In recent years, with the improvement of substation automation level, computer monitoring system, microcomputer protection device, microcomputer fault recording device and various data management machines have been widely used in integrated substation, and the cooperation of these automatic devices needs a precise and unified time. When the power system fails, it can not only realize the operation monitoring and post accident fault analysis of all systems in the whole station under the unified time benchmark, but also analyze the cause and process of the accident through the sequence and accurate time of each protection action, switch opening and closing. With the increasing complexity of the power grid, the improvement of the installed capacity and the expansion of the power grid, providing the clock benchmark of standard time has become an urgent need for the power plant, substation and even the whole power system. The unification of the clock is an important measure to ensure the safe operation of the power system and improve the operation level, and it is one of the most basic requirements of the integrated substation automation system.
1、 Advantages of GPS clock satellite synchronization system
The substation adopts computer monitoring system, automation and line microcomputer protection device, fault recording device, electric energy billing system, SCADA system, etc. of different manufacturers. The time synchronization forms of the substation mainly include the following:
(1) each equipment supplier adopts its own independent clock, and each clock has a certain deviation in timing accuracy due to the difference of product quality, so that each system of the whole plant cannot carry out data analysis and comparison on the basis of unified time benchmark, which brings great hidden dangers to the correct fault analysis and judgment afterwards.
(2) the time synchronization is realized through the master station time synchronization. The master station of the dispatching center sends the time synchronization command through the communication channel to synchronize the clock of each power station in the system. This method requires a special communication channel. Because the distance from the dispatching center to each substation is different and the communication delay is also different, it can only ensure that the system clock is at the level of 100 millisecond error.
(3) a small GPS receiver is adopted, multiple RS232 ports are provided, and serial port cables are connected to each computer one by one to realize time synchronization. But in fact, this synchronization method also has disadvantages, and the length of the cable used cannot be too long; The response speed of the server and the delay of the client directly affect the timing accuracy. Moreover, each station often has different devices to receive clock synchronization signals, with different interfaces, such as RS-232 / 422 / 485 serial port, pulse, IRIG-B code, dcf77 format interface, etc; The number of devices is also different, resulting in insufficient or lack of certain types of interfaces of GPS devices. One or even several GPS receivers need to be added, which is often limited by insufficient funds or no installation location.
(4) Use GPS satellite clock to synchronize the system. GPS (Global Positioning System) is a global satellite navigation and positioning system established by the U.S. military. A special receiver receives the signals transmitted by satellites and can obtain position, time and other relevant information. The GPS system sends a signal every second with a time accuracy of 1 μ Within s, the signal can be reliably received at any time and anywhere in the world. The satellite continuously sends its own ephemeris parameters and time information. The time information sent by GPS includes year, month, day, hour, minute, second and IPPs (standard second) signals, so it has high frequency accuracy (up to the order of l0-12) and time accuracy. The application of GPS satellite synchronous clock system in the integrated substation has obvious advantages, which can realize the operation monitoring and post accident fault analysis of all systems in the whole station under the unified GPS time benchmark. Various automation equipment of substation (such as fault recorder, microcomputer protection device, monitoring system, etc.) unify the time benchmark of substation and dispatching center according to the accurate clock synchronization signal provided by GPS, which improves the time accuracy of SOE and greatly improves the safety and stability of power system after power system failure, It provides strong evidence for analyzing the fault situation and the sequence of circuit breaker action, and creates good technical conditions for power grid safety and stability monitoring and control system.
GPS satellite clock synchronization system can well solve the problem of unified time reference in substations and realize accurate time synchronization in stations and even between stations. At present, it has become the best time synchronization scheme and the inevitable trend of technical development. According to the requirements of technical code for automation system of 110 ~ 220kV substation of Guangdong power grid, we have used time synchronization system to calibrate substation devices in new stations or comprehensive self transformation stations in recent years. In September 2005, Guangdong Power Grid Corporation issued the technical specification for GPS time synchronization system of Guangdong Power Grid Substation, and the management, design, installation, test and operation of GPS time synchronization system of newly-built or reconstructed stations are implemented in accordance with the requirements of the technical specification.
