AU2017100471B4 - A condition monitoring device for monitoring an electric machine - Google Patents

Abstract

A CONDITION MONITORING DEVICE FOR MONITORING AN ELECTRIC MACHINE In aspects, the present invention discloses a condition monitoring device comprising a plurality of sensors including at least one magnetic field measuring unit for measuring a first value of magnetic field strength along a first axis substantially parallel to the axis of the rotor of an electric machine and a second value of magnetic field strength along a second axis, at least one vibration sensor, for measuring a first value of vibration along the first axis and a second value of vibration along the second axis, a temperature sensor, for measuring a temperature of an area proximal to the electrical machine; and an acoustic sensor, for measuring sound around the electrical machine. The condition monitoring device further includes one or more processors configured to receive measurements from the plurality of sensors and determine the condition of the electrical machine based on the received measurements.

Description

2017100471 28 Apr 2017 1 A CONDITION MONITORING DEVICE FOR MONITORING AN ELECTRIC MACHINE Technical Field [0001] The current invention relates to the field of condition monitoring of electric machines, and more particularly, the current invention relates to detection and determination of faults in a motor using condition monitoring device having a plurality of sensors.

Background Art [0002] Conventionally, assessment of status and detection of faults in a motor is done using a plurality of diagnostic devices and techniques have been developed so far. Among them, the most widely used in industry are vibration monitoring and current signature analysis.

[0003] The above mentioned methods rely on measurement of motor current and vibration for detecting faults in the motor. The above mentioned methods, for carrying out measurements, require sensors and other equipment which are often cumbersome to install, and are expensive. Moreover, the current and voltage sensors have to be installed inside terminal box of the motor, which is often time consuming and requires the motor to be shut down. Further, improper installation of sensors can result in damage to the motor, faulty monitoring or can cause safety concerns.

[0004] Therefore, in light of the above discussion, there is a need for a condition monitoring device that solves the problems mentioned above. 2017100471 28 Apr 2017 2

Summary of the Invention [0005] The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification.

[0006] In one aspect, the present invention discloses a condition monitoring device for monitoring and assessing a condition of an electrical machine. The condition monitoring device comprises a housing body capable of being affixed to a body of the electrical machine. The housing body houses a plurality of sensors including at least one magnetic field measuring unit, at least one vibration sensor, an acoustic sensor and a temperature sensor. The magnetic field measuring unit measures a first value of magnetic field strength along a first axis substantially parallel to the axis of the rotor of the electric machine and a second value of magnetic field strength along a second axis. The second axis is at an angle to the first axis.

[0007] The vibration sensor measures at least one of a first value of vibration along the first axis and a second value of vibration along the second axis. The temperature sensor measures a temperature of an area proximal to the electrical machine and an acoustic sensor, for measuring sound around the electrical machine.

[0008] The condition monitoring device includes one or more processors configured to receive measurements from the plurality of sensors, and determine the condition of the electrical machine based on the received measurements. Additionally, the condition monitoring device includes a network interface configured for communication with a remote service device 130.

[0009] In an embodiment the housing body is affixed to the body of the electric machine using an adapter. The housing body is screwed onto the adapter. In another embodiment, the housing body unit further comprises a rod capable of being inserted between two adjacent ribs of the electric machine for press fitting the housing body to the body of the electric machine. In another embodiment, the condition monitoring device includes an energy source, housed in the housing body, for powering the plurality of sensors, the one or more processors, and the network interface. In another embodiment, the condition monitoring device includes an energy harvesting module from harvesting power from at least one of leakage magnetic field of the electric machine, and heat flux of the electric machine. 2017100471 28 Apr 2017 3 [0010] Systems of varying scope are described herein. In addition to the aspects and advantages described in this summary, further aspects and advantages will become apparent by reference to the drawings and with reference to the detailed description that follows.

Brief Description of the Drawings [0011] The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the drawings, in which: [0012] Figure 1 illustrates a motor with a condition monitoring device mounted on the body of the motor, in accordance with various embodiments of the present invention; [0013] Figure 2 illustrates a plurality of mounting configurations for mounting the condition monitoring device on the body of the motor, in accordance with various embodiments of the present invention; [0014] Figure 3 illustrates the various components of the condition monitoring device, in accordance with various embodiments of the present invention; and [0015] Figure 4 illustrates an adaptor affixed to the body of the electric machine, in accordance with various embodiments of the present invention.

