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  Electric machine with a damping deviceUSPTO Application #: 20060238061Title: Electric machine with a damping device Abstract: An electric AC machine includes a primary section and a secondary section. The primary section has a region facing the secondary section and a region facing away from the secondary section. The region facing the secondary section has windings adapted to receive an AC current. The winding of the primary section has at least one phase conductor which at least partially extends in or on the region of the primary section facing away from the secondary section, thereby producing a magnetic field that extends outside the secondary section. This arrangement can reduce overvoltages and eliminate voltage breakdowns at the star point of winding strands of a synchronous motor. (end of abstract)
Agent: Henry M Feiereisen, LLC - New York, NY, US Inventors: THOMAS HOPPE, Dietmar Stoiber USPTO Applicaton #: 20060238061 - Class: 310183000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060238061. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This application is a continuation of prior filed copending U.S. application Ser. No. 10/943,503, filed Sep. 17, 2004, which claims the priority of German Patent Application, Serial No. 103,432,930, filed Sep. 18, 2003, pursuant to 35 U.S.C. 119(a)-(d), the contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] The present invention relates to an electric machine with a damping device. The electric machine is an AC machine or a three-phase machine, and can be implemented as a rotary machine or as a linear motor. [0003] Nothing in the following discussion of the state of the art is to be construed as an admission of prior art. [0004] Electric machines, in particular synchronous motors, are frequently constructed by inserting specially formed winding wires in rotor or stator grooves. The winding wires are connected at the winding head to form winding strands. A winding strand can have several coils, depending on the number of poles. In three-phase machines, each phase has at least one winding strands, with the winding strands being connected at a star point. An exemplary a three-phase synchronous motor with four poles has three winding strands, each having four coils that are connected at the star point. The input voltages of the three-phase current are connected to the terminals of corresponding winding strands located on the other side of the star point. [0005] The windings of linear motors and more recently also of synchronous motors, which must have a high torque, are implemented in exciter coil technology. In other words, the magnetic cores are made of laminated metal sheets with teeth that operate as pole cores. The prefabricated coils are placed on the individual pole cores and suitably connected. The prefabricated coils are made of a support or coil bobbin which is fabricated of an electrically insulating material, and include insulated copper wires which are typically applied by machines. Optionally, the support can also be removed after the winding has been completed, if the windings themselves have enough stability. [0006] The electric machine can receive electric power from a converter, which can be an inverter. The converter can include, for example, an inverter, a DC link circuit and a rectifier. [0007] During operation of electric motors powered by pulse converters, the switching operations of the converter can cause voltage peaks between the motor winding and the grounded motor body. The motor winding operates as a reactant network conductor that is capacitively coupled to ground via the winding insulation. The voltage peaks are particularly large at the end of the reactant network conductor, which is frequently the star point of the winding. The reactant network conductor is also characterized by resonances and a resonant frequency. If all input terminals of the motor winding are simultaneously switched hard in one direction, then an electric oscillation with a characteristic frequency is produced between the motor winding and ground potential, which decays only slowly due to the weak natural damping. If the switching operations on the input terminals are periodic and their fundamental frequency or harmonics are close to the characteristic frequencies of the reactant network conductor of the motor winding, then the voltage peaks can become so large as to diminish the useful life of the insulation. Voltage peaks due to switching operations are therefore undesirable. [0008] Breakdowns at the star point of three-phase motors constructed with the exciter coiled technique can occur in particular in large converter installations. [0009] Similar problems can occur with electric machines suffering from transient overvoltages. The overvoltages should hence be limited to prevent breakdowns. For example, as disclosed in German patent publication no. DE 38 26 282, a voltage-dependent metal oxide resistor can be connected in parallel with a coil for limiting the overvoltage. German patent publication no. DE 28 34 378 discloses short-circuited winding sections for damping transverse fields. Likewise, German patent publication no. DE 24 33 618 discloses a method for damping transient overvoltages in a synchronous machine by applying transverse field damper rods. [0010] European patent publication no. EP 0 117 764 describes a method for suppressing overvoltages produced by resonance phenomena through application of ferroelectric isolators disposed between the coil windings. European patent publication no. EP 0 681 361 addresses the problem associated with higher harmonic oscillations which can occur in converters and rectifiers employing power thyristors. The damper winding is then connected with capacitors to form resonant circuits. The resonant circuits have a resonance frequency which is 6 n times greater than a fundamental frequency of synchronous machine. In this way, higher harmonic oscillation of the fundamental can be absorbed. [0011] Nevertheless, there remain problems of breakdowns in the star point of a synchronous motor produced with exciter coil technique. German patent publication no. DE 100 49 817 discloses an induction device as well as a method for operating electric machines that reduce the risk of a breakdown in the star point. This published patent application discloses an induction device with a winding arrangement having a winding start and a winding end for inducing a magnetic field in a magnetizable core and a lossy magnetizable device. The winding start and the winding end of the winding assembly are routed through or around the lossy magnetizable device in such a way that a magnetic flux is excited in the lossy magnetizable device. [0012] A drawback of conventional devices is the need for additional installation space and added costs. [0013] It would therefore be desirable and advantageous to provide an improved damping device for an electric machine, which is compact and can be manufactured cost-effectively. SUMMARY OF THE INVENTION [0014] According to one aspect of the invention, an electric AC machine includes a primary section and a secondary section. The primary section has a first region facing the secondary section and a second region facing away from the secondary section. The first region includes windings adapted to receive an AC current. The electric AC machine further includes at least one phase conductor, which at least partially extends in or on the second region and produces a magnetic field that is located outside the secondary section. [0015] According to another aspect of the invention, an electric AC machine includes a primary section and a secondary section, with the primary section having a plurality of windings adapted to receive an AC current and a closed conducting loop with at least one winding. [0016] Advantageous embodiments of the invention may include one or more of the following features. [0017] According to one advantageous embodiment, the region facing the secondary section is made of a magnetic material and does not include an air gap. The region facing the secondary section can be made as a single unitary piece with the region facing away from the secondary section. [0018] Advantageously, the windings are located in grooves which are formed by the teeth of the primary section. The teeth of the primary section located on the side of the primary section facing the secondary section can be made as one-piece with the primary section. [0019] Damping is achieved by placing at least one phase conductor of a winding in the region of the primary section facing away from the secondary section. Damping is caused by the magnetization of the region of the primary section that faces away from the secondary section. Advantageously, the magnetic fields necessary to produce an electromagnetic force of the electric DC machine are not affected by the damping fields. According to an advantageous embodiment of the electric machine, the phase conductor or conductors are guided in a cavity of the primary section. The primary section surrounding the cavity forms the core of the damping inductance. In an advantageous embodiment, the core of the damping inductance is separated by an air gap. According to another advantageous embodiment, the core of the damping inductance is formed by the primary section and by a bridge, which together form the cavity. [0020] According to another advantageous embodiment, the phase conductors of all three phases of a three-phase machine are routed through the cavity of the core of the damping inductance. Ideally, the sum of the three-phase current of the three phases is equal to zero. [0021] According to another embodiment, a feed and a return conductor of a strand having approximately zero current is routed through the core of the damping inductance. Continue reading... Full patent description for Electric machine with a damping device Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electric machine with a damping device patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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