GB2484960A

GB2484960A - Smart motor disconnection switch

Info

Publication number: GB2484960A
Application number: GB1018206.1A
Authority: GB
Inventors: Kevin Kitching; Clifford Bradshaw
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-10-28
Filing date: 2010-10-28
Publication date: 2012-05-02
Also published as: GB201118670D0; GB201018206D0; GB2485446A

Abstract

A smart motor disconnection switch (SMDS) isolates electric power supply to an electric motor. Incorporated with the switch unit is a energy management, condition monitoring and diagnostic system including a set of sensors, a processing unit 25, a memory 23 and an output interface 22 for communicating alarms, warnings and calculate operating values to a supervisory computer . The sensors may include a motor vibration sensor mechanically connected to the casing of the motor, electric current and voltage sensors using a current transformer (CT) coil 17 and magnetic flux sensors. The processing unit is connected to the sensors and determines the energy consumption and condition of the motor system such as power consumption, load level, run-hours, over-temperature, over-voltage, phase imbalance, time to next lubrication and excessive vibration. When abnormal conditions are detected, a series of alarms and/or warnings states are automatically communicated to the operating personnel. The supervisory computer may be in communication with a central web-based server and energy reduction techniques may be applied, as well as management of the motor stock.

Description

Smart Motor Disconnection Switch

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangements of parts, preferred embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein: FIGURE 1 is a perspective view of the motor, smart meter and motor power supply cabinet according to the preferred embodiment of the invention; FIGURE 2 is a schematic diagram of the unit i illustrated in FIGURE 1; FIGURE 3 is a schematic diagram showing the main processing tasks.

DETAILED DESCRIPTION

The present invention will be described in the context of the exemplary motor, driven device and management system shown in FiGURE 1. The combined motor 8 and driven device 7 will be referred to as the motor system 9. Examples of typical driven devices would be a pump, fan or compressor. The energy management, condition monitoring and diagnostic system consists of a SMDS unit 1, a supervisory computer 14 and a web-based data analysis and reporting system 15. This web-based software tool will be referred to as the motor management tool.

The SMDS unit I is preferably connected to the supervisory computer 14 through a wireless communication link 12. Similarly, the supervisory computer 14 is connected to a web server via a secure network link incorporating a firewall. In that manner, a central operator station 16 with access to the same secure web-based motor management tool may be alerted to the condition indicated by the SMDS unit 1 and take appropriate actions.

With continued reference to FIGURE 1, the electric motor 8 receives power from a remote Motor Control Cabinet (MCC) 11 through a set of power lead wires 5 and 6. In addition, the SMDS unit 1 includes an integrated manual disconnection switch 2 for isolation of the electric motor. It is envisaged that the SMDS unit 1 can replace the existing disconnection switch, further simplifying installation. The SMDS unit 1 includes a set of three discrete motor condition display indicia 4 including fault indicia, caution indicia and normal operation indicia.

Lastly, in order to exchange data with the supervisory computer 14, the SMDS unit I includes a wireless communication device 3. The wireless link 12 adheres to industrial Wireless standards for communicating command and parameter information. It is anticipated that several SDMS units will exist in close proximity and communicate back to single local supervisory computer for that particular region of the facility, Therefore, a wireless mesh grid concept is utilised to improve robustness in the field.

FIGURE 2 shows a function block schematic representation of the SMDS unit I illustrated in FIGURE 1.

With continued reference to FIGURE 2, the SMDS unit includes a plurality of functional subsystems. A microprocessor unit 24 executes various diagnostic algorithms stored in an algorithm memory 24 and performs various diagnostic calculations utilizing a data memory 23 which also includes retentive memory so important historical states are not lost during any loss of power Current Transformer (CT)-coils 17 are used to measure the electrical properties of the motor power supply. An interface to the CT-coils 17 and other motor system sensors 18 is provided by a signal conditioning 19 and analogue to digital conversion modules 20. Power is provided to the processor unit and to other components forming the SMDS unit 1 from a combined power supply and battery unit 26. The primary power source is taken from a single phase of the motor cables 5 coming from the MCC. In the event of power loss from the MCC, a battery unit provides auxiliary power. This feature is essential for condition monitoring applications where it is imperative to consider the complete historical profile of a device. Such a scenario woyld be a bearing heat soak following an emergency shut-down.

The motor system sensors 18 are connected to the processor unit 25 via a signal conditioning 19 and analogue to digital converter 20. The signal conditioning unit 19 consists of analogue anti-aliasing filters. The analogue to digital converter converts the filtered analogue signals generated by the plurality of sensors into a digital value for ready use by the processor unit 25. Examples of analogue sensors include motor stator temperature, motor bearing temperature, driven device temperatures, a set of motor current sensors, a set of motor voltage sensors, and vibration sensors 10.

