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Qualitrol-Iris Power DIAGNOSTIC NEWS April 2012 Why Do So Few Plants Perform Rotor Hipot Testing? By: Greg Stone Inside this issue: Why Do So Few Plants Perform Rotor Hipot Testing? 1,4 IRMC—Las Vegas 1 Training Courses 2 New Condition-Based Maintenance Technology 2 Iris Introduces Advanced 3,4 Endwinding Vibration Technology Expanded Qualitrol-Iris Power Offices Around the World 4 QCMC—Beijing and Dubai 4 In past articles I have talked about maintenance high potential (hipot) testing of stator windings. It seems that about 50% of large utilities do such routine hipots every 5 to 10 years or so to find serious stator winding insulation defects. Few industrial operators of motors and generators seem to do stator hipot testing. But it is apparent that almost no machine owners do routine hipot testing on their synchronous rotor windings. This was pointed out by Relu Ilie of Israel Electric at an EPRI conference last year. Since then Relu and I wrote an extensive article on maintenance hipot testing that was published in the March 2012 issue of the IEEE Electrical Insulation Magazine. Part of that article focused on rotor hipot testing. The stator winding hipot level for new stators has been set for years in IEC and IEEE/ANSI standards. The acceptance test is 2E + 1 kV rms, AC applied between phase and ground, where E is the rated phase-to-phase voltage. IEEE 56 (which is withdrawn but a revised version is near to completion) suggests that the stator winding be given a routine or maintenance hipot on a regular basis. The hipot level suggested in IEEE 56 is about 60 – 80% of the new winding hipot. This voltage is approximately the voltage that a stator winding would experience during a severe voltage transient. A new rotor winding (rated less than 500 V DC) is subject to an AC hipot of about 10 times normal rated DC voltage, with a minimum test voltage of 1500 V AC. Thus a 400 V DC rotor is tested with 4 kV rms AC before it is put into service. These acceptance hipot levels are set by IEC and ANSI standards. For rotor routine or maintenance testing, no hipot test is suggested in IEC or IEEE standards, although some OEMs do suggest one. Not surprisingly, there is also no suggested rotor winding hipot level. The reason for the lack of a suggested maintenance hipot test is not clear. Of course every plant manager is wary of maintenance hipots, since they bring with them the risk of a failure, and thus an extended outage. But the same reason holds for stator windings, and yet surveys show that many plants do perform this test. Perhaps it is because rotor windings are usually isolated from the rotor body, and a single ground fault can be tolerated. Continued on page 4... UPCOMING EVENTS 2012 EPRI Australian Reliability Workshop Brisbane, Australia Apr 12-14 GE 7F Users Conference San Antonio, TX May 14-18 HydroVision 2012 Louisville, KY July 17-20 IRMC/QCMC 2012 June 25-28, 2012 For the first time, the Iris Rotating Machine Conference will be held in Las Vegas, NV! For this 15th annual conference the program has changed to provide attendees with parallel sessions on Rotating Machines, Gas Insulated Switchgear, and Transformers. This conference will be 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, large motors and generators. There will be ample time for participants to take in the local sites as well as network with colleagues. Renaissance Las Vegas Hotel 3400 Paradise Road Las Vegas, NV 89169 Visit www.irispower.com for more information or email Karen Howard at [email protected] Qualitrol-Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2 Telephone: 905-677-4824; Fax: 905-677-8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com Page 2 Iris Power Introduces New Condition-Based Maintenance Technology 2012 Training Courses Partial Discharge Seminar, Jakarta, Indonesia May 28-30 HydroGenerator Maintenance Course, Nashville, TN September 25-27 EL CID ACE Course Nashville, TN September 25-27 Advanced Partial Discharge Course, Stockholm, Sweden October 1-2 Partial Discharge Course, Long Beach, CA November 13-15 For more information, contact: [email protected] Condition-based maintenance (CBM) is the process of making maintenance decisions based on the information collected through condition monitoring. To be effective, CBM requires 3 steps: the acquisition of condition data; data processing for detection of anomalies and symptoms of problems; and maintenance decision making. Ideally, CBM allows maintenance personnel to do only the right things, minimizing spare parts cost, system downtime and time spent on maintenance. Condition-based monitoring of specific components of motors and generators has become common practice for many utility and industrial customers. For example, CBM of stator winding insulation systems has been accomplished with a high degree of confidence and reliability through on-line PD monitoring. The following are the 3 steps above: Acquisition of Condition Data –TracII and GuardII continuous on-line PD monitors, the latest generation of this evolving technology. Data Processing for Detection of Anomalies – 250,000 record PD database which provides