2、 Brief introduction and working principle of GPS satellite clock synchronization system
The GPS satellite clock synchronization system uses RS232 interface to receive the signal from GPS satellite, and then converts it into interface standard (RS232 / RS422 / RS485, etc.) and time code output (irig_b code, ASCII code, etc.) meeting various requirements through protocol conversion and local time conversion of main CPU central processing unit. GPS satellite clock synchronization system is generally composed of GPS satellite signal receiving part, CPU part, output or expansion part, power supply part and human-computer interaction module.
GPS clock synchronization system mainly has three time synchronization modes: synchronization pulse output, serial time information output and IRIG-B code output. Pulse synchronization output mode, that is, the synchronization clock outputs an accurate synchronization pulse every certain time interval. The timing device performs timing after receiving the synchronization pulse to eliminate the travel time error of the internal clock of the device. The disadvantage of pulse synchronization is that it can not directly provide time information. If the time source of the time service device is wrong, it will go wrong all the time. The serial synchronous output mode is to output the time information in the form of serial data stream. Various time service devices receive the serial time information once per second to obtain time synchronization. During the time interval when the broadcast timing is not received, the device clock has its own time error problem. The serial time synchronization is more complex than the pulse time synchronization. In addition, in the receiving process, the time spent in information processing will also affect the time synchronization accuracy, Therefore, it is mainly used to mark the time of events. If the time synchronization accuracy is to be improved, the second time synchronization pulse signal needs to be given during field application. The rising edge of 1PPS (second pulse) signal is used to realize the synchronization of external clock and GPS clock, and the synchronization error is restrained within the range meeting the requirements of system accuracy.
IRIG-B code output mode is the time code standard for time synchronization of various systems issued by IRIG organization. Among them, the most widely used version is IRIG-B code, referred to as B code for short. B code is output in the form of BCD code, once per second, including 100 pulses. The output time information is: second, minute, hour and date sequence. B code signal generally has four forms: TTL level mode, RS422 level mode, RS232 level mode and modulation signal (AM). Pulse timing and serial port timing have their own advantages and disadvantages. The former has high precision, but can not directly provide time information; The time accuracy of the latter is relatively low, especially in the multi cell mode or when there are multiple managers and subsystems in the monitoring system, the time accuracy is particularly affected by the serial communication delay. B-code timing takes into account the advantages of both. It is a timing method with high precision and standard time information. When the intelligent equipment of the substation adopts B-code timing, it no longer needs the communication message timing of the fieldbus and GPS to output a large number of pulse contact signals. According to the technical specifications, IRIG-B code (DC) clock synchronization signal shall be adopted for all newly put into operation bay level equipment of substation automation system requiring time service.
3、 Access and application of GPS satellite clock synchronization system in integrated substation
The current GPS satellite clock synchronization system supports hard time synchronization (pulse node PPS, ppm, PPH), soft time synchronization (serial port message), coded time synchronization (IRIG-B, dcf77) and network NTP time synchronization, and meets the time synchronization interface requirements of different equipment at home and abroad. The microcomputer protection device, measurement and control device, fault recorder The equipment at the station control layer of the automation system can be connected to the GPS clock synchronization system. GPS timing interfaces generally include: RS232 serial port output, RS485 serial port output, non modulated IRIG-B output signal, sub pulse 1ppm output signal, second pulse 1PPS output signal, etc. In the integrated substation, there are often many different new and old devices that need to receive clock synchronization signals, and there are many types of interfaces. In practical engineering applications, several time synchronization methods are often used together, so it is necessary to add hard contacts or network time synchronization to unify the time. For example, many equipment in the substation automation system do not support B-code timing, so the timing mode combining serial port timing and 1ppm pulse timing is mostly adopted. The serial port timing will accurately the time reference of the intelligent equipment to the millisecond level, and 1ppm will send a pulse every whole minute to act on the clock reset line of the intelligent device, so as to realize the accurate synchronization of the clock. Intelligent devices with B-code timing function can no longer accept serial communication message timing in principle, otherwise time jump will occur, while more advanced intelligent devices will add a criterion in the communication program. Only when the B-code timing function fails can they accept serial port timing.
The clock synchronization system of substation is composed of master clock, time signal transmission channel and time signal user equipment interface (expansion device). The master clock is generally set in the control center of the substation, including standard chassis, receiving module, receiving antenna, power module, time signal output module, etc. it realizes GPS time synchronization for substation equipment and bay layer ied equipment (including intelligent electric energy meter, etc.) as required, and has clock synchronization network transmission correction measures.
