In the war film, we often see such a scene. Before the military operations, in order to accurately follow the operational plan, the commanders must perform timely operations before the operations. In today's intelligent process, substation automation is getting higher and higher, and the intelligent actions of its components need to be carried out at the same time. The unified network time reference is essential for the synchronization of measurement and control.
Time term introductionWe say "every minute and minute have passed!" How do we define time? The terminology of time concept that people often refer to is like World Time, International Atomic Time, Coordinated Universal Time, etc.
World Time (UI) is the standard time for Greenwich. Greenwich is home to the original Greenwich Observatory in the southern suburbs of London, England, and it is the starting point for the geographical longitude of the world. The world always reflects the position of the earth in space, and corresponds to the cycle of spring, summer, autumn and winter, day and night, and is a time that people are familiar with and essential in daily life.
The International Atomic Time (TAI) is the time during which the two hyperfine levels of the ground state of a helium atom located at sea level transition in a zero magnetic field for a period of 9,192,631,770 cycles. Due to the stability of the physical properties of the atomic clock, its time is the most accurate.
Coordinating world time is essentially an atomic time, because its second length is defined to be equal to the time of the atom, only at the moment of human intervention, as close as possible to the world. Coordinated Universal Time is precisely a time-dependent system, and it is close to astronomical time by the leap second mechanism, so it has now become a widely used time system instead of Greenwich Mean Time.
Common clock source
The clock source is used to provide a standard clock signal, and the timing system mainly includes two types of wireless timing and wired timing. Wireless timing systems, such as satellite global positioning systems, mainly include the US GPS, the Russian GLONASS, the European Space Agency's Galileo program, and China's Beidou navigation satellite system. At present, the most widely used power system is the GPS system. The GPS transmits the signal once every second with a time precision of less than 1us. The time signal includes the year, month, day, hour, minute, second and 1 PPS (standard seconds) signal, and the GPS can output various types of time-coded signals. It includes IRIG_B time code, pulse code and serial time message and other types of time-coded signals to meet the timing requirements of different interface devices.
The cable timing system uses the network or private line as the carrier, such as the communication network timing system. The network time protocol NTP is the most popular Internet time transmission protocol, but it can only provide the timing accuracy between 1-50MS, which cannot meet the measuring instrument. And the precision required for industrial control, in order to solve the need for distributed network timing synchronization for measurement and control applications, the IEEE1588 standard was formed at the end of 2002, and its synchronization accuracy can reach a subtle range, thus effectively solving the real-time problem of distributed network systems. Sexual problems.
The importance of substation timing systemThe intelligent substation adopts the GPS timing device as the master clock of the whole time-to-time system, and the process layer time synchronization generally adopts the PPS and IRIG_B timing; the time synchronization of the station control layer and the interval layer adopts the IEEE1588 PIT network, and the device acts as the time-to-time network. The last point is the slave clock of the entire time system.
The power system is a real-time system. The state quantity of the system changes every time. Safety and reliability are the insurmountable principles of the power grid system. In order to ensure the reliable operation of the entire intelligent substation system, the entire network cannot be separated from a unified time base. The IEC61850 standard divides substations into station control, bay and process layers. The process layer equipment, due to the transmission of sampled values, trip information, and the need to achieve microsecond synchronization accuracy, the timing accuracy of the intelligent substation test equipment DT6000 series can reach the synchronization accuracy of us, fully meet the timing accuracy of each layer of the intelligent substation Claim.
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