Discussion on Design Scheme of 35 kV Digital Substation
At present, substation integrated automation technology has been widely used in China. However, there are still some technical limitations in the application of substation integrated automation technology. In addition, as the structure of the power system becomes more complex, the voltage level is getting more and more The higher, the higher requirements for system operation management. As digital transformer technology and intelligent primary electrical equipment technology mature and become practical, as well as the development and application of computer high-speed networks in the real-time network of power systems, digital substation technology has gradually been applied in China. Digital substation technology represents the development direction of substation automation technology. The IEC61850 standard has laid a technical standard for digital substation technology. The development and practicalization of digital primary equipment and digital communication technology have also made it possible to build digital substations according to IEC 61850.
1 Key technologies of digital substations As far as the current technological development status is concerned, digital substations are built on the basis of the IEC 61850 communication specification and consist of intelligent primary equipment such as electronic transformers (ECT, EVT), intelligent switches, and networked secondary equipment It is constructed according to the substation layer, bay layer and process layer. It can realize the information sharing and interoperability of modern substations among intelligent electrical equipment in substations. Its key technologies mainly include the following aspects.
1.1 IEC61850 standard In terms of concept, the IEC61850 standard mainly focuses on the following four aspects:
(1) Functional modeling. Starting from the communication performance (PICOM) requirements of the substation automation communication system, the functional model of the substation automation system (Part 5) is defined.
(2) Data modeling. Using an object-oriented approach, a data model based on a client / server structure (Part7-3 / 4) is defined.
(3) Communication protocol. Defines the data access mechanism (communication service) and the mapping to the communication protocol stack. For example, the network between the substation layer and the bay layer uses the abstract communication service interface to map to the MMS (IEC61850-8-1), at the bay layer and process layer. The network between is mapped into a serial unidirectional multipoint or point-to-point transmission network (IEC61850-9-1) or a process bus based on the IEEE802.3 standard (IEC61850-9-2) (Part 7-2, Part 8/9 ).
(4) Substation automation system engineering and conformance testing. A structured language (Part 6) based on XML (Extensible Make up Language) is defined to describe the topology of substations and automation systems and IED structured data. To verify interoperability, Part 10 describes IEC 61850 standard conformance testing.
1.2 Electronic transformers Electronic transformers are divided into two categories: active electronic transformers and passive electronic transformers. Active electronic transformers use Rogowski air-core coils or low-power iron core coils to sense the measured current, and capacitive (resistance, inductance) voltage dividers to sense the measured voltage. The remote module converts the analog signal to a digital signal and transmits it through the communication fiber. The passive electronic transformer uses the Faraday magneto-optic effect to sense the measured current signal, the Pockels electro-optic effect to sense the measured voltage signal, and transmits the sensing signal through the optical fiber.
1.3 Intelligent primary equipment According to the definition of IEC 62063: 1999, intelligent switching equipment refers to high-performance switching equipment and control equipment, equipped with electronic equipment, sensors and actuators, not only has the basic functions of switching equipment, but also With additional functions, especially in monitoring and diagnosis.
1.4 Networked secondary equipment IEC 61850 is applied to the communication within the substation to fully utilize the latest technology of network communication to realize the information sharing, interoperation and flexible configuration of functions of the secondary equipment.
2 System design principles According to the requirements of digital substations and the functions that each layer needs to achieve, for a typical 35 kV substation, a digital substation model is established, and the system structure and configuration scheme are given. The design plan should be advanced, and at the same time as a practical application, it should also fully consider the development and operating experience of high-voltage electrical equipment and secondary equipment (IED) at home and abroad.
The design process is implemented in the following steps:
(1) Establish a 35 kV substation model and give the electrical main wiring and IED configuration.
(2) Analyze the hierarchical network characteristics of digital substations and establish a fully digital substation automation system network.
(3) Select the high-voltage electrical equipment and secondary equipment of the digital substation for the network of fully digitalized substation automation system.
3 System design plan
3.1 The main wiring and IED configuration of the substation The following design is considered according to the conventional 35 kV substation: equipped with 2 load regulating transformers; 35 kV single bus section, two incoming lines, one main and one backup; # 1 入 线 所One 35 kV direct-distribution transformer is used as the backup power supply; 10 kV single bus section is divided into six lines for each section; centralized reactive power compensation is divided into two, which are respectively connected to 10 kV I and II buses. The electrical wiring is shown in Figure 1.
