【正文】 132kV and 275kV networks to meet the transportation requirements of the country39。(2) 275kV network, which began in the 20th century, the late fifties, when the Playford B power station in the Port Augusta power plant generating capacity increased after the northern part of Adelaide and another one between the transport circuit (1) 132kV network, which early in the 20th century began to use the fifties, when the transmission circuit is also another one located in Adelaide and Port Augusta power station has been established between a remote. So drop the network transmission line capacity limits should be considered a factor. Power To achieve availability, a practical power system must be able to continue in a predictable way to run, even in some areas suffer from some of the pressure (including transmission and distribution line short circuits, power generation unit failure, the auxiliary power unit capabilities to do as intended to achieve ), the same is true. To limit the power dynamics of the system in the normal operating range is to meet the power required for the quality of an operational necessity. These constraints (transient stability of the weak signal stability) affect the capacity of electricity transmission network elements. The relationship between factors In a closely related network (such as a merger of urban multilevel transport circuits, shortdistance transmission lines and substation pound), according to transmission lines, transmission temperature levels to assess the ability and capacity of transmission lines is reasonable. But for a very long transmission lines and across a wide area (usually covering the main urban area) networks, pressure drop factor is often used to measure the performance of transmission lines (in the heat capacity below the level of extreme circumstances). Power system ponents (such as capacitors and proprietary control systems) can reduce some special line constraints. In these areas, a number of professional and technical assessments are often used to determine the transmission line constraints. 5 SA Network History The current transmission network, back in Adelaide SA power pany power plant in the eastern plains, and Osborne, as well as between 1 to 66KV voltage power supply of Adelaide around the mountain when the establishment of links to use. Expansion of this network has experienced for several years, there had been the voltage levels are as follows: Figure 1 (see page 8) depicts a typical power system structure. 4 power system performance limiting factor Every power structure of the system are subject to a number of constraints dominate, these factors determine the upper and lower limits of their operation. The power system operation means that the power system from the majority of all the limiting factor in the restrictions. Special restrictions is bound by the limit to run with the power system configuration and operating point varies. Due to the slip have been identified all electrical power network, the interaction between elements in the system, which can easily run from one state to another state or to consider other network errors of independent elements to infer the system performance. In general, according to the special structure of the entire network of technical research is necessary. Technical evaluation criteria included in an appropriate time frame for power system simulation. This technique quite mathematical, and the interpretation of results also requires specialized skills. Some of the power system performance in determining the main factors that must be considered are as follows: Temperature Current through a circuit (bare wire, insulated cables) will generate heat. The circuit depends on its ability to continue to diversion in the absence of serious physical damage (and simmered fire, loss of physical strength) cooling performance (lost index), this heat often through the surrounding medium (air, insulation, soil) to achieve . Maximum current carrying capacity to determine the heat requirements of network circuits rated value, of course, this does not include the transmission of additional current. Pressure Drop In most cases, the current flows through the network line, can have led to the end of the line voltage is lower than the transport terminal voltage. In order to ensure supply reliability and power quality, all the nodes in the network voltage conditions necessary to maintain the rated voltage up and down in a small range (usually in the rated voltage of + / 5% in). Other parameters remain unchanged in the line of cases, when a large number of longdistance power transmission when the end of the line will lead to significant pressure drop. On a specific segment (a specific length and structure), the line pressure drop of the current flowing through the circuit increases with increasing. Therefore, the section of the line voltage drop depends on the physical structure of the line (length, concrete structure), as well as lines to carry the current. (2) power distribution applications in a wide range of decentralized regional and even a small amount of electricity transmission, which usually uses lowvoltage, safe and feasible means. The characteristics of distribution systems are often decided by the design of the circuit, these circuits are mainly radial in nature, and it converted into a selective configuration capability is limited. Distribution systems are generally across a wide area. Is oneway flow of power. Distribution line failures of large power systems is relatively small impact on overall function. 3 Typical structure of Electric power system network can be viewed as a pyramid (or tree) structure, in this structure, the generator in the top of the pyramid, for feeding a mon distribution network, the user through a separate subscriber line (grid) from the pyramids at the bottom of