Preventive maintenance techniques to ease the maintenance activities of hydropower stations. *Corresponding author

Transcription

1 Proceedings of the International Symposium on Current Research in Hydraulic Turbines CRHT VI March 14, 2016, Turbine Testing Lab, Kathmandu University, Dhulikhel, Nepal Paper no. CRHT Preventive maintenance techniques to ease the maintenance activities of hydropower stations Balendra Chhetry 1*, Bhola Thapa 1, Hari Prasad Neopane 1 and Biraj Singh Thapa 2 1 Turbine Testing Lab, Department of Mechanical Engineering, Kathmandu University, Nepal 2 Waterpower Laboratory, Norwegian University of Science and Technology, Norway *Corresponding author ([email protected]) Abstract Preventive maintenance is one of the techniques to improve the equipment life and avoid unplanned maintenance activities in hydropower stations. The plant outage of hydropower stations can be reduced to some extend by adopting the preventive maintenance technique. This paper elaborates the maintenance technique adopted in some of hydropower stations in Nepal. The paper also illustrates the preventive maintenance software build for hydropower stations, aiming to explore the application of the software in hydropower stations to reduce the forced outage of the machine. Keywords: Preventive maintenance, force outage, SAJILO Hydro preventive maintenance software 1. Introduction The reliable operation of hydropower plants with minimum O&M cost is key consideration for long rung sustainability of hydropower development. The economic operation of an electric utility system requires the simultaneous solution of all aspects of the operation scheduling problem in the face of system complexity, different time-scales involved, uncertainties of different order, and dimensionality of problems [1]. An effective maintenance strategy is essential in delivering safe and reliable electric power to customers economically [2]. The reliability of system operation and production cost in an electric power system is highly affected by the maintenance outage of generating facilities [3]. Experience of running hydropower station reveals that even after detailed project planning/quality control measures taken at various stages from inception to commissioning several unforeseen problems do take place during the operation and maintenance resulting in forced outages/low generation and load shedding etc. causing misery to the consumers and undesired set back to the overall economy [4]. Sediment induced turbine wear in hydraulic machinery is probably the most serious problem in operation and maintenance of hydropower projects in Himalayan region [5]. Besides damage of underwater components numbers of operation and maintenance problems are encountered due to sedimentation. This consequently leads to outages of the unit, resulting loss in generation, with consequent loss of revenue. Experience shows that most of run-off rivers hydropower projects in Nepal have been suffered prolonged forced outage because of frequent shutdown of the machine due to problems come across during operation of the machine. Corrective maintenance scheduling has been in practice to solve the operational

