Installation of a wide-area maintenance system for hydroelectric facilities in Thailand will allow the Electricity Generating Authority of Thailand to reduce man-hours required for plant operation and maintenance, decrease unit downtime and extend the time between inspections and overhauls.
By Kanchit Ngamsanroaj and Hisashi Takamine
Most of the 1,560 MW of hydropower plants in Japan are unmanned. Operations and maintenance of these plants are handled using a wide-area maintenance system, in which one office manages multiple facilities. Unmanned plants are equipped with remote monitoring systems that continuously record data from various devices, such as tailrace level, turbine discharge, and generator vibration. Condition-based maintenance is used.
In Thailand, all the principal hydro plants — 22 sites with total capacity of 3,424 MW — are manned for maintenance and operation. Time-based preventive maintenance is the primary method used. With equipment being repaired and/or replaced based solely on the passage of time, the maintenance cycles are shorter than those in Japan.
To take advantage of the innovations in hydro plant operation and maintenance in Japan, the Electricity Generating Authority of Thailand (EGAT) decided to install a remote monitoring system for demonstration at its 30 MW Mae Ngat plant. The goal of this installation was to verify the possibility of establishing a wide-area maintenance system in Thailand.
Hydro generation in Thailand
The hydro plants in Thailand are concentrated in the northern and northeastern areas. EGAT's 20 plants total 99% of the more than 3,500 MW of hydro capacity, with the remaining 1% being small plants (up to 10 MW) owned by the Department of Alternative Energy Development and Efficiency (DEDE) under the control of the Ministry of Energy and Provincial Electricity Authority (PEA).
Many hydro plants in Thailand have been operating for several decades, and their maintenance needs are increasing. Maintenance upgrading and conversion to more efficient maintenance methods are being implemented to improve operating rates and extend maintenance cycles.
Thus, the need to build a wide-area maintenance system is high for the future operation of hydro plants in Thailand. Under EGAT's maintenance system, multiple facilities around the same river or in the same area are controlled by the main hydro plant, with 400 to 500 staff, including those for indirect departments. EGAT plays a central role in the maintenance and operation of hydro plants in Thailand, also overhauling plants owned by DEDE upon request.
Installing a wide-area maintenance system in Japan
In the late 1970s and early 1980s, most hydro plants in Japan were shifted to a system involving the centralized observance of representative items using remote monitoring and control systems, as well as patrol from the maintenance bases several times a month. This transition was made mainly to keep up with the increased number of plants coming on line and to improve the management of electric power companies. It was possible to provide maintenance and operation for more plants with a minimum number of staff.
There are some disadvantages to unmanned operation, including the difficulty of detecting signs of abnormality at an early stage and the impossibility of continuously collecting detailed device data. To solve these problems, Hokkaido Electric Power Co. Inc. (HEPCO) developed a remote monitoring system to collect maintenance data and transmit it to the office in real time. Subsequently, each electric enterprise developed a remote monitoring system to suit its maintenance needs. The number of system installations has increased dramatically with the advancement of functions and decrease in price of personal computers and sensors in recent years. Today, this setup has become an essential tool in the efficient and advanced maintenance and operation of hydro plants in Japan.
All of HEPCO's 53 hydro plants, with a total capacity of 1,231 MW, are unmanned. The rate was around 50% in 1970 but reached 100% in 1986. HEPCO developed a remote system that can monitor almost all the numeric and failure data of its power plants in real time. The system was implemented gradually, starting mainly with large and/or remote plants. The system is now installed at almost 80% of HEPCO's hydro plants, contributing greatly to improvements in the quality of maintenance by determining appropriate device inspection cycles and improving recovery time from accidents.
Installation of wide area monitors
For this project, a remote monitoring system with HEPCO's specifications was installed on Unit 1 at the Mae Ngat plant in Thailand. For the installation and demonstration, EGAT and HEPCO formed a working group. The tasks of this group were to conduct a demonstrative installation of the remote system and develop an installation guide concerning planning, design, procurement and construction. This group also conducts joint examination of analysis methods for maintenance data collected from the system to demonstrate the feasibility of introducing and expanding the construction of the wide-area maintenance system, including maintenance methods suitable for the deteriorating conditions of facilities.
Figure 1, on page 36, shows the locations of the plants involved in the demonstration system project. The Mae Ngat and 779.2 MW Bhumibol plants were considered the most suitable because an organizational structure for the operation was already in place at Bhumibol, which is the central power plant in the area and has control over Mae Ngat.
The remote system can transmit data and provide monitoring and maintenance support for multiple remotely situated plants from the centrally located maintenance office. It does this by connecting slave PCs installed at the plants to a master PC installed at the office in charge of system maintenance.
