A Centralized Strong Seismic Oscillation Monitoring System

Transcription

1 2017 5th International Conference on Mechanics and Mechatronics (ICMM 2017) ISBN: A Centralized Strong Seismic Oscillation Monitoring System Yi ZHANG 1, Rui-Jun ZHU 1, Bo JIN 2, Xian-Long HE 3 1 National Electric Investment Group Jiangsu Offshore Wind Power Co. LTD, Yancheng, , China 2 Zhejiang East China Engineering Safety Technology co. LTD, Hangzhou, , China 3 Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics, China Earthquake Administration, Harbin , China Abstract: Strong seismic oscillation response characteristics of Wind Power Tower and Dam are important basis for rapid assessment the damage of such structure after earthquake; Strong seismic oscillation monitoring is also an important part of this Power station structure s safety monitoring system. However, the existing strong seismic oscillation monitoring system has some defects, such as high cost of equipment and maintenance, automation analysis ability is not strong and electromagnetic interference is weak. A new centralized strong seismic oscillation monitoring system is designed in this paper: First of all, we designed a centralized strong seismic oscillation monitoring recorder which has 24 channels and designed a kind of waterproof accelerometer. Then, a practical and effective solution is proposed for the common 50Hz power frequency interference and error triggering. Finally, we design a set of remote data receiving and on-line analysis software, which can automatic analysis and report timely, it is easy to management too. Compared to the traditional distributed strong seismic oscillation monitoring system, this new system has the advantages of low equipment cost, unattended, automatic processing of strong seismic oscillation monitoring events, small probability of false triggering, the parameters such as intensity can be timely reported, and it can also achieve the interaction with smart phones through SMS, . This new centralized system has been deployed in a plurality of Water Power Stations and Wind Power Stations. Recently several strong earthquake events have verified the main characteristics and reliability of this system. 1 Introduction In our country, a lot of Water Power Stations and Wind Power stations have been built in Yunnan, Sichuan, East China Sea, Taiwan strait, Bohai Sea and other earthquake prone areas. Although these Power Stations are designed in accordance with the seismic performance of 8 degrees and 9 degrees[1,2], but whether the actual seismic performance can meet the seismic design requirement still cannot be too sure. If Dams or Wind Power Towers are destroyed seriously by strong earthquakes, at the same time we cannot grasp the situation of earthquake and take measures as soon as possible, there will be very serious secondary disasters [3~7]. We assume that there is no earthquakes, the severe vibration will still happen in such structure. For example, In May 2005, when the water reached a new high level, Longyangxia Hydropower Station experienced increased vibration In the process of Dam discharge[8], the self-excited vibration is often accompanied by the vibration of the gate[9], serious consequence can occur, if the vibration was too sever and the worker couldn t deal with it in time[10]. Therefore, the highly automated vibration monitoring system is necessary to the Dam and Wind Power Tower, and it is useful to real-time control the seismic acceleration response characteristics of such structure. The system can provide rapid seismic assessment and the necessary parameters, such as maximum acceleration, response spectrum and seismic intensity, from the monitoring point, it also can make earthquake safety alarm in time, so that we can catch precious time for the rescue and the prevention of secondary disasters after the earthquake, and make sure the safety of personnel and equipment. The existing strong vibration monitoring system is mainly distributed. The basic structure of this kind of strong seismic oscillation monitoring system is that each monitoring point is consist of one Three-axis force balanced accelerometer and one 3 channel strong seismic oscillation monitoring recorder, then transmit data to the monitoring room in real time. The main advantage of the distributed strong seismic oscillation monitoring system is that the cables from sensors to recorders are very short; it avoids the strong electric field interference in the weak signal transmission process, such as 50Hz power frequency and so on. Its drawback is that each monitoring point should be equipped with a strong vibration recorder, and each strong vibration recorder costs around 4~10 million, resulting in the cost of system equipment is too high; In addition, the strong seismic oscillation monitoring recorder needs regular maintenance, resulting 27

