Abstract : Networking and intelligence are the future development directions for hydropower station speed governors. This paper, starting from the design of the Gezhouba Intelligent Speed Governor, presents design schemes for the speed governor in terms of network topology and hardware structure, elaborates on the design ideas for redundancy and reliability in network communication, proposes a network time synchronization scheme for the speed governor, and introduces the data structure using IEC61850 communication. Research shows that the new generation of speed governors solves the problems of connection between the speed governor and monitoring system equipment and system networking, meeting the construction requirements of intelligent hydropower stations and providing high reference value for the design of future intelligent hydropower station speed governors.
Keywords : Intelligent network communication redundancy, IEC61850 protocol, network time synchronization
0. Overview
At present, the construction of intelligent hydropower stations is in full swing, representing the future development direction of the power industry, and reliable network communication is the foundation of intelligent hydropower station construction. This requires the corresponding power station basic equipment speed control system to have a high-speed and reliable communication network, redundant and reliable design, advanced control strategy and convenient and flexible communication interface to realize the reliable, safe and economical operation of power plant units [1]. However, most of the speed controller products that have been put into production and are under design in China have not realized the special requirements of the current intelligent power grid environment, and have not fully considered Ethernet communication interface, GPS time synchronization and fieldbus [2].
This article introduces the hardware configuration, network redundancy scheme, communication with external equipment, and network time synchronization method of the speed control system's core control, using the dual-redundant turbine governor based on the X203586 controller recently developed by NARI Group Corporation for the Gezhouba Hydropower Plant of the Three Gorges Group as an example. This lays a good foundation for the design and promotion of intelligent hydropower plant speed governors in the future.
1. Control system and network structure
A unified data platform is a basic feature of a smart hydropower station. The local level of a hydropower station includes different equipment such as monitoring, governor, excitation, and auxiliary equipment systems. The current integrated platform of the hydropower station arranges the local data acquisition and measurement according to the structural hierarchy of "process layer", "interval layer" and "station control layer", and adopts a two-layer network: the station control layer network adopts the MMS network, and the process layer network adopts the GOOSE network and SV network. The entire station network adopts high-speed fiber optic Ethernet [3].
The station control layer consists of a monitoring system host (operator station) and an intelligent device interface machine. The intelligent device interface machine can connect the speed control system, monitoring LCU equipment, etc. to the station control layer MMS network, monitor the system, realize the management and control of the interval layer, process layer equipment and other equipment functions, form a station monitoring and management center, and can communicate with the remote dispatch center. The communication standard conforms to DL/T860 (IEC61850) [3].
Considering the aforementioned unified data platform architecture, the control and communication structure of our speed regulation system is shown in Figure 1 below: Firstly, the control core of the speed regulation system uses B&R's most advanced X20CP3586 controller, with two redundant control systems configured (see the redundant X20 controller in the figure). Corresponding common I/O modules are configured, including analog input (X20AI4622)/output (X20AO4622) modules, digital input (X20DI9371)/output (X20DO9322) modules, and frequency measurement and pulse output modules (X20DS131). 9) The system consists of a serial communication module (X20IF1086). The analog input module acquires analog quantities such as active power, guide vane opening, and head of the speed control system. The analog output module outputs analog quantities such as guide vane, blade, and speed, and sends them to the monitoring system. The digital input module executes commands for unit start-up, shutdown, grid connection, and load increase/decrease, enabling the speed control system to perform sequential control of the unit. The digital output module outputs the governor's status and fault alarms for centralized monitoring. The frequency measurement module acquires unit speed and grid frequency, while the pulse module controls the stepper motor of the governor's mechanical system. The communication module communicates with the monitoring system and the power plant's HOMIS system. This completes all the control functions of the speed governor.
Figure 1: Redundancy structure diagram of speed regulation system control and communication
As previously emphasized, network communication and its reliability are crucial requirements for the construction of intelligent hydropower stations. We have implemented a detailed design for the system's network communication, as shown in Figure 1. Firstly, the two controllers communicate synchronously via Ethernet POWERLINK, enabling real-time data sharing. In the event of a system failure (such as power outage, program error, or module failure), the system automatically switches to the other without manual intervention. The two controllers also communicate with the common I/O module via Ethernet POWERLINK, with the host controller automatically controlling the I/O devices. Communication between the two controllers and the monitoring host computer uses the IEC61850 protocol to access the MMS network. This is achieved by using a B&R PC810 industrial computer as the communication gateway, installing the IEC61850 conversion protocol to achieve communication with the MMS network. Ethernet lines A and B connect to controllers 1 and 2 respectively through the communication gateway. This ensures that a failure of any gateway or network connection node does not affect communication between the controllers and the MMS network, thus achieving a dual-network cross-redundancy mode. In addition, we designed a backup channel for data exchange between the speed controller, monitoring system, and HOMIS system. Two serial interfaces were added to the IO module to enable real-time communication with these devices. This ensures that even if the network is completely interrupted, we can still exchange data with the host computer using the backup channel, demonstrating the high reliability of the system communication.