Detailed Description [0016] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments, which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the embodiments. The following detailed description is, therefore, not to be taken in a limiting sense.

[0017] Figure 1 illustrates a condition monitoring device 120 for monitoring and assessing a condition of an electrical machine 110 (also referred to as motor 110), mounted on the body of the electrical machine 110. The condition monitoring device 120 comprises a housing body capable of being affixed to a body or shell of the electrical machine 110. 2017100471 28 Apr 2017 4 [0018] The housing body houses a plurality of sensors (shown in figure 3). The plurality of sensors includes a magnetic field measuring unit 330, vibration sensor 340, an acoustic sensor 350, and a temperature sensor 360. The magnetic field measuring unit 330 measures a first value of magnetic field strength along a first axis (illustrated in figure 2 as axis 260) substantially parallel to an axis of the rotor (illustrated in figure 2 as axis 230) of the electric machine 110. Additionally the magnetic field measuring unit 330 measures a second value of magnetic field strength along a second axis (illustrated in the figure as axis 270) at a reference point, wherein the second axis 270 is at an angle to the first axis 260.

[0019] It is to be noted by a person skilled in the art that while current invention discloses a single magnetic field measuring unit for measuring magnetic field strength in two axes, such a magnetic field measuring unit can include two or more magnetic field sensors each for measuring magnetic field strength along one axis. In another embodiment, the magnetic field measuring unit comprises two or more magnetic sensing elements (for example coils) along with a single transmitter. In another embodiment, the magnetic field measuring unit can resolve magnetic field strength in two components along the first and second axis.

[0020] The vibration sensor 340 measures a first value of vibration along the first axis 260 and/ or a second value of vibration along the second axis 270. The temperature sensor 360 measures a temperature of an area proximal to the electrical machine 110.

[0021] The acoustic sensor 350 measure sound around the electrical machine 110, particularly sound around the drive side of the motor 110. To distinguish background noise from noise originating from the motor, particularly the bearing, values relating to frequencies which are not associated with the bearing are filtered out.

[0022] In an embodiment, one or more sensors from the plurality of sensors are digital sensors capable of taking equi-spaced samples at periodic intervals. In another embodiment, the one or more sensors from the plurality of sensors are analog sensors with an integrated analog to digital converter.

[0023] In an embodiment, to ensure that measurements taken are during the running condition of the motor 110, measurement values are compared against predetermined thresholds. Only when the measurements are over the predetermined thresholds, the measurements are recorded. In an 2017100471 28 Apr 2017 5 embodiment, the predetermined thresholds are decided by experimentation. In another embodiment, the predetermined thresholds are determined during installation of the motor.

[0024] In another embodiment, the magnetic field measuring unit 330, acoustic sensor 350 and temperature sensor 360 records and transmits measurement data upon receiving a signal from the vibration sensor 340 or a motor drive indicating that the motor 110 has been started.

[0025] In an embodiment, where the sampling rate of the magnetic field measuring unit 330 is not constant or where the samples from the first and second axes are taken at different sampling periods, interpolation (linear, cubic or spline) is performed, to get an approximately equi-spaced and simultaneous magnetic field data of magnetic field strength from the first and second axes. Upon getting the interpolated continuous magnetic field data of the first and second axes, the magnetic field data is de-trended to remove static background magnetic flux and the drift experienced by the magnetic field measuring units. De-trending is performed using techniques known in the art.

[0026] The condition monitoring device 120 includes one or more processors 320 configured to receive measurements from the plurality of sensors, and determine the condition of the electrical machine 110 based on the received measurements. In an embodiment, the processors 320 periodically acquire measurement data from the plurality of sensors. In an exemplary embodiment, where the electric machine 110 is an induction motor, the processors 320 receive magnetic field data, perform a Fourier transforms on the data received in relation the two axes and checks the unbalance in the amplitude of the slip frequency on the two axes. If the unbalance is above a pre-defined threshold, then a fault is detected.

[0027] In an embodiment, upon detecting a fault, the processors 320 are configured to classify the fault and determine the severity of the detected fault. Continuing exemplary embodiment in relation the magnetic field data, the detected fault is subsequently classified as broken rotor bar or misalignment by checking whether the dominant component is present in the axial or radial magnetic field. The severity of the fault is directly proportional to the amount of unbalance present in the magnetic field at the slip frequency.