2 problems in hydropower stations. The time and cost of corrective maintenance is always in higher side and may affect the allocated maintenance budget of the plant and affect the plant performance as the pattern of equipment failure is uncertain. Nepal Electricity authority is the leading government organization to generate, transmit and distribute adequate, reliable and affordable power by planning, constructing, operating and maintaining all generation, transmission and distribution facilities in Nepal's power system both interconnected and isolated. The total energy generation of fiscal year of 2013 has registered 2,350 GWh whereas the total outage hour of the plants during the fiscal year is 133, hours [6]. Outages of the plants, such as planned outage and force outage are an excellent indicator for performance of the plant. The planned outage is determined by the provisions made for inspections and repair work of the damaged components necessary to upgrade the plant performance. Some unforeseen problems are encountered during operation of machine which leads to increase the force outage of the plant. The force outage illustrates the real condition of the plant and machine. The hydropower development companies are continuous focus on rise of cost for hydroelectric plants and electric energy. It is natural to be maintaining those high-value assets through maintenance, and operation with correct methods, for save it from rapid deterioration and increase the long term life span. In 1954 the Japanese scientists and engineers discovered the preventive maintenance [7]. Preventive and corrective maintenance scheduling have been implemented in hydropower stations. Preventive maintenance is defined as the maintenance carried out at predetermined intervals or according to prescribed criteria and intended to reduce the probability of failure or the degradation of the functioning of an item [8] whereas corrective maintenance is defined as the maintenance carried out after fault recognition and intended to put an item into a state in which it can perform a required function [9]. Maintenance scheduling is necessary to ensure quality and reliable operation of equipment to minimize the force outage of the plant. Preventive maintenance program can be considered to attain maximum plant availability and equipment reliability, and to reduce forced outages. The program also helps to reduce the unexpected failures during operation of machine of hydropower stations. Preventive maintenance covers inspection, replacement, repair of any piece of equipment or component based on time and set parameters. It even includes painting, lubrication, cleaning, adjusting and minor component replacement to extend the life of equipment. Its main purpose is to minimize costly break down and unplanned shutdowns of the units. 2. Maintenance Scheduling of Hydropower Stations Maintenance management has been the subject of many articles during the last decades, where thorough discussion on maintenance optimization models, maintenance techniques, scheduling, performance models, information systems and policies can be found [10]. Maintenance scheduling is another interesting area that needs more investigation [11]. United States Department of the Interior Bureau of Reclamation published maintenance scheduling for mechanical equipment [12] and electrical equipment for hydropower stations [13]. These papers give the guidelines and advice the procedure for maintenance of mechanical and electrical equipments for hydropower stations. It described types of maintenance adopted in hydropower stations where intent of preventive maintenance is to prevent maintenance problems or failures before they take place by following routine and comprehensive maintenance procedures. Reliability centered maintenance (RCM) have been in picture for maintenance of hydropower stations. A guideline for development of small hydropower projects published by Alternate Hydro Energy Center Indian institute of technology is defined RCM as a process used to determine the maintenance requirements of any physical asset in its operating context. In this approach basic thrust is to eliminate more costly unscheduled maintenance and to minimize preventive maintenance. This approach is required

3 well managed monitoring system and proper documentation. Besides these, RCM system not compromise the breakdown maintenance, it is not well accepted in sediment laden hydropower projects, especially hydropower stations of developing countries. Conditioned based maintenance scheduling (CBMS) also been in practiced in hydro power station which includes the monitoring systems to predict problems and possible failures. The CBMS includes the analysis of oil, vibration, temperature and other equipment parameters to predict the problems in future. This approach acts as the part of the maintenance itself as it involves the test and examination of the equipment and its parameters. It is difficult to adopt the CBMS due to expensive of monitoring the entire equipments of hydropower stations. Preventive maintenance scheduling has been become popular in hydropower stations as it focus on the inspection of the components in systematic manner. It considers the frequency of daily, weekly, monthly and yearly inspection of the component as per the nature of their function in the system. The daily and weekly checks include the inspection of operating parameters of the equipment during running condition of generating units such as temperature of oil for turbine and generator bearing, air and oil pressure of the governor system, water leakage from the draft tube and shaft seal and other parameters. The monthly checks include the inspection of the equipment including weekly inspection with requirement short shutdown of the units for rectification of the parts of the equipment. The inspection of oil filters, heat exchanger, shaft seal, and other similar type of checks under this inspection. It is necessary to inspect the machine more critically after operating the units in flood season to determine the condition of underwater components of the turbine. The schedule includes the inspection of turbine such as runner, guide vanes and operating linkage, wearing rings and facing plates and bearings. The observed data and results of the inspection help to plan the long term maintenance of equipment such as overhauling of the machine. 3. Performance of Hydropower Stations in Nepal In most hydropower stations in Nepal, preventive maintenance is not considered seriously and conventional maintenance practice has been adapted to repair and maintenance of components. Maintenance personnel are not aware of new maintenance technology and follow the conventional trend of inspection as in mid year of In some hydropower stations, maintenance personnel patrolled every hour in the power station and recorded the values of temperatures, pressures, oil-water levels and other measurement without knowing the importance and impact of measurement in operation of generating units. Several log books of recorded measurement are maintained which increase burden of paper work and create dummy responsibility among the workers. The author has made a case study of Modi Khola HEP and presented the impact of operational problems in energy generation due to lack of preventive approach during operation of the plant [14]. The table 1 shows the availability factor of some of major hydropower stations in Nepal.

