Patent Application
20170160301
(None)
This disclosure relates to the monitoring of rotating machinery. More particularly, this disclosure relates to monitoring a rotational characteristic of a rotating shaft such as rotational speed and angular position using an accelerometer fixed to the rotating shaft.
Non-limiting and non-exhaustive embodiments of the disclosure are described, including various embodiments of the disclosure with reference to the figures, in which:
Several different types of rotating machinery are used throughout industry and utilities. For the most part, electric power is generated by rotating a rotor in a stator using a prime mover connected to the rotor by a rotating shaft. Motors use electric power to produce mechanical power delivered by a rotating shaft. It has been estimated that around 45% of the electric power generated globally is used by electric motors. Monitoring and maintenance of electric power generators and electric motors helps to prolong the lifetimes of the equipment and make efficient use of such rotating machinery.
Intelligent electronic devices (“IEDs”) are often used to monitor and control electric power generators and electric motors. IEDs may receive inputs from electric power generators and electric motors such as, for example, signals from the electric power provided to a motor, signals from the electric power produced by a generator, signals from rotors and/or stator of motors or generators, and the like. IEDs may monitor such equipment using the electrical signals. IEDs may also receive inputs from other sensors to monitor such rotating equipment. For example, a speed switch may be used to output a signal that a shaft is rotating. A rotation monitor may be used to output a signal related to a rotational speed and/or position of a rotating shaft. Rotation monitors typically require an encoder mounted to the rotating shaft and a reader (such as an optical reader) configured to read the encoder. Such rotation monitors are bound in accuracy by the granularity of the pattern of the shaft-mounted encoder, and require a specialized reader. Such encoders must be specifically configured for the particular shaft (e.g. size and clearance) to be monitored. Further, the encoder must be carefully aligned with the reader. Rotation of a rotating shaft may also be monitored using a toothed wheel apparatus mounted to the rotating shaft. Rotation of the toothed wheel mounted to the rotating shaft may be monitored using a reader. As with the system of an encoder and reader, the toothed wheel system must be particularly designed for the rotating shaft, and requires alignment of the reader with the toothed wheel.
Disclosed herein are apparatuses and systems for monitoring a rotating shaft using a shaft-mounted accelerometer. The apparatuses and systems may calculate a rotational speed of the rotating shaft and/or an angular position of the rotating shaft. The embodiments of the disclosure will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the disclosed embodiments, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the systems and methods of the disclosure is not intended to limit the scope of the disclosure, as claimed, but is merely representative of possible embodiments of the disclosure. In addition, the steps of a method do not necessarily need to be executed in any specific order, or even sequentially, nor need the steps be executed only once, unless otherwise specified.
In some cases, well-known features, structures or operations are not shown or described in detail. Furthermore, the described features, structures, or operations may be combined in any suitable manner in one or more embodiments. It will also be readily understood that the components of the embodiments as generally described and illustrated in the figures herein could be arranged and designed in a wide variety of different configurations.
Several aspects of the embodiments described may be implemented as software modules or components. As used herein, a software module or component may include any type of computer instruction or computer executable code located within a memory device and/or transmitted as electronic signals over a system bus or wired or wireless network. A software module or component may, for instance, comprise one or more physical or logical blocks of computer instructions, which may be organized as a routine, program, object, component, data structure, etc., that performs one or more tasks or implements particular abstract data types.
In certain embodiments, a particular software module or component may comprise disparate instructions stored in different locations of a memory device, which together implement the described functionality of the module. Indeed, a module or component may comprise a single instruction or many instructions, and may be distributed over several different code segments, among different programs, and across several memory devices. Some embodiments may be practiced in a distributed computing environment where tasks are performed by a remote processing device linked through a communications network. In a distributed computing environment, software modules or components may be located in local and/or remote memory storage devices. In addition, data being tied or rendered together in a database record may be resident in the same memory device, or across several memory devices, and may be linked together in fields of a record in a database across a network.
Embodiments may be provided as a computer program product including a non-transitory computer and/or machine-readable medium having stored thereon instructions that may be used to program a computer (or other electronic device) to perform processes described herein. For example, a non-transitory computer-readable medium may store instructions that, when executed by a processor of a computer system, cause the processor to perform certain methods disclosed herein. The non-transitory computer-readable medium may include, but is not limited to, hard drives, floppy diskettes, optical disks, CD-ROMs, DVD-ROMs, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, solid-state memory devices, or other types of machine-readable media suitable for storing electronic and/or processor executable instructions.
