Several factors for the calculation of short-circuit (s.-c.) currents have been introduced in previous sections, the origin of which will be explained within this section. · Voltage factor c_max and c_min for different voltage levels as per Table 4.1. · Correction factor using the %/MVA or the p.u.-system as mentioned in Chapter 2. · Impedance correction factors for synchronous machines, power station units and transformers as per Tables 3.2, 3.3, 3.5 and 3.6. · Factors for the calculation of different parameters of the short-circuit current based on the initial short-circuit current as per Chapter 4. The factors are necessary as the method of the equivalent voltage source at the short-circuit location is used for the calculation of short-circuit currents which is based on some simplifications such as neglecting the load current prior to fault, assuming the tap-changer of transformers in middle-position, calculating the impedance of equipment based on the name-plate data or on data for rated operating conditions and neglecting voltage control gear for generators and transformers. The main task of short-circuit analysis is to determine the maximal short-circuit current which is one of the main criteria for the rating of equipment in electrical power systems. It is obvious that the parameters of the short-circuit current as calculated with the equivalent voltage source at the short-circuit location will differ from those currents, which may be measured during short-circuit tests or may be calculated with transient network analysing programmes. In order to obtain results on the safe side without uneconomic safety margin the correction factors will be applied. Detailed deductions of the various correction factors are given in IEC 60909-1:1991-10.

Inspec keywords: short-circuit currents; power system faults; transient analysis; power system transients

Other keywords: equivalent voltage source; voltage factor; transformers; generators; maximal short-circuit current; correction factor; impedance correction factors; voltage control gear; synchronous machines; safety margin; electrical power systems; tap-changer transformer; power station units; transient network analysing programmes; IEC 60909-1:1991-10

Subjects: Power systems