Patent Application
20120101768
The present invention relates generally to diagnosing thermal anomalies in stator windings in an electrical machine such as a generator, and more particularly to using resistance temperature detectors (RTDs) to diagnose thermal anomalies in stator windings.
Thermal anomalies in the stator windings of a generator can occur for any number of reasons, e.g., excessive vibration, inadequate cooling, etc. The result of such anomolies can lead to insulation failure of the windings. This may lead to excessive heating in the region and result in a stator ground fault, which can be costly to address. The inability to diagnose and avoid stator ground faults at an early stage often exascerbates the severity of damage and time of outage.
In one aspect of the invention, a system for evaluating thermal behavior in an electrical machine is provided, comprising: as input system for obtaining RTD readings over time from at least one sensor in a stator winding; a normalization system for normalizing each RTD reading with respect to armature current; and an analysis system for analyzing a trend in a set of normalized RTD readings to indicate thermal behavior of the stator winding.
In another aspect of the present invention, a system for evaluating thermal behavior in an electrical machine is provided, comprising: an input system for obtaining a set of resistance temperature detector (RTD) readings from a plurality of sensors in a common axial location in a stator winding; a calculation system for calculating a difference value between a maximum value and a median value from the set of RTD readings; and an analysis system for analyzing a trend over time in a set of difference values to indicate thermal behavior of the stator winding.
In a further aspect, a computer program comprising program code embodied in at least one computer-readable storage medium is provided, which when executed, enables a computer system to implement a method of evaluating thermal behavior in an electrical machine, the method comprising: obtaining resistance temperature detector (RTD) readings over time from at least one sensor in a stator winding; normalizing each RTD reading with respect to armature current; and analyzing a trend in a set of normalized RTD readings to indicate thermal behavior of the stator winding.
Various embodiments of the present invention are directed to evaluating and diagnosing thermal anomalies in stator windings using resistance temperature detectors (RTDs). Technical effects of the various embodiments of the present invention include the ability to identify thermal anomalies at an early stage, thus providing the capability of avoiding costly outages associated with stator wire ground faults. Additional technical effects include the ability to evaluate and trend thermal behaviors of the winding, and to provide an alarm if a predefined threshold is exceeded.
Electrical machines such as generators generate heat as a result of current passing through the windings. Cooling mechanisms are incorporated into generators to address the heat issues and RTDs are commonly utilized to ensure that the temperature of the generator, and particularly the stator windings, is below allowable limits.
Embodiments of the invention utilize RTDs to evaluate thermal behaviors in the winding and identify thermal anomalies at an early stage. The temperature monitored by each RTD is generally proportional to the amount of current passing through it, the resistivity of the windings and the ambient temperature. By analyzing trends within the RTD data, anomalies can be identified.
In the first approach, changes in RTD values are normalized with respect to current and resistivity at the corresponding ambient temperature. In general, normalization refers to the division of multiple sets of data by one or more common variables in order to negate that variables' effect on the data, thus allowing underlying characteristics of the data sets to be compared. This thus this allows data on different scales to be compared, by bringing them to a common scale. When normalized, rising RTD values result in a constant output for an electrical machine running under consistent operating conditions (i.e., constant operating pressure and coolant properties). Trending of normalized RTD values are thus used to indicate thermal behavior of the windings. For example, an increasing (i.e., positive) trend indicates an anomaly in the windings. An alarm may be generated if the increasing trend exceeds a configurable parameter (e.g., a 15% increase) for a predefined amount of time (e.g., 10 hours).
where ΔTi is a difference between the RTD temperature and the ambient temperature, ρ is the resistivity of the windings and Ia is the armature current.
Next, at S4, trend analysis system 24 makes a determination whether Ki has changed more than a predetermined percent with respect to a baseline value. The baseline value for the normalized temperature may for example be calculated as a one-month average of the temperature rise. If no significant change is detected, i.e., no at S4, then no action is taken since no anomaly is indicated. If a change is detected, then at S5 trend analysis system makes a determination whether the change persists in Ki for more than some predetermined amount of time. If the change does not persist, i.e., no at S5, then no action is taken. If yes, then at S6, an anomaly is indicated and alarm system 26 generates a thermal anomaly information alarm 34.
Referring again to
In both approaches, the inputting and filtering done by input/filtering system 29 may be implemented as a single function or separate functions. Accordingly, although shown as a single function, it is understood that inputting and filtering may be done separately. One of the filtering processes may include checking the validity of the RTD sensors. This may be done, e.g., by:
In various embodiments of the present invention, aspects of the systems and methods described herein can be implemented in the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In one embodiment, the processing functions may be implemented in software, which includes but is not limited to firmware, resident software, microcode, etc.
Furthermore, the processing functions can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system (e.g., processing units). For the purposes of this description, a computer-usable or computer readable medium can be any computer readable storage medium that can contain or store the program for use by or in connection with the computer, instruction execution system, apparatus. Additional embodiments may be embodied on a computer readable transmission medium (or a propagation medium) that can communicate, propagate or transport the program for use by or in connection with the computer, instruction execution system, apparatus, or device.
The computer readable medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device). Examples of a computer-readable medium include a semiconductor or solid state memory, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include a compact disk—read only memory (CD-ROM), a compact disk—read/write (CD-R/W) and a digital video disc (DVD).
In any event, computer system 10 (
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
While the disclosure has been particularly shown and described in conjunction with a preferred embodiment thereof, it will be appreciated that variations and modifications will occur to those skilled in the art. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.
