Abstract:
A rotary machine includes at least one rotating member and at least one stationary member positioned such that a clearance gap is defined between a portion of the at least one rotating member and a portion of the at least one stationary member. The clearance gap has a measurable radial dimension and a measurable magnetic flux is generated in the clearance gap at least partially by relative movement between the stationary member and the rotating member. A method of monitoring a clearance gap measurement system for the rotary machine includes providing at least one clearance gap measurement assembly. The measurement assembly has at least one dimension measurement apparatus and at least one magnetic flux measurement apparatus. The method also includes positioning the at least one measurement assembly on the stationary member to facilitate measurements of the clearance gap during operation of the rotary machine.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to rotary machines and more particularly, to methods and apparatus for monitoring turbine generators. 
     Many known hydroelectric turbines include a multiple-bladed rotor mounted within a housing coupled in flow communication with an elevated fluid source, such as a reservoir. Water from the source enters a pipe and travels downhill to the hydroelectric turbine. As the water descends, gravitational potential energy is transformed into kinetic energy in the form of mechanical hydraulic energy. The water is then channeled through the turbine wherein it imparts rotation within the turbine. At least one generator rotor is rotationally coupled to, and driven by the turbine rotor. Some known electric generators typically use a plurality of magnets coupled to a rotor and a plurality of stationary wire coils coupled to a stator to convert the turbine&#39;s rotational energy into electric energy. 
     In some known generators, rotor components and stator components are separated by an air gap that is typically measured in distance units. During operation, a magnetic field generated by the magnets mounted to the rotor passes through a portion of the air gap defined between at least a portion of a surface of the rotor and at least a portion of a surface of the stator. The effectiveness of the transmission of the magnetic field through the air gap is at least partly dependent on maintaining the dimensions of the air gap, i.e., the radial distance between the rotor surface and the stator surface. However, asymmetric and/or transient loads induced to the rotor may cause the rotor to deflect such that the air gap dimension is reduced and/or altered to be non-uniform. The changes to the dimensions of the air gap may adversely affect the magnetic field. Moreover, in the event of a generator malfunction, for example, short circuited windings, the effect on the magnetic field may also be adverse. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a method of monitoring a rotary machine is provided. The rotary machine includes at least one rotating member and at least one stationary member positioned such that a clearance gap is defined between a portion of the at least one rotating member and a portion of the at least one stationary member. The method includes providing at least one measurement assembly to determine a width of the clearance gap. The at least one measurement assembly includes at least one measurement apparatus and at least one magnetic flux measurement apparatus. The method also includes positioning the at least one clearance gap measurement assembly on the stationary member to facilitate measurements of the clearance gap during operation of the rotary machine. 
     In another aspect, a clearance gap measurement assembly is provided. The assembly includes at least one clearance gap radial dimension measurement apparatus and at least one clearance gap magnetic flux measurement apparatus. 
     In a further aspect, a rotary machine is provided. The machine includes at least one rotating member and at least one stationary member positioned such that a clearance gap is defined between a portion of the rotating member and a portion of the stationary member. The machine also includes a clearance gap measurement system. The system includes a clearance gap measurement assembly that includes at least one clearance gap radial dimension measurement apparatus and at least one clearance gap magnetic flux measurement apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a portion of an exemplary generator that may be driven by a hydroelectric turbine; and 
         FIG. 2  is a schematic view of an exemplary clearance gap measurement assembly that may be used with the generator shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a portion of the clearance gap measurement assembly shown in  FIG. 2 ; and 
         FIG. 4  is a block diagram of an exemplary air gap monitoring system that may be used with the generator shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a cross-sectional schematic view of an exemplary rotary machine  100  that may be driven by a hydroelectric turbine (not shown in  FIG. 1 ). In the exemplary embodiment, rotary machine  100  is a synchronous, three-phase, 60 Hz, separately-excited generator  100  that includes a salient pole rotor  102  and a stator  104 . Alternatively, generator  100  is any type of generator including, but not limited to, round rotor generators. Also, alternatively, rotary machine  100  may be an electric motor that includes, but is not limited to, salient pole motors. Rotor  102  includes a rotor shaft  106  that includes an exciter end  108  and a turbine end  110 . Rotor shaft exciter end  108  is rotatingly coupled to an exciter (not shown in  FIG. 1 ) and turbine end  110  is rotatingly coupled to the hydroelectric turbine. Alternatively, turbine end  110  is coupled to a drive such as, but not limited to, a gas, steam, and wind turbine (neither shown in  FIG. 1 ). Rotor  102  also includes a plurality of salient poles  112 , about which excitation windings  114  are wound with a plurality of turns on each pole  112 . 