2 in higher maintenance costs. The existing mainstream distributed strong seismic oscillation monitoring system was developed before 2000, its main task is to record and transmit strong seismic oscillation monitoring data, so it is very weak in the automatic analysis and reporting aspects. Besides this, the daily work to the Wind Power station and Water Power Station will cause large local vibration, which may lead to a monitoring point mistakenly triggered. Therefore, to be mistakenly triggered and false alarm is also one of the shortcomings of the distributed strong seismic oscillation monitoring system. A new monitoring system for strong seismic oscillation monitoring of the structure of Power station is designed in this paper. First of all, we designed a waterproof package for our existing force balanced accelerometer to make it available underwater. Then a 24 bit and 15 channels synchronous strong seismic oscillation monitoring recorder is designed, the number of strong seismic oscillation monitoring recorders in Power station's strong seismic oscillation monitoring system has been reduced by 4/5, and the cost has been cut by half. For the problem that because of the cable used to transmit signal to the recorder becomes longer, the probability of interference by the strong electric field of the Power station and the no triggering problem of the system are increased, a very practical solution was proposed. finally, In accordance with <the technical specification for monitoring strong vibration safety of hydraulic structures>, a set of software for remote data reception and on-line analysis of strong vibration data of Power stations has been compiled, which realized the automatic generation of Power station strong earthquake event reports and send out event reports and original data files automatically by , it also makes it possible that quickly reporting of the running state of each monitoring equipment in the system, intensity value and the maximum acceleration value in the form of text messages. This new strong vibration monitoring system has been applied in Gongguoqiao water power station, Dachaoshan water power station, Wudongde water power station, East sea wind power station, Binhai H2 wind power station and other Power station, and several recent strong earthquake events proved that the system's practical application effects meets the design requirements, and it had strong automation performance and quickly reporting performance, it was also convenient in management. Waterproof package design was carried out for our existing QZ2013 force balance accelerometer in this paper. First, we fixed the accelerometer in a round cylinder with a mounting base. Then, the signal transmission cable was protected by underwater special flexible waterproof fiber tube. Finally, filled up cylinder with waterproof glue, the cable output joint adopted compression type waterproof joint. The overall structure is shown in Figure 1.After the QZ2013 accelerometer is packaged by this waterproof package, it has been used in Strong vibration monitoring of foundation piles of an offshore platform, at 20 meters underwater. Figure 2 showed the full time waveform of strong seismic oscillation monitoring, which was collected by the underwater strong vibration monitoring point of Gongguoqiao hydro power station, after the sensor has been working more than 1 year. This figure showed that after the waterproof package design of QZ2013, this censor can be used underwater for a long term. Figure 1. Structure of waterproof package for Accelerometer. 2 Design of Waterproof Package for Force Balance Accelerometer Compared with other kinds of accelerometers, force balance accelerometer has the advantages of high sensitivity, good low frequency performance [11]. It is one of the main censor choices of strong seismic oscillation monitoring system. The power station monitoring environment is rather bad, especially that the bottom part of the power station is often flooded for power station leakage, therefor, the censor used for monitoring the power station must have strong waterproof performance. 28

3 Figure 2. Strong vibration waveform of one underwater monitoring point of GongGuoqiao hydropower station (May 20, 2017, 0, 2, 3.7 earthquake occurred in Yunlong County, Dali, Yunnan) dispersing Step-down power dissipation to every one of them. The mature linear power module LM1085IT was chosen, transform the power supply from 12v to 5.8v,then others mature linear power module LP3873ES-5.0 and LP3873ES-3.0 were chosen to transform the power regularly to 5v and 3v,to supply power to AD chip, Memory chip, ARM9 chip and others. In order to further improve the working life of power supply module, based on supplying power through two roads theory, one work and another can have a rest,circuit board was designed in this paper. The optimized block diagram of the multichannel strong seismic oscillation monitoring recorder is shown in figure 4. 3 Design of Multichannel Strong Seismic Oscillation Monitoring Recorder The structure of core circuit board of the strong seismic oscillation monitoring recorder is shown in figure 3; it is a special data acquisition instrument, which requires long uninterrupted operation. Compared to the universal data acquisition instrument, it requires higher stability and longer service life, because the strong seismic oscillation monitoring recorder may need to wait for several years before one strong shock events occur. So the service life of a strong seismic oscillation monitoring recorder usually exceeds 10 years. This period exceeds the lifetime of most power modules. Therefore, it is the key issues in design of strong seismic oscillation monitoring recorder to improving the stability and service life that how to optimize the design structure of power module for strong seismic oscillation monitoring recorder. Figure 3. Basic structure of core circuit of strong seismic oscillation monitoring recorder. To solve this problem, the power supply module of the circuit board was optimized, and the stability and the service life of the multi-channel strong seismic oscillation monitoring recorder are improved. The specific design method is as follows: The power supply module is the life source of the strong seismic oscillation monitoring recorder, it is the most vulnerable module too, and the main reason for the problem is that the power consumption of the power module is too large, so that the temperature of the power module is too high. In order to avoid the high working temperature, multistage step-down mode was adopted in this paper, so that we can make the working temperature of each regulated power supply module lower, by Figure 4. Block diagram of the power supply module for the core circuit of the strong vibration recorder. This design adopted two independent roads to supply power. Each road consists of 3 voltage regulator modules which formed two stage step-down circuits, and 1 cooling fin that was covered on 3 voltage regulator modules, and on temperature sensor that mounted on the heat sink. The value of two digital temperature sensors was timed read by chip LPC2378ARM, to compare with the set temperature threshold which default was set to 60 degrees. If the temperature of the power supply module in operation exceeds the threshold value, then start another power supply road by controlling the logical selection circuits to keep these two modules in working at the same time, 30 seconds later, cut off the input power and output power of the high temperature one to re-entering single power supply road mode. 4 Studies on Disturbance of Strong Electric Field in Power Station and False Triggering Of Strong Seismic Oscillation Monitoring Many high voltage cables are embedded in the power station of the power station, there is a strong electric field around it, and as a result, obvious 50Hz power frequency interference signal often exists in the signal of weak current equipment, such as strong vibration monitoring equipment and other dynamic monitoring equipment. The ambient vibration signal is shown in Figure 5. As shown in Fig. 5, the frequency of the interference signal is prominent not only in the 50Hz, but also at the frequency points such as 5, 10, 15, 20, 25, 30, 55, 35, 40, 45, 50, and 29