In this scheme, the 35 kV substation adopts the integrated design of protection and measurement and control. The # 1 and # 2 main transformers are each equipped with a main transformer differential protection measurement and control device, which provides a ratiometric current differential with dual slope and double inflection point differential braking characteristics. Protection and differential flow breaking protection function. In addition, the two sets of protection can also provide over-current backup protection for the high and low voltage sides of the transformer. The functions of measurement and control include differential and braking current, second and fifth harmonics, current and other measured values, as well as events and fault recording, data recording and other functions. 35 kV # 1, # 2 incoming line and bus coupler are equipped with a line protection device, which mainly provides complete overcurrent, quick break and line differential protection. Two main transformers protect one screen for each group, and two protection groups for incoming line and bus coupler each have one screen.
For the 10 kV feeder system (including incoming lines, transformers, motors, busbars, etc.), there are two configuration methods. The first is a decentralized installation mode. An integrated feeder protection device is configured on each 10 kV feeder to provide Current and quick-break protection, other protection functions include voltage and frequency protection, circuit breaker failure protection, etc. The functions of measurement and control include reclosing, fault location, breaker operation times and breaking current statistics, simultaneous detection, event and fault recording, various power and demand measurement functions, and 10 kV feeder protection is installed on the corresponding feeder On the switch cabinet. The second way is the installation mode of group screen mode. One multi-feeder protection device is arranged at each bus of 10 kV. One such protection can provide monitoring and protection functions for five 10 kV feeders at the same time Protection, the latter installation method is selected here. The multi-feeder protection is installed in the 35 kV main control room or 10 kV distribution room through the group screen. The 10 kV I, II two-section bus only needs two multi-feeder protection devices for each The feeder, transformer and bus coupler provide protection. The two sets of protection each have a screen.
The substation layer is equipped with two main and standby remote control hosts and two back-end monitoring hosts, as well as engineering stations, man-machine workstations and other equipment. The entire system has a total of five screens placed in the main control room.
In order to make the substation compatible with some smart devices that do not support IEC61850 (such as UPS, DC screen, arc suppression system, watt-hour meter, etc.), a separate IEC61850 communication management machine, time-matching equipment and other auxiliary equipment are set up in the plan. It is to convert these smart devices to comply with the IEC61850 specification, and at the same time to achieve unified time synchronization.
3.2 Substation network networking
3.2.1 Process layer network The largest data outflow on the process layer is now in the process of sample value transmission between the electronic transformer and protection, measurement and control. The sample value transmission has high real-time requirements. In addition, interlocking between protection, measurement and control devices, tripping and closing commands between protection and intelligent switches also have high real-time and reliability requirements. Therefore, the real-time and reliability of process layer communication is the most critical issue.
There are four schemes for the process layer networking, which are the interval-oriented principle, the location-oriented principle, the single bus principle and the function-oriented principle. Among them, the space-oriented networking scheme has a clear structure and is easy to maintain. Interoperability and even interchangeability can be obtained at both the IED level and the interval level. In the early stage of the implementation of IEC61850, due to lack of sufficient interoperability practical experience, this solution makes the interoperability of the bay layer easier to be guaranteed, so this solution is used in this design for networking and a 100MB fiber redundant process bus ring The network ensures the real-time and reliability of the transmission of sampled value messages and trip GOOSE messages. The specific construction is as follows:
The 35 kV part and the 10 kV part are each networked at an interval. After the ECT / EVT of these two parts collects the current / voltage signals from the primary side, they are respectively connected to the merge unit set in this interval. The merge unit adopts IEC61850- The 9-2 standard processes the sampled values, and the processed sampled information is connected to the process layer ring network through an industrial Ethernet switch within the interval, so that the sampled value information can be shared and transmitted on the process layer ring network. Into protection and measurement and control equipment. Like the merging unit, the intelligent switching device is connected to the process layer ring network through an industrial Ethernet switch in this interval, and then transmitted to the protection and measurement and control equipment. The merging unit and the intelligent switching device are respectively connected to the two switches. In this case, two switches in the same interval can achieve network redundancy. If one of the switches fails, it will not affect the transmission safety of important data at the process level.
3.2.2 Substation layer network The substation station-level network mainly handles the communication of IED between the bay layers, at the same time, it must exchange information with the background man-machine workstations and engineering stations, and carry out two-way information exchange with remote dispatching through remote control devices. The substation network can also be directly connected to the power data network through network equipment.
