The Configuration and Communication of Integrated Substation Automation Systems AbstractBased on a discussion of the feature of a substation, the paper presents the concept that a substation is composed of basic units (BC). The hardware structure of the IED of a BC is described. Next, the paper discusses the communication mode of the current integrated Substation Automation Systems (ISA) and describes the hardware structure and the functions of the ISA with fieldbus. At last the paper presents trends in the development of ISA.Keywords substation automation communication fieldbus 1. IntroductionSince the beginning of 90s, hundreds of ISA system have been put into operation in China. These systems have played a very important role in substation performance have been demonstrated in many ways. This system should be a multi-function integrated and uniformly designed real time control system with high efficiency and reliability. It should implement a most all the functions of secondary equipment of modern substation, realize the real time data sharing and exchange, and should be expandable for future use. How to design an ISA system to meet all the above requirements is discussed in the paper.First, after a discussion of the feature of substation, the paper presents the concept that a substation is composed of basic units (BC), such as lines, transformers, busses and Volt Ampere Reaction (VAR) compensation equipment, and so on. The circuit breakers and switches are merged in the relevant BCs as their attached control facilities. The hardware structure of a BC is described. Next, the paper discusses the communication mode of the current ISA and points out the fieldbus would be the way to realize reliable, real-time and accurate information communication among intelligent electronic device (IED). Then,if presents the configuration and functions of the distributed ISA with fieldbus. At last, the paper presents trends in the development of ISA.2. Basic Units and ConstructionA substation is a very important unit in power system for power transmission and distribution. A substation is required to run continuously, reliably and stably. Substations of various voltage levels and capacity have a similar configuration which is composed of power transmission and distribution facilities such as transformers, VAR devices with different voltage levels. The distinction between different sub stains is the quantity and voltage level of facilities and the way connection only.To monitor and control the substation operation, a bus is equipped with potential transformers (PT) and there are current transformers (CT) in each winding of the transformer, each line and the switchgear bay of the VAP equipment. IN the secondary system, instantaneous values of voltage and current are obtained through PT and CT, and these values are further analyzed and processed to give operational data of the substation such as voltage, current and power etc. Nom-electrical data such as oil temperature and gas signals are also provide for transformers and VAR equipment. Status data of circuit breakers, isolator switches and other auxiliary equipment in the switchgear bays are gathered through auxiliary contacts and transducers. The substation secondary system collects and processes all these data to detect any fault or abnormality. If there is a fault, the secondary system will send out a circuit breaker tripping command to the switch bay corresponding to the faulted equipment so that the fault can be isolated. If there is abnormality, a warning signal will be given.It has been shown by relevant reference that the fault characteristics of buses, lines, transformers and VAR equipment are different from each other as a result of their different physical feature. Therefore requirements for their monitoring and control are different from each other.For faults in lines, transformers, VAR equipment or buses, there are no other control measures than tripping the circuit breakers of the corresponding equipment.Under normal operation condition, transformers and VAR equipment participate in voltage and VAR control coordinated by the system to meet the requirements of power network voltage level and VAR compensation.Coordinated by the secondary system, several circuit breakers may be controlled to maintain power system stability or power supply reliability of the substation. Common examples are under frequency load shedding and bus automatic transfer.To summarize, the main features of a sub stain system are:Buses, lines, transformers and VAR devices are the basic equipment in a substation. They function together to transfer and distribute power.Requirements for the monitoring and control of buses, lines, transformers and VAR devices differ from each other.A large amount of data in a substation is from switchgear bays, a small data to them.Protection and measurement for monitoring have the same data source but different require