Introduction of Digital Substation

New digital substation is a modernized substation which is composed of intelligent primary devices (digital CT/PT and intelligent circuit breaker or GIS) and networked secondary devices based on lay-oriented structure, to realize information-sharing and interoperability between each intelligent device. Compared with the traditional substation, the digital CT/PT, intelligent primary devices, merging unit and optical fiber connection are adopted to replace the electric CT/PT, traditional primary devices and electric cables between primary devices and secondary devices.

Presently, NR offers the complete solution and all kinds of the intelligent devices applied in new digital substation including digital CT/PT, intelligent circuit breaker/GIS and complete sets of secondary devices based on IEC 61850 protocol.

The PCS-9250 series digital CT/PT of voltage level ranged from 35 KV to 500KV, PCS-220 series merging units, PCS-9820 series intelligent control devices for circuit breaker, PCS-222 series intelligent interposing relays and PCS-900 HV digital protective relays have been successfully put into service in many complete digital substations in China.

System Configuration and Communication Network of Digital Substation

The communication network of whole system can be divided into three levels, which are bay-level, process-level and station level.

Remote workstations, Dispatching centers, RTU and protection information subsystem in process level can communicate with the IEDs in bay level via the network which wholly adopts IEC61850 protocol. With perfect IEC61850 engineering tools, SCL documents in accordance with IEC61850-6 standardization can be formatted and thus information interaction between engineering tools from different manufactures can be realized.

Based on different requirements of process level, two solutions for digital substation are provided.

Digital substations supporting digital CT/PT and GOOSE service

As shown in Figure 1, in the process level, digital CT/PT and intelligent circuit breakers are adopted. All sampling AC quantities are acquired by the IEDs via optical communication with merging unit instead of electrical cables in traditional substation. Various real-time tripping/closing and protection information are transported via GOOSE network. The whole substation adopts standardized IEC61850 protocol for information interaction.

Digital substation supporting digital CT/PT and intelligent control panel

In this solution, digital CT/PT and intelligent GIS control device are adopted. The protection and control function, intelligent control function of GIS are integrated in the PCS-9820 intelligent control device which is placed near the GIS, thus the number of control cable is reduced. The intelligent control device can communication with remote workstations or other IEDs via communication network using IEC 61850. This solution optimizes and simplifies the secondary circuits and this shows reliability and advantage of digital substation.