With continued reference to FIGURE 2, the analogue CT-coils 17 includes a set of motor current and voltage sensors. Each of these sets of sensors are connected directly to the power lead wires 6 connecting the electric motor 8 to the SMOS unit. Preferably, the motor current sensors 17 are arranged as current transformers on each power line to generate a voltage proportional to the current flowing through the respective power lead wire. Further, each of the motor voltage sensors 17 preferably includes a voltage division circuit (transformer) to provide a suitably scaled voltage for the analogue to digital converter.

Lastly, a vibration sensor 10 is mechanically connected to the casing of the motor 8 to provide a voltage signal proportional to the amount of vibration experienced along a single axis of the motor. As illustrated, the vibration sensor 10 is connected to the motor casings at a central location. However, one or more vibration sensors may be disposed about the various internal and/or external surfaces of the motor system to provide one or more vibration signals. The analogue vibration signals are passed through analogue filters within the signal conditioning module 19 to avoid aliasing issues and then converted to digital signals by the ND mechanism.20 for use by the processor unit 25.

With yet continued reference to FIGURE 2, the processor unit 25 executes various diagnostic algorithms from programs stored in an algorithm memory 24. Further, the processor unit 25 utilizes a data memory 23 to perform various calculations and to store variables. In addition, the digital output unit 21 controls the status LEDs.

With reference now to FIGURE 3, the functional operation of the SMDS unit will be described first and then with reference to the functional operation of the supervisory computer 14. Finally the functionality of the motor management tool 14 will be detailed.

The SMDS unit 1, the supervisory computer 14 and web-based motor management tool 15 execute a respective set of instructions and logical operations in order to effect the motor energy management and diagnostic functions according to the present invention. Although the operation of the motor and smart meter will be discussed in conjunction with the operation of the supervisory computer, it is to be noted that according to the present invention, the SMDS unit 1 may be operated independent of the supervisory computer 14 such as when the communication link 12 is disconnected or during other conditions where the supervisory computer 14 is not necessary for basic operation.

The diagnostics and prognostics apparatus utilise various analytic techniques such as those which generally fall under the category of current signature analysis which has been shown to detect certain mechanical problems such as bearing failure, rotor problems and electrical insulation breakdown. Basic filtering and other signal processing and classification algorithms are used by the SMDS unit 1 to determine the key energy performance indices and health of the motor system.

Electrical motor diagnostics (EMD) is used in evaluating the condition of the electric motor circuit. Motor circuit analysis, or MCA, provides information about the winding and ground insulation system and the motor rotor when equipment is de-energized. Motor current signature analysis, or MCSA, provides a fast Fourier transform (FFT) spectra and demodulated spectra of current in order to detect rotor, air-gap, and load-related faults while equipment is energized. FFT is a mathematical technique for efficiently calculating the frequency response of sampled time signals. An electrical signature analysis, or ESA, provides an FFT spectra of both the voltage and current of the motor circuit in order to detect current-related faults and supply faults while equipment is energized.

The prognostication performed in the apparatus 14 of the future state of the system is in terms of both physical condition such as stator insulation and estimate of degradation rates and operation impact as a function of degradation. This prognostication not only protects equipment and insures operational readiness, it also allows integrated motor control centres to adjust system usage for optimum machinery system performance or to achieve targeted machinery life. The prognostication of system degradation executed in the unit 14 allows maintenance planning to proceed in an efficient manner to provide optimum plant system utilization. Several analytical methods are implemented in the unit 14 to accurately perform machinery diagnostics and prognostics.

Finally the web-based motor management tool 15, manages all the energy and diagnostics data being generated by the various SDMS units and supervisory computers on the site.

Apart from providing basic graphical display of ihe captured historical data, it also calculates key performance metrics. These metrics are then used in a Metering & Targeting technique to identify and reduce energy consumption and costs. Finally a set of custom design reports are automatically generated and issued via email to the identified key personnel.

Management of the motor stock is assisted by tracking automatically for each motor factor such as the loaded run hours, maintenance intervals, bearing temperatures and vibration levels.

While particular embodiments of the present invention have been shown and described, it should be clear that changes and modifications may be made to such embodiments without departing from the true scope and spirit of the invention. It is intended that the appended claims cover all such changes and modifications.

S

SUMMARY

Hence, in summary the invention provides a method and apparatus for combined energy management and real-time electric motor diagnostics with condition monitoring. While the motor is energized, dynamic operating parameters are determined and communicated to a central supervisory computer. Notification signals are generated if predetermined criterions are satisfied. The SMDS unit is integrated with the motor disconnection switch in order to simplify installation. The device includes a set of sensors, a processing unit, a memory and an output interface for communicating alarms, warnings and calculated operating parameter values or the like to a central web-based motor management tool to alert a remote operator or maintenance personnel. In a normal operating mode, the processing unit calculates a general class of derived motor operating parameters such as power consumption, load utilisation level, run-hours, over-temperature, over-voltage, over-current, excessive vibration, and phase imbalance. A web based motor management tool manages all the captured data from the various SDMS units and supervisory computers around the site. Energy reduction techniques are applied as well as management of the motor stock. Summary reports are generated and issued automatically to key personnel.