Abstract:
A system includes a plurality of sensors configured to detect an electrical voltage and an electrical leakage current associated with an operation of an industrial machine, and a controller including a processor and a selection device. The selection device is configured to receive from the plurality of sensors a first input corresponding to the electrical voltage, and a second input corresponding to the electrical leakage current. The first input is paired with the second input to generate a paired input. The selection device is configured to transmit an output to the processor based at least in part on the paired input. The output includes an indication of the electrical leakage current or a dissipation factor associated with the industrial machine.

Description:
[0001]    The subject matter disclosed herein relates to industrial machines and, more specifically, to systems for monitoring leakage currents that may be associated with the industrial machines. 
         [0002]    Certain synchronous and/or asynchronous machines such as electric motors and generators may experience leakage currents on the stator windings of the machines during operation. Specifically, because the stator windings may include metal windings in close proximity, the stator windings of the motor may be subject to inherent capacitance (e.g., capacitive current leakage). Electric machines may also experience leakage currents due to less than optimal or ineffective insulation protecting the stator windings (e.g., resistive current leakage). On the other hand, capacitive leakage is an inherent characteristic of a motor controlled primarily by design details. In any case, if leakage currents go undetected and/or are left to persist, the leakage currents may possibly contribute to damage (e.g., mechanical damage, thermal damage, and so forth) to the stator windings or other components of the electric motor. It may be desirable to provide methods to improve monitoring of leakage currents of electric motors or other synchronous and/or asynchronous machines. 
       BRIEF DESCRIPTION 
       [0003]    Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
         [0004]    In accordance with a first embodiment, a system includes a plurality of sensors configured to detect an electrical voltage and an electrical leakage current associated with an operation of an industrial machine, and a controller including a processor and a selection device. The selection device is configured to receive from the plurality of sensors a first input corresponding to the electrical voltage, and a second input corresponding to the electrical leakage current. The first input is paired together with the second input to generate a paired input. The selection device is configured to transmit an output to the processor based at least in part on the paired input. The output includes an indication of the electrical leakage current or a dissipation factor associated with the industrial machine. 
         [0005]    In accordance with a second embodiment, a system includes a first sensor configured to obtain an electrical voltage measurement associated with an operation of an electrical industrial machine, a second sensor configured to obtain an electrical leakage current measurement associated with the electrical industrial machine; and a controller communicatively coupled to the first sensor and the second sensor. The controller includes a processor configured to receive a paired input corresponding to the electrical voltage measurement and the electrical leakage current measurement, receive a line frequency input corresponding to an operational frequency associated with at least one phase conductor electrically coupled to the electrical industrial machine, and to determine a dissipation factor associated with the at least one phase conductor of the electrical industrial machine based at least in part on the paired input and the line frequency input. 
         [0006]    In accordance with a third embodiment, a system includes a plurality of sensors configured to obtain existing electrical line voltage and electrical leakage current measurements associated with stator windings of an alternating current (AC) motor and a controller. The controller includes a memory configured to store a historical record of electrical line voltage and electrical leakage current measurements associated with the stator windings of the AC motor over a time interval, and a processor configured to receive the existing electrical line voltage and electrical leakage current measurements and to determine a change of electrical leakage current or a change of dissipation factor associated with the stator windings of the AC motor by comparing the existing electrical line voltage and electrical leakage current measurements to the historical record of electrical line voltage and electrical leakage current measurements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0008]      FIG. 1  is a block diagram of an embodiment of a industrial machine and control system including a controller, in accordance with present embodiments; 
           [0009]      FIG. 2  is a block diagram of an embodiment of the controller of  FIG. 1  including an I/O module and a carrier module, in accordance with present embodiments; 
           [0010]      FIG. 3  is a detailed block diagram of the carrier module of the controller of  FIG. 1 , in accordance with present embodiments; and 
           [0011]      FIG. 4  is a series of plot diagrams illustrating detectable electrical voltage and electrical leakage current signals associated with the industrial machine of  FIG. 1 , in accordance with present embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0013]    When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0014]    Present embodiments relate to a control system useful for monitoring stator winding capacitive and/or resistive leakage currents, and for preventing these monitored leakage currents from contributing to damage (e.g., mechanical damage, thermal damage, and so forth) to the stator windings or other components of an electric motor or other synchronous and/or asynchronous machines. The control system may receive leakage current inputs via a number of high sensitivity current transformers (HSCTs), voltage inputs via a number of high voltage sensors (HVSs), and/or temperature inputs from temperature sensors, all of which may continuously (or selectively) monitor the stator windings. The present embodiments may also provide for improved processing and filtering techniques, which may allow for more efficient control and monitoring of the leakage currents on the stator windings of, for example, an electric motor. For example, in certain embodiments, the leakage current inputs and voltage inputs received by the control system may be paired together to offset certain variations (e.g., frequency harmonics, frequency and/or phase distortions, and so forth) that may be otherwise present in the received leakage current and voltage inputs. Similarly, in certain embodiments, the control system may include an internal memory (e.g., an on-site and/or on-board storage or database) that may be used to store a historical record of the operating parameters (e.g., leakage current inputs, voltage inputs, temperature inputs, and so forth), which may be utilized to provide for improved response time in detecting the leakage currents and performing control actions to preclude the possibly damaging effects of the leakage currents. The control system may also directly receive the input line frequency of the stator windings, which may be used as an indicator in determining the presence of leakage currents. 
