How to Avoid Severe Incidents at Hydropower Plants
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International Journal of Fluid Machinery and Systems DOI: http://dx.doi.org/10.5293/IJFMS.2017.10.3.296 Vol. 10, No. 3, July-September 2017 ISSN (Online): 1882-9554 Original Paper How to Avoid Severe Incidents at Hydropower Plants Masashi Yasuda1 and Satoshi Watanabe2 1 Hydropower Department, JPower 15-1, Ginza 5-Chome, Chuo-ku, Tokyo, Japan [email protected] 2Department of Mechanical Engineering, Kyushu University 744 Motooka, Nishi-ku, Fukuoka, Japan [email protected] Abstract Hydropower is now changing its role from the energy generator into the most powerful and reliable tool for stabilizing the electrical network, especially under the increase of intermittent power sources like wind-power and solar-power. Although the hydropower plants are the most robust generating facilities, they are not immune from unexpected severe incidents having long downtime, considerable restoration cost and sometimes fatalities. The present paper provides some study results about severe incidents in the conventional hydropower plants, mainly about the flood, fire and electro- mechanical troubles, except for the incidents of civil facilities. It also provides some possible scenarios which may lead some measures how to avoid such incidents. Finally, it provides some comprehensible recommendations to avoid severe incidents based on experiences. Keywords: hydropower plant, severe incident, flood, fire, turbine failure, generator failure 1. Introduction Hydropower is now changing its role from the renewable energy generator into the most powerful and reliable tool for stabilizing the electrical network, especially under the increase of intermittent power sources like wind-power and solar-power. Although the hydropower plants are the most robust generating facilities, they are not immune from unexpected severe incidents having long downtime, considerable restoration cost and sometimes fatalities. JPower is the largest wholesale power company in Japan, having a hydropower fleet comprising from 53 conventional hydropower plants (hereinafter it is abbreviated as HPP) of 3,600 MW and 7 pumped storage plants (hereinafter it is abbreviated as PSPP) of 4,970 MW in Japan and participating the operations of one PSPP (720MW) and a few HPPs in overseas. JPower started the hydropower developments from the early 1950’s and provided many technical consulting services for the overseas hydropower projects from 1960’s. Figure 1 shows some pictures of JPower’s hydropower plants. Note: From left to right of the first row; Sakuma Dam, Kuttari Dam and Oku-tadami HPP From left to right of the second row; Numappara PSPP, Okukiyotsu PSPP and Kalayaan PSPP (Philippines) Fig. 1 Some hydropower plants of JPower Received August 30 2016; accepted for publication April 24 2017: Review conducted by Young-Seok Choi. (Paper number O16029K) Corresponding author: Masashi Yasuda, [email protected] 296 The present paper provides some study results about severe incidents in the conventional hydropower plants, which have been experienced by JPower as well as the collected one from the publicized papers. It also provides some possible scenarios, which may provide some measures how to avoid such incidents. Finally, it provides some comprehensible recommendations and prospects to avoid severe incidents based on the studies. It is an objective of this paper to provide some practical approaches and recommendations to avoid any future and similar incidents. Since the authors are not the expert of civil engineering, so that the topics of dam, gate and waterway are excluded from this paper. In addition, the severe machinery incidents of pumped storage plants had been already publicized in IAHR 2016 [1], so that the subjects of the present paper are mainly limited to the flood, fire and machinery incidents in conventional hydropower plants. 2. General tendencies of incidents in Hydropower plants Figure 2 shows the probability of machine troubles per year and per one unit for each power plant type, which was obtained after analyzing 16,500 incidents, occurred at about 1,800 generating units in Japanese hydropower plants from 1995 to 2004 [2]. For an example, it indicates that the probability ratio of turbine failure in pumped storage type is about 0.33, which means that a pump- turbine has one failure per three (3) year’s operation averagely. The total ratios are around 1 to 2 for each hydropower type, i.e. the average Japanese hydropower plant has one (1) or two (2) machine troubles per year and per unit, therefore it may be said that the Japanese hydropower plants are generally well-maintained with minimal failures. Although this figure shows only machine failures, it indicates that the