4 Table 1: Availability factor of major hydropower stations of Nepal for fiscal year 2012/2013 S.No Name of Power Station Installed Capacity ( MWh) Total Machine Hours Total Running Hour Total Outage hours Availabilty factor in % 1 Kali Gandaki 'A' , , , Middle Marsyangdi , , , Marsyangdi , , , Kulekhani , , , Kulekhani , , , Trishuli , , , Gandak , , , Modi , , , Sunkoshi , , , Ilam (Puwakhola) , , , Chatara , , , Panauti , , , Seti , , , Fewa , , , Total : 359, , , The paper describes the loss of energy generation of hydropower stations and the performance of the plant due to force outage of the machine. Total generation at Modi Khola power station was at its lowest since its commissioning because of long shut down for maintenance of a cooling system failure caused by sediment. Similarly, the balancing pipe of head cover at Kaligandaki was replaced because of damage in pipe, requiring tunnel dewatering due to malfunction of main inlet valve. Some reasons for force outage of the Modi Khola HEP are identified such as increase temperature in turbine bearing temperature, leakage in shaft seal and vibration of the machine. There are several reasons behind the force outages at the plant, such as ineffective maintenance plan, a lack of awareness of preventive maintenance techniques, unsystematic management and storage of spare parts, poor documentations and drawings, lack of proper record- keeping of past maintenance of the machine components. The availability of equipment, such as electro mechanical and hydro mechanical equipments for power generation depends on their quality, errection and alignment of the components and the experience of the plant operator. Besides these, implementation preventive maintenance program can minimize the loss of generation to some extent by considering the operational problems before it occurs. 4. Preventive Maintenance Software Program for Hydropower stations 4.1 General The maintenance of the generating machine need to be organized to ensure that each component of the plant is regularly inspected and make necessary adjustments for smooth operation of the hydro power plants. The results of each inspection should be recorded, so that the history of individual components is available for future reference and to evaluate the performance of the plant. The lack of proper maintenance scheduling causes the decrease in functioning of components of the plant which results frequent breakdown of the machine and declination in generating capacity. The aging of the plant, unscheduled maintenance and frequent breakdown are the main factors to increase the deterioration of the equipment. The deterioration of the equipment can be minimized by implementing preventive maintenance technique in hydropower stations. 4.2 Discussion on SAJILO HPMS Preventive maintenance software is developed, SAJILO HPMS for hydropower stations aiming to improve operational efficiency of the machine, bring the transparency and accountability in maintenance

5 work, maintain the proper Inventory control of consumables, reduce the paper work for maintenance activities and minimize the operation & maintenance cost. The concept of the SAJILO software is shown in figure 1. Figure 1: Flow chart of SAJILO Hydro Preventive maintenance software The software has provision to make a database by entering the details of equipment and component of the hydropower stations. Database of individual hydropower stations can be generated, maintained and recorded for the maintenance of the equipments. The database is important feature of the software where past maintenance activities of the equipment are stored which helps in to perform the similar type of maintenance. The database also contains the information of the machine availability, which can be useful to determine the operational efficiency of the plant and analyze the performance of the plant. The equipment of Electro mechanical system, such as generator, exciter, turbine, governor, and other auxiliary system are breakdown in to their respective components. It is necessary to identify the jobs for each component of respective equipment so that inspection approach can be made for different nature of jobs. The software can generate the work orders for the inspection, such as patrol inspection, routine inspection and periodic inspection of components including their nature of frequency of occurrence. Each job has its own Weightage, so responsibilities to handle the job is mentioned in work order. These provisions bring the transparency and accountability among the workers to perform the maintenance work. The figure 2 shows the work order for mechanical components of hydropower station. The work order contains the information of inspection activities such as parts to be inspected, skill level required to handle the jobs, tentative time allocation to perform the jobs and frequency interval of the jobs for next work order including the mode of generating units. Each job is assigned to skill level as per the nature of inspection to be performed with the mode of operation such as, unit operation, unit stop and plant stop condition. The work orders give the clear instructions and guide lines to the maintenance personnel to execute the assigned jobs.