         [0015]    With the foregoing in mind, it may be useful to describe an industrial machine and control system, such as an example industrial machine and control system  10  illustrated in  FIG. 1 . As depicted, the system  10  may include an industrial machine  12  including a number of stator windings  14 , a number of leakage current sensors  16 ,  18 , and  20 , and a number of voltage sensors  22 ,  24 , and  25  all communicatively coupled to a controller  26 . The industrial machine  12  may be any single or multi-phase synchronous and/or asynchronous machine useful in converting an electrical power input into a mechanical output to drive another system or device. For example, in certain embodiments, the industrial machine  12  may be a single or multi-phase electric motor, or in other embodiments, a generator. Thus, as illustrated, the industrial machine  12  may include the stator windings  14 . As it may be appreciated, the stator windings  14  may include single or multi-phase conductors (e.g., phases a, b, c) that may be coiled around an iron magnetic core to form magnetic poles when energized with an electrical current. Although not illustrated, it should be appreciated that the magnetic field generated by the windings of the stator windings  14  may rotate a drive shaft. 
         [0016]    As previously noted, a number of leakage current sensors  16 ,  18 , and  20  may be communicatively coupled to each of three-phases (e.g., phases a, b, c) of the stator windings  14 , and by extension, the machine  12 . In certain embodiments, the leakage current sensors  16 ,  18 , and  20  may include, for example, high sensitivity current transformers (HSCTs), other current transformers (CTs), or any devices that output a signal (e.g., AC/DC voltage or current) proportional to a detected electrical current flowing through the electrically and/or communicatively coupled phase conductors  27 . As also illustrated, a number of voltage sensors  22 ,  24 , and  25  may be communicatively coupled to each of the three-phases (e.g., phases a, b, c) of the stator windings  14 , and by extension, the machine  12 . The voltage sensors  22 ,  24 , and  25  may include, for example, any of various high voltage sensors (HVSs) (e.g., high voltage dividers) useful in producing a voltage proportional to a detected voltage on the three-phase conductors  27 . 
         [0017]    In certain embodiments, the leakage current sensors  16 ,  18 , and  20  may be communicatively coupled to corresponding leakage current sensor interface modules  28 ,  30 , and  32  corresponding to each of the three-phase conductors  27  (e.g., phases a, b, c) of the stator windings  14 . The leakage current sensor interface modules  28 ,  30 , and  32  may be useful in processing the outputs of the leakage current sensors  16 ,  18 , and  20  (e.g., on-site), and subsequently delivering the leakage current sensor outputs to the controller  26 . Similarly, the voltage sensors  22 ,  24 , and  25  may be communicatively coupled to corresponding voltage sensor interface modules  34 ,  35 , and  36  corresponding to the three-phase conductors  27  (e.g., phases a, b, c) of the stator windings  14 . The voltage sensor interface modules  34 ,  35 , and  36  may be useful in processing the outputs of the voltage sensors  22 ,  24 , and  25  (e.g., on-site), and subsequently delivering the voltage sensor outputs to the controller  26 . 
         [0018]    In certain embodiments, the controller  26  may be suitable for generating and implementing various control algorithms and techniques to control the current and/or voltage of the stator windings  14 , and by extension, the output (e.g., speed, torque, frequency, and so forth) of the machine  12 . The controller  26  may also provide an operator interface through which an engineer or technician may monitor the components of the system  10  such as, components (e.g., leakage current sensors  16 ,  18 , and  20  and voltage sensors  22 ,  24 , and  25 ) of the machine  12 . Accordingly, as will be further appreciated, the controller  26  may include one or more processors  37  that may be used in processing readable and executable computer instructions, and a memory  39  that may be used to store the readable and executable computer instructions and other data. These instructions may be encoded in programs stored in tangible non-transitory computer-readable medium such as the memory  39  and/or other storage of the controller  26 . Furthermore, the one or more processors  37  and memory  39  may allow the controller  26  to be programmably retrofitted with the instructions to carry out one or more of the presently disclosed techniques without the need to include, for example, additional hardware components. 
