FIELD OF INVENTION
The present invention generally relates to rotating electrical machines . More particularly, the present invention relates to an improved retaining ring adaptable to the induction motors.
BACKGROUND OF INVENTION
Rotors of electrical machines comprises field winding, for example, coil winding for synchronous, motors and cage winding for induction motors. In the core portion, a winding is supported by a slot tip and a slot wedge but in the overhung portion, the winding has to be protected against the centrifugal forces generated due to rotation of the rotor.
Different methods are available for the protection of the winding overhang from the centrifugal forces. For the high speed and higher diameter rotors, the retaining rings are used to support the overhung portion of the field winding.

Depending on the speed of rotation of the rotor, weight of the overhung winding and the diameter of the ring, the stress level in the retaining ring varies, and accordingly the material of ring with suitable minimum yield point stress (YPS) is selected.
In squirrel cage induction motors conventionally alloy steel forged retaining rings, which can attain variable YPS values, are used. YPS value for the alloy steel forged retaining rings ranges from 500 N/sq.mm. to 900 N/sq.mm. The construction of induction motor allows use of a retaining ring having a small cross-section which warrants use of high tensile material for manufacture of a retaining ring. In contrast, the synchronous motor construction allows a larger cross-section of the retaining ring, hence a retaining ring formed of material with lower tensile strength, such as Cu Al Ni castings, are used. Maximum YPS of Cu Al Ni castings are 400 N/sq.mm.
However, the prior art retaining rings made of forged alloy steel adapted for induction motors has the disadvantages that the same is quite costly and manufacturing/delivery cycle is longer.

OBJECTS OF INVENTION:
It is therefore an object of the invention to propose an improved retaining ring to support overhung portion of field winding of induction motors, which eliminates the disadvantages of prior art.
Another object of the invention is to propose an improved retaining ring to support overhung portion of field winding of induction motors, which is cost-effective.
SUMMARY OF THE INVENTION
According to the invention, there is provided an improved retaining ring for induction motors which constitute cast rings made of an alloy material comprising copper, aluminium and nickel. The manufacturing process of the alloy metal is selected such that the maximum YPS value of the cast rings when produced from the alloy material attains to 500 N/sq.mm.

It may be noted that the maximum YPS-value of the available Cu Al Ni casting is 400 N/sq.mm.
Thus, wherever the design calculations of the field windings of the rotors requires a retaining ring with YPS value of 500 N/sq.mm., the high tensile Cu Al Ni cast rings of the invention can be adapted. Whenever, the design calculations of the field windings of the rotors permits the use of a retaining ring with YPS-value of 400N/sq.mm, the existing Cu Al Ni cast rings can be adapted instead of alloy steel forged rings for the induction motors.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
Fig. 1 A part-sectional view of a rotor showing the arrangement of an improved retaining ring in induction motors.
DETAIL DESCRIPTION OF THE INVENTION
As shown in figure-1, the rotor of an induction motor includes a rotor core (4), shrink-fitted on a shaft (5). The rotor core (4) is having a plurality of equally distributed slots on the outer periphery which accommodate a plurality of rotor

bars (2). The rotor bars (2) are projected on either sides from the rotor core (4) and are brazed with a short circuit ring (3) on both the sides to form rotor winding overhangs.
During rotation of the rotor, the overhung windings of the rotor are subjected to centrifugal forces, the value of which depends on the speed of rotation of the shaft (5), weight of the overhung winding to be supported, and the diameter of the ring (3) . When the value of the centrifugal forces exceeds a predetermined limit, a retaining ring (1) is used to prevent the failure of the overhung portion of the winding .
The retaining ring (1) is shrink-fitted on the short circuit ring (3), and the overhung portion of the rotor bar (2) to take the centrifugal forces of the rotor winding overhang. In the induction motors, the construction of the rotor is such that only a small cross-sectional area is available for the retaining ring (1) to be fitted to the short-circuit ring (3). Hence, a smaller size retaining ring (1) capable of providing a higher YPS-value, and cast from Cu-AI-Ni alloy material is provided. Thus, the inventive cast-ring is a non-ferrous cast ring.

We Claim:
1. An improved retaining ring adaptable to the rotors of induction motors, the induction motor comprising a rotor core (4) disposed on a shaft (5), the rotor core (4) having a plurality of slots angularly and equitably disposed over the outer periphery, each slot accommodating a rotor bar (2) which rotor bars (2) projecting on either sides from the rotor core (4), the rotor bars (2) being brazed with a short circuit ring (3) on both sides of the rotor core (4) to form rotor winding overhung portions which are susceptible to high centrifugal forces corresponding to the rotational speed of the rotor including the weight of said overhung portions; and a retaining ring (1) shrink-fitted with the short-circuit ring (3) to prevent failure of the overhung portions of the windings, the improvement is characterized in that:
- the retaining ring (1) is cast from an alloy material comprising Cu-Al-Ni, and in that the manufacturing process of the alloy metal is so selected that the cast ring is enabled to provide a maximum YPS-value of 500 N/sq.mm.

2. A rotor as claimed in claim 1, with the retaining ring (1) cast from an alloy
material comprising Cu-AI-Ni having a min. YPS of 400 N/sq. mm.
3. An improved retaining ring adaptable to the rotors of induction motors, as
substantially described and illustrated herein with reference to the accompanying
drawings.

The invention relates to an improved retaining ring adaptable to the rotors of induction motors, the induction motor comprising a rotor core (4) disposed on a shaft (5), the rotor core (4) having a plurality of slots angularly and equitably disposed over the outer periphery, each slot accommodating a rotor bar (2) which rotor bars (2) projecting on either sides from the rotor core (4), the rotor bars (2) being brazed with a short circuit ring (3) on both sides of the rotor core (4) to form rotor winding overhung portions which are susceptible to high centrifugal forces corresponding to the rotational speed of the rotor including the weight of said overhung portions; and a retaining ring (1) shrink-fitted with the short-circuit ring (3) to prevent failure of the overhung portions of the windings. The retaining ring (1) is cast from an alloy material comprising Cu-AI-Ni, and in that the manufacturing process of the alloy metal is so selected that the cast ring is enabled to provide a maximum YPS-value of 500 N/sq.mm.