W.M. McDermid

Bio: W.M. McDermid is an academic researcher from Manitoba Hydro. The author has contributed to research in topics: Partial discharge & Stator. The author has an hindex of 11, co-authored 53 publications receiving 489 citations.

Practical on-line partial discharge tests for turbine generators and motors

Abstract: Several utilities have found partial discharge testing to be very useful for identifying motors or generators with deteriorated stator winding insulation. Such partial discharge tests are sensitive to problems associated with overheated insulation, loose stator bars, and pollution, all of which can cause in-service failures with long associated outages and high repair/rewind costs. Unfortunately, the partial discharge test is not widely applied since present test methods require considerable skill to perform, and/or require machine outages. These problems are due to the stator winding partial discharges being masked by high levels of internal and external electrical noise. The authors describe how partial discharge tests have now been developed which eliminate the effect of noise, thus allowing plant personnel to perform the test without any machine outage. >

A digital technique for the on-line measurement of dissipation factor and capacitance

Abstract: This paper reports a computer-aided system for on-line monitoring of dielectric dissipation factor tan /spl delta/, and capacitance of HV apparatus. The method employs the discrete Fourier transform (DFT) which is performed on the scaled down analog voltage and current signals obtained using a digital storage oscilloscope (DSO) board. The results are displayed using the graphic user interface implemented with graphic (G) language, This technique uses optimal values of measurement parameters as indicated by software simulation and laboratory tests. Field tests were conducted at Manitoba Hydro's Dorsey station to evaluate the insulation of a 230 kV current transformer unit using the developed system.

IEEE guide for the measurement of partial discharges in AC electric machinery

Abstract: The IEEE Guide to the Measurement of Partial Discharges in Rotating Machinery was first published in 2000 as a trial use guide and became a full use document in 2002 It was re-affirmed in 2005 with minor revisions In 2010 the working group agreed that the document requires updating in a number of areas to reflect progress in diagnostic technology A PAR was issued in 2010 under the new title IEEE Guide for the Measurement of Partial Discharges in AC Electric Machinery This paper discusses those aspects of the document that are being updated

Unusual PD pulse phase distributions in operating rotating machines

Abstract: The position of partial discharges (PD) with respect to power frequency phase position has long been known to provide useful information on the nature of deterioration of electrical insulation. In the past, virtually all such data has been from PD tests performed in the laboratory on static models or equipment. Improvements in the past 15 years in noise elimination technology have made it possible to monitor the PD activity (number, magnitude and phase position) in the HV stator windings of operating motors and generators. Over a two year period, the PD activity was recorded on more than 100 motors, hydrogenerators and turbine generators, and the pulses analyzed with respect to the ac phase position, with a resolution of 3.6/spl deg/. In the majority of stator windings, the PD pulses occurred in the expected portion of the ac phase, i.e. Between 0 and 90/spl deg/ as well as between 180 and 270/spl deg/. However a significant number of instances were recorded where the pulses appeared to be shifted /spl sim/30/spl deg/. This is probably due to the phase-to-phase electric stress which occurs in the endwinding portion of a three phase stator winding. In many other machines, the PO phase positions were very different from the expected patterns determined from static tests. In some of these cases, such results were obtained on machines with suspected loose stator windings. It seems reasonable to conclude that the unusual PD patterns may be due to the influence of moving stator coils on the PD patterns. Such an influence is not easy to simulate in static laboratory tests. PD pulse phase analysis is shown to be a useful means of helping to determine the main deterioration mechanisms of stator insulation systems of operating motors and generators. >

