## Case Study  
### Case I: Distribution Network Information Interaction  
In addition to traditional power systems, feeders can also be connected to distributed energy sources. Taking a typical multi-feeder distribution network system as an example, the application of the power virtual plane layer in the software development process is analyzed, as shown in Figure 6. In order to reflect the diversity of distribution automation systems, it is assumed that the IEDs of the four feeders have different sensing and control methods. The IED1 is equipped with a circuit such as a transformer and an analog-to-digital converter for which can directly collect analog signals. And it also has an optical coupler and a relay circuit for direct acquisition and control of the distribution network switch. IED2 is not directly connected to the power primary system, but communicates with other devices through the CAN network. It realizes the perception and control of the distribution network by exchanging information that directly reflects the power distribution network. IED3 uses an information processing method similar to IED2. But it uses Ethernet as a communication network, and the electrical quantity information is encapsulated by the IEC61850 protocol. On the basis of IED3, IED4 uses cryptographic techniques such as encryption algorithms for message information to enhance information security. The above four IED automation systems are very different in the underlying processing. IED1 directly collects the field electrical quantity data of the physical layer through the driving layer function, or directly controls the switch. The IED2 first obtains a CAN message from the network driver, and then obtains power data information by parsing the CAN message at the communication protocol layer. The packet processing of IED3 at the driver layer and the communication protocol layer is similar to that of IED2. IED3 obtains network packets through the Ethernet driver, and then parses communication protocols such as TCP/IP to obtain power data packets. Since the power data is packaged in the IEC61850, specific power data values are generally extracted at the power protocol layer by an analytical method such as assn.1. In the underlying driver layer, communication protocol layer and power protocol layer, the message processing of IED4 is exactly the same as IED3, except that IED4 uses security methods such as encryption for power data values. Therefore, IED4 adds a cryptographic process such as encryption and decryption of the data layer before obtaining the specific power data value. This paper describes the main flow of power data interaction between field IED and power advanced applications in the form of pseudo code. The meaning of main pseudo code is shown in Table 1. When the distribution network IED adopts more communication and transmission methods, the corresponding processing flow is more. However, in the virtual plane layer, data sharing is provided to the power advanced application in a unified way. The virtual plane uses common format for transient data exchange (COMTRADE), as a unified format for invoking electrical data in advanced applications of the distribution network. As a common power data standard, the COMTRADE data format has good versatility and is widely used in power information systems, which helps to enhance the portability of the software [25]. Other forms of data formats can also be used in the virtual plane according to practical distribution network information processing needs. At the same time, it is noted that COMTRADE concentrates multiple power data simultaneously in the form of files. In order to meet the needs of extracting a single power source data in advanced applications, and avoid repeatedly extracting power source data from the entire COMTRADE file structure, a single power source data structure is defined in this article. Figure 6: Information Handling of Distribution Network Based on Virtual Plane.