Combined with the actual operation experience and actual situation, taking the comprehensive self transformation of 110kV Zhongxing station as an example. A GPS time synchronization system screen is installed in the substation protection room and high voltage room respectively, and a standard synchronization clock body is configured. The master clock completes the reception and processing of GPS satellite signals and provides standard synchronization time signals to the signal expansion device (RS422 level mode IRIG-B); And each master clock has internal punctuality function. Each standard synchronization clock body shall be able to receive two IRIG-B (DC) time code time information functions. When the internal clock of the master clock receives the external time reference signal, it is synchronized by the external time reference signal. When the external time reference signal is not received and recovered, it maintains a certain travel time accuracy until the external time reference signal is recovered and automatically switches to the normal working state. The Zhongxing substation of comprehensive self transformation adopts Ethernet networking, and some old equipment of manufacturers only have RS232 serial port or RS485 interface. The newly installed main transformer line measurement and control device, #1 main transformer protection, #2 main transformer protection and all line protection of 10kV High voltage chamber have B-code interfaces. 422B code timing is adopted, and RVVP two core shielded communication cable is selected, 1 is +, 2 is -. Each device is connected to the B-code output label section of GPS synchronous clock device in turn. 110kV fault recorder has no B code interface, and the empty contact is connected with minute pulse and second pulse to realize hard contact time synchronization. The RS232 serial ports of the two telecontrol hosts are respectively connected to the GPS time synchronization system for time synchronization, #3 main transformer protection and 110kV line protection devices are old models, which can not realize B-code time synchronization, and can only realize integrated automatic network time synchronization with the local monitoring background through the telecontrol host.
In 500kV BOLUO station, as shown in Figure 1, a set of master clock is set in 500kV relay protection room and 220kV relay protection room respectively to be responsible for time synchronization of secondary equipment in this room, including soft time synchronization, hard time synchronization (1PPS, 1ppm, differential signal) and coding time synchronization (IRIG-B, dcf77). The time signal receiving unit for protecting the main clock of the cell not only receives the GPS time signal of the cell, but also receives the GPS time signal of another cell as a standby standard time source input (input in IRIG-B time code mode through optical fiber). The two main clocks can be standby for each other. When there is a problem in the time signal receiving unit of one cell (for example, the satellite cannot be tracked, the antenna is damaged, etc.) In addition, a set of extended clock is set in the main control room. The main clock and the time expansion device are connected through optical fiber. The time signal receiving unit obtains the time signal from the two main clocks respectively, which are standby for each other and automatically switches to complete the time synchronization and expansion of the equipment in the room The device receives the time information provided by the master clock and provides multiple output interfaces to other devices through expansion.
In order to ensure the function, accuracy and efficiency of the GPS satellite synchronous clock system, daily maintenance and repair work shall be done. All components of the GPS timing system shall be checked regularly. First, check whether the antenna signal on the device display panel is normal, and then check the number of satellites locked on the display panel (generally greater than 3), After the above two items are normal, compare the time displayed on the display panel with the time displayed or printed on each time synchronization equipment to confirm that the time synchronization units of all equipment involved in time synchronization in the time synchronization system work normally, and regularly patrol each component in the system to ensure the reliability of the whole system.
A monitoring device shall also be installed in the GPS screen, and the alarm contact output of operation status, including power loss alarm, IRIG-B signal loss alarm and self inspection abnormal alarm of the device, so as to timely respond to GPS operation. During normal operation, the power indication should be normal, and the “1PPS” pulse indicator flashes once a second. When the “IRIG-B signal disappearance alarm” is sent, it indicates that the machine has not correctly received the IRIG-B input signal, and further inspection should be carried out.
GPS satellite synchronous clock system is widely used in comprehensive self transformation stations and new stations. It can not only effectively reduce the workload of maintenance and operation personnel, but also provide a unified and standard time benchmark for most operation equipment in our substation, facilitate the analysis and tracing of various events in operation, and improve the automation level of power system, It provides a strong technical guarantee for the substation and even the whole power grid to move forward to a higher management level.