probabilities of failures are dependent on both the equipment and the hydropower types. The run of river type has the lowest probabilities of failures because of the continuous operation with less frequent start-stops, meanwhile, the pumped storage has the highest ratio due to its frequent start/stops and complicated configurations. Fig. 2 Probabilities of failures for each power plant type [2] Table 1 shows the distribution of 985 incidents occurred in around 1,260 Japanese hydropower plants from 2004 to 2012 [3], which are comparatively serious incidents to be reported to the Government due to a law. It is very obvious that a half of incident is related to the flood. Another main cause is the maintenance troubles, mainly due to the degraded machine by the longtime operation. This table has no distinction between the HPPs and PSPPs, so that it shows the general tendency of HPPs due to the majority. Table 1 Distribution of incidents in Japan from 2004 to 2012 [3] (in percentage) Design Maintenance Other Natural Flood Earthquake Others Total Problem problem Disaster Civil facilities 0.3 4.6 6.9 2.2 1.7 1.7 17.5 Turbine 1.8 8.6 1.2 0.0 0.7 2.2 14.6 Generator 1.8 4.7 1.6 0.0 0.5 1.6 10.3 Main Circuit Eq. 1.5 1.8 16.6 0.4 1.4 1.4 23.2 Station Service Eq. 0.3 1.4 2.9 0.0 0.6 0.8 6.1 Control Eq. 0.2 2.5 18.7 0.2 0.3 1.1 23.0 Others 0.4 1.6 0.6 0.4 0.8 1.4 5.3 Total 6.4 25.3 48.6 3.2 6.1 10.4 100.0 Figure 3 shows the tendency of 1,687 incidents recorded in the same reports [3] for Table 1 from 1988 to 2012. It is clear that the number of incidents due to natural disasters is increasing year by year. The maintenance failures like the degradation of machines are also increasing. Figure 4 shows the breakdown of the natural disasters. It is obvious that the flood is dominant. 297 500 Landslide Storm Snow and Ice and 4% 1% 400 Avalanche 4% Lightning 300 4% Earthquake 200 5% 100 Number of IncidentsNumber of 0 1988-1992 1993-1997 1998-2002 2003-2007 2008-2012 Flood 82% Era Design Failure Maintenance Failure Natural Disaster Others Fig. 3 Tendencies of various incidents [3] Fig. 4 Breakdown of natural disasters [3] Figure 5 shows the incident number for each range of the downtime by analyzing 1,300 incidents occurred in 109 generating units, comprising of 85 generating units in fifty-two (52) HPPs and 24 units in seven (7) PSPPs, from 2004 to 2015. Figure 6 shows the accumulated downtime for each range from the same data of Figure 5. Although the outages longer than one month were merely one percent of all incidents in the number, those severe incidents occupied sixty-two (62) percent of the total downtime. It means that the majority of total downtime is due to the rare but serious incidents, not due to the daily, frequent and minor ones. That is why the severe incidents should be reduced to achieve better maintenance of the plant. Meanwhile, another view may be possible for those figures, like the current good maintenance is keeping almost all the incidents within the minimal outage hours, so that only unexpected incidents sporadically happen and they are inevitable. However, if we want to achieve a higher maintenance level, it is necessary to reduce the severe incidents into minimal level. 10 days to More Less than 3 hour to 1 month than 1 3 hour 1 day 2% month 1% 6% 1 day to 1% 1 day to 10 days 10 days 16% Less than 15% 3 hour More More 41% than 1 than 10 3 hour to month days 1 day 62% 16% 40% Fig. 5 Breakdown of number of incidents Fig. 6 Breakdown of total downtimes Table 2 shows the distributions of severe incidents, picking out the serious mechanical breakdown and/or severe incidents having considerable downtime more than 10 days, from the same data of Fig.5 and Fig.6. Table 2(a) shows the records of HPPs and Table 2(b) shows that of PSPPs. The majorities of severe incidents in the conventional hydropower plants are also floods and degraded machine troubles. The typical flood damages were the clogging of tailrace outlet and/or intake with mud and debris. Machine troubles happened by various causes, including the oil leakages from Bulb runner hub, oil leakage and water intrusion in bearing oil reservoir, loosen terminal bolts at circuit breakers and generators, detachment of counter weight of intake gate, etc. Table 2 Distribution of severe incidents in hydropower plants (in percentage) (a) Conventional Hydropower plants (b) Pumped Storage Plants Design/ Maintenance/ Natural Design/ Maintenance/ Natural Total Total Manufacturing Deterioration Disaster Manufacturing Deterioration Disaster Civil facilities 0.0 8.3 33.3 41.7 0.0 0.0 0.0 0.0 Turbine 0.0 19.4 8.3 27.8 0.0 20.0 0.0 20.0 Generator 2.8 8.3 0.0 11.1 10.0 40.0 0.0 50.0 Main Circuit 2.8 8.3 0.0 11.1 10.0 0.0 10.0 20.0 Station Service Circuit 0.0 5.6 2.8 8.3 0.0 0.0 0.0 0.0 Control Eq.