A backup data network for power system automations based on satellite communication

Abstract

Power system automations technologies are essential for power system operations and controls. A variety of communication systems including optical fiber, microwave and power line communications are used to transmit these EMS/SCADA data. In these communication modes, fiber communication is used to transmit IEC 101/104 protocol data in most power grids due to its large bandwidth and high reliability. However, fiber is very fragile when large natural disasters happen. Earthquake, snow-ice strike, hurricane would probably destroy the infrastructures of the fiber systems. In some tough geographical areas such as mountainous West Sichuan Plateaus, the construction and operation of fiber communications are very costly and difficult. After 2008 5.12 Sichuan Earthquake Sichuan Electric Power Corporations started to investigate some alternative communication systems against natural disasters. Compared to traditional fiber communications, VSAT communication (Very Small Aperture Terminal for satellite communications) has 3 advantages: (1) The setup of a VSAT station is convenient and flexible. (2) The VSAT system is robust against natural disasters since it does not need wired cable or fiber. (3) The setup and operation of VSAT system is cost effective in some tough geographic areas. In Sichuan Power, we proposed an new data networks for EMS/SCADA data transmission based on VSAT systems. The structure of our system is a star-like topology: we place the VSAT communication terminals to some substations and power plants in areas which cannot afford fiber infrastructures economically or geographically. A central VSAT station is set on Power Dispatching Center. All data in VSAT system are based on TCP/IP protocol. The first problem for such a system is to select suitable VSAT communication modalities. We chose SCPC (Single Carrier per Channel) over TDMA (Time-Division Multiplex Access) as our favorable modality because SCPC could provide reliable and persistent data link and easy to manage. A detailed analysis will be included in full text. For IEC 101 protocol, the traditional 2M channel is transferred to IP packets to access the VSAT system. For IEC 104 protocol, data is directly accessed to VAST system through Ethernet connections. Since the satellite link is not stable due to a variety of environmental reasons, traditional TCP may have large transmission delay or even cannot be used in such environments. To meet the requirements of IEC protocols in transmission delay, we developed a TCP/IP accelerator dedicated for satellite communication based on SCPS-TP (Space Communication Protocol Standards - Transport Protocol). The SCPS-TP is modified version of traditional TCP/IP protocol adapted to space communications and it considers the effects of packet loss due to satellite link outage. A SCPS-TP based TCP/IP accelerator is added to each VSAT terminal in order to minimize the transmission delay. Our experiences showed that such VSAT system a very useful and robust in power systems against disasters.