     Windings  114  are coupled in electrical communication with the exciter via slip rings (not shown in  FIG. 1 ) through which excitation power is transmitted to generate a magnetic field (not shown in  FIG. 1 ) that rotates with rotor  102 . Alternatively, generator  100  is a permanent magnet generator such that rotor  102  includes enclosed permanent magnets (not shown in  FIG. 1 ) that generate the magnetic field. Also, alternatively, windings  114  may be coupled in electrical communication with a direct current electrical power source such as, but not limited to, batteries and/or rectifiers. 
     In the exemplary embodiment, stator  104  includes a plurality of teeth  116  (only two illustrated in phantom in  FIG. 1 ), that each have a radially inner periphery  117  that defines a plurality of slots  118  (only one illustrated in  FIG. 1 ). Stator windings (not shown in  FIG. 1 ) are positioned within slots  118 . A clearance gap  120  is defined between a radially inner periphery of stator  104  and a radially outer periphery of rotor  102 . Gap  120  facilitates magnetic coupling of rotor  102  and stator  104  to enable varying voltage and varying current to be generated within the windings of stator  102 . A plurality of power supply cables (not illustrated in  FIG. 1 ) electrically couple generator  100  to a power delivery system (not illustrated in  FIG. 1 ). Rotor shaft  106  is rotatable about an axis of rotation  122  that may be at any orientation that facilitates attaining predetermined operational parameters of generator  100 . 
     Generator  100  also includes a housing (not illustrated in  FIG. 1 ) that facilitates isolating generator  100  from an external environment, and at least one clearance gap measurement assembly  200 , described in more detail below. Assembly  200  is coupled to stator teeth inner periphery  117 , is illustrated in phantom in  FIG. 1 , and measures a width  121  of clearance air gap  120  and magnetic field as discussed further below. 
     In operation, rotation of the turbine rotates rotor shaft  106  and subsequently rotates rotor poles  112  within stator  104 . Rotor windings  114  generate a magnetic field that traverses clearance gap  120 . Rotational movement of rotor  102  causes the magnetic field to interact with the stator windings to subsequently generate a voltage in the stator windings. Subsequently an electrical current is generated that is transmitted to the power delivery system. Uniformity of clearance gap  120  facilitates enhancing the generation of the magnetic field by rotor  102 . However, mechanical loads and thermal stresses induced on rotor  102  may cause rotor  102  to shift such that clearance gap  120  is not uniform. A non-uniform clearance gap  120  may alter the shape and strength of the magnetic field between rotor  102  and stator  104 . Moreover, formation of a short circuit condition associated with a plurality of windings  114  may also affect the strength of the magnetic field. 
       FIG. 2  is a schematic view of gap measurement assembly  200 .  FIG. 3  is a cross-sectional schematic view of a portion of assembly  200 . In the exemplary embodiment, a plurality of clearance gap measurement assemblies  200  are positioned within generator  100  to facilitate measuring width  121  of gap  120 . In general, assemblies  200  may be positioned anywhere within generator  100  that enable assemblies  200  to function as described herein. In the exemplary embodiment, assemblies  200  are fixedly secured to the inner periphery  117  of stator teeth  116  using methods that include, but are not limited to, adhesives, retention hardware and tack welding. Alternatively, a plurality of measurement assemblies  200  may be positioned within slots  118 . In one embodiment, each assembly is substantially rectangular in shape. Alternatively, assemblies  200  may have any shape that enables assemblies  200  to function as described herein. 
     Measurement assembly  200  includes a width measurement apparatus  202  and a magnetic flux measurement apparatus  204 . In the exemplary embodiment, apparatus  202  is a parallel plate, capacitive proximity probe  202  and apparatus  204  is an induction loop. Alternatively, apparatus  202  and  204  are any components that perform as described herein. Each assembly  200  includes at least one cable  206  that facilitates powering apparatus  202  and  204  and facilitates transmission of gap width  121  and magnetic flux signals. In the exemplary embodiment, each cable  206  is electrically coupled with apparatus  202  and  204  via a terminal connection enclosure  208 . Moreover, each cable  206  is routed through a cable passage (not illustrated in  FIGS. 2 and 3 ) formed within, or in the vicinity of, stator  104 . 
     Apparatus  202  includes a first electrically insulating material layer  210  that electrically isolates an inner plate  212  from stator tooth periphery  117 . Apparatus  202  also includes a second electrically insulating material layer  214  that electrically isolates inner plate  212  from an outer plate  216 . Layers  210  and  214  extend between terminal connection enclosure  208  and plates  212  and  216  to facilitate insulating enclosure  208  from plates  212  and  216 . A power supply wire  218  electrically coupled to an electrical power source (not shown in  FIGS. 2 and 3 ) supplies power to inner plate  212  and facilitates generating an electrostatic field (not illustrated in  FIGS. 2 and 3 ) between plates  212  and  216 . In addition, apparatus  202  also includes a signal wire  220  that is electrically coupled to a remote monitoring system (not illustrated in  FIGS. 2 and 3 ) to transmit signals indicative of a width  121  of gap  120 . 