Because the voltage, current value and status signals need to be shared between the equipment at the bay layer and between the bay and substation layers, and the number of bay IEDs is large and the amount of data transmission is large, in order to avoid network congestion and ensure communication reliability, the substation layer The network uses a 1000 MB dual-fiber switched Ethernet ring network structure to ensure bandwidth and reliability. The spacer layer is the protection, control and measurement of digital intelligent electronic equipment supporting the IEC61850 standard, and is installed in a centralized group. There are # 1 main transformer screen, # 2 main transformer screen, 35 kV two incoming lines, bus coupler screen, two sides of 10 kV feeder protection screen, each unit is an independent network unit, can exchange information between each other, based on IEC61850 The standard specification is connected to the ring network bus and exchanges information with other units, master stations and dispatching systems. The background control room issues control commands to the protection and measurement and control devices through the substation network. The GPS device also provides unified timing to the entire station through the substation network. In addition, the remote control system is also connected to the external power dispatching network from the substation layer network through the router. According to the above network analysis of 35 kV digital substation process layer and substation layer, the specific network construction is shown in Figure 2.
4 Electrical equipment equipment configuration
4.1 Current / Voltage Transformers and Merging Units As mentioned above, electronic current / voltage transformers are divided into active and passive types. Due to their simplicity, reliability and good stability, active current transformers have entered Active transformers are mostly used in commercial operation. Optical transformers have a great advantage in ultra-high voltage systems, but they are still in the process of continuous improvement. Therefore, under the current technical conditions, active transformers are used for transformers of various voltage levels in 35 kV substations. The specific configuration options are as follows:
Select a pair of electronic current transformers with a protection level and a measurement level output in the 35 kV # 1, # 2 incoming line part; in 35 kVI, a pair of feeder part of the â…¡ section feeder part with a protection level and a An electronic current transformer with a measuring stage output; an electric voltage transformer with a protection level (measurement) and a zero-sequence voltage is installed at the 35 kV I, â…¡ busbar; one is selected for the 35 kV bus coupler Electronic current transformer with a protection level and a measurement level output.
At 10 kV I, the incoming section of the section II bus selects a protection level and a measurement level of electronic current transformers; at 10 kV I, each feeder section of the section II bus also selects a protection level and a measurement -Level electronic current transformer; at 10 kV I, section II busbar section, select one with a protection level (measurement) and an electronic voltage transformer for zero-sequence voltage; 10 kV busbar section select one with An electronic current transformer with a protection level and a measurement level output.
The merging unit is responsible for transmitting the current on the 35 kV and 10 kV lines collected by the active transformer, and the voltage signal is transmitted to the process bus via the optical fiber Ethernet via the IEC61850-9-2 standard. The specific configuration scheme is as follows:
At the 35 kV I, II section bus, each equipment is a combined unit, which collects the three-phase line protection and measurement current values ​​of the 35 kV # 1, # 2 incoming and outgoing parts, and at the same time collects the 35 kV I, II section bus single Phase line voltage value and zero-sequence voltage value, in which the merging unit at the 35 kV section II bus is also responsible for collecting the current value of the 35 kV bus coupler.
At 10 kVI, section II bus, each equipment is a combined unit, which collects 10 kV I, section II bus input and 10 feeder parts for three-phase line protection and measurement current value, and at the same time collects 10 kV I, section II bus The single-phase line voltage value and zero-sequence voltage value, of which the merging unit at the 10 kV section II bus is also responsible for collecting the current value of the 10 kV bus coupling part.
4.2 Intelligent circuit breaker In the digital substation, the research and field application of intelligent switching equipment lags behind one step. Therefore, under the current technical conditions, there are not many smart switching devices available. At present, the main products are still produced by some foreign manufacturers. Domestic manufacturers have also been developing smart switching devices suitable for various voltage levels, of which 35 kV And 10 kV smart switchgear has started trial.
In this scheme, 35 kV and 10 kV intelligent switchgear are intelligent complete switchgear, equipped with intelligent protection (control) devices. Such devices should have the functions of automatically collecting AC volume and monitoring the status of circuit breakers. Communication with other IEDs in the station. Another solution is to use conventional switchgear, and then install the protection, measurement and control integrated device based on IEC61850 standard and intelligent operation box on the switchgear to realize the function of intelligent switchgear.
