Download Diagnostic News On-Line Monitoring of Partial Discharge in Voltage Source January 2015

Diagnostic News
January 2015
Inside this Issue:
On‐Line Monitoring of Partial Discharge in Voltage Source Variable Speed Drives Now Possible 1,2 EVAII Endwinding Vibration Accelerometer 1,3 Howard Sedding Joins Iris Power 4 Brad Spacinsky—New Operations Manager 4 COMET & IRMC 5 2015 Training
Schedule
5
UPCOMING EVENTS
2015
EPRI—
TGUG January 19‐23, Amelia Island, FL EPRI—
LEMUG January 26‐29, San Jose, CA Energy January 27‐29, Generation Bismarck, ND Conference 501 F&G February 23, User Group Savannah, GA Meeting NETA March 2‐5, Power Test Nashville, TN Western Turbine Users March 15‐18, Long Beach, CA On-Line Monitoring of Partial Discharge in Voltage Source
Variable Speed Drives Now Possible
By: Greg Stone Since they were first introduced over 10 years ago for military applications, it has been known that the voltage impulses from voltage source, pulse width modulated (VS‐PWM) vari‐
able speed drives may lead to more rapid dete‐
rioration of stator winding insulation system in windings rated 3.3 kV and above. The voltage impulses are created by the rapid switching of the transistors within the drive. The reasons for an increase in the risk of rapid insulation deterio‐
ration due to these impulses include [1]:  More and bigger PD within internal ground‐
wall insulation voids due to higher peak volt‐
ages from the drive switching.  The high frequency content of the drive volt‐
age impulses causes high currents to flow in the stress relief coatings which may lead to overheating and high PD from degraded coatings. Thus, it is not surprising that many endusers who own such variable speed drives will often want to install an on‐line partial discharge moni‐
toring system. While the LCI, current source inverter and cycloconverter types of drives do not cause a problem for on‐line PD monitoring, the VS‐PWM drives do. The most popular drive for medium and high voltage motors is now the VS‐PWM drive. The main issue with monitoring VS‐PWM drives is the short risetime voltage impulses that are inherently produced by the transistor switches within the drive. The voltage switching impulses can have risetimes as short as 500 ns, with magnitudes of 2000 V or so. The short risetime creates frequencies up to almost 1 MHz. If the PD sensor is a capacitor – the capacitor will Continued on page 2... Iris Introduces the EVAII— A Third Generation
Endwinding Vibration Accelerometer
Vibration of stator bars and coils outside of the stator slot (endwinding vibration) is becoming a more common cause of motor and generator stator winding failure. If one does a regular inspection of the machine, such dete‐
rioration can be detected well before a stator winding fault by looking for signs of fretting dust, greasing and/or cracks in the varnish that often coats the endwindings. However, the preferred method of detecting stator end‐
winding vibration without requiring a machine outage and disassembly has been the direct measurement of vibration using fiber optic accelerometers mounted at critical locations of the endwinding. Online monitoring can also provide the benefit of correlating the vibration with operational temperature and load. Westinghouse developed the first practical endwinding vibration monitoring system using fiber optic accelerometers in the 1980s, and many machine manufacturers now supply fiber optic accelerometers that use a variety of optical phenomena. Iris has been supplying fiber optic acceler‐
ometers for more than 5 years. However, the sensors had a relatively large volume and, as with all other fiber optic accelerometer ven‐
dors on the market, experienced some failures after only a few years in service. This lead us Continued on page 3... Qualitrol‐Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2 Telephone: +1‐905‐677‐4824; Fax: +1‐905‐677‐8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com Page 2...