The main functions of the system are:
— Monitoring/maintenance support. Data on individual devices can be collected and monitored. If a failure occurs or preset low or high limits are exceeded, a warning is displayed on the monitor of the master PC;
— Turbine-generator run/stop status and failure analysis. Past status can be reviewed using a data analysis function;
— Patrol. Equipment status data obtained in the past can be displayed and printed to determine maximum/minimum values and operating time on a monthly or annual basis; and
— Monitoring data backup and file conversion. All device status data are stored on hard disks at the plant and master PCs and can be saved externally. Data can be output in the form of CSV files and can be processed or presented using spreadsheet programs.
Verifying the system
It is necessary to set basic conditions to design the electric circuits of the remote monitoring system and select the sensor installation positions, to prevent this installation from interfering with operation and maintenance of the plants. Sufficient examination must be conducted, taking into account the conditions of individual plants.
The software work group set the names of all the monitoring items to meet the limitations of the software (a maximum of 20 characters may be used to display the name of a monitoring item). Display terms other than monitoring items and phrases printed by the report function also were checked to make them easy to understand for EGAT's operators and maintenance staff. The software used was an English translation of the remote system created for HEPCO.
Because most Japanese power companies have their own communication networks, data can be transmitted via a dedicated communication line. Thus, the software for the remote system was designed on the assumption that the plant and master PCs would be connected constantly via a dedicated line. Because EGAT's corporate LAN and public line were the only communication lines available at Mae Ngat, the LAN connection method was selected using media converters, which interconverts computer serial port (RS232-C) and Ethernet. For LAN connection, EGAT assigns IP addresses to the plant and master PCs.
A communication line test was conducted before construction of the remote system to confirm the possibility of data transmission between Bhumibol and Mae Ngat. Data were collected for 2.5 months, during which time EGAT's engineers practiced methods of system operation and information acquisition for data analysis that they learned from HEPCO's staff. Figures 2 and 3, on pages 38 and 40 respectively, show examples of display windows during the demonstration period.
Analyzing maintenance data
At EGAT's plants, maintenance is conducted by resident staff, but operators of small plants may also conduct simple maintenance work. Engineers of the main plants plan and implement overhauls and other large-scale disassembly inspections. During routine maintenance/inspection, data are collected hourly and recorded on paper. However, EGAT does not use the CBM method. It basically applies time-based maintenance, in which devices are repaired and replaced based on the passage of time.
Mae Ngat contains two 4.5 MW Kaplan units that began operating in 1985. The plant annually generates 41 GWh of electricity. There are four maintenance shifts (one standby), with two operators per shift. In total, Mae Ngat has 44 staff, including the plant manager, eight operators, five maintenance staff (technicians), security guards and other supporting staff.
The Bhumibol plant contains eight Francis units with a total capacity of 779.2 MW. Units 1 to 6 are 82.2 MW each, Unit 7 is 115 MW and Unit 8 is 171 MW. Units 1 and 2 began operating in 1964 and were repaired in 1992 and 1993. Units 3 through 6 were installed between 1967 and 1969 and were repaired in 1996 to 2000. Unit 7 began operating in 1982 and Unit 8 in 1996. The plant annually generates 1,054 GWh of electricity.
There are four maintenance shifts (one standby), with nine operators per shift. In total, Bhumibol has 508 staff — 96 in operations, 106 in maintenance, 125 in civil maintenance and 181 others. Maintenance of Bhumibol is conducted by three mechanical engineers, six electrical engineers, five civil engineers and 45 technicians. Bhumibol has control over another three plants: Mae Ngat, the 124.5 MW Ban Yang and the 210 MW Ban Khun Klang. Supporting staff from Bhumibol are dispatched for regular inspections and other large-scale maintenance work on these plants.
Applying the system to EGAT's maintenance method
For EGAT's turbine-generators, operators perform instrument readings every hour, and maintenance staff conduct patrol once a day. EGAT can replace this hourly recording with the remote system. By comparison, HEPCO personnel perform patrol only every two weeks.
EGAT conducts periodic inspections every two years and major overhauls every six to eight years. The inspection cycle may be extended by about a year by analyzing past data — including generator coil temperature, bearing temperature, bearing vibrations, pressure pulsation and operating time of auxiliary machines — and by understanding device conditions using the remote system. Some of EGAT's periodic inspection items, such as bearing disassembly, may also be omitted using the remote system. HEPCO conducts periodic inspections every three to six years and major overhauls every 10 to 18 years as needed.
In addition, it will be possible to determine the service life of devices and extend the device upgrading cycle using the remote system. This can apply to the diagnosis of deterioration of runners and other mechanical parts and mechanical deterioration of stator coils of generators and other electrical parts.
Following are possible analysis methods and the expected effects of the remote monitoring system installed at Mae Ngat:
— Generator stator coils. Temperature rise is a major cause of insulation deterioration in stator coils, making management of coil temperature an important factor in prolonging service life. By grasping the highest temperature and the trend of temperature rise using data from the remote system, it will be possible to conduct maintenance and inspection of air coolers, pipes and other equipment at the most appropriate time and use coils in the best condition for a long period of time. Eventually, extension of the overhaul cycle can be expected.
