Abstract: This paper first summarizes the main features of digital substation, and analyzes the characteristics of hierarchical distribution of 220 kv digital substation. The station control layer, interval layer and process layer are respectively described. On this basis, 220 kv digitization is carried out. The main technical problems in substation construction are discussed and studied. Finally, the problems that should be paid attention to when constructing 220kv digital substation are put forward, which has important practical significance for the current digital construction of substation.
With the advancement of society and the advancement of modern computer-based information technology, power technology has made great progress in recent years. The emergence and application of intelligent primary equipment and networked secondary equipment have made the construction of substation a good technical foundation. This paper takes the construction of 220kv digital substation based on iec61850 as an example, attempts to expound and analyze the characteristics and architecture of 220kv digital substation, and discusses the main technical problems in the construction of 220kv digital substation, in order to build or transform other digital substations. Provide useful lessons.
1. Characteristics and architecture of 220kv digital substation
1.1 Feature Analysis
Digital substation, as its name implies, is compared to the traditional concept of substation, which is digitized or reconstructed or constructed by a substation in the traditional sense. The foundation of its establishment is the application of modern information technology. The 220kv digital substation is based on the application of iec61850 for modeling and communication. Its technical characteristics are summarized, namely: "the primary equipment intelligence, the secondary equipment network, and the iec61850 standard" are the three main characteristics.
1.2 General architecture
For a conventional 220kv substation, there are generally three voltage levels, namely 220kv, 110kv and 10kv. Therefore, after the transformation according to the iec61850 standard, the substation's architecture reflects the characteristics of layered and distributed. In terms of logical structure, the substation equipment is divided into three levels: station control layer, bay level and process layer. Substation goose network and manufacturing message for universal objects
(1) Process layer: The conventional 220kv substation outlet interval uses voltage transformer (vt) and current transformer (ct). The difference is that the digital substation uses electronic voltage transformer (evt) and electronic current. Transformer (ect). And connected to the merging unit, thereby achieving the merging and synchronization of the data, and providing corresponding data information to the interval layer protection measurement and control metering device.
(2) Spacer: It is composed of intelligent devices such as protection devices, measurement and control devices, and fault recorders. The spacer layer of the 220kv digital substation based on the iec61850 standard uses goose to transmit information.
(3) Station control layer: The station control layer of 220kv digital substation, its structure mainly includes: global positioning system (gps), background monitoring, network bus, Baoxin network, anti-misoperation system. It should be pointed out that since the goose network is formed between the process layer and the bay level, the goose jump (close) gate, the collection of each interval switch and the interlock between the devices are effectively realized.
2. Main technical problems in the construction of 220kv digital substation
2.1 Current and voltage loop access method
The current-voltage circuit of the conventional self-station is generally connected in a point-to-point manner. The current and voltage on the secondary side of the transformer are connected to the protection and measurement and control device by the control cable, and AC sampling is realized in the protection and measurement and control device. After the optical fiber transformer of the 220kv digital substation adopts the output of the optical fiber, the current is no longer the alternating current and the alternating current voltage, but the digital coded information after sampling. The technical problems derived from this need to be studied.
2.2 Coordination of the longitudinal differential current protection device on both sides of 220kv line
Most of the 220kv lines are equipped with longitudinal protection. Among them, the vertical current differential protection is mainly used. At present, when constructing a 220kv digital substation, digital equipment is generally only used in the newly built 220kv substation. When the substation of the 220kv line is expanded and the substation is extended, the conventional primary and secondary equipment are still used, and digital equipment is not used. Otherwise, the expansion interval device will not be able to access the common secondary equipment such as the existing busbar protection, fault recorder, or the existing bus voltage transformer.
2.3 Protection trip mode
For 220kv substations, there are often two or three sets of protection devices and even more sets of protection to jump the same circuit breaker. The conventional comprehensive self-station only needs to connect the multiple sets of tripping circuits that are protected to the circuit breaker to the operating circuit of the circuit breaker in parallel, so that multiple sets of protection can be tripped separately without affecting each other. For 220kv digital substations, the protection devices are all fiber-optic trips and cannot be directly connected in parallel. The 220kv digital substation protection trip circuit uses optical fiber to transmit digital trip commands.
2.4 How to achieve isolation when equipment operation and single protection and overhaul
Due to the importance of 220kv lines, busbars, main transformers, etc., they are equipped with dual protection. The protection trip output of the 220kv digital substation is realized by optical fiber, and the hard platen cannot be installed. Therefore, when a set of protection exits due to failure, change of fixed value, etc., the protection of the return protection and the operation and the effective isolation of the circuit cannot be realized, and the obvious disconnection point is maintained. However, if it cannot be effectively isolated from the running equipment and the circuit, it will be forced to stop the equipment once the protection device is out of operation, and the 220kv equipment configuration dual protection will lose its meaning.
2.5 Ways of fault recording
The access volume of the conventional integrated self-station fault recorder is mainly AC current, AC voltage, circuit breaker position, protection trip, etc., just connect the corresponding loop with the control cable to the corresponding position of the fault recorder. Unified sampling and unified recording. For the 220kv digital substation, the optical quantity cable is used to record the digital information sent by the transformers, intelligent terminals, protection devices and other devices of each transformer. Since the sampling is done by different devices, how to clock these devices to analyze the accident.
3, should pay attention to matters
From the relevant data collected by the author for engineering construction and operation practice, it is found that the following common problems in the construction of 220kv digital substation need to be noted:
3.1 Digital sampling and protection coordination problems of different manufacturers' equipment
The equipment used in the current 220kv digital substation is different from the domestic and foreign manufacturers. Although iec61850 has relevant regulations on the processing and transmission of data, there are differences in the understanding of the standards. From the dynamic simulation experiment conducted by the author, it is found that some mainstream manufacturers at home and abroad lack uniform standards in the details of structural design and internal processing of transformer devices. This will undoubtedly have adverse effects on the good and stable operation of the digital substation, which requires us to unify the actual project in the construction of the digital substation beforehand, to avoid the trouble that the built system does not have to be in operation.
3.2 goose information check
From the practice point of view, the secondary equipment such as protection, measurement and control acquires the sampling data and sends the trip control command through the goose form. Therefore, the traditional method cannot be detected. How to verify the correctness and completeness of the sampled data? What is the content of the device verification and inspection when it is offline? Which tools do you need to configure? These issues should be clearly defined.
3.3 Intelligent terminal security
In the construction of 220kv digital substation, the intelligent terminal breaker is a transitional scheme that extends to the secondary equipment site as secondary equipment such as protection control. Therefore, due to the consideration of various harsh weather conditions outside the environment or other external environmental influences, there must be corresponding plans to achieve corresponding strategies for moisture, high temperature, small animals, and electromagnetic interference prevention.
3.4 Cable laying and marking
In the construction of 220kv digital substation based on iec61850 standard, the application of optical fiber has increased due to the application of digital device, and the cable connection between devices has been greatly reduced. Therefore, this means that the traditional cable trench design scale, laying form, marking specifications and other aspects are not compatible with the current digital substation construction. How to design, lay and mark the application characteristics of digital substation fiber, remains to be explored on this issue. With further improvement.
4, the conclusion
In summary, the digital construction of substations is a dynamic process that will change with the advancement of science and technology. Therefore, we must constantly sum up experience, find problems, and solve problems. Actively and continuously promote the digitalization and intelligent construction of substations, so that power provides a strong guarantee for the national economic construction and the improvement of people's quality of life.
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