         [0019]    In certain embodiments, the controller  26  may also host various industrial control software, such as a human-machine interface (HMI) software, a manufacturing execution system (MES), a distributed control system (DCS), and/or a supervisor control and data acquisition (SCADA) system. For example, in one embodiment, the controller  26  may be a Motor Stator Insulation Monitor (MSIM)™ available from General Electric Co., of Schenectady, N.Y. Thus, the control system may be a standalone control system, or one of several control and/or monitoring systems useful in monitoring and regulating the various operating parameters of the machine  12 . As will be further appreciated, the controller  26  may be used to monitor leakage currents I a,l , I b,l , and I c,l  and/or dissipation factor (DF) that may be associated with the three-phase (e.g., phases a, b, c) stator windings  14 . Specifically, leakage currents I a,l , I b,l , and I c,l  may appear in one or more phases of the stator windings  14  in the forms of capacitive leakage currents or resistive leakage currents. The total leakage current (e.g., the sum the capacitive leakage currents and the resistive leakage currents) may possibly cause mechanical damage or thermal damage to the stator windings  14  if left to persist. 
         [0020]    Turning now to  FIG. 2 , a block diagram of an embodiment of the controller  26  is illustrated. As depicted, the controller  26  may include an input-output (I/O) module  38  and a carrier module  40 . In certain embodiments, the I/O module  38  may include a number of current I/O ports  42 ,  44 , and  46  (e.g., for receiving the outputs of the leakage current sensors  16 ,  18 , and  20  from the leakage current sensor interface modules  28 ,  30 , and  32 ), a number of voltage I/O ports  48 ,  50 , and  52  (e.g., for receiving the outputs of the voltage sensors  22 ,  24 , and  25  from the voltage sensor interface modules  34 ,  35 , and  36 ), and a number of temperature I/O ports  54 ,  56 , and  58 . Temperature outputs may be received from one or more resistance temperature detectors (RTDs), thermocouples, or other temperature sensors that may be communicatively coupled to the stator windings  14  for detecting the temperature associated with the stator windings  14 . 
         [0021]    As further depicted by  FIG. 2 , the three-phase leakage current signals (e.g., leakage current I a,l , leakage current I b,l , and leakage current I c,l ,), three-phase voltage signals (e.g., voltage V a , voltage V b , and voltage V c ,), and temperature signals (e.g., temperature a , temperature b , and temperature c ) may be transmitted to the carrier module  40 . As previously noted, the three-phase current signals, voltage signals, and temperature signals may be used by the controller  26  to detect capacitive and resistive leakage currents of the stator (e.g., I a,l , I b,l , I c,l ) and/or a change in dissipation factor that may become present on one or more phases of the stator windings  14  of the machine  12 . In certain embodiments, the carrier module  40  may include various configurations useful in facilitating the processing and/or filtering of the three-phase current signals, voltage signals, and temperature signals received at the respective I/O ports  42 - 58  of the I/O module  38 . 
         [0022]    For example, in certain embodiments, the carrier module  40  may include a matched input pair multiplexer (mux) block  60 . The matched input pair mux block  60  may be any circuitry (e.g., hardware) or other system (e.g., software system or data selector) useful in selecting between a number of analog and/or digital input signals (e.g., current signals, voltage signals, and temperature signals) and outputting the selected signals. Specifically, in certain embodiments, as discussed herein, the matched input pair mux block  60  may be used to match or pair each current signal (e.g., leakage currents I a,l , I b,l , and I c,l ) with the corresponding the voltage signal (e.g., voltage V a , voltage V b , and voltage V c ,) for each of the three phases of the stator windings  14  of the machine  12 . For example, as illustrated in  FIG. 2 , leakage current I a,l  received at the I/O port  42  may be matched and/or paired with the corresponding phase voltage V a  received at the I/O port  48 . Similarly, the leakage current I b,l  received at the I/O port  44  may be matched and/or paired with the corresponding phase voltage V b  received at the I/O port  50 , and so forth. Specifically, because the current and the voltage of each phase of the stator windings  14 , for example, may be interdependent, pairing the current and voltage inputs may offset any variations (e.g., frequency harmonics, frequency and/or phase distortions, and so forth) in the current and voltage signals. In this manner, the controller  26  may detect leakage currents and/or variations in dissipation factor on the stator windings  14  of the machine  12  with a higher degree of certainty since variations that may otherwise be present between the current inputs and the voltage inputs may be substantially reduced. Thus, any significant variations in the operating currents and/or voltages on one or more phases of the stator windings  14  may be indicative of leakage currents (e.g., capacitive and/or resistive leakage currents) and/or change in dissipation factor. 
