【正文】 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. 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: (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. (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 132kV and 275kV networks to meet the transportation requirements of the country39。s current expansion carried out. 6 The current SA transmission network Summary The current SA transmission network is a densely populated area covered by the 275kV and 132kV of the meshed network. It supplies the one tied to user needs and regional information services, and run on different voltage levels of the distribution network. SA Internet backbone can be vividly than as running in the north or south of a broad transport corridors, as shown in Figure 2 (see page 9). The sake of brevity, Figure 2 emphasizes the primary user area is the urban area of Adelaide, while the needs of the north and south are small. These three regions of demand for electricity power stations. While each area of supply and demand of electricity is uneven, but in the north and south, or between the two channels have considerable power exchange, depending on user requirements throughout the network and the exact distribution of power for each power plant. The following description of SA transmission network has six main substations: (1) Northern region: Davenport (2) Southern region: Southeast (3) Adelaide: Bala, Cherry Gardens, TIPS, Magill Figure 3 (see page 9) describes the SA with these major substation distribution network the main transmission channel. Other minor shock and the role of the middle of the distribution substation in Figure 3 are ignored, so in order to be more concise. Network transmission capacity Northern transport channel consists of four 275kV transmission lines pose. Two 275KV SA transmission network constitutes the first line (the socalled eastern and western lines), they are more than 50 years of history, mainly used to meet the transportation needs of Playford B power station, the station network is now only SA generating capacity of a small part. Small capacity of these lines and can not be in the North Channel to make significant contributions. In fact these lines are considered in conjunction with the network of secondary distribution lines rather than as the main transport routes north of the main line. Now rely mainly on the northern twochannel delivery of more advanced lines (1985), this line has a moderate level of transmission capacity. These two lines using a mon tower, which means that there is a certain degree of risk, that if some accident caused by th