* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Structure Design of On-line Monitoring System for Power Supply Insulation
Tektronix analog oscilloscopes wikipedia , lookup
Regenerative circuit wikipedia , lookup
Power electronics wikipedia , lookup
Automatic test equipment wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Telecommunication wikipedia , lookup
Oscilloscope history wikipedia , lookup
Analog television wikipedia , lookup
Oscilloscope types wikipedia , lookup
Battle of the Beams wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Signal Corps (United States Army) wikipedia , lookup
Analog-to-digital converter wikipedia , lookup
Radio transmitter design wikipedia , lookup
Valve RF amplifier wikipedia , lookup
Rectiverter wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Telecommunications engineering wikipedia , lookup
Cellular repeater wikipedia , lookup
Index of electronics articles wikipedia , lookup
Structure Design of On-line Monitoring System for Power Supply Insulation ZHANG Kai, HU Shunbin College Mechanical and Electrical Engineering, Agricultural Electrification and Automation, Agricultural University of Hebei, P.R.China, 071001 [email protected] Abstract Modern national economy have more and more dependence on power supplying. Therefor, the requirement for safe operation and power supply reliability of electric power system is higher and higher. As one of the most important measure for reliable and safe running of power system, insulation preventive test for electric power system plays a crucial role in checking and supervising of transformer insulation. With the continuous development of the power industry, the defects and weak points of traditional insulation preventive test is becoming more and more obvious. So it has important realistic meaning to develop on-line monitoring technology of insulation. Key words On-line Monitoring, Dielectric Loss, Simultaneous Sampling, Digital Filter 1 Introduction With the development of electric power industry, the rank of voltage and the workload of the insulation preventive test have been increasing constantly, and the weak points of traditional test measure is being unfolded step by step. For example: equipment need quit running before experimentation and set up temporary line; test voltage is so lower than operation voltage that can not reflect the equipment 's credit condition of insulation; the test cycle is long, and much manpower and material resource are wasted. The appearance of on-line monitoring technology of insulation makes on-line diagnosis for insulation be carried out, which makes up well the shortage of traditional measure efficiently. At present, the commercial products of this kind of on-line monitoring system for substation has been developed by western developed countries, and the tentative standard for condition-based maintenance of some equipment has been summarized. Power supply companies in China attach great importance to the development of the on-line monitoring technology. Despite late start, its development is quite fast in our country. But at present, some important items of on-line mornitoring such as technology standand, product designing, monitoring items, acceptance index has not been unified in China. In this paper, on-line monitoring of insulation for high voltage equipment in large-scale substation or power plant will be the study object and a kind of on-linemonitoring system of insulation will be mainly interpreted. 2 General Design of The System 2.1 Monitoring Content of The System There are a lot of varieties of electrical equipment and they are different in structure, and each of them has different on-line monitoring items. The main equipment and their main monitoring items are: ⑴Transformer: Chromatographic analysis for gases in oil-filled and its on-line monitoring for partial discharge. ⑵GIS(gas-insulated metal-enclosed switchgear): Differentiate the partial discharge signal with the others by using UHF Method, then differentiate the fault types based on the spectrum characteristics of the signal and the location on AC voltage waveform when discharging. ⑶Capacitive Equipment(include capacitive bushing, transducer, coupled capacitor):The value of dielectric loss and capacitance. Correct the error led by the changing of temperature, humidity and load.⑷Arrester: Resistive current of metal oxide surge arrester without gaps(MOA). ⑸Circuit Breaker: Recording the journey~time curve when the circuit breaker switching. Extracting the mechanical motion parameters. Monitoring the voltage and current waveform of the operating coil. Monitoring and analyzing the 340 mechanical vibration signal out of the body of the circuit breaker. Measuring the leak current of tension and rising bar. Measuring the resistance of static loop and dynamic loop. 2.2 System Structure The on-line monitoring system of insulation for substation can be generally divided into six modules as extraction of signals, signal pretreatment, synchronous sampling, digital signal processing, main controller and computer software for management. A element class is constituted with appropriative