— Sealing parts. While wear on sealing parts can be determined by measuring the volume of wear or leakage of the material, it is difficult to make these measurements during operation. If wear progresses and leakage increases, the operating time and frequency of the drainage pump of the turbine top cover will increase, and operating intervals will become shorter.
Using the remote system, it will be possible to estimate the wearing condition indirectly. However, leakage from the sealing device part changes with the generator operation condition, dam water level, deterioration of other parts, and other factors. Thus, comprehensive evaluation should be made taking these factors into account. Another effective method is management in combination with temperature data by installing temperature-sensing elements near the sealing parts. Effects that can be expected are optimization of the time of overhaul based on the operating frequency of the drainage pump and extension of the generator inspection cycle by grasping the leakage trend.
— Turbine-generator overhaul. A factor that affects the turbine-generator overhaul is deterioration in the performance and function of parts that must be disassembled according to their structure. However, it is possible to estimate equipment condition by controlling the deterioration factors and changes that occur due to deterioration. Through management and analysis of equipment data that affect deterioration, it is possible to extend the service life of equipment and optimize the overhaul cycle using the remote system. To improve the estimation accuracy, it is necessary to obtain data from before and after the replacement of actual parts, in addition to that accumulated by the system.
Outcomes and benefits
This demonstration project confirmed the effectiveness of constructing a wide-area maintenance system at EGAT-owned hydro plants in Thailand. The utility is now considering the full-scale introduction of this system. To ensure the establishment of CBM and other maintenance methods under the system, it will be necessary to continue capacity building in EGAT, including follow-up on the data analysis methods of the remote monitoring system.
It is possible to shift smoothly to a wide-area maintenance system by installing the master PC at a central hydro plant and PCs at multiple plants to be monitored, as in the case of this demonstration project. For this purpose, Thailand will be divided into north, northeast, central and south areas, and the central power plant of each area will serve as a maintenance center.
In fact, EGAT is scheduled to install hydropower plants at six irrigation dams. These plants are to be in operation by 2014. For efficient placement of a limited number of engineers and other human resources, it is necessary to install a remote monitoring system for these plants.
Because the condition of equipment can be followed in a timely manner with installation of the remote system, it is now possible to extend the inspection and overhaul cycles. The quantitative effects are based on the assumption that periodic inspections and overhaul cycles can be extended to 1.5 times as long using this system under the following hypothetical conditions:
The target facility is Unit 1 at Mae Ngat. The evaluation period is 40 years. The inspection cycle can be extended by one year for periodic inspections (to be performed every two to three years) and four years for overhauls (to be performed every six to 10 years). Periodic inspections require 11 days and 15 persons per day, for personnel costs of THB2 million (US$66,000). Overhauls require 30 days and 20 persons per day, for personnel costs of THB7.2 million ($237,000).
The following effects can be expected:
— Reduced maintenance man-hours. Extending the periodic inspection and overhaul cycles makes it possible to reduce the number of maintenance staff. Reducing the number of man-hours worked by engineers will enable their centralization to hydro plants and their allocation to maintenance with DEDE and other organizations. An estimated 2,025 man-hours can be saved by reducing the cycle of periodic inspections and overhauls. For example, before the demonstration, 2,130 man-hours were required for periodic inspection; this was reduced to 1,485 man-hours. For overhaul, 3,600 man-hours were required; this was reduced to 2,400 man-hours.
— Reduced maintenance cost. By extending the inspection cycle, the inspection frequency and cost can be reduced. It is also possible to track the condition of devices without disassembly, and the efficiency of inspection work can be improved using data collected by the remote system.
— Reduced CO2 emission by decreasing the operating hours of thermal plants. By reducing the frequency of periodic inspections and overhauls, it is possible to shorten shutdown periods. Because extra operation of thermal plants to cover for these shutdown periods can be reduced, it is also possible to reduce the fossil fuel cost and CO2 emission.
Because it is possible to cut out five periodic inspections and two overhauls over 40 years, power generation at the Mae Ngat hydro plant can be increased by 12,420 MWh. And, as a result of reducing the operating hours of thermal plants for the same amount of power generation, fuel costs can be saved and CO2 emissions can be reduced by about 6.3 tons.
Kanchit Ngamsanroaj is senior engineer with Electricity Generating Authority of Thailand. Hisashi Takamine is an electrical engineer with Hokkaido Electric Power Co. Inc. in Japan. They were the project coordinators for this collaborative project between EGAT and HEPCO.
This article has been evaluated and edited in accordance with reviews conducted by two or more professionals who have relevant expertise. These peer reviewers judge manuscripts for technical accuracy, usefulness, and overall importance within the hydroelectric industry.