4.3 Switch The main network component of the Ethernet switch in the process layer communication, due to the harsh electromagnetic environment where the process layer communication is located, and the real-time requirements of the sampled values ​​and GOOSE information, the industrial Ethernet switch was selected in the plan.
This industrial Ethernet switch should meet the equipment requirements of the substation environment in IEC61850-3. It is more robust than ordinary switches, can be installed on standard DIN rails, and has redundant power supply. The connectors use a solid DB-9 structure or The more robust M-12 interface with IP67 protection level is used to meet the harsh industrial site environment, can resist vibration, corrosion and electromagnetic interference, greatly improving the reliability of equipment and networks. The switch adopts the duplex full-duplex switching mode, and supports IEEE802.1q (Virtual Local Area Network) and IEEE802.1p (Priority Label), two protocols that are closely related to the quality of network communication services. Among them, IEEE802.1q defines a port-based virtual local area network (VLAN), and IEEE802.1p defines the priority of message transmission. The latter is very important for the real-time transmission of sampled value messages and tripped GOOSE messages on the process bus. When the data communication load on the process bus is heavy, by placing a high priority label on the sampled value message and the trip GOOSE message, it can be ensured that these two types of messages will be forwarded preferentially in the switch.
In terms of network structure, industrial Ethernet switches use the network architecture of the optical fiber double ring network and the ring network redundancy protocol. The fiber network has high anti-interference. The ring network redundancy protocol is relative to the standard Ethernet STP (spanning tree protocol) And RSTP (Rapid Spanning Tree Protocol) disconnection recovery time has been significantly improved, such as the industry's leading industrial switch manufacturer MOXA's proprietary ring redundancy protocol MOXA Turbo Ring protocol, which can be Switch to the backup path within ms to maintain uninterrupted operation of the communication, greatly improving the recoverability of the network. The number of optical ports and electrical ports can be flexibly selected as required.
In addition, due to the importance of the information transmitted by the merging unit, protection equipment and switch controller, they should be directly connected to the switch port, that is, to ensure that they each enjoy independent bandwidth.
5 Digital substation construction transition plan At present, the application and implementation of the domestic digital substation system is still in its infancy, especially the unconventional transformers still need to overcome some technical difficulties. There are too few intelligent primary devices that meet the requirements in China and can be promoted and applied. As far as embedded intelligent devices are concerned, the technology of applying 1 000 MB Ethernet at the process level is not yet mature; such problems determine that the promotion of digital substations cannot be completed in one step, and must be implemented in different engineering schemes in stages according to the actual situation in various places.
The first stage: the substation automation system truly implements IEC 61850 at the substation layer and the bay layer to realize the interconnection and interoperation between IEDs of different manufacturers; while the process layer equipment uses conventional equipment, and the bay layer equipment uses traditional point-to-point hard-wired connection Into conventional transformers and circuit breakers; at present, many digital substations that have been put into operation adopt this scheme.
The second stage: on the basis of not changing the existing conventional primary equipment, complete the intelligentization of the process-level equipment by adding analog input merging units and intelligent control units to or near the primary equipment body; all the analogue inputs of the bay-level equipment are cancelled , In and out, only through communication according to IEC61850-9-1 / 2 with the merge unit, according to GOOSE and intelligent control unit; the partition layer and process layer are completely digitally connected, eliminating a large number of point-to-point hard-wired connections. This scheme is more mainstream.
The third stage: the substation layer, bay layer and process layer are all digitized. The process layer equipment uses unconventional transformers and intelligent primary equipment. The process layer measurement, monitoring and control are all digitized and networked. The 1 000 MB double-ring network architecture is used. The substation bus and process bus are combined into one, maximizing The realization of information sharing and system integration is the ultimate development direction of digital substations in the future. However, due to unconventional transformers, intelligent circuit breakers and other intelligent primary equipment, there are still a large number of technical problems that have not been solved, so this solution is basically in the stage of exemplary exploration in the current practical engineering application.
6 Conclusion Digital substations are the future development direction of substation automation. This paper first introduces the key technologies of digital substations. Based on the IEC61850 standard, a 35 kV digital substation model is designed. The content includes system main wiring, substation network, IED and electrical equipment configuration Wait. Judging from the current development and operating experience of high-voltage electrical equipment and secondary equipment (IED) at home and abroad, the construction of digital substations also requires a relatively long process, which can be transformed first, then new stations, partially digitized, and then completely The road to digitization. In this regard, the article finally proposes a transition plan for building a digital substation based on IEC61850.
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