In addition, the communication between the controller and the human-machine interface is via Ethernet through a switch, using B&R's internal IMA protocol, which has high real-time performance and reliability. In addition to ordinary user parameter settings and information display functions, it can also meet advanced functions such as user data recording, storage, waveform recording, and event logging.
In terms of communication content, the current monitoring system can send out information such as power setpoint, head, and clock, and can realize power closed-loop control and clock calibration of the speed control system. The speed controller can send information such as speed, guide vane opening, unit active power, fault quantity, and status quantity through the 61850 protocol. This information can be shared on the MMS network, and all devices connected to the network can obtain it in real time.
2. IEC61850 network communication
The IEC61850 standard was developed by the International IEC Committee. It is a standard system established based on interoperability requirements and mainly considers the communication of communication networks and systems in substations. At present , domestic and foreign power equipment manufacturers are conducting research and application work around IEC61850, and have proposed that the development direction of IEC61850 is to achieve "plug and play" and ultimately realize "one world, one technology, one standard" in industrial control communication [4].
This project utilized a PC810 industrial control computer provided by B&R and the IEC61850 communication software system independently developed by NARI Group Corporation, and applied it to the new generation governor of Gezhouba Dam. It employs a layered distributed architecture and object-oriented modeling technology, enabling self-description of data objects. Following the IEC61850 specification, we established logic nodes for governor power control, water level control, and opening control; designed data models for power setting and head setting; and developed data structures for speed, power, guide vane opening, fault quantities, and status quantities transmitted by the governor. These arrays were described, providing an effective channel for interoperability and seamless integration between the governor and the power station monitoring system. This achieved the transformation and upgrade from traditional communication protocols to the "IEC61850 standard," laying the technical foundation for the future full realization of intelligent hydropower station systems.
3. Network time synchronization
The timing of the speed controller is crucial. Important signal changes, both internal and external, need to be recorded with accurate clock information. Especially when the system malfunctions, only under the control of a unified and accurate clock system can the sequence of events be accurately recorded, thus providing a reliable basis for analyzing the cause, type, and development process of the accident.
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, which can meet the time synchronization interface requirements of different devices at home and abroad. Network time synchronization is implemented in the form of communication messages. This time includes the complete time including year, month, day, hour, minute, second and millisecond. Because network time synchronization is relatively easy to implement, it is widely used[5]. In this project, the speed controller is planned to use network soft time synchronization for GPS time synchronization.
The GPS clock source acquires standard clock signal information from GPS satellites and transmits this information over the network. The power station is equipped with a time synchronization server and time synchronization software. The X20 speed controller is physically connected to the server via Ethernet. The server clock source acts as an SNTP server, and the X20 speed controller acts as an SNTP client. The GPS clock source, acting as the SNTP server, transmits the time signal over the network, and the speed controller, acting as the SNTP client, receives the time signal, thus synchronizing the speed controller with the standard time source. The communication protocol of the speed controller as an SNTP client can be implemented by calling the corresponding functional modules in the software.
In addition, we have also considered a backup time synchronization channel, that is, by monitoring the host computer MMS network, clock information can be sent to the speed controller, including year, month, day, hour, minute, and second. Time less than a second can be obtained through the speed controller's internal clock (minimum 5 milliseconds).
4. Conclusion
Intelligentization and digitalization are the future directions of hydropower station automation development. As an important component, the speed governor must fully meet and adapt to the needs of current technological development. This paper starts from the design of the Gezhouba intelligent speed governor and proposes design ideas for the speed governor in terms of network communication, hardware structure, and network time synchronization. The new generation speed governor will fully support the IEC61850 communication protocol system, solve the connection problem between the speed governor and monitoring system equipment and the system networking problem, meet the construction requirements of intelligent hydropower stations, and provide high reference value for the design of future intelligent hydropower station speed governors.
Currently, the three sets of intelligent speed governors for Gezhouba Power Plant have been produced and manufactured. They passed the user's factory acceptance test at the end of February 2014 and have been shipped to the site for installation and commissioning. We look forward to the smooth commissioning of the new generation of speed governors, which will lay a good foundation for the power plant to achieve intelligent operation.
About the Author
Cai Weijiang (born in 1970) holds a master's degree and is a senior engineer. He started working in 1992 and has been working at the State Grid Electric Power Research Institute ever since. His main research and design work includes hydropower station turbine speed regulation and automatic control devices.
