e uptime m 1• 11 gazine Hydro: Magnetic flux • A06 module • Field news Case study / Magnetic flux • Turbo-machinery diagnostics Turbo-machinery e uptime m 1• 11 gazine # 1/06 3 Technical News Effective Hydropower Monitoring Demands Magnetic Flux Monitoring of Hydro Generators oday’s global installed hydro- In this issue we also present the new 7 Product Update – Dedicated power capacity of approximately SM-610-A06 hydro monitoring mod- Hydro Monitoring Hardware T 780 GW, represents approximately ule to the VC-6000 data acquisition 8 Field News – Hydro Monitor- 20% of the world’s electricity or about system. The introduction of the SM- ing Projects in Southwestern 88% of electricity from all renewable A06 simplifies vibration monitoring of China sources. Despite rapid development medium sized units for both safety 9 Case Study – Early detection from other renewable energy sources and condition monitoring applications of a compressor impeller crack such as wind, biomass and solar, using Compass 6000. In most cases 14 Field News – Hydro Monitor- hydropower capacity has grown in a single module is sufficient for moni- ing Projects in Turkey leaps and bounds over the years and toring an entire hydro unit! 15 Case Study – VC-1500 is still growing. Only 25% of the po- Selected for monitoring small tential capacity has been realized up Visit our web site for more informa- hydroelectric generating units to now! In this powerful sector of the tion on our hydro monitoring tech- in Norway energy market, what does this mean niques, applications and products. 20 Events 2011/12 in terms of hydro machine operation In addition to the hydro theme for this and maintenance? A lot; machine issue of Uptime, there is also a spe- uptime is more important now than cial feature section on turbo-ma- ever before! chinery diagnostics. Diagnostic services have always played an im- This issue of Uptime is dedicated to portant role in the expertise we offer hydropower generating unit monitor- our customers, and we are including ing. Brüel & Kjær Vibro have been a case story on this particular sub- monitoring hydropower turbines for ject. This demonstrates how we can Uptime Megazine is a newsletter pub- turn measurement data into action- lished by Brüel & Kjær Vibro to keep you over 15 years worldwide. With signifi- up-to-date with new machine monitoring cant experience in monitoring all types able information that provides the trends and technologies. This issue fo- of machines in all types of hydroelec- longest lead time to failure, enabling cuses on hydroelectric power station tric configurations, ranging from under you to be proactive in machine main- monitoring. 1 MW to 700 MW, Brüel & Kjær Vibro tenance activities so they can be If you have comments, ideas or case have developed and implemented undertaken in a planned manner. I stories, please contact: monitoring strategies ranging from am delighted to launch this special The Editor, Uptime Megazine, Brüel & Kjær Vibro, simple safety installations to compre- edition of Up- DK-2850 Naerum, Denmark. hensive safety/condition monitoring time, and hope Tel.: +45 7741 2500 applications involving advanced you enjoy read- Fax: +45 4580 2937 measurement techniques for the gen- ing it! E-mail: [email protected] Copyright 2011, all rights reserved erator, shaft/bearings, turbine and Editor-in-chief: Shohan Seneviratne auxiliaries. Read more about this in Managing Editor: Mike Hastings the case story and technical article in Alfred Schübl Design&Production: Gitte Blå Design Cover photo: Ermenek dam, monitored by this issue of Uptime. Hydro key VC-6000 Compact Monitor. account manager 2 uptime megazine • 01/11 technicalfocus turbo-generators used in other utilities Purpose for Magnetic Flux rotate at 3000/3600 rpm. The slow monitoring the Monitoring of rotation of the hydro generators ne- magnetic flux cessitates many rotor poles in order The magnetic flux Hydro Generators to generate power at line frequency. monitoring technique An enormous rotor is therefore need- is primarily intended for ed to accommodate the large number detecting shorted rotor of poles, sometimes exceeding 12 m turns and incipient ground in diameter. Such a large generator, faults on rotor salient pole windings. with a relatively small air gap, is sus- A short generally occurs if the winding ceptible to small deformations that insulation is damaged or degrades Special monitoring techniques can create enormous imbalance forc- over time. A shorted turn on a rotor are needed to monitor the unique es. The resulting vibration can cause pole will not necessarily require the premature failure of bearings and machine to be immediately shut down design of hydro generators. other components. for service but it will degrade perfor- mance. It can cause hot spots and n order to extract the maximum The massive