On-line monitoring of partial discharges in a HVDC station environment

Abstract: This paper deals with the on-line measurement of partial discharges (PD) in a high voltage direct current (HVDC) converter station. The HVDC station is a particularly challenging environment for measurement due to elevated interference levels caused from the switching of thyristor-controlled converters. In this work, online PD measurements were performed on two specimens; one is an HVDC converter transformer and the other an HVDC converter wall bushing. The measurements were performed in the high-frequency range from 400 kHz to 30 MHz with modern wideband PD measurement instrumentation. Results demonstrate that on-line measurement of PD in an HVDC station environment is possible and that a combination of input filtering and modern signal processing methods for feature extraction can be used to mitigate the converter interference. The feature extraction method used plots partial discharge data on a time-frequency classification map. The map enabled isolation of individual PD phenomena, and demonstrated that trending to monitor insulation degradation is possible with online partial discharge measurement. Furthermore, specific strategies for PD measurement and analysis are developed for each of the transformer and bushing specimens.

Partial discharges. Their mechanism, detection and measurement

Abstract: Different partial discharge (PD) detection and measurement procedures suitable for use on cables, capacitors, transformers and rotating machines are examined and compared. Both narrow and wide bandwidth PD detectors are considered; particular attention is given in regard to their suitability to different types of electrical apparatus and cable specimens under test as well as their applicability to discharge site location and their capability to detect different forms of PD. A rather substantial portion of the discussion is devoted to the use of intelligent machines as applied to PD pattern recognition in terms of either PD pulse-height/discharge epoch (phase) distributions or discharge pulse shape attributes.

Review of condition monitoring of rotating electrical machines

Abstract: Condition monitoring of rotating electrical machinery has received intense research interest for more than 30 years. However, electrical machinery has been considered reliable and the application of fast-acting digital electrical protection has rather reduced the attention operators pay to the equipment. The area based upon current literature and the author's experience is reviewed. There are three restrictions: only on-line techniques for rotating machines are dealt with; specific problems of variable speed drives are not dealt with, except in passing; conventional rather than emerging brushless, reluctance and permanent magnet machines of unusual topology are concentrated upon. The art of condition monitoring is minimalist, to take minimum measurements from a machine necessary to extract a diagnosis, so that a condition can be rapidly inferred, giving a clear indication of incipient failure modes. The current state of the art is reviewed in the following ways: survey developments in condition monitoring of machines, mechanically and electrically, over the last 30 years; put that work in context alongside the known failure mechanisms; review those developments which have proved successful and identify areas of research which require attention in the future to advance the subject.

Condition monitoring techniques for electrical equipment-a literature survey

Abstract: Increasing interest has been seen in condition monitoring (CM) techniques for electrical equipment, mainly including transformer, generator, and induction motor in power plants, because CM has the potential to reduce operating costs, enhance the reliability of operation, and improve power supply and service to customers. Literature is accumulated on developing intelligent CM systems with advanced practicability, sensitivity, reliability, and automation. A literature survey is felt necessary with an aim to reflect the state-of-the-art development in this important area. After introducing the concepts and functions of CM, this paper describes the popular monitoring methods for and research status of CM on transformers, generators, and induction motors, respectively. The paper also points out the potential benefits through the utilization of advanced signal processing and artificial intelligence techniques in developing novel CM schemes.

Partial discharge diagnostics and electrical equipment insulation condition assessment

Abstract: Partial discharge (PD) measurement has long been used as a test to evaluate different insulation system designs, and as a quality control test for new equipment. However, in the past 20 years, PD measurement has been widely applied to diagnose the condition of the electrical insulation in operating apparatus such as switchgear, transformers, cables, as well as motor and generator stator windings. Improvements in the capabilities as well the lower cost of sensors, electronics and memory is partly the reason for the increased popularity of PD diagnostics. Another reason has been the development of methods-including the use of ultrawide band detection-to improve the reliability of the PD measurement in the presence of noise. In addition, rapid progress is being made in automated pattern recognition techniques that also helps to suppress noise. This paper reviews the various PD measurement technologies that have been specifically developed to improve PD diagnostic methods, and outlines how they have been implemented for stators, cables, transformers and switchgear. Areas for further research are also presented.