From 1975 to 1990, Greg Stone was a Dielectrics Engineer with Ontario Hydro, a large Canadian power generation company. From 1990 to 2021, he was employed at Iris Power L.P. in Toronto Canada, a motor and generator condition monitoring company he helped to form. He has published two Wiley-IEEE Press books on motor and generator winding maintenance, a book on partial discharge testing and has authored more than 200 papers concerned with rotating machine windings. Greg has presented invited lectures at dozens of Universities and Research Institutes on five continents. Since 1980 he has also been active in creating and updating many IEEE and IEC standards concerned with partial discharges and rotating machine insulation testing. Greg Stone has a PhD from the University of Waterloo, Canada, in Electrical Engineering and is a Fellow of the IEEE and a Fellow of the Engineering Institute of Canada. He has several awards from IEEE, IEC, CIGRE and the US-based Electric Power Research Institute (EPRI).
What is your background?
For the first third of my career, I was with a large electric power company in Canada where I was involved with specialized electrical testing of motors, generators, transformers, power cables and switchgear. The aim was to determine when maintenance was required to avoid an in-service (and often catastrophic) failure. During this time, I was fortunate to work on a large research project sponsored by the North American electric utility industry to develop an on-line partial discharge (PD) test for motor and generator stator windings. Partial discharges are small electrical sparks which can both age the insulation leading to failure, as well as give a warning that something bad may happen – just like a blood pressure test does for humans. The test I helped to develop could be performed and interpreted by utility staff themselves, greatly lowering test cost. Eventually three colleagues and I left the utility in 1990 to found a company called Iris Power L.P., which commercializes the sensors and instruments for the test. The test was very successful, is now being used on tens of thousands of machines around the world, since it lets machine owners know when stator winding maintenance is needed. Since PD testing is just one test for motors and generators, and following on another Electric Power Research Institute (EPRI) project, I also helped to write a Wiley/IEEE Press book on motor and generator windings – how they are made, how they fail, how to test them and how to fix them. We are now in the process of writing the third edition of that book. All this has been helped by my participating in IEEE and IEC standards-making.
What are the most profound changes you have seen in your field across your career?
In the ‘good old days’ owners of large power equipment used in utilities and industries such as petrochemical, pulp/paper and mining, would shut down equipment (and thus lose revenue) every year or so to test the condition of the equipment. Again, the idea was to prevent in-service failures. Nowadays, high voltage equipment owners want to keep the equipment running all the time, and so prefer to use on-line condition monitoring (for which PD is just one tool). This trend has been powered by developments in sensors, electronics and of course software that was not available when we started out. Today, advanced statistical modelling and AI are being used by centralized condition monitoring stations to rapidly identify what equipment is behaving oddly and thus needs a closer look. None of this would have been possible in the ‘good old days’.
What motivated you to write Practical Partial Discharge Measurement on Electrical Equipment?
In some sense COVID did, plus my decision in 2021 to retire from full time employment at Iris Power L.P.. It seems that writing books has become my retirement project😊. Wiley had approached me in 2020 to start writing a third edition of the Machine Insulation book. I had already been thinking that although there are tens of thousands of research papers and case study articles written about PD testing, and there are a number of books written by academics on the physics of PD, there were no English-language books of a practical nature. Yet most PD testing in electrical equipment factories, utilities and industry are done by technicians and engineers who are not researchers, are not interested in the detailed physics of PD or some of the arcane theories about PD testing. They want to understand the basics of what PD is, what they need to know to do a good test and how to interpret the results. Thus, we wrote the book specifically for the folks who do the testing.
Who is the primary audience for Practical Partial Discharge Measurement on Electrical Equipment?
The primary focus for the book are the thousands of technicians and engineers who do routine PD testing as part of their job. These folks will work for manufacturers of power transformers, switchgear, cables and rotating machines rated above 1000 V. Most technical standards require PD testing before the electrical equipment can be shipped to the customer. Equipment owners also do off-line or on-line PD testing on a regular basis to make sure the equipment is in good condition and does not need repairs. Such people usually do many types of tests, and PD testing is just one part of their job. The book will also be of use to engineering students who are taking a course in high voltage engineering or as a reference book for engineering students researching condition monitoring of electrical equipment.
What are the key challenges this audience faces?
There are many vendors of PD equipment, all making competing claims about technology and efficacy. There are also thousands of research papers that have been published about PD technology that tend to be difficult to understand unless one is already knowledgeable in the field. Our hope is that this book will educate its readers on the major technologies that are available and help them to cut through the competing commercial claims about technology and test result interpretation. Even though two of the authors were associated with vendors of PD test equipment, we have worked hard to make the book technology neutral, by explaining the pros and cons of all the successful approaches to measure PD.
How does your book solve this need/challenge?
We cover the basics of why PD occurs, the measurement technologies, and interpretation up front. Then there are separate chapters on how to perform PD testing on each major type of electrical equipment, switchgear, cables, etc.) Each chapter describes what PD can detect for that type of equipment, has a review of the relevant IEEE and IEC standards, the relevant sensors and instrumentation typically used for that type of equipment, plus an extensive discussion on test interpretation. Thus, if you only want to measure PD on power transformers, you don’t need to read the chapters on cable, rotating machines, etc. Also, the authors include people who worked for PD test equipment manufacturers as well high voltage equipment manufacturers and end-users. Thus, we have tried to reach a balance between test equipment manufacturers and end-users.
What have been the biggest rewards?
Writing the first book on the market specifically intended for PD test users. Also, the four authors each have more than 30 years of experience doing PD tests, so to be able to make that accumulated knowledge available to new technicians and engineers entering the field has been very rewarding. The Amazon reviews of the book, as well as the review in the January 2024 issue of the IEEE Electrical Insulation Magazine have been very favorable – which is good for the ego.
What unique features do you think make the book stand out in the market?
The chapters on PD testing associated with each type of electrical equipment.
What current projects are you working on?
I am now working on an extensive revision of the 2nd edition of the Wiley/IEEE Press book “Electrical Insulation for Rotating Machines”, published in 2014, to recognize the explosion in new technology that is being applied to electric vehicle and aircraft motors, as well as wind turbines. The next edition will also add new tests and a myriad of new test methods and applicable standards.
Where can we find you online?
I have a very basic personal website stonedielectrics.com.