         [0023]    In certain embodiments, at least one of the three voltage phases (e.g., phase voltage V a ) may be input directly to a line frequency conditioning block  64 , while the temperature signals (e.g., temperature a , temperature b , and temperature c ) may be input to a temperature conditioning block  62  to condition temperature signals for performing temperature compensation in the PCM  66 . The line frequency conditioning block  64  may be a hardware system (e.g., microcontroller or other processor), software system, or any combination thereof, useful in detecting the line frequency or input frequency (e.g., 50-60 Hz or similar frequency rating) of one or more of the three-phase conductors  27  (e.g., phases a, b, and c). Specifically, as illustrated in  FIG. 2 , the three-phase voltage signal V a , for example, may be sampled directly to determine input frequency and/or phase, which may provide further indication of leakage currents (e.g., capacitive and/or resistive leakage currents) and/or dissipation factor on the stator windings  14  of the machine  12 . In particular, by filtering the direct input line frequency received at the line frequency conditioning block  64 , the controller  26  may be able to determine input line frequency more accurately and provide for improved response time that may be otherwise unavailable using less advanced techniques such as a phase lock loop (PLL). 
         [0024]    In certain embodiments, the matched input pair mux block  60  and the line frequency conditioning block  64  may transmit the paired leakage current and voltage output signals and the input line frequency to a sensor portable core module (PCM)  66  for processing and routing. The PCM  66  may include an internal processor  68  and an internal memory  70 . The internal processor  68  may be a general purpose processor, system-on-chip (SoC) device, or some other processor configuration that may be useful in sampling and/or calculating the three-phase current signals (e.g., leakage current I a,l , leakage current I b,l , and leakage current I c,l ,), three-phase voltage signals (e.g., voltage V a , voltage V b , and voltage V c ,), and temperature signals (e.g., temperature a , temperature b , and temperature c ) transmitted to the carrier module  40 . In certain embodiments, the internal memory  70  may be an on-board memory among other memory devices that may be included within the controller  26 . Specifically, the internal memory  70  may be used to store a historical record of data collected for detecting leakage currents (e.g., capacitive and/or resistive leakage currents) and/or dissipation factor on the stator windings  14  of the machine  12 . 
         [0025]    In certain embodiments, the internal processor  68  of the controller  26  may use the historical data stored by the internal memory  70  to perform probabilistic and statistical techniques such as regression analysis (e.g., linear regression, non-linear regression, ridge regression), data mining, trend estimation, and/or other similar techniques to measure trends in the three-phase current signals (e.g., leakage current I a,l , leakage current I b,l , and leakage current I c,l ,), three-phase voltage signals (e.g., voltage V a , voltage V b , and voltage V c ), and temperature signals (e.g., temperature a , temperature b , and temperature c ). In some embodiments, the controller  26 , for example, via the internal processor  68 , may compare the three-phase current signals (e.g., leakage current I a,l , leakage current I b,l , and leakage current I c,l ) to the historical data (e.g., leakage current measurements) collected over some time interval (e.g., less than approximately 1 day, less than approximately 1 week, less than approximately 1 month, less than approximately 1 year, less than approximately 2 years, less than approximately 5 years, less than approximately 10 years, less than approximately 20 years, less than approximately 30 years, or less than approximately 35 years). In certain embodiments, the time interval may be fixed or user-configurable, and thus may be adjusted, for example, by an operator or engineer. It should be appreciated that the historical comparisons may be executed directly in the controller  26  since the historical measurement data may be stored to, for example, the internal memory  70 . Specifically, by providing the internal memory  70  (e.g., on-board memory and/or on-site storage or database), the internal processor  68  may access the historical data more quickly and determine faults, leakage currents (e.g., capacitive and/or resistive leakage currents), dissipation factor, and/or other anomalies more efficiently, thus allowing the controller  26  to respond to such faults or detections of leakage currents associated with substantially improved response times. 