IED 120 is configured to monitor and protect the motor. IED 120 may receive measurements of the electric power delivered to the motor 104 by the electric power delivery system 140 using, for example, current transformers (CTs) to monitor electrical current to the motor 104, potential transformers (PTs) to monitor the voltage of the electrical power to the motor 104, and the like. The IED 120 may be configured to disconnect power to the electric motor 104 under certain conditions. For example, during startup, if the IED 120 detects that the motor is receiving electric power but is not turning the rotating shaft (a “locked rotor” condition), the IED 120 may be configured to disconnect electric power to the motor 104 by, for example, signaling a circuit breaker (not separately illustrated) to open. Many operating conditions of the electric motor 104 may be monitored using the current and/or voltage signals from the electric power supplied to the motor 104 including, for example locked rotor conditions, overcurrent, arc flash, thermal conditions, broken bar, efficiency, and the like.
IED 120 may include various inputs for accepting signals related to the operation of the electric motor 104. For example, IED 120 may be configured to directly monitor a temperature, and thus include an input for receiving a signal related to a temperature. A signal related to the temperature may be provided by a thermocouple in proximity with the equipment to be monitored and in electrical communication with the IED 120 to provide the signal thereto. The IED 120 may include an input for receiving a signal related to the rotational speed and/or angular position of the rotating shaft 100 as described above, such may be from a speed switch, encoder/reader, toothed wheel and reader, or the like.
In the illustrated embodiment, a signal corresponding with the rotation of the rotating shaft may be provided by a wireless access point 110 in wireless communication with a shaft-mounted sensor 102. The shaft-mounted sensor 102 may be configured to provide a signal wirelessly to the wireless access point 110 related to the rotational speed and/or angular position of the rotating shaft 100. As will be described in more detail below, the shaft-mounted sensor 102 may include an accelerometer, a power supply, and a wireless transmitter to wirelessly provide a signal related to an acceleration of the rotating shaft. The acceleration may be related to a radial acceleration of the rotating shaft, a tangential acceleration of the rotating shaft or the like. The acceleration may be related to an acceleration due to gravity. The acceleration may be related to a combination of a radial and/or tangential acceleration from the rotation of the rotating shaft and an acceleration due to gravity. The shaft-mounted sensor 102 may be configured to wirelessly transmit one or more signals related to the detected acceleration to the wireless access point 110.
The wireless access point 110 may be in communication with the IED 120 to provide the one or more signals from the shaft-mounted sensor 102 to the IED 120. The IED 120 may then calculate certain rotational components of the rotating shaft from the one or more signals from the shaft-mounted sensor. For example, the IED 120 may be configured to calculate a rotational speed of the rotating shaft 100 using a signal related to the acceleration from the shaft-mounted sensor 102 due to the rotation of the rotating shaft 100 and a distance from the center of the rotating shaft to the shaft-mounted sensor. In another embodiment, the IED 120 may be configured to calculate an angular position of the rotating shaft using a signal related to the acceleration due to gravity detected by the shaft-mounted sensor 102.
The wireless access point 110 may further be in communication with a monitoring system 130. The monitoring system 130 may be a local or remote computing device, an access controller, a programmable logic controller, a Supervisory Control and Data Acquisition (“SCADA”) system, or the like. The monitoring system 130 may similarly be configured to receive the signals originating from the shaft-mounted sensor 102 and calculating rotational components of the rotating shaft 100 from the signals. For example, the monitoring system 130 may be configured to calculate a rotational speed, angular position, or the like, of the rotating shaft 100 using the signals.
IED 120 may be configured to separate the generator 204 from the electric power delivery system 140 upon detection of certain operating conditions of the generator 204 by, for example, opening a circuit breaker connecting the generator 204 to the electric power delivery system 140. IED 120 may further be configured to control the prime mover 206 in response to conditions detected from the output of the generator 204. For example, the prime mover 206 may be a diesel engine, and the IED may be configured to maintain a certain output of the generator by controlling the fuel provided to the diesel engine.
