Secondary system: It is a system composed of relay protection, safety automatic control, system communication, dispatching automation, DCS automatic control system, etc.
The secondary system is an indispensable and important part of the power system. It is to realize the contact monitoring and control between people and the primary system, so that the primary system can run safely and economically.
Facing the rapid advancement of new power system construction, the secondary system faces problems such as inaccurate measurement, protection failure, uncoordinated control, and incomplete monitoring. Monitoring capacity building to ensure the safe and reliable operation of new systems.
1. The composition and function of the secondary system
The primary equipment of the power system bears the heavy responsibility of power energy flow transmission, while the main task of the secondary system is to realize real-time monitoring, fault prevention and operation control, which is an important core to ensure the safety of power transmission and power supply.
2. Secondary system configuration
The secondary system consists of the master station at the dispatching end, the master station at the centralized control end, the master station for marketing measurement, the protection equipment automation equipment at the substation end, the station control layer equipment and software, the measurement and power quality equipment, communication and safety equipment, auxiliary equipment, and station The power supply and other equipment and systems are responsible for the tasks of measurement, protection, control, and monitoring. The substation, dispatching end, and centralized control end jointly realize the real-time collection, transmission, and processing of equipment operation data, alarm information, and monitoring data. The scope of the secondary system is relatively wide, and this report focuses on the protection and monitoring technology related content of the substation
3. Functional positioning of the secondary system
3.1 Realize the protection control, measurement monitoring, and remote monitoring network security functions of equipment in the station
3.2 Support dispatching center's demand for power grid operation monitoring and control
3.3 Support centralized control station to carry out centralized monitoring of substation primary and secondary equipment and auxiliary equipment and equipment management requirements
3.4 Support the needs of operation and maintenance, equipment management and emergency duty in the station
3.5 Support marketing needs for electricity data collection and energy meter equipment management
4. Changes brought about by the new power system
my country has strategically proposed the development goals of "carbon peaking, carbon neutrality" and "building a new type of power system". New energy power generation represented by wind power and photovoltaics will grow rapidly, and the power structure of the power system will undergo profound changes.
4.1 Highly controlled changes in power supply characteristics and enhanced harmonic content
4.2 Fault mechanism changes Fault characteristics weaken frequency offset
4.3 Digital transformation of power grid
4.4 State depth monitoring
4.5 Massive Concurrency of Data
5. Problems faced
5.1 Ignore the influence of different control response stages
5.2 Ignoring the influence of different unit control strategies
5.3 Inaccurate calculation and short-circuit contribution of new energy
5.4 The action performance of the traditional power frequency AC protection is severely challenged: the sensitivity decreases, the forward direction is misjudged as the reverse direction, and the action speed decreases
5.5 There are blind spots in the secondary system function guarantee: incomplete equipment monitoring coverage, insufficient remote monitoring information, and insufficient utilization of equipment data
5.6 The technical configuration of the secondary system needs to be optimized: the data collection method is not uniform, the network structure needs to be simplified, the equipment functions are cross-duplicated, and the data planning needs to be integrated
6. Thinking about secondary system coping strategies
6.1 Reconstruct the secondary system of the substation:
6.1.1 Optimize the data collection method:
Unify digital collection, unify the application methods of electromagnetic transformers and electronic transformers, and unify optical fiber transmission; configure the collection and execution unit with integrated merge unit and intelligent terminal function according to the equipment interval. Due to the problem of digital quantity measurement and traceability, the settlement metering device is temporarily Still using electromagnetic transformers and cable sampling; adapting to the application of different types of electromagnetic and electronic transformers; combining the merging unit and the intelligent terminal into one, significantly reducing the number of equipment, reducing the number of optical ports, and simplifying the secondary circuit; The sampling and tripping methods of secondary equipment are unified, reducing the combination of secondary equipment models.
6.1.2 Optimize device functions:
Multi-function measurement and control is configured according to intervals, integrating measurement and control, PMU, and assessment measurement; intelligent wave recorder integrates fault recording, network analysis, and online monitoring of secondary equipment; integrates settlement measurement, power quality monitoring; similar functions are combined to reduce the number of equipment; The secondary circuit improves the reliability of the circuit and improves the efficiency of equipment operation and maintenance.