levels of concern for insulation condition. Maintenance Decision Making – Interpretation of the PD trend, the effect of load, temperature, etc on PD, and Pulse Phase Analysis data allows users to determine the failure mechanism(s) occurring and thus the necessary maintenance. Many other rotating machine components have similar on-line monitoring technologies which can be combined with PD to provide a complete rotor and stator on-line condition assessment. Ideally all these technologies can be integrated into a single hardware and software platform with a common interface and installation. Recognizing this need, Iris Power has now developed the GuardII platform which encompasses technologies including partial discharge, air-gap flux, endwinding vibration, shaft voltage and current monitoring, and current signature analysis (induction motors) which are appropriate for complete on-line machine condition assessment. The GuardII system now includes a NEMA 4X base unit (FPGA-based processor for remote Ethernet and local USB communications, diagnostics, data archiving memory, and alert calculations) with optional plug-in cards for specific diagnostic technologies. The GuardII system can be configured with a combination of inputs, and field upgraded with new technologies as outages and sensor installations allow. As well as one common hardware case, the GuardII platform includes a common WindowsTM software suite called the Iris Application Manager. All diagnostic data from the GuardII can be downloaded to an Iris Information Database (IID) giving users one common repository for condition-based monitoring data. Future developments will add more condition-based monitoring technologies to the GuardII line as well as more tools to turn the measured data into actionable knowledge about the health of your equipment. Qualitrol-Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2 Telephone: 905-677-4824; Fax: 905-677-8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com Page 3 Iris Introduces an Advanced Endwinding Vibration Monitoring System EVTracII Monitor Dual Axis Endwinding Vibration Accelerometer As discussed in the last issue of Diagnostic News, vibration of the stator bars and coils outside of the stator slot (endwinding vibration) is becoming a more common cause of motor and generator failure. If one does regular inspections of the machine, such deterioration 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 endwinding vibration without requiring a machine outage and disassembly has been the direct measurement of the vibration using a fiber optic accelerometer mounted at critical locations of the endwinding. Westinghouse developed the first practical endwinding vibration monitor using fiber optic accelerometers in the 1980s, and many machine manufacturers now supply fiber optic accelerometers based on various physical phenomena. Iris Power-Qualitrol has now developed both stand-alone and integrated monitors for use with most installed fiberoptic accelerometers, including our own. The stand-alone endwinding vibration monitor is called the EVTracII. It is based on the TracII platform (see page 2), that will enable continuous monitoring of all the endwinding sensors in a motor or generator, plus a stator core accelerometer and various operating parameters (stator temperature, load, etc). The EVTracII trends total vibration displacement in mils or microns (over the frequency range 20 to 1000 Hz) as well as the displacement at various selected frequencies (such as rotational speed and 100 or 120 Hz). Alerts and alarms can be set for any of these displacements. In addition, the frequency response over the range 20-1000 Hz can be displayed for more in-depth analysis. Assuming dual axis (radial and tangential) accelerometers are used, EVTracII has the ability to simultaneously measure the displacement in the radial and tangential directions so that the exact movement of the stator winding at that location can be determined. Such information is critical in designing an upgraded stator endwinding support system, if it is needed. EVTracII prototypes have been in use for about a year. The attached figure shows the output from a hydrogen-cooled turbine generator located in the Midwest USA. EVGuardII is the next evolution of the GenGuard product, first introduced in 1994. EVGuardII facilitates a complete motor or generator integrated monitoring system. The EVGuardII can be expanded to include on-line partial discharge as well as magnetic flux monitoring, in a single box and using a uniform software platform for all of the different types of sensors. The products and services Iris Power provides for endwinding vibration monitoring include: Kits composed of 6 or 12 single or dual axis accelerometers together with an optional single axis accelerometer for the stator core; an electro-optical converter and an air or hydrogen cooled penetration. Bump testing together with modal analysis to help find the optimum 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 EVGuardII continuous monitoring systems. These monitors can be used with any accelerometers providing a 100 mV/g output. Training and/or expert analysis of vibration data Technical