Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-10-04
2003-11-11
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S214000, C310S058000, C310S269000, C174SDIG002, C174SDIG002, C174SDIG002, C174SDIG002
Reexamination Certificate
active
06646363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotating electric machine.
2. Discussion of the Background
Examples of rotating electric machines are synchronous machines, normal asynchronous machines as well as double-fed machines, alternating current machines, applications in asynchronous static current converter cascades, outerpole machines and synchronous flux machines.
The machine according to the invention is intended in the first place as a generator in a power station for generating electric power.
In the present application the terms “radial”, “axial”, “tangential” and “peripheral” constitute indications of direction defined in relation to the rotor of the machine unless expressly stated otherwise.
For vertical rotating electric machines with salient poles, known as Salient Pole Machines, coil supports are conventionally used between the different poles. The reason for this is that the rotor poles comprise pole pieces provided with a winding so that solenoids (magnet coils) are formed. Since the pole has a certain width, the long sides of the coil will not be situated in an axial plane running through the centre of the rotor, i.e. an axial plane through the long sides of the coil will be displaced parallel to an axial plane through the radial centre line of the corresponding pole. Part of the centrifugal force arising when the rotor rotates will therefore influence the long sides with a tangential force in the direction of the periphery. This force will endeavour to press the metal in the coil winding away from contact with the pole piece. The long sides of the coil thus run the risk of being bent out and, in the worst case, coming into contact with each other, which may give rise to powerful short circuits which in turn cause disturbing magnetic imbalances.
In order to prevent short circuits of the type described above, therefore, special coil supports are fitted in the pole gap, i.e. the gap or space between two adjacent poles, when deemed necessary. The task of these coil supports is thus to keep the coil windings in place. Coil supports are especially common in coils in high-speed machines.
Conventional coil supports usually consist of one or more whole-block supports, i.e. solid, substantially V-shaped supports, arranged a suitable axial distance from each other in each pole gap. Since it is desirable for the coil support to support the entire solenoid winding, each coil support will substantially block the entire area between two adjacent poles, i.e. the pole gap. The small space between two rotor poles which is not blocked by the coil support is used for ventilation so that cooling air can flow axially to cool the poles and later also the stator, depending on the type of rotating machine and the type of ventilation principle utilized. The spaces referred to are essentially the small space available near the air gap, between the rotor poles and the stator, and the equally limited space between the rotor windings and the rotor itself.
The types of ventilation which are relevant are the so called Midi-concept, axial ventilation and radial ventilation. In the Midi-concept the rotor body is used as a fan and the air passes axially through the pole gap from one side of the machine. In the case of axial ventilation axial fans are mounted on the rotor, usually two fans, one on the upper and one on the lower side. The air effects cooling of the poles and is transported axially to radial openings in the stator where it also has a cooling effect. In the absence of radial openings in the stator, however, the alternative using two axial fans is not possible. One-way axial ventilation or radial ventilation (air flowing radially through the rotor) can however manage the ventilation without radial openings in the stator core. However, radial ventilation is not possible with small rotor diameters.
It is obvious that the cooling air, or possibly some other type of gas used for cooling, able to pass the coil supports is in many cases insufficient to achieve satisfactory cooling of the machine.
The flow of cooling air permitted to pass through the pole gap is also limited by the maximum rise in temperature permissible for the air and also by the air speed having to be restricted. The latter is because, when the air is conducted through the pole gaps, it is accelerated to a speed approaching the peripheral speed of the rotor. This results in an increase in the kinetic energy of the air which is entirely lost, however, when the air leaves the machine. A retarding moment is thus caused, and consequently a power loss, which is directly reflected in the efficiency of the machine. Since these ventilation losses are directly proportional to the air flow, it is therefore desirable to have as little air resistance as possible.
According to a known device, in which an attempt is made to solve the problem of insufficient ventilation, the coil supports have been provided with apertures in order to increase the available area for the flow of cooling air. Unfortunately, these coil supports in many cases still fail to provide satisfactory ventilation. Furthermore, the coil supports force the air away from the coils which results in at least some of the air flow instead flowing closer to the stator and thus passing too far away from the coils to be of any use.
From the document U.S. Pat. No. 3,740,600 is previously known a coil support or brace which supports only part of the coil windings, namely those windings which are closest to the rotor piece. The purpose of the brace is to prevent separation of the coils from the poles by the tangential component of centrifugal force acting on the coils. The reason that the brace is designed to support only the innermost windings is that these windings, in the disclosed configuration of the poles, are particularly subjected said forces. Similar devices are also known from U.S. Pat. No. 5,036,238, GB-A-2 022 327 and DE-A-25 20 511.
Through U.S. Pat. No. 5,036,165 is known a conductor, in which the insulation is provided with an inner and an outer layer of semiconducting pyrolized glass fibre. It is also known to provide conductors in a dynamo-electric machine with such an insulation, as described in U.S. Pat. No. 5,066,881 for instance, where a semiconducting pyrolized glass fibre layer is in contact with the two parallel bars forming the conductor, and the insulation in the stator slots is surrounded by an outer layer of semiconducting pyrolized glass fibre. The pyrolized glass fibre material is described as suitable since it retains its resistivity even after the impregnation treatment.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a rotating electric machine designed to eliminate the above-mentioned problems and whereby satisfactory ventilation is obtained in an efficient and simple manner.
This object is achieved by a machine of the type described herein.
Accordingly, the coil supports are arranged in pairs, and each coil support in a pair is shaped so that it supports only a part of the solenoid windings of the two adjacent poles. To continue, two coil supports in a pair are arranged axially and radially displaced in relation to each other to allow a cooling gas to flow between the coil supports. Through this arrangement the advantage is gained that the area of the flow path for the air through the pole gaps is increased and the air resistance is decreased. A larger amount of air (or other gas) can thus pass at the same flow rate, and a higher degree of cooling is obtained. Alternatively, the same amount of air may be allowed to pass at a reduced rate, whereby said power losses are reduced and the efficiency of the machine increases. This in turn offers the advantage of being able to use only one fan instead of two, as is normal with axial ventilation. Satisfactory ventilation of the coil-end package beneath the stator is also made possible with this single fan. As compared to known devices for supporting only part of the windings, the present invention has the considerable advantag
Edman Arne
Kylander Gunnar
Landgren Nils-Ivar
Leijon Mats
ABB AB
Mullins Burton S.
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