6.1.3 Simplify the network configuration: the acquisition execution unit and the bay layer equipment adopt point-to-point direct connection communication, and cancel the process layer network; take advantage of the station control layer networking advantages to protect, measure and control a small amount of interlocking GOOSE information to interact through the station control layer network; reduce equipment The total number of physical ports and switches has been reduced by more than 66%; the devices at the process layer and the interval layer are directly connected by optical fiber, which improves the reliability of transmission and transmits according to the classification of information and services to ensure the quality of network communication and network performance; The protection adopts the direct sampling and jumping method, with few intermediate links in the loop, high real-time performance and high reliability; the natural synchronization of sampling data adopts the direct sampling and jumping method, which is more conducive to ensuring the "four characteristics" of relay protection.
6.1.4 Optimizing SCD configuration
Realize the decoupling of protection measurement and control equipment information configuration and function configuration (CID and CCD); standardize equipment function configuration to achieve fixed configuration; implement online monitoring and comparison verification of SCD file version, check code and other information to improve SCD; configuration tools The level of standardization and humanization, the device connection relationship is displayed intuitively through graphics; the SCD file is fixed on the comprehensive application host for configuration and management; after the device is put into operation, there is no need to modify the configuration on site; the impact range of the SCD change is controllable, and the reconstruction and expansion will not affect irrelevant equipment. The scope of influence is equivalent to that of conventional stations. The standardized visual design of SCD configuration tools is easy for operation and maintenance personnel to understand and use; through SCD online management and control, the consistency of SCD and field device configurations is guaranteed.
6.1.5 Optimizing the station control layer system
Equipment optimization: all professional hosts are integrated into a monitoring host and a comprehensive application host; all communication gateways are unified into a real-time gateway and a service gateway;
Function optimization: According to business application requirements, 24 functions in 5 categories of the station control layer are optimized into 19 functions in 4 categories, including operation monitoring, operation control, intelligent application, and master station support services;
Remote support: strengthen the intelligent analysis in the station, reduce the upload of raw data, and support remote monitoring through remote data and service calls
Replace general-purpose hardware devices with software modules, streamline station control layer devices, and eliminate special devices and isolated systems
Unified platform deployment, using standardized hardware and open software to support flexible expansion and upgrade of the system
Unified communication protocol, centralized data resources in the station, and integrated monitoring of main and auxiliary equipment in the station
6.1.6 Optimizing the auxiliary control system
Substation auxiliary control system: integrates online monitoring of primary equipment, fire protection, safety precautions, dynamic environment system and online intelligent inspection system, spans Zone I, Zone Il and Zone IV, and realizes online monitoring of the operating status of primary equipment in substations and the operating environment of substations full perception and control of
Unified protocol: unify the protocol of wired access equipment in Zone II, reduce protocol conversion links, and improve transmission efficiency; unify the interface protocol of the video surveillance system and inspection robot, and realize the simplified equipment of video image and inspection applications by the online intelligent inspection host: Cancel the online monitoring comprehensive monitoring unit, general on-site module, RS485 on-site module and access control on-site module; configure the online intelligent inspection host (edge IoT agent) in the IV area, realize the unified data access in the IV area, reduce the number of hosts and standardize the partition: Add a secure access area for wireless sensor devices to realize flexible networking, expand the scope of information collection, improve device perception capabilities, and meet network security requirements
6.2 Control the fault law and propose the principle of relay protection
The structure of the new energy unit control system is complex, the control strategy is diverse, the fault characteristics are strongly coupled with the control response, and the phase characteristics are obvious. The fault characteristics within the limited time window of protection are complex and difficult to accurately analyze.
6.3 Strengthen the supporting role of the control system to the power grid
Fault Current Harmonic Suppression and Negative Sequence Component Control—New Energy Fault Active Control Protection Principle Specific Electric Quantity under New Energy Fault Active Control—Active Control Strategy Based on New Principle of Specific Frequency Fast Protection and Energy Storage Control Response—Active Comprehensive Control and Protection Collaborative Technology
6.4 Improving the monitoring ability of power grid and equipment
Improve the high-precision sampling capability in the wide temperature range, realize the unified collection of basic data; realize the accurate measurement of broadband data
Build a high-performance platform through technologies such as efficient access to massive data, platform opening, and security protection; research on master-substation service intelligence collaboration multi-level model dynamic splicing and intelligent application technology to achieve holographic perspective and precise monitoring of equipment.