sensor, cable for analog signal transmission and multiple gated plate, which can be regarded as a structure designed for concrete and different object. The object can be a group of same type equipment (the three phase of A, B, C in the same group), several group of same type equipment, or the phase A of different type equipment. It can be designed flexibly base on the different condition of the substation. One of the element class’s failure don’t influence on the others, that the reliability of the system is improved. On the purpose of industrialization and reducing cost, signal is centralized sampling and processing. So a type of cable for signal transmission is customized to ensure that signal can be transmitted unfailingly. The system structure shows as the following figure: CT CT Passive Sensor Signal Pre-Processing Wave Amplifying CT Multi-Channel Gating MOA MOA Synchronous Sampling Circuit Active Sens or Signal Pre-Proces sing Wave Amplifying Signal Processing and Master Module MOA Phase locked and frequency multiplying Reference Voltage MIS System Amplifying and Re-shaping Voltage Sensor Dialing and Fiber Communication Computer Serial Communication Alarming Printing Figure 1 The signal processing module and master module determine which equipment to be monitored based on the command sent by computer, then gating the line by relay and monitoring the equipment which has been selected. The signal which reflect the insulation status is caught by a type of high-precision sensor. The output signal of sensor is not only weak, but seriously interfered. If sampling it directly, the sampling frequency must be enough high to ensure that the signal isn’t distortion. But if do so, amount of calculation of digital filter will be ncreased and the digital filter effect will be influenced. So the signal must be pre-processed before sampling. Because the system need high phase-precision, we designed a synchronous sampling circuit to sampling multiplex signal in the same time. This method can eliminate the extra phase difference come from sampling channels switching. By synchronous sampling, fixed phase difference between voltage channel and current channel can be work out accurately, and which can eliminate the phase-shifting out from signal channels to some extent by subtracting the value when calculating dielectric loss tangent. Do Digital filtering and spectrum 341 analyzing with the sampling signal, then work out the parameters of on-line monitoring for insulation. At the end, send the parameters to computer to be processed, analyzed and diagnosed through serial communication module. Then the computer can make data report and change tendency curve of equipment insulation status, give the limit alarm of parameters changing, record the data and send it to on-line MIS system through optical fiber network(or MODEM) simultaneously for administrators’ browse and query. 3 Design of Slave Microcomputer System Because different substation has different amount of equipment, the amount of channel on the slave microcomputer system can’t be determined priorly. The system is designed in modular structure, which could be devided into control module, power module, signal processing module, pre-channel module and backplane. All the other modules are pluged in the backplane, so the backplane is regarded as the bus plate which connect all the other modules on it. See the structure of the system below: Power Module Control Module Signal Processing Module Pre-Channel Module sensor Computer Figure 2 Power module supply the system with every kind of voltage source. Switch power is used in the power module which can run at 16 265 V AC or DC imput. There are four kind of source can be supplied by the power module, which has the very strong adaptability of power. Control module is the core module of the device. The MCU which is used in the device is a highly integrated 16 bit control chip, has independent watchdog circuit. There are high speed synchronous sampling circuit and input surge suppression circuit in this module. Moreover, the module is furnished with basic RS232 communication interface circuit, so bidirectional communication can be achieved between device with the host computer and maintenance engineers can do verification and maintenance on the system by special maintenance software through the interface. Signal processing module accomplish the function of input signal amplification, signal filter&signal channel selection, and impedance transformation. Operational amplifier with high ability of common-mode rejection is used by the system. Moreover, enjoying about the same parameters and working environment, every one of this kind of amplifier has about the same drift when some environment parameters such as operating temperature has changed. A type of hardware low-pass filter is designed in the module to pre-processing signal, to the effect that sampling and signal filter. The signal channel selection circuit accomplish the function of selecting out of the signal required to be monitored among plenty of input signal. Pre-channel module has the main function of sending the signal which out from sensor