     In the exemplary embodiment, magnetic flux measurement apparatus  204  is a closed-loop, electrically-conducting material that includes, but is not limited to, a metal material and/or metal alloys. In the exemplary embodiment, apparatus  204  is a known guard element or a shield used with a known air gap sensor that has been modified. For example, in one embodiment, apparatus  204  is a modified 4000-series 50 mm air gap sensor commercially available from General Electric Bently Nev., Minden, Nev. The guard element is typically an electrically conductive band that includes a split defined within a portion of the guard, wherein the guard is generally perpendicular to the gap width being measured. The guard facilitates directing an electrostatic field generated by an air gap sensor that is similar to apparatus  202 , such that the field is concentrated between the sensor and rotor  102 . Typically, the guard is maintained at approximately the same voltage as the sensor. The split defined within the guard mitigates generation of electrical currents within the guard that subsequently facilitates mitigation of electrical interference within the air gap sensor. In the exemplary embodiment, apparatus  204  is substantially similar to the guard with the exception that the guard element split is sealed to form the closed loop. Moreover, apparatus  204  is configured to generate voltage when exposed to a magnetic field. As such, apparatus  204  is not externally powered. 
     In the exemplary embodiment, magnetic flux signals are transmitted to the monitoring system via at least one wire (not illustrated in  FIGS. 2 and 3 ) used within cable  206 . Alternatively, magnetic flux signals are transmitted to the monitoring system via a wire  220  used in conjunction with gap distance signals. In another alternative embodiment, apparatus  204  is not co-planar with plate  216 , but rather may be adjacent to insulating layer  210  such that no electrical contact exists between apparatus  204  and periphery  117  and plate  212 . In this alternative embodiment, the original guard associated with the known air gap sensor may be maintained with assembly  200 . Also, in a further alternative embodiment, the guard (not illustrated in  FIGS. 2 and 3 ) for assembly  200  is maintained with an associated split and apparatus  204  is positioned adjacent to, and either circumferentially internally, or circumferentially externally, to the guard. Moreover, in an alterative embodiment, apparatus  204  includes a plurality of conductive loops that are each positioned within an individual, parallel plane (or, layer) within apparatus  204 . 
     In operation, as rotor poles  112  rotate past stator teeth outer periphery  117 , clearance gap width  121  is measured by apparatus  202 . When gap width  121  remains substantially constant and capacitance features of apparatus  202  are maintained substantially constant, apparatus  202  transmits a substantially constant gap width signal (not shown in  FIGS. 2 and 3 ). If clearance gap width  121  changes, the capacitance of apparatus  202  changes and the gap width signal transmitted from apparatus  202  to the monitoring system via wire  220  is changed or varied. 
     Also, in operation, apparatus  204  is exposed to the varying magnetic field generated within gap  120  and a varying voltage that is proportional to the varying strength of the magnetic field, i.e., the magnetic flux density, is generated and transmitted to the monitoring system. Voltage generated in apparatus  204  is also proportional to the number of turns within apparatus  204  and the amount of surface area of apparatus  204  that is perpendicular to the magnetic field lines of flux. Rotor  102  and stator  104  are configured, and assembly  200  is positioned, to facilitate increasing the number of the magnetic lines of flux that are substantially perpendicular to apparatus  204 . 
       FIG. 4  is a block diagram of an exemplary clearance gap monitoring system  250  that may be used with generator  100 . In the exemplary embodiment, system  250  includes at least one assembly  200  positioned on the radially inner periphery  117  of at least one stator tooth. Assembly  200  is configured to measure a radial distance dimension i.e., a width  121  and a magnetic flux of clearance gap  120  between periphery  117  and rotor pole  112 . Moreover, assembly  200  is electrically coupled with at least one data processing assembly  252  via a sensor cable  254  routed through cable passage  256 , an intermediate electrical junction box  258 , and a data processing assembly input cable  260 . Electronic signal devices that may include, but not be limited to, at least one of signal conditioning apparatus (not shown in  FIG. 4 ) may be positioned within junction box  258  and/or elsewhere to facilitate electronic signal transmission as discussed herein. In the exemplary embodiment, sensor cable  254 , junction box  258 , and cable  260  cooperate to define a plurality of processor input channels  262 , i.e., at least one gap dimension channel and at least one flux measurement channel (neither shown in  FIG. 4 ). Alternatively, a network of transmitters and receivers operating in the radio frequency (RF) band may be used to define input channel  262 . Junction box  258  is configured to receive a plurality of cables similar to sensor cable  254 . Moreover, data processing assembly  252  is configured to receive a plurality of cables similar to cable  260 . In the exemplary embodiment, cable  254  includes a power supply wire  218 , a dedicated gap distance measurement wire  220  (both shown in  FIG. 3 ) and a dedicated flux measurement wire (not shown in  FIG. 4 ). Alternatively, gap distance and flux measurements are transmitted over a common wire  220 . 
