Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-04-26
2003-07-22
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C029S596000
Reexamination Certificate
active
06597080
ABSTRACT:
TECHNICAL FIELD
This invention relates to the field of rotating electric machines in general and, in particular, to a process for manufacturing a rotating electric DC machine, as specified in the preamble to claim
1
, which is attached.
BACKGROUND
Rotating electric DC machines with a rated output below ca. 350 kW are generally designed to be uncompensated. This means that the stator of the DC motor is provided only with main poles for magnetization and commutating poles. It is the task of the commutating poles to make sure commutation occurs without harmful sparking at the edges of the brushes, since harmful spark formation results in high maintenance requirements due to abnormal wear on the brushes and commutator.
In most cases, DC motors with a rated output above ca. 350 kW are designed with compensating windings. This means that, in addition to the previously mentioned windings, the motor's stator is also provided with a compensating winding. The coils of the compensating winding are placed in winding slots in the main poles, so that each coil of the compensating winding fills the slots of two adjacent main pole halves.
The compensating winding greatly reduces the so-called armature reaction. Without the compensating winding, the armature reaction causes a distortion of the magnetic flux in the main pole that is dependent on the direction of rotation, causing a degradation in performance. The compensating winding provides numerous advantages over the uncompensated DC motor. Examples of this include the following: greater utilization, i.e. a higher torque for a given rotor diameter; higher overload capacity; lower moment of inertia with otherwise identical performance; higher armature voltage and, thus, higher output power can be achieved because a higher mean lamination voltage is permissible without the risk of commutator sparking; better linearity between armature current and torque, which improves the possibility of regulating the load and rotational speed of the DC motor. The latter can be utilized, for example, to increase the so-called field-weakening region of the DC motor, i.e. the rpm range that is achieved by regulating the field circuit.
At the same time, however, the compensating winding creates a number of disadvantages, in the form of a cost increase of ca. 15-20% for the DC motor and reduced inductance, which leads to higher current ripple. This creates a higher noise level and, in certain cases, a DC motor that is more sensitive because of disturbances in the commutation process.
Customers' performance needs are such that a compensating winding provides the optimal solution:
in rare cases, at powers under 350 kW;
in ca. 30% of the DC motors in the power range of 350-500 kW;
in ca. 50% of the DC motors in the power range of 500-1,000 kW;
in ca. 70% of the DC motors in the power range of 1,000-1,500 kW;
in practically all DC motors in the power range above 1,500 kW.
Because of the higher cost of compensating windings and the fact that it is not actually needed in many applications, DC motor manufacturers prefer to make DC motors with a variable design: uncompensated or with a compensating winding, depending on customer needs. This has been unprofitable with the conventional technology available, however, since the two design principles require significantly different rotor diameters for a given stator size. The space required by the compensating winding limits the rotor diameter for a given stator size.
With the solutions available using conventional technology, the compensating winding design determines the rotor diameter, if the idea is for the basic design to make possible both alternatives—uncompensated and compensated winding—in a single motor size (with the same center height). As a result, the rotor diameter in the uncompensated alternative is smaller than it could be if the motor were designed exclusively as uncompensated. The reduction is such that in approximately half the cases the performance can be achieved with a motor size smaller than the motor in an exclusively uncompensated design, which results in a more cost-effective solution, i.e. lower price/performance. For economic reasons, the limitations of conventional technology make it impossible to produce DC motors of the same motor size using alternative solutions: uncompensated and with compensating winding, respectively. In principle, this means that two totally different motors must be constructed for the two designs, with the accompanying tool costs and an increased number of versions to administer and to stock parts for. Thus, in practice, most DC motor manufacturers choose to make their motors exclusively uncompensated or compensated for a certain motor size.
The technical limitations of conventional technology result in costly compromises, both for motor manufacturers and for customers. The motors may be uncompensated, which results in unnecessarily large and expensive motors for handling high overloads, for example.
Uncompensated DC motors also have an unfavorable relationship between moment of inertia and performance, which means the motor must be overdimensioned for some applications. The alternative with compensating winding means that unnecessarily expensive motors are used in a large number of applications in which the performance requirements are modest. Due to the limitation of conventional technology described above, most DC motors over ca. 350 kW, regardless of the manufacturer, are made with compensating winding.
Considering the statements above, it is clear that no economically feasible solutions are available for creating the basic design of DC machines in such a way that, depending on the customer's needs, the same machine size can be made either as uncompensated or compensated. Consequently, there is a great need to find an economically favorable solution that would make it possible, as needed, for machines of a certain size to be made as uncompensated or compensated, with no significant limitation on the rotor diameter and, thus, on the performance of either type of machine.
DESCRIPTION OF THE INVENTION
The invention eliminates the problems indicated above in an effective and suitable manner.
One general object of the invention is to bring about a solution to the problem of creating a rotating electric DC machine of a certain size, so that it can be produced at a reasonable cost for both an uncompensated design and with compensating winding.
Based on the considerations above, it is a basic object of the invention to find a simple means of additionally improving the power output of a compensated rotating electric DC motor of a certain size, i.e. with a certain center height, and, more specifically, to accomplish this using a method that, at an acceptable cost, will make it possible for a machine of the specified size to be made with an uncompensated design, with a rotor diameter that is maximal from the standpoint of its technical dimensioning, and with a compensated design, with just as large a rotor diameter as the uncompensated version.
In accordance with the invention, a process is made available for producing a rotating electric DC machine of the above-mentioned kind with which it will be practically possible to move the slots in the main pole of the machine for the compensating winding radially outward from the center of the stator to permit the optimal increase in rotor diameter. This is achieved by making the coil ends of the main coil taper radially outward. Thus, space is created in an advantageous manner for the compensating winding in the displaced slots, at the point where the compensating winding comes out of the winding slot. In another alternative or supplemental embodiment in accordance with this invention, additional space is made for the compensating winding where it comes out of the slots by angling the coil ends of the main coil radially outward.
In accordance with one embodiment of the invention, the outer turns in the coil ends are wound with a greater length than the inner turns in them. This produces the tapered shape in the coil e
ABB AB
Dykema Gossett PLLC
Waks Joseph
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