Although not separately described above, several operating conditions of rotating equipment may be monitored by IEDs. For example, generator protection IEDs may monitor and control for over/under speed protection, power output, frequency, stator or rotor faults, brush liftoff, and the like.
Although specifically described in conjunction with the monitoring of rotating shafts of generators and motors, embodiments described herein may be used to monitor the rotational speed and/or angle of any rotating shaft. In various embodiments, the rotating shaft may be a rotating shaft of a motor, a generator, a transmission shaft, a drive shaft, an axle, a crankshaft, or the like.
Furthermore, it should be noted that the wireless access point 110 illustrated in
In several embodiments described herein, the shaft-mounted sensor 102 may be configured to wirelessly transmit signals according to an established protocol such as, for example, WiFi, Bluetooth, Zigbee, or the like. In such an embodiment, the IED 120 may include a wireless interface to wirelessly communicate with the shaft-mounted sensor 102. Furthermore, the IED 120 may include a standardized input that may receive a wireless interface for receiving the wireless communications from the shaft-mounted sensor 102. For example, the IED 120 may include a serial port or a USB port, and the wireless interface may include a Bluetooth-to-serial converter such as, for example, the SEL-2925 Bluetooth Serial Adapter available from Schweitzer Engineering Laboratories, Inc. of Pullman, Wash., USA. The wireless interface may receive the wireless transmissions from the shaft-mounted sensor 102 and provide such signals to the IED 120. Alternatively, the IED may include an integrated wireless interface for communication with the shaft-mounted sensor 102.
The accelerometer 302 may be configured to detect an acceleration and provide a signal corresponding to the detected acceleration for use by the processor 308 and/or transmitted by the wireless transmitter 306. The processor 308 may be configured to control the accelerometer 302 and the wireless transmitter 306. The wireless transmitter 306 may be configured to transmit a signal related to the output of the accelerometer 302, communications from the processor 308, and the like. The wireless transmitter 306 may include or be in communication with an antenna device 314 for wireless transmission of the signal. The wireless transmitter 306, as has been described above, may be configured to transmit a signal according to a predetermined protocol such as, for example, Wi-Fi, Bluetooth, Zigbee, or the like.
The accelerometer 302 may operate according to piezoelectric, piezoresistive, capacitive principles or the like, including combinations thereof. The accelerometer 302 may be a MEMS accelerometer. The accelerometer 302 may be configured to measure accelerations of up to around ±3000 g.
The shaft-mounted sensor 102 may be mounted to the shaft 100 using one or more of various attachment means. In one embodiment, the shaft-mounted sensor 102 may be fixed to the shaft 100 using an adhesive between the shaft 100 and the shaft-mounted sensor 102. In another embodiment, the shaft-mounted sensor 102 may be fixed to the shaft 100 using a mechanical clamping mechanism. In other embodiments, the shaft-mounted sensor 102 may be fixed to the shaft 100 using more than one mounting techniques such as an adhesive and a mechanical clamping mechanism.
The shaft-mounted sensor as illustrated and described herein may be used to provide a signal related to the acceleration measured by the accelerometer 302. Such a signal may be used by an IED or a monitoring system to calculate a rotational speed and/or angular position of the rotating shaft as described herein. In other embodiments, the processor 308 may use the signal from the accelerometer to calculate a rotational speed and/or angular position of the rotating shaft as described herein. In such embodiments, the processor may be pre-set or programmable with the radius of the rotating shaft. The processor may be configured to transmit the calculated rotational speed and/or angular position using the wireless transmitter.
In still other embodiments, the processor may be configured to compare the calculated rotational speed with a predetermined threshold. The processor may be pre-set or programmable with the predetermined threshold. In such embodiments, the processor may be configured to cause the wireless transmitter to transmit a message when the predetermined threshold is crossed. In one particular embodiment, the shaft-mounted sensor may be configured to transmit a speed sensor message once the calculated rotational speed reaches a predetermined threshold. The IED or other monitoring system may be configured to interrupt operation of the rotating machinery if the speed switch message is not received within a predetermined time from starting the rotating machinery. In other embodiments, the threshold may be set above a nominal operating condition of the rotating machinery. The processor may be configured to cause the wireless transmitter to transmit a message indicating that the rotational speed of the shaft has exceeded the threshold. The IED or other monitoring system may use such message in protection and monitoring of the rotating machinery.
