the rotor core, either does not exist at all or is inadequate on account of the lack of contact pressure, so that scorching may occur when the amortisseur bars are carrying current. At the high rotational speeds during normal operation, however, the amortisseur bars and locking wedges are pressed outward by the centrifugal forces produced and are fixed by the corresponding wedge shape of the slots, so that the play is removed and at the same time sufficient contact with the amortisseur rings or segments and the rotor core is produced and ensured.
In order to avoid the adverse effects of the mechanical play when the machine is stopped or at low rotational speeds of the machine, it has been proposed in U.S. Pat. No. 5,122,698 to insert spring strips curved in the transverse direction into the slot below the amortisseur bars, which spring strips press the amortisseur bar (and the locking wedge above it) against the bevels in the side walls of the slot and at the same time press the projecting ends of the amortisseur bars against the amortisseur ring. However, even during fitting, the inserted spring strips result in very high frictional forces when the locking wedge is pushed in, so that in this solution a special lever mechanism has to be used for the pushing-in (FIG. 6 in U.S. Pat. No. 5,122,698) and ease of fitting by hand is no longer possible.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to improve an electrical machine of the type mentioned at the beginning in such a way that, in the case of the amortisseur bars provided in the rotor, both ease of fitting and sufficient applied pressure of the amortisseur bars are achieved even when the machine is stopped or at low rotational speeds of the machine.
The object is achieved in a machine of the type mentioned at the beginning in that prestressable spring elements are arranged in a distributed manner on the underside of the amortisseur bars, which spring elements, in the prestressed state, enable the amortisseur bars to be pushed into the slots without hindrance and, after the prestressing has been removed, press the amortisseur bars against the supporting means and at the ends of the rotor against the amortisseur rings or amortisseur segments. The essence of the invention consists in fixing the amortisseur bars in the slots and electrically connecting them to the amortisseur ring by means of spring elements, even when the machine is stopped, by loading the amortisseur bars with a sufficient applied pressure. In this case, the spring elements are designed to be prestressable. For the fitting (pushing-in) of the amortisseur bars, the spring elements are prestressed (or compressed) in such a way that they produce no additional frictional forces when the amortisseur bars are being pushed in. If the amortisseur bar has been fitted (pushed in), the prestressing is removed, and the spring elements expand between the underside of the amortisseur bar and the base of the slot and press the amortisseur bar radially outward into the wedge seat of the slot or against the amortisseur ring.
In principle, it would be conceivable to arrange the spring elements in a sunk position in the amortisseur bars. This would have the advantage that the slots for accommodating the amortisseur bars could be retained unchanged in their cross-sectional shape. However, such a sunk arrangement would lead to a local reduction of the cross section of the amortisseur bars and thus to an undesirable increase in the electrical resistance. In order to avoid this, the underside of the amortisseur bars, in a first preferred embodiment of the invention, is of flat design, and, to accommodate the spring elements, in each case a gap-like intermediate space is provided below the amortisseur bars in the slots.
A second preferred embodiment of the machine according to the invention is distinguished by the fact that the individual spring elements are fixed to the respective amortisseur bar. As a result, the spring elements, together with the amortisseur bar, can be pushed into the slot without problem and are also secured against slipping during the subsequent operation.
A preferred development of this embodiment is distinguished by the fact that the amortisseur bars each have a plurality of through-holes, that the spring elements are each fixed in one of the through-holes and can be prestressed through this through-hole, that each spring element has a clamping sleeve with an internal thread, which clamping sleeve reaches into the associated through-hole in the amortisseur bar and thus fixes the spring element to the amortisseur bar, and by means of which clamping sleeve the spring element can be pressed against the underside of the amortisseur bar against the spring force and can thus be prestressed, and that a clamping bolt is provided in each case in order to prestress the spring elements, which clamping bolt is screwed with a male thread through the respective through-hole into the clamping sleeve of the spring element to be prestressed. The clamping bolt prestresses the spring elements in a simple manner and secures them against slipping when the amortisseur bar is being pushed in. If the amortisseur bar has been pushed in, the clamping bolts are simply slackened or unscrewed. The spring elements are thus activated and press the amortisseur bar into the slot, while they continue to remain fixed by the clamping sleeves.
In this case, the spring elements are preferably designed as leaf- or disk-shaped springs.
REFERENCES:
patent: 3909931 (1975-10
Brem Ernst
Tommer Josef
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Lam Thanh
Ramirez Nestor
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