4 so forth. Therefore, when the sensor output signal is disturbed by a strong electric field, the interference signal is not only concentrated in the 50Hz, but there are a number of harmonic interference signals with 5Hz as the power station frequency, which cannot be eliminated by filtering methods. Figure 5. Environmental vibration signals of No. #5 strong vibration monitoring point in the Power station of Da Chaoshan Hydropower Station. In view of this problem, a large number of interference signal cancellation methods and several experiments have been carried out in Da Chaoshan Power station. We did experiments on No. #5 strong vibration monitoring point which existed Strong electromagnetic interference, the cable between this point with recorder have 5 cores, 360 meters long. Sensors and recorders were supplied with 12V DC power; both sensors and recorders use the same power source. Experimental process and results are shown in table 1. 30

5 Table 1. Experimental process and results. Experiment Number Experimental Condition 1 The interference signal shielding method 1: pack the aluminum foil film box and set on thick wall steel pipe for cable. Mode of power supply 1: The sensor and recorder share one 12V DC power output from the power adapter, and the power adapter is placed near the recorder. 2 On the basis of method 1, the power supply mode is changed: using the batteries that are carried on the recorder to supply power to the recorder and the sensor. 3 On the basis of method 1 and the power supply mode 1, after making the 12V power produced by adapter passed through a 4 band stop filter, whose bandwidth is set to 45~55Hz,then supply the power to recorder and sensor. 4 On the basis of method, change the way of power supplying. First, keeping the same way using the adapter to supply 12v power to the recorder, then pull the 220v AC power line near to censor, finally, using adapter to transmit the power to12v to the censor. Maximum ambient vibration before experiment (m/s^2) Maximum ambient vibration after experiment (m/s^2) From the experimental results it can been seen that the disturbance signal of the output signal of No.5 strong vibration monitoring sensor is basically eliminated after that, first step, we pull the 220V AC to the near ground of the sensor then the voltage was switched to 12V DC to power the sensor. As shown in Figure 6, other methods did not work. The experimental results show that the interference signal was added into 12V DC power signal during the transmission process, rather than the measured weak signal from the sensor. In order to further verify the reliability of this method, we have adopted the power supply method for the sensors of #2 and 4# monitoring points which have obvious interference, after that the interference of #2 and #4 monitoring points were eliminated too. Table 2 is the maximum environmental vibration statistics of 5 monitoring points. measuring point number Cable length(m) Table 2. The maximum environmental vibration statistics of 5 monitoring points. Layout position Maximum ambient vibration when sensors are powered by remote 12V(m/s^2) Maximum ambient vibration of sensors at short distance 12V power supply(m/s^2) #1 30 top left side #2 135 top right side #3 420 left side of the Power station #4 278 central Power station high #5 350 Power station bottom It shown in table 2 that applying power to sensor after transform 220v AC to 12v AC through a power supply adapter near the accelerometer can reduce the environment interference to a normal value. Therefore, this power applying method can eliminate the strong electromagnetic interference in the strong vibration monitoring of the Power station. Because the daily operation of power station always cause great vibration in the part structure of power station, it is easy to lead some monitoring points to been triggered successfully and generate strong vibration information mistakenly. To solve this problem, the trigger mode of the new power station vibration monitoring system had been optimized combined with the implementation of strong seismic oscillation monitoring project at Da Chaosan Power station. And one method that multi-point synchronous triggering was proposed. When more than 60% monitoring points reached the trigger condition, the system will judge to be an earthquake event and enter the trigger mode. The actual application effect of the optimized trigger mode of the strong seismic oscillation monitoring system is shown in table 3. It is shown in table 3 that if the strong vibration monitoring system was triggered based on single point triggered mode, it would be easy to record a lot of data of non-earthquake events and false earthquake information, which is unfavorable to automatic management of power station safety monitoring system. After optimized to multi-point synchronous triggering mode, except for four mistaken triggers happened in Wu Dongde in 6 months which were caused by construction blasting, there was no mistaken trigger in Da Chaoshan or Gong Guoqiao Power station. Therefore the model based on synchronous triggering of multiple monitoring points can reduce the false triggering event of Power station monitoring system. 31