On-Line Monitoring of Partial Discharge in Voltage
Source Variable Speed Drives Now Possible
Figure 1: Photo of 80 pF capacitive couplers installed on the motor terminal box of a variable speed drive motor. The couplers (circled in red) are partly concealed behind the power cables. Figure 2: Example of a PD plot from an operating 7.2 kV, 45 MW motor fed by a VS‐PWM variable speed drive. have a very low impedance to 1 MHz, especially if the capacitor is 1000 pF or more (at 1 MHz, the impedance of a 1000 pF sensor is only a few hundred ohms). The result is that a significant portion of the switching impulses are conducted through the capacitor and applied to the test instrumentation. The resulting noise from drive switching can be hundreds to thousands of times the magnitude of the stator winding PD, making even the most knowledgeable expert incapable of extract‐
ing the PD from the switching noise, especially if the PD system works in the 10 MHz or lower frequency range. Iris Power was first approached about 10 years ago to install an on‐line PD monitoring system on 7.2 kV motors fed from a VS‐PWM drive. Rather than scale up the existing PDAlert product for inverter drives from 1000 V to 7200 V, we instead modified the existing 80 pF cou‐
plers and the TGA‐B. About 2 years later, the prototype system was installed in the Middle East. The standard 80 pF capacitive couplers were used as the PD sensors (Figure 1). With a 50 ohm load, the lower cutoff fre‐
quency is 40 MHz, which partly suppresses the drive switching noise. However, additional filtering with a customizable, multi‐pole filter is often needed on each capacitive coupler. A change was also needed for the TGA‐B instrument. All conventional PD instruments display the PD with respect to the power frequency AC cycle (a pulse phase analysis plot, sometimes known as a phase‐resolved PD plot—see Figure 2). In the past the TGA‐B was expecting either 50 Hz or 60 Hz power fre‐
quency. If the frequency was neither of these, then the instrument would not “synchronize”. Continued from page 1... For variable speed drive applications, the TGA‐B had to be modified to work with a range of “fundamental” frequencies. After the installation of the prototype in 2007, we discovered that the instrument still could not synchronize to the fundamental fre‐
quency. The reasons were complex. Partly it was due to the reduced fundamental frequency voltage that was measured on the output of the 80 pF PD coupler when the fundamental fre‐
quency was well below 50 Hz. There were also problems establishing the voltage zero crossing when the fundamental frequency was “contaminated” with all the switching impulses. In addition, if the speed was such that the plant power frequency (50 or 60 Hz) was close to the fundamental frequency, a low frequency modu‐
lation could result that confused the synchroni‐
zation process. The solution was a separate capacitive voltage divider that emphasized the fundamental frequency, rather than the higher frequency switching impulses. The result was the first on‐line PD monitor‐
ing system in the world that successfully meas‐
ured the stator winding PD fed by a medium voltage VS‐PWM drive. Example PD data is shown in Figure 2. The system has been operat‐
ing since 2007, and other systems have been supplied to multiple endusers in the Middle East, as well as endusers in Asia and North America. References  M. Stranges, G.C. Stone, D. Bogh, “Voltage Endurance Testing of Stator Insulation Systems for Inverter Fed Machines”, IEEE Indus‐
try Applications Magazine, Nov 2009, pp 12‐18.  G.C. Stone, I. Culbert, S.R. Campbell, “Progress in On‐Line Measurement of PD in Mo‐
tors Fed by Voltage Source PWM Drives”, IEEE Electrical Insulation Conference, Philadelphia, June 2014, pp 172‐175.§ Qualitrol‐Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2 Telephone: +1‐905‐677‐4824; Fax: +1‐905‐677‐8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com Page 3...
EVAII—Endwinding Vibration Accelerometer
to develop a new generation of sensors that was both smaller and had proven ruggedness to work in the stator endwinding environment for many years, if not decades. The result is the patented EVAII acceler‐
ometer. This next‐generation sensor offers significant improvements over all other sen‐
sors on the market, including:  Small sensor head (dual axis: 35x14x10 EVAII fiber optic accelerometer EVAII fiber optic hydrogen penetration Continued from page 1... that the electrically non‐conducting materials of the EVAII are not sensitive to electrical fields.  Pressure testing up to 400 psig of the pene‐
tration and fiber optic feedthrough cable bundle used to pass the signal through the gas seal in hydrogen‐cooled generators. The products and services Iris Power provides for endwinding vibration monitoring include: mm, single axis: 30x9x10 mm) to provide greater flexibility when choosing installa‐
tion locations.  The same fiber used to send and receive the light resulting in fewer connections offering an easier installation.  Temperature rating of ‐50 to 230°C, which is suitable for installation in virtually all rotating machine applications.  A vibration output that is independent of temperature.  Exceptionally wide dynamic range.  Immunity to magnetic fields.  Total interchangeability in parts, providing shorter delivery time. Unlike most other sensors, the EVAII no longer has to be cali‐
brated for a specific electro‐optical converter. As with all Iris sensors, the EVAII has passed rigorous long‐term accelerated aging tests in an independent test facility to ensure reliability, long life, and that the sensors themselves will never pose a risk of stator endwinding failure. These tests include:  Kits composed of 6 or 12 single or dual axis  A series of accelerated aging tests at ex‐
 A technical team who has been applying treme vibration and temperature levels, intended to ensure the EVAII and feedthrough cable have a life equivalent to at least 10 years of continuous online op‐
eration at high temperature and with se‐
vere vibration.  Partial Discharge (PD) testing which showed no observed PD activity up to 34 kV AC with a 3 pC sensitivity, indicating endwinding vibration technology for more than 30 years, and has the most extensive independent interpretation knowledge in the industry. In 2004 we were the first vendor to publish what levels of vibration were accept‐
able in stator endwindings. Contact your Iris Power‐Qualitrol sales rep‐
resentative for more information and technical papers on this subject. § accelerometers together with an optional single axis accelerometer for the stator core; an electro‐optical driver (EOD) box; and a junction box for air‐cooled machines or a penetration feedthrough assembly for hydro‐
gen‐cooled generators. The EOD is not built into the penetration, which reduces thermal and vibration stress on the EOD, and facili‐
tates servicing without the need of a unit outage.  Expert bump testing services together with modal analysis to determine the optimal locations for the accelerometers (see the January 2012 issue of the Diagnostic News for information on how critical this step is).  Either the EVTracII or the GuardII EV module continuous monitoring systems (see the April 2013 issue of the Diagnostic News). These monitors can be used with any accelerome‐
ter that provides mV/g output. Alternatively the EOD can be connected to an existing vibration monitoring system that is compati‐
ble with its 100 mV/g output.  Training and/or expert analysis of vibration data. Qualitrol‐Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2 Telephone: +1‐905‐677‐4824; Fax: +1‐905‐677‐8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com Page 4...
