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Three-phase short-circuit current calculation of power system planning, design, operation must be carried out in the calculation of analytical work. At present, the three-phase short-circuit current has become troubled over many of the key issues of power system operation. However, during the three-phase short-circuit current calculation, the design, operation and research departments of the different calculation methods, which may cause short-circuit current calculation of the conclusions of the differences and short-circuit current to determine the difference between standard and short-circuit current restrictions different.

If short-circuit current calculations are somewhat conservative, it may result in unnecessary waste of the investment; if biased optimism, the system will be safe and stable operation of the catastrophic dangers buried. Thus, in-depth study of the standard short-circuit current calculation based on comparing the different conditions of short-circuit current calculation of short-circuit current calculation of the impact of the conclusions, as well as for grid computing and short-circuit current limit to provide a more realistic approach and thinking.

1 short-circuit current calculation method

Classic method of calculating short-circuit current: The variable ratio of 1.0, does not consider the line charging capacitance and parallel compensation, regardless of load current and the effects of load, the node voltage from 1.0, no-load generator. Short-circuit current calculation of the standard IEC main standards and ANSI standards, China is the IEC standards used. GB provides short-circuit current calculation method, calculation conditions. GB recommended three-phase short-circuit current calculation method is the equivalent voltage source method, the calculation conditions are as follows: ① not consider non-rotating load data and run the way of excitation; ② neglect and non-revolving line load capacitance of the parallel admittance; ③ with the transformer tap, the switch position will be deemed to be the main tap location; ④ excluding arc resistance; ⑤ 35 kV and above the maximum system short-circuit current calculation, the equivalent voltage source taking a nominal voltage of 1.1 ( Calculation of rated voltage 1.05 pu), but not exceeding the maximum operating voltage equipment.

For network planning, operation department, the largest three-phase short-circuit current calculation is the calculation of the main content. Calculation, the power grid, power grids of the different departments may use different calculation conditions. Differences mainly concentrated in the transformer ratio, the selection of the node voltage. Variable transformer check than 1.0, the change from the ratio of the actual operation; node voltage may take 1.0, 1.05 may also be taken. Both are used in different combinations, it is clear that this will affect the outcome of short-circuit current calculation. Root of the problem is often calculated based on the inherent computational procedures set up to calculate, and calculation procedures due to lack of sufficient flexibility. In fact, if I understand the requirements of short-circuit current calculation, calculation of staff is calculated on the results obtained from the appropriate processing. Some commercial software also provides a flexible conditions for short-circuit current calculation capabilities. �

2 the impact of short-circuit current calculation factors

United States PTI's PSS / E to provide a trend based on the short-circuit current calculation and the use of classical methods, ANSI standards or IEC standards, the choice of short-circuit current calculation. The use of IEC standards, allows the user to arbitrarily set the initial value calculation of short-circuit current conditions. The options can be set include: ① variable than the choice: 1.0 or normal ratio; ② consider whether or not charging capacitor; ③ or, taking into account the parallel compensation; ④ voltage node; ⑤ generator power factor. To this end, the use of PSS / E program of its own examples of the different initial conditions on the results of short-circuit current calculation of the impact analysis.