6 Figure 2: Work order for inspection of mechanical components The work order shows the parts need to inspect for turbine and governor equipment. The work order WO has included turbine parts for the inspection of guide bearing, manhole and sealing by allocating the jobs to respective parts. The inspection of manhole is carried out by checking the tightness of bolts and job is estimated to be carried out in approximately three hours. The skill level required to handle the job is assigned for helper where generating unit is in stop condition as the possibilities of leakage accident may occur during inspection. The inspection interval of the job is allocated for frequency of one month, means the same job will generate automatically in work order after one month of the manhole inspection so that preventive approach can be assured. Figure 3: The detail list of turbine parts The software also has a provision to organize the details of the components of the equipment so that inventory can be made in future reference. Figure 3 shows the detail list of various parts of the turbine. The equipments installed in hydropower stations are of different brands from the different manufacturer. It is necessary to make a database of the equipments and their components so that their spare parts can be easily traceable and purchase to maintain the stock for replacement and repair during maintenance. The software has a feature to analyze the result of inspection and maintenance activities during execution of the work orders. The software generates the reports of activities performed and the status of individual work order, such as scheduled and unscheduled. The scheduled of work order is indication of normal state of component whereas unscheduled point to abnormality of the equipment. Inspection of each component

7 according to the inspection guide line is required to determine and evaluate, for judging the time of repair and replace of the equipment, for planning of long term maintenance. 5. Conclusion Operation and maintenance includes the activities required to run a Hydropower stations. The cost associated with maintenance work has significant effect on total operational costs of the hydropower plant, hence proper operation and maintenance planning is vital for sustainability of the hydropower projects. Operating conditions are required to be monitored and recorded as it contains the information of causes of failures and faults which help to determine the performance of the plant and to make the strategies for long term maintenance plan. SAJILO hydro preventive maintenance software can be used as maintenance scheduling tool for hydropower stations to organize the maintenance activities and to maintain the track records of the equipment. Acknowledgement Authors would like to thank Mr. Chandan Bachhar for his contribution in making programme to prepare the SAJILO hydro preventive maintenance software. References [1] Y. Yare and G. K. Venayagamorthy, A Differential Evo-lution Approach to Optimal Generator Maintenance Scheduling of the Nigerian Power System, Power and Energy Society General Meeting Conversion and De-livery of Electrical Energy in the 21st Century, Pittsburg, July 2008, pp [2] J Anders, Probability Concepts in Electric Power Systems, John Wiley & Sons, Hoboken, [3] Sunday Olayinka Oyedepo, Richard Olayiwola Fagbenle; A Study of Implementation of Preventive Maintenance Programme in Nigeria Power Industry Egbin Thermal Power Plant, Case Study, Energy and Power Engineering, 2011, 3, [4] AHEC/MNRE/SHP Standards/ E&M Works Guidelines for Operation and Maintenance of Small Hydropower Station. [5] B Thapa, Sand Erosion in Hydraulic Machinery Doctoral thesis at NTNU, [6] Nepal Electricity Authority, Annual review Report : [7] Cassad, C.R & Kutanoglu, E. (2005). Integrating Preventive Maintenance Planning and Production Scheduling for a Single Machine. Journal of IEEE TRANSACTIONS ON RELIABILITY, 54, [8] EN 13306:2001, Maintenance terminology, European Committee for Standardization, 200. [9] IEC , International Electrotechnical Vocabulary Chapter 191 : Dependability and Quality of Service. International Electrotechnical Commission (IEC), [10] H. Wang, A survey of maintenance policies of deteriorating systems, European Journal of Operational Research, vol. 139, no.3, pp , [11] D. Sherwin, A review of overall models for maintenance management, Journal of Quality in Maintenance Engineering, vol. 6 no. 3, pp , [12] United States Department of the Interior Bureau of Reclamation, Maintenance Scheduling for Mechanical Equipment, Facilities Instructions, Standards, and Techniques Volume 4-1A Revised 2009.

8 [13] United States Department of the Interior Bureau of Reclamation, Maintenance Scheduling for Electrical Equipment, Facilities Instructions, Standards, and Techniques Volume 4-1A January 2012 [14] Chhetry B, Thapa B, Thapa BS., Assembly design to ease turbine maintenance in sediment-laden conditions. International journal on hydropower and dams. 2014:82-8.