area of the generator force the field current to increase. It energy available from a particular also makes it susceptible to hot can also create an unbalance that Iwater head, the hydrogenerating spots, looseness, and other irregu- results in excessive vibrations and units at a hydroelectric power station larities. There are several specialized overheating. have to rotate at relatively slow measurement techniques to detect speeds; 50-300 rpm. and diagnose these problems, but There are several factors that affect this article will focus on one such the magnetic flux density; namely the This makes the hydro generators technique; the magnetic flux meas- physical air gap between the stator unique as electrical machines, since urement. and poles, temperature of the wind- 01/11 • uptime megazine 3 ings and the exciter field current and Figure 1. Prepa- voltage. Therefore to more accu- ration of a hydro rately monitor to alarm limits and to generating unit simplify trending, magnetic flux stator (prior to should be correlated to these pro- installing the cess parameters. The most important magnetic flux correlation for a magnetic flux meas- sensor). urement, however, is with the air gap measurements. This helps to deter- mine if a generator unbalance is due to physical reasons (change in air gap) or electrical reasons (a shorted channels or between the ends of the pared to alarm limits in the Compass pole turn). windings. The sensor measures the monitoring system and then stored in magnetic flux of each passing rotor the database. Variations in the magnetic flux meas- pole face. The signal from the condi- urements can be small, so an accu- tioning unit is referenced to a phase/ The magnetic flux sensor resembles rate measurement is required for speed tacho, so the signal from each an air gap sensor (e.g. Brüel & Kjær each pole. As an example, on a 72- individual pole can be identified. Vibro EQ 2431) and in fact both are pole machine with 20 turns/pole, a These signals are conditioned, com- installed in the same way, but this is single shorted turn will reduce the magnetic flux measured by only 5%. Sensor The magnetic flux sensor system (e.g. Brüel & Kjær Vibro EQ 2430) includes a long thin sensor that is permanently glued to the inner wall of the stator. It is attached to a signal conditioning box/ power source a few meters away by signal wires that pass though the stator ventilation Figure 2. Magnetic flux sensor shown on the left, air gap sensor shown on the right. 4 uptime megazine • 01/11 Hall Effect – The theory behind the operation of the magnetic flux sensor The magnetic flux sensor measures the magnetic flux density using the Hall ef- fect. This principle was discovered by Dr. Edwin Hall in 1879 but has only been used within the last 30 years since the development of solid state electronics. Imagine a thin rectangular conductor or Figure 3. Com- semi-conductor that has current flowing pass 6000 plot through it. In the absence of a magnetic above showing field, there would be no voltage across the the raw time width of the conductor perpendicular to the signal that is current flow, as shown in Figure 5. The saved in the Hall effect occurs if a magnetic field cuts database for perpendicular through the rectangular diagnostic pur- conductor. This produces a potential poses. across the width of the conductor, that is proportional to the current and the flux Figure 4. Maxi- density of the magnetic field perpendicular mum peak value to the conductor, as shown in Figure 6. extracted for each pole (single val- A Hall effect element similar to ue) to be used for that shown in the figures monitoring, trend- below is built into the mag- ing and alarming netic flux sensor. Assum- purposes. ing the sensor current is technical constant, the output focus where the similarity ends. The air gap sensor voltage of the sensor operates on a capacitive prin- sensor, i.e. the Hall ciple for measuring distance between effect voltage VH, will be the stator wall and the passing rotor directly proportional to pole face. The capacitive current the strength of the mag- measured between the sensor plate netic field of each passing and the passing rotor pole is propor- rotor pole. tional to the dielectric value between these surfaces, which in turn is pro- portional to the physical distance (i.e. the air gap). A magnetic flux sensor measures the magnetic field between the stator and the passing rotor pole face and operates on an entirely different principle, namely the Hall Figure 5. No magnetic field present. effect (see the inset describing the theory behind the Hall effect). Data Monitoring and Diagnostics The magnetic flux signal is used in an automatic monitoring capacity to detect a possible shorted turn. It is also used in a diagnostic capacity as a plot display to distinguish, for ex- Figure 6.