         [0026]    Turning now to  FIG. 3 , which provides a more detailed illustration of the carrier module  40 . As depicted, the matched input pair mux block  60  (also illustrated in  FIG. 2 ) may include input pins A 0 -A 7  and B 0 -B 7  for receiving the paired voltage signals (e.g., voltage V a , voltage V b , and voltage V c ) and current signals (e.g., leakage current I a,l , leakage current I b,l , and leakage current I c,l ). As further illustrated, and also previously noted with respect to  FIG. 2 , the paired voltage signals and leakage current signals may be output via output pins A_OUT and B_OUT to analog-to-digital converters (ADCs)  72 , and then to the internal processor  68  for processing and further routing. In certain embodiments, one of the phase voltages (e.g., V c ) may be calculated based on the phase voltages V a  and V b . For example, should the machine  12  be configured in a three-phase balanced configuration, the phase voltages V a , V b , and V c , may generally be of equal magnitude separated by a phase difference of approximately 120°. Thus, the phase voltage V c  may be calculated via generated V c -block  73  based on the inputs of the phase voltage V a  and V b  inputs. In other embodiments, phase voltage V c  may be calculated by computing a vector sum of the phase voltages V a  and V b . In this way, the controller  26  may determine the phase voltages V a , V b , and V c  using, for example, only two actual voltage sensors  22  and  24  (e.g., as opposed to one voltage sensor  22 ,  24 , and  25  for each phase), which may contribute to reduced system complexity. In other embodiments, methods to process the voltage and leakage current signals may include using one line voltage signal (e.g., V a ) and adding phase adjustments associated with each current signal (e.g., leakage current I a,l , leakage current I b,l , and leakage current I c,l ,). Yet still, in another embodiment, a method to process the voltage and leakage current signals may include capturing each signal and performing one or more post processing techniques according to any user-desired configuration and/or combination. 
         [0027]    In certain embodiments, as further illustrated in  FIG. 3 , additional line frequency conditioning blocks  64  may be provided to the internal processor  68 . The additional line frequency conditioning blocks  64  may be based on the current signals (e.g., leakage current I a,l , leakage current I b,l , and leakage current I c,l ,) and voltage signals (e.g., voltage V a , voltage V b , and voltage V c ,). As noted above with respect to  FIG. 2 , the controller  26  may perform stator winding capacitive and resistive leakage current measurements by calculating the phase and magnitude of leakage current (e.g., I a,l ), which may be derived by the internal processor  68  based on the direct input line frequency inputs received by way of the line frequency conditioning blocks  64 . 
         [0028]    As an example illustration,  FIG. 4  depicts a voltage input plot  74  (e.g., AC voltage signal  80 ), a three-phase current input plot  76  (e.g., leakage current signals  82 ,  84 , and  86 ), and a leakage current-voltage (I-V) plot  78  (e.g., AC voltage signal  80  and leakage current signal  88 ). It should be appreciated that the voltage signal  80  of plot  74  may be a representation of one of the phase voltages V a , V b , and V c . Similarly, the total leakage current signal  88  of plot  78  may be a represention of one of the leakage currents I a,l , I b,l , and I e,l  of plot  76 . The plot  78  illustrates the phase angle  90  between the voltage input signal  80  and the leakage current input signal  88 . The phase angle  90  may be used to derive the capacitive and/or resistive leakage currents that may be present on the stator windings  14  of the machine  12 . As previously noted, in this way, the controller  26  may be able to determine input line frequency and/or phase more accurately and improve response time, all of which may be otherwise unavailable using a phase lock loop (PLL). 
         [0029]    Technical effects of the present embodiments relate to a control system useful for monitoring stator winding capacitive and resistive leakage currents and to prevent the leakage currents from contributing to damage (e.g., mechanical damage, thermal damage, and so forth) to the stator windings or other components of an electric motor or other synchronous and/or asynchronous machines. The control system may receive leakage current inputs via a number of high sensitivity current transformers (HSCTs), voltage inputs via a number of high voltage sensors (HVSs), and temperature inputs from temperature sensors, all of which monitor the stator windings. The present embodiments may also provide for improved processing and filtering techniques, and thus more efficient control and monitoring of the leakage currents of the stator windings of, for example, an electric motor. For example, in certain embodiments, the leakage current inputs and voltage inputs may be paired together to offset certain variations (e.g., frequency harmonics, frequency and/or phase distortions, and so forth) that may be otherwise present in the leakage current and voltage inputs. Similarly, in certain embodiments, the control system may include an internal memory (e.g., an on-site and/or on-board storage or database) that be used to store a historical record of the operating parameters (e.g., leakage current, voltage, temperature, and so forth), which may provide for improved response time in detecting the leakage currents and performing control actions to preclude possibly damaging effects of the leakage currents. The control system may also directly receive the input line frequency of the stator windings, which may be used to calculate leakage current measurements. 
         [0030]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.