Howard Sedding Joins Iris Power
We are very pleased to announce that Dr. Howard Sedding, a very well‐known expert in the field of electrical insulation assessment, has joined Qualitrol‐Iris Power as an Insulation Engineer. In this role Howard will support Iris Power’s growing line of products for assessing the condition of the electrical insulation in motor and generator windings. In particular his expertise in the measurement and interpretation of partial discharge will greatly expand Iris’s capabilities. Howard graduated in electrical and electronic engineering at University of Strathclyde and then acquired MSc and PhD degrees. His PhD Thesis was on the degradation of epoxy mica insulation used in rotating machines. Most of Dr. Sedding’s career was spent working at the Research Division of Ontario Hydro, later known as Kinectrics. Interestingly, he worked on the development of the stator slot coupler (SSC), which is a partial discharge sensor sold by Iris Power especially for large hydrogen‐
cooled turbine generators. Howard was involved in, or responsible for, numerous projects related to the specification, testing, monitoring and maintenance of solid, liquid and gaseous electrical insulation systems in a wide range of high voltage electrical equipment, such as rotating machines, cables, switchgear and transformers. Most recently he was manager of 40 specialists at Kinectrics who performed these services. He is an active member of numerous technical committees, and contributed to many IEEE and IEC standards concerned with electrical insulation. Specifically he is the Chair of the Canadian committee for TC 112 (electrical insulation) and is the Canadian representative for CIGRE SC A1 (rotating machines). Howard has authored and co‐authored more than 100 technical papers (several of which won best paper awards) and is co‐author of the book “Condition Monitoring of Rotating Electrical Machines” published by the Institution of Engineering and Technology in 2008.§ Brad Spacinsky—New Operations Manager
Brad Spacinsky has been promoted to the position of Operations Manager at Iris Power. Brad will be managing the Manufacturing, Purchasing, Field Service and Technical Support teams. Brad will ensure that all products and services are delivered on time and safely. He will maintain the goals for quality and on‐time delivery and provide all necessary tools for continuous improvement of the operations group. Brad has been employed with Iris Power for over 9 years, starting out as an Applications Engineer & International Projects Manager prior to moving into the role of Field Service Manager 3 years ago. Brad is a Professional Engineer in Ontario and a graduate of McMaster University’s Bachelor of Engineering program. Brad is replacing Paul Magder who is retiring from Iris Power after a career of 20 years! Paul was instrumental in the organization of the Manufacturing Department in the early years of Iris. He also led the effort to certify Iris as ISO9002 and later as ISO9001.§ Qualitrol‐Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2 Telephone: +1‐905‐677‐4824; Fax: +1‐905‐677‐8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com Page 5...
COMET & IRMC
In December 2014 the first Conference on Online Monitoring of Electric Assets (COMET), was held in Austin, Texas in affiliation with the University of Texas Center for Electromechanics. The program provided parallel sessions on Rotating Machines and Transmission System Equipment and was devoted not just to presentations on condition monitoring tools, but also to educating attendees on the practical aspects of implementing condition‐based maintenance in transformers, switchgear, and large motors and generators. One hundred and forty people from 11 countries participated in the 4‐day program. Two days were devoted to tutorials by Iris Power experts on PD interpretation, stator core testing, and the requirements for new squirrel cage induction and synchronous motors. These were very well Bob Hebner, Director of the Center for Electromechanics at the University of Texas, and COMET 2014 Chair, makes keynote presentation. attended by participants from both the Rotating Machines and Transmission tracks. In 2015 COMET will be held once again in Austin, Texas in November. The 2015 event will follow the same general program but with only one day of Rotating Machines papers and tutorials will be on topics of interest to Transmission System Equipment. In addition to the annual COMET, based on feedback from our users, the Iris Rotating Machine Conference (IRMC) will return on June 22‐25, 2015 in Nashville, TN! The IRMC program will be back to the traditional one including user group meetings, a walk‐in clinic and tutorials. Look for further information coming your way soon! Bryan Moore of Georgia Power presents his paper on testing of rewound motors. 2015 Training Schedule
EL CID Course March 17‐19, Toronto Turbogenerator Maintenance Course Partial Discharge Course April 21‐23, Toronto May 12‐15, Houston, TX EL CID Course September 15‐17, Toronto Hydrogenerator Maintenance Course October 20‐22, Baltimore, MD Qualitrol‐Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2 Telephone: +1‐905‐677‐4824; Fax: +1‐905‐677‐8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com