support to reduce the endwinding vibration levels, if they are excessive. Continued on page 4... Vibration spectrum with displacements of 6.4 mils p-p and 3 mils p-p at 120 and 60 Hz, respectively from an operating 2-pole turbine generator Qualitrol-Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2 Telephone: 905-677-4824; Fax: 905-677-8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com QCMC 2012 With the success of the first Qualitrol Condition Monitoring Conference in Dubai, UAE last November, we are pleased to confirm that there will be a second QCMC in Dubai in 2012. Also, a QCMC will be held this year, for the first time, in Beijing, China. The QCMC is a technical conference offering both indepth half-day courses on condition monitoring methods, as well as presentations on stateof-the-art aspects of electrical equipment design, failure and repair. As with the North American based IRMC, this information is provided in a non-commercial environment by world-class experts offering a range of points-of-view. Visit the Qualitrol-Iris Power website for more details as they become available. QCMC Beijing October 22 and 23, 2012 BJ Broadcasting Tower Hotel Jianguomenwai Street Chaoyang District, Beijing QCMC Dubai November 19—21, 2012 JW Marriott Dubai Abu Baqer Al Siddique Road Dubai, UAE Why Do So Few Plants Perform Rotor Hipot Testing? - continued from page 1 - Advanced Endwinding Vibration Monitoring System However if the rotor winding ground insulation is weak generally, a second ground can lead to massive circulating currents and consequent damage to the rotor body. At the EPRI meeting mentioned above, it seems few or no maintenance engineers were doing a hipot on generator rotor windings. Furthermore, few seemed interested in it. In spite of this, I think there is an argument for doing routine hipot testing of rotors. It involves transient voltages. Just like the stator hipot test level is partly based on simulating the transients that can occur in service, the same can be done for rotor windings. Mr. Ilie has reviewed the publications that discuss the transients that rotor windings can see. Some of the causes of transients include: Opening of the rotor winding DC supply circuit breaker can cause an AC transient voltage due to the chopping of the current and Ldi/dt. Transient voltages from thyristor operation in static excitation systems Shorts on the terminals of the stator winding will “transformer couple” transient voltages from the stator winding to the rotor winding Out of phase synchronization events. Based on an analysis of these transients, it seems that these transients could be up to 5 times the DC voltage. Thus a maintenance hipot of about 50% of the acceptance hipot seems reasonable. If you want more detailed information you might want to check out the March issue of the IEEE Electrical Insulation Magazine. I would appreciate your opinions on whether hipot testing should be done on rotor windings. Although Iris Power-Qualitrol is relatively new to the hardware associated with endwinding vibration monitoring, it has broad experience with continuous machine condition monitoring since it introduced continuous machine monitoring systems in 1994 (based on prototypes Iris Power staff had been developing since 1982). Iris Power’s staff of world-class motor and generator experts have over 25 years of experience with fiber optic endwinding vibration monitoring – both with the technology involved and with interpretation of the results. In the late 1980s Iris’ Joe Kapler first used fiber optic endwinding sensors to monitor the vibration levels in a two pole, 210 MW, hydrogen-cooled turbine generator that was resonant near 120 Hz. In his 2004 book, “Electrical Insulation for Rotating Machines”, Dr. Greg Stone published some of the first guidance for interpreting such results beyond the simple concept of trending. He was also a coauthor of the 2011 EPRI Report PID 1021774 entitled “Generator Stator Endwinding Vibration Guide”. This expertise and experience has allowed Iris Power to develop a monitoring system that offers the optimal sighting of the sensors, long lived accelerometers, a state of the art monitor as well as comprehensive training on its use and results interpretation. Contact your Iris Power sales representative for more information. - continued from page 3 - Qualitrol—Iris Power Continues to Expand Offices around the World! Iris now has sales and field service specialists located in 8 counties, and will shortly be expanding to more. At present we have sales and field service people in the following offices: Brazil (2 people) Canada (8 people) China (6 people) India (3 people) Switzerland (2 people) UAE (1 person) UK (1 person) USA (5 people) This expansion of offices makes serving our customers more timely and cost-effective. Many of these offices have opened since Iris Power was acquired by Qualitrol two years ago. Our staff in China: Rick Wu (Manager), Sales: David Peng, Jason Lin, and Tiger Wang Field Service Staff :Len Qin, Feiyu Liu Qualitrol-Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2 Telephone: 905-677-4824; Fax: 905-677-8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com