According to the embodiment illustrated in
where:
The embodiment illustrated in conjunction with
The measured acceleration as illustrated in
In some embodiments the rotational speed of the rotating shaft may be calculated using a period of the periodic waveform from the measured acceleration 554. A time between positive peaks (or negative peaks) may be measured to determine a period of the periodic waveform. The inverse of the period is a frequency of the periodic waveform, and hence a frequency of the rotating shaft in revolutions per second. Such frequency can be used to determine the rotational speed in the desired units such as, for example, revolutions per second, revolutions per minute, radians per second, or the like.
In embodiments where the rotating shaft is configured with its axis in the horizontal, the acceleration due to gravity will be −1 g, and the amplitude of the waveform of the measured acceleration 554 will be 1 g. For example, the amplitude of the measured acceleration 606 illustrated in
In embodiments where the measured acceleration includes a component due to the acceleration of gravity such as where the rotating shaft is in a non-vertical orientation, an angular position of the rotating shaft may be calculated. That is, where the shaft is configured with its axis not in the vertical, the measured acceleration will be a periodic waveform with an offset related to the rotational speed of the rotating shaft, an amplitude related to the orientation of the shaft from horizontal to vertical, and a periodicity that can be used to calculate an angular position of the rotating shaft. For example, a difference between the measured acceleration and the average acceleration can be normalized by the amplitude of the waveform, and used to calculate the angular position in radians or degrees. Such calculation may be expressed as Equation 4:
where:
The angular position of the rotating shaft 100 may be calculated during operation and at standstill using the measured tangential acceleration 704 and measured radial acceleration 554. The angular position a of the rotating shaft can be calculated using the measured tangential acceleration 704 and a difference 710 between the measured radial acceleration 554 and the radial acceleration due to the rotation of the shaft, which may be approximated using an average radial acceleration. As discussed above, any of several methods may be used to calculate the average radial acceleration such as, for example, use of a low-pass filter. The angular position a of the rotating shaft may be calculated using Equation 5:
where:
In certain embodiments the angular position of the rotating shaft may be used to calculate the rotational speed of the rotating shaft. The angular position of the rotating shaft may be calculated according to any of the embodiments described herein. To calculate the rotational speed of the rotating shaft, the difference in angular position with respect to time may be calculated using, for example, Equation 6.
where:
In one embodiment, the processor of the shaft-mounted sensor is configured to calculate the rotational speed of the shaft using the angular position of the rotating shaft. In other embodiments an IED may be configured to calculate the rotational speed of the shaft using the angular position of the rotating shaft.
Rotating shafts of rotating machinery in industry and utility are configured in a wide array of diameters and nominal rotational speeds. The radial acceleration to be measured by a shaft mounted accelerometer according to the various embodiments herein is a function of the rotational speed of the rotating shaft and the distance from the center of the rotating shaft to the acceleration sensing component of the shaft-mounted accelerometer. Thus, accelerometers according to the various embodiments herein may be used to measure a wide range of acceleration. Table 1 shows several different radial acceleration values that may be measured by accelerometers on shafts of different radii and at different rotational speeds:
The useful range of accelerometers used to measure radial acceleration on a rotating shaft may be extended according to several embodiments herein. An accelerometer of a shaft-mounted sensor according to embodiments such as is illustrated in
In certain embodiments, the accelerometer may be oriented within the shaft-mounted sensor such that an axis of the accelerometer is oriented at a known angle from collinear with the radius of the rotating shaft. The shaft-mounted sensor may be configured to use the known angle in its calculation of the acceleration by multiplying the acceleration from the accelerometer by the range extension factor to yield the measured acceleration.
While specific embodiments and applications of the disclosure have been illustrated and described, it is to be understood that the disclosure is not limited to the precise configurations and components disclosed herein. For example, the systems and methods described herein may be applied to an industrial electric power delivery system or an electric power delivery system implemented in a boat or oil platform that may not include long-distance transmission of high-voltage power. Moreover, principles described herein may also be utilized for protecting an electric system from over-frequency conditions, wherein power generation would be shed rather than load to reduce effects on the system. Accordingly, many changes may be made to the details of the above-described embodiments without departing from the underlying principles of this disclosure. The scope of the present invention should, therefore, be determined only by the following claims.