     Data processing assembly  252  includes at least one processor and a memory (neither shown in  FIG. 3 ), at least one input channel  262 , at least two output channel  264 , and may include at least one computer (not shown in  FIG. 4 ). In the exemplary embodiment, each output channel  264  includes a cable  264  that is electrically coupled to at least one output device  266 , i.e., an operator interface terminal (OIT&#39;s)  266  and/or data processing assembly  252 . Output channels  264  also include at least one gap width channel and at least one flux measurement channel (neither shown in  FIG. 4 ). Alternatively, a network of transmitters and receivers operating in a predetermined portion of a radio frequency (RF) band may be used to define plurality of output channels  264 . 
     As used herein, the term computer is not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a processor, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits (neither shown in  FIG. 4 ), and these terms are used interchangeably herein. In the exemplary embodiment, memory may include, but is not limited to, a computer-readable medium, such as a random access memory (RAM) (neither shown in  FIG. 4 ). Alternatively, a floppy disk, a compact disc—read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) (neither shown in  FIG. 4 ) may also be used. Also, in the exemplary embodiment, additional input channels (not shown in  FIG. 4 ) may be, but not be limited to, computer peripherals associated with OIT&#39;s  266  such as a mouse and a keyboard (neither shown in  FIG. 4 ). Alternatively, other computer peripherals may also be used that may include, for example, but not be limited to, a scanner (not shown in  FIG. 4 ). Furthermore, in the exemplary embodiment, additional output channels may include, but not be limited to, additional data displays and operational control mechanisms (neither shown in  FIG. 4 ). 
     Processors for assembly  252  process information, including clearance gap position signals and magnetic flux signals from assemblies  200 . RAM and storage device store and transfer information and instructions to be executed by the processor. RAM and storage devices can also be used to store and provide temporary variables, static (i.e., non-changing) information and instructions, or other intermediate information to the processors during execution of instructions by the processors. Instructions that are executed include, but are not limited to, resident conversion and comparator algorithms. The execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions. 
     In operation, when rotor shaft  106  is deflected away from nominal axis of rotation  122 , width  121  of gap  120  around the circumference of generator  100  may become non-uniform. Assemblies  200  monitor the dimensions and magnetic fluxes of gap  120  and transmit the associated clearance gap width  121  and magnetic flux measurement signals, or gap width  121  and flux signals, (neither shown in  FIG. 4 ) to assembly  252 . The gap width and flux measurement signals are typically voltages or electrical current signals converted to separate dimension and flux measurements by at least one resident conversion algorithm for each of the width and flux measurements within the processors of assembly  252  (not shown in  FIG. 4 ). Examples of conversion algorithms may include, but are not limited to, integration algorithms to convert the varying flux voltage signals that are proportional to the rate of change of magnetic flux within gap  120  to magnetic flux values that may be interpreted by an operator. In an alternative embodiment, distance and flux values are transmitted on a single channel, and a discrimination algorithm is used to discriminate between the distance and flux signals and to route each for separate transmission to separate portions of assembly  252  for further processing. The processed gap dimension and flux signals are subsequently transmitted by output channels  264  to OIT&#39;s  266 . Evaluation of the gap dimension and flux signals by an operator is facilitated by both of the signals originating from a substantially common point within generator  100  and both signals being generated and obtained at a substantially common time. 
     The methods and apparatus for a generator clearance gap measurement system described herein facilitate operation of a hydroelectric turbine generator. Specifically, the generator clearance gap measurement assembly as described above facilitates an efficient and effective clearance gap radial distance and magnetic flux measurement scheme. More specifically, such measurement assemblies facilitate a smaller instrumentation footprint within such generators since only one assembly need be positioned within the generator rather than two independent sensors. Moreover, such assemblies also facilitate time and location synchronization of distance and flux measurements. Such measurement assemblies facilitate reduced capital and installation costs, generator reliability, and reduced maintenance costs and generator outages. 
     Exemplary embodiments of generator measurement systems as associated with hydroelectric turbine generators are described above in detail. The methods, apparatus and systems are not limited to the specific embodiments described herein nor to the specific illustrated hydroelectric turbine generators. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.