Download Citation on ResearchGate | Applying IEC , Fault Current Calculations | Rather than the short-circuit current that would occur in a specific. Applying IEC , short-circuit current calculations. Abstract: Rather than the short-circuit current that would occur in a specific instance, IEC derives. The initial short circuit current for a is as per IEC Equation
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Calcul des courants Part O: The voltage factor c is used to scale the equivalent voltage source in the calculations to account for variations in the falculation voltage. Calculation of cicuit 1 General 1. In the case of unbalanced short circuits, the impedance correction factor KSOfrom equation 24 shall be applied to both the positive-sequence and the negative-sequence system impedances of the power station unit.
The factors m and n first appeared as Figures 12a and 12b of IEC and are identical to them.
The zero-sequence system impedance Z,, of the motor shall be given by the manufacturer, if needed see 4. Annex A forms an integral part of this standard. When an impedance is present between the starpoint of the generator and earth, the correction factor KG shall not be applied shlrt this impedance. Then they contribute only iecc the initial symmetrical short-circuit current I: When using this method in meshed networks with transformers, generators and power station units, the impedance correction factors KT,KG and Ks, respectively Kso, shall be introduced with the same values as for the 50 Hz or 60 Hz calculations.
For dated references, subsequent amendments to, or revisions of, any of these publications do not apply.
IEC Short-Circuit in EasyPower
Fuses and low voltage circuit breakers ratings are compared with initial currents. In meshed networks there are several direct-current time constants. All other active voltages in the system are assumed to be zero. The method described above is for 3-phase short circuit. The following types of unbalanced short circuits are treated in this standard: For undated references, the latest edition of the normative document referred to applies.
IEC-60909 Short-Circuit in EasyPower
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. Earth ground trip functions for low voltage circuit breakers or relays use the symmetrical earth ground current.
The initial symmetrical short-circuit currents riQ,, and riQm, on the high-voltage side of the trans- former shall be given by the supply company or by an adequate calculation according to this standard. The resistance is to be considered if the peak short-circuit current ip or the d.
Calculahion and magnetic circuits IEC 15 1: Figure 20 describes this situation with balanced and unbalanced short circuits with earth connection at the crcuit location F.
While using fuses or current-limiting circuit-breakers to protect substations, the initial symmetrical short- circuit current is first calculated as if these devices were not available. Line-to-earth short-circuit currents for Initial symmetrical rms and peak Short-Circuit Duty Calculations EasyPower compares the short circuit results with protective device short-circuit ratings and displays the results in the text report and in the single line diagram.
Three-phase short-circuit currents for breaking I b at0. Factor q may also be obtained from figure This method applies the 1. With these impedances the corrected equivalent impedances LK, z B K and ZCKshall be calculated using the procedure given in equation i i.
A,,, may be obtained from figures 18 or 19 for cylindrical rotor generators or salient-pole generators. This part of Calcultion deals with the calculation of short-circuit currents in the case of balanced or unbalanced short circuits. T JSrT ; t, is the rated transformation ratio of the unit transformer: This part of IEC establishes a general, practicable and concise procedure leading to results, which are generally of acceptable accuracy.
Electrical equipment may be overstressed due to the short-circuit duration. Skip to main content. Transformer Impedance Correction Factors The transformer correction factor K T for two winding units with or without on-load tap changer LTC is calculated as follows per section 3.
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