[0028] Additionally, the condition monitoring device 120 includes a network interface 370 configured for communication with a remote service device 130 and a memory module 2017100471 28 Apr 2017 6 operatively coupled to the one or more processors 320. The severity of the fault indicator is stored in the memory associated the processors 320 and sent to a remote service device upon request. In an embodiment, the network interface 370 includes an antenna 380 of a particular shape for allowing communication via EM radiation while being in close proximity to metallic surfaces.

[0029] Subsequent to the analysis the one or more processors 320 communicates, via the network interface 370, with a remote service device and a data concentrator to indicate the condition of the electric machine 110. The network interface 370 is capable of communicating over wireless media such as Bluetooth, Wireless HART, etc.

[0030] The data concentrator transmits data regarding condition of the electric machine, received from the condition monitoring device 120 to the historian for remote storage.

[0031] In an embodiment, the housing body is made of plastic or non-ferromagnetic material. When the housing body is made of non-ferromagnetic metallic material, in an embodiment, the housing body includes a non-metallic or plastic window for allowing radiofrequency communication (originating from the network interface) to pass through.

[0032] In an embodiment, an adapter 410 (as shown in figure 4) is provided for affixing the housing body to the body of the motor 110. In an embodiment, the adapter is affixed to the body of the motor 110 using adhesive or clamping mechanisms known in the art. Housing body is affixed to the adapter by screwing the housing body onto the adapter.

[0033] In another embodiment, the housing body unit is affixed to the body of the electric machine 110 using a rod capable of being inserted between two adjacent ribs of the electric machine for press fitting the housing body to the body of the electric machine.

[0034] In an embodiment, the condition monitoring device includes an energy source 310, housed in the housing body, for powering the plurality of sensors, the one or more processors 320, and the network interface 370. By having an energy source 310 inside the condition monitoring device 120 and a wireless network interface 370, need for wires is eliminated. In an embodiment, an energy harvesting module (such as a thermoelectric generator, and the like) is provided for harvesting power from at least one of leakage magnetic field of the electric machine, and thermal energy of the electric machine, for charging the energy source. 2017100471 28 Apr 2017 7 [0035] The whole assembly is geared toward low-cost production, assembly and installation. To make the installation as easy as possible, the device is battery powered to completely eliminate any cabling requirements. Thus continuous low-cost condition monitoring of the motor is achieved.

[0036] In accordance with the current invention, to perform condition monitoring of electric machine 110, the operator simply has to install the condition monitoring device 120 on frame of the electric machine 110, akin to the name plate.

[0037] This written description uses examples to describe the subject matter herein, including the best mode, and also to enable any person skilled in the art to make and use the subject matter. The patentable scope of the subject matter 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 language of the claims.

Claims (5)

1. Claims What is claimed is:

   1. A condition monitoring device (120) for monitoring and assessing a condition of an electrical machine (110), the condition monitoring device (120) comprising: a. a housing body capable of being affixed to a body of the electrical machine (110); b. a plurality of sensors housed within the housing body, the plurality of sensors comprising: i. at least one magnetic field measuring unit (330) for measuring a first value of magnetic field strength along a first axis substantially parallel to the axis of the rotor of the electric machine and a second value of magnetic field strength along a second, axis, wherein the second axis is at an angle to the first axis; ii. at least one vibration sensor (340), for measuring at least one of a first value of vibration along the first axis and a second value of vibration along the second axis; iii. a temperature sensor (360), for measuring a temperature of an area proximal to the electrical machine; and iv. an acoustic sensor (350), for measuring sound around the electrical machine (110); c. one or more processors (320) configured to receive measurements from the plurality of sensors, and determine the condition of the electrical machine (110) based on the received measurements; d. a network interface (370) configured for communication with a remote service device 130; and e. a memory module operatively coupled to the one or more processors.
2. 2. The condition monitoring device (120) as claimed in claim 1, wherein the housing body further comprises a rod capable of being inserted between two adjacent ribs of the electric machine (110) for press fitting the housing body to the body of the electric machine (HO).
3. 3. The condition monitoring device (120) as claimed in claim 1, wherein the housing body is capable of being affixed to an adaptor attached on the body of the electric machine.
4. 4. The condition monitoring device (120) as claimed in claim 1, wherein the condition monitoring device (120) includes an energy source (310), housed in the housing body, for powering the plurality of sensors, the one or more processors (320), and the network interface (370).
5. 5. The condition monitoring device (120) as claimed in claim 1, further comprising an energy harvesting module for harvesting power from at least one of leakage magnetic field of the electric machine (110), and heat flux of the electric machine (110).