The initial symmetrical current is calculated based on section 4. Impedances 2, between the starpoint of transformers and earth are to be introduced as 3 2, into the zero-sequence system without a correction factor. Peak current based on method c: The capacitances of lines overhead lines and cables of low-voltage networks may be neglected in the positive-, negative- and zero-sequence system. Z THV is the impedance of the unit transformer referred to the high-voltage side without correct factor K T ;. Electrical equipment may be overstressed due to the short-circuit duration. For the short-circuit impedance of synchronous generators in the zero-sequence system, the following applies with KG from equation 1 8:
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Calculation of currents 1 General 1.
IEC section 6 provides a sample calculation as a benchmark test for software programs to compare. The impedances in systems connected through transformers to the system, in which the short circuit occurs, have to be transferred by the square of the rated transformation ratio.
EasyPower uses the following c factors as the default for maximum lec minimum short-circuit conditions.
This part of IEC establishes a general, practicable and concise procedure leading to results, which are generally of acceptable accuracy.
Asymmetrical values can be used with protective devices that respond to the asymmetrical currents. This fault is beyond the scope of, and is therefore not dealt with in, this standard. You can modify these idc as needed in the short circuit options.
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Lec- lire: In a system of low voltage breakers with ZSI, when the current through any circuit breaker exceeds the short time pickup its restraining signal is sent to upstream circuit breakers. Except for special cases, the zero-sequence short-circuit impedances at the short-circuit location differ from the positive-sequence and negative-sequence short-circuit impedances. Short-circuit equipment duty report Voltage Sensitivity Analysis Short-circuit on any bus results in voltage drop in other near buses in the system.
The results of the short-circuit current calculation have an acceptable accuracy also in the case of untransposed overhead lines. Operational data and the load of consumers, tap- changer position of transformers, excitation of generators, and so on, are dispensable; additional calculations about all the different possible load flows at the moment of short circuit are superfluous.
The following types of unbalanced short circuits are treated in this standard: For three-winding transformers with and without on-load tap-changer, three impedance correction factors can be found using the relative values of the reactances of the transformer see 3.
This phenomenon is not dealt with in this standard. For unbalanced faults, equations 868788 and 89 are used. Normally, the steady-state short-circuit current Ik is smaller than the symmetrical short-circuit breaking current 1. I tables, charts, graphs, figures When a number of short circuits occur with a short time interval in between them, the resulting Joule integral is the sum of the Joule integrals of the individual short-circuit currents, as given in equation 1 Neglecting the -zero-sequence capacitances of lines in earthed neutral systems leads to results which are slightly higher than the real values of the short-circuit currents.
Steady-state short-circuit current I k Steady-state short-circuit current I k is calculated based on section 4. For simplification, it is permitted to use the same value of Kas for the three-phase short circuit. Z S is the corrected impedance of a power station unit with LTC to the high-voltage side.
IEC TR 60909-4:2000
Breaking currents are calculated at 0. The following methods are supported for meshed networks as per section 4.
For the examples in figures 1Ib and 1 IC, the initial symmetrical short-circuit current is calculated with the corrected impedances of the generator and the power station unit see 3. The factor K shall, be calculated according to 4.
Short circuit tests accordig to the standard (IEC ) (PSCAD Short Circuit Standard)
However, 6099-4 to agreements based on this part of IEC are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For higher temperatures than 20 OC, see equation 3.
The correction factor Kso shall also be applied to the zero-sequence system impedance of the power station unit excepting, if present, an impedance component uec the star point of the transformer and earth.
Short circuits may have one or more sources, as shown in figures 11, 12, and Fuses and low voltage circuit breakers ratings are compared with initial currents. Factor n for the heat effect of the a. The following values for the fictitious resistances RGfmay be used for the calculation of the peak 609094 circuit current with sufficient accuracy.
All other static converters are disregarded for the short-circuit current calculation according to this standard.