6 Name of power station Wu Dongde Power station (monitoring of slope strong vibration during construction) Table 3. Statistics of false triggering times before and after triggering mode optimization of strong seismic oscillation monitoring system. The number of false triggering of the independent trigger mode within 6 months Gong Guoqiao Power station Da Chaoshan Power station 73 0 The number of false triggering in 6 months based on multi point synchronous triggering discriminant model 5 Software Design for Remote Monitoring and On-Line Data Analysis of Power Station Strong Seismic Oscillation Monitoring Remote monitoring and on-line analysis software of power station strong seismic oscillation monitoring data is the brain of power station strong seismic oscillation monitoring system, It can remotely and timely master the operation status of the strong vibration monitoring equipment on the power station site, can real-time receive data waveform, have the function of seismic events judgments and alarm and others function. The basic flow chart of the data reception and on-line analysis software for the strong seismic oscillation monitoring system of the Power station is shown in figure 6. Figure 6. Basic flow chart of remote data receiving and on-line analysis software. 6 Introduction of Actual Application Effect of New Strong Seismic Oscillation Monitoring System This system had been using in Wu Dongde Gong Guoiqiao Da Chaoshan Man Lashan and other power station to monitor the strong vibration, and it also has experienced the test in many strong seismic oscillation monitoring events. Table 4 shows the statistical of strong vibration monitoring system during seismic events of GongGuoqiao power station in Table 4. The statistical of strong vibration monitoring system during seismic events of GongGuoqiao Power station in Basic situation of earthquake events Yangbi 5.1 earthquake, Yunnan; March 27th occurred at 07: earthquake occurred in Yunlong, Dali, Yunnan; May 20th occurred at 00:02 System data logging status SMS alert system System mail delivery All the 7 monitoring points recorded Strong vibration response data All the 7 monitoring points recorded Strong vibration response data Received the earthquake intensity and maximum peak automatically send by SMS report at 07:57 Received the earthquake intensity and maximum peak automatically send by SMS report at 00:04 Received seismic events, advanced analysis reports and strong seismic oscillation monitoring data files automatically send by mail, at 07:58 Received seismic events, advanced analysis reports and strong seismic oscillation monitoring data files automatically send by mail, at 00:05 Summaries China is an earthquake prone country, and the Power station is important projects. If the degree of strong vibration response and power stationage is not timely mastered after earthquake, severe secondary disasters such as power station break will occur. A new strong vibration monitoring system was designed in this paper, it has many functions such as the earthquake events quick report by message, report generation automatically and send out by mass mail, data files 32

7 automatic delivery by mail, daily remote management and operation status automatic SMS report and other functions. Therefore, compared with traditional strong vibration monitoring system, this new system has higher automation ability. The new system has been applying to many Power stations, and had verified the system's high degree of automation and reliability through a number of seismic events. References [1] DL/T , Technical specification for safety monitoring of strong vibration of hydraulic structures[s] Beijing: China Electric Power Press, [2] NB , Code for seismic design of hydraulic structures in hydro power projects[s] Beijing: China Electric Power Press, [3] Zhou Hao. Research on Power stationage detection method of Power station shaking table model test [D]. Dalian University of Technology, [4] Liu Fuhai. Shaking table test study on seismic failure mechanism of earth rock Power station [D]. Dalian University of Technology, [5] Xu Guang, Shu Kezhong, Guo Yonggang, etc. Progress of seismic safety monitoring technology for hydraulic structures in China [J]. Hydro power and pumped storage, 2012, 36(2): [6] Shu Kezhong, Zhang Lifei, Zhu Liwu, etc. Power station strong earthquake safety monitoring[m].beijing: China Water Conservancy and Hydropower Press,1996. [7] Zhang Fan, Yan Jungang, Li Rui, etc. Application of strong seismic oscillation monitoring observation in Power station monitoring of Xiaolangdi Power station water control project [J]. North China Earthquake Sciences, 2010, 28(4): [8] Ding Xiaolong. Experimental study on Power station vibration of Longyangxia Hydropower Station [J]. Shaanxi electric power, 2010, 38(3): [9] Yan Genhua. Study on flow induced vibration monitoring and strong vibration control technology of Power station sluice gate structure [J]. Power station and safety, 2016(3): [10] Yang Li, Yang Shaohua. Application of strong seismic oscillation monitoring observation in Power station monitoring of power station [J]. Hydro power and pumped storage, 2013, 37(3): [11] Li Caihua. Design and analysis of force balance acceleration sensor [J]. Sensors and Microsystems, 2005, 24(8):