to the signal processing module. Different substation has different amount of equipment, the amount of channel of the system can’t be known priorly. So we only preset 32 channel on the pre-channel module, and preset 8 faucets for pre-channel module. If the substation has only small amount of equipment, no more than two or three the module will be need. The slave microcomputer device of the system has the complete function of software and hardware self-checking and independent WATCHDOG circuit, so it possess the strong ability of preventing interference; support multiplicate communication methods, offer RS232 or RS485 communication interface, can configure computer network interface based on the user requirement too. Hardware modularization make it be configured flexibly and expediently based on the user requirement and the 5~ 342 system can be expediently maintained 4 Design of The Management Software for Computer The software accomplish the function of on-line monitoring system of insulation for substation, they are system register, permission management, dipatching management, data management, communication management. See the figure below: Entry Software System Permission Management Dispatching Management Data Management Communication Management Figure 3 Permission management is to prevent that irrelevant personnel who isn’t allowed modifying the related configuration and monitoring data. Dipatching management can set what equipment to monitoring and the monitoring time, and offer the operation state, dispatching status of the monitored equipment. Data management is used to record, upload, copy, list print and display the monitoring data of each equipment and terminal. The data can be displayed in several kinds of forms such as table, figure, and so on. So people can judge the insulating performance of the equipment by the data to eliminate the latent danger in it’s bud. Communication management is constituted by two part. One is the communication with the slave microcomputer which sent monitoring parameters to this computer, and the other is the communication with the superior main control room and electric company. The second is the most important one. So the electric company can confirm the operation status of equipment by remote browsing the monitoring data of the substation. In addition, the system can timed patrol the insulation status of equipment, and alarm once the monitoring data exceed the threshold value. The software has primary failure diagnostics function, so it can do simple fuzzy logic reasoning on the monitoring data to judge if the equipment is in failure. If so, it will alarm and offer the possible reason of the problem. 5 Conclusion The accuracy of the measurement is a key index which determines the device is putting into operation or not in future, and eliminating the interference of voltage fluctuation and harmonic is a critical problem in the capacitive sample measurement. The design of high-accuracy double shielding passive sensor solve the problem well. By comparing with others, we find the scheme of on-line monitoring system for insulation mentioned in this paper has characteristic of : ⑴Self-correcting technique. It can eliminate the error of discreteness and drift when measuring the element parameters. ⑵Multichannel synchronous sampling technique. It can eliminate the stochastic disturbance of the system and ensure the measurement accuracy. ⑶Tendency comparative method united with relatively comparison method to analyzing equipment status. ⑷Quick phaselock frequency automatic tracking technique. The system can track the changing of frequency, sampling accurately after frequency fluctuating. ⑸Using fast anti-aliasing 343 Fourier transform algorithm(FAF"I') to eliminate the error led by frequency aliasing. ⑹Multi-tier distribution structure. The system possesses characteristic of good extension, can meet the need of every kind scale of substation of 35KV and above with different amount of equipment. ⑺ Using modularization design method. Card can be changed on line. System composition can be configured flexibly. We can add monitoring items and alter monitoring function at any time. As one of the most potential power system technology, the research direction of on-line mornitoring technology will be centralization, high intellectualization and high precision, and it will enjoy undoubtedly broad prospects in applications as the software and hardware technology developing at very fast spreed. References [1]Zhu Deheng,Tan Kexiong. Electricity Diagnostic Technique for Insulation. China Power Press, 1999 [2]Zhang Huiping. Analysis on Operation Status of On-Line Monitoring Capacitive Equipment[D]. First Edition. Department Electric Machine of Tsinghua University, 2002 [3]Zhou Wuzhong. The Repair, Diagnosis and Preventive Test for Power Equipments. First Edition. China Power Press, 2002 [4]Guan Gen,He Jingliang. On-Line Mornitoring of Insulation and Condition Maintenance for Power Equipments. China Power Press, 2000 [5]Lei Guofu,Chen Zhanmei etc. Diagnostic Technique for Insulation for High Voltage Equipments. Hydraulic and Electric Press, 1994 344