Buy IEC/TR Ed. Short-circuit currents in three-phase a.c. systems Part 4: Examples for the calculation of short-circuit currents from SAI Global. The results meet requirements of IEC and match the example provided in IEC TR section 6. The IEC standard terminology is used in the user. The International Electrotechnical Commission (IEC) is the leading global IEC TR , Short-circuit currents in three-phase a.c. systems – Part 4.
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If the highest partial short-circuit current of the power station unit at the high-voltage side of ie unit transformer with off-load taps is searched for, choose l-pT. Despite these assumptions being not strictly true for the power systems considered, the result of the calculation does fulfil the objective to give results which are generally of acceptable accuracy.
CE1- Instead of: This is the first step to obtaining most values. Regardless of the time of short-circuit occurrence, the discharge current of the shunt 60909–4 may be neglected for the calculation of the peak short-circuit current. The correction factor Ks shall also be applied to the zero-sequence system impedance of the power station unit, excepting, if present, an impedance component between the star point of the transformer and earth.
I k autre s Z S is the corrected impedance of a power station unit with LTC to the high-voltage side.
Display of short-circuit currents You can view jec currents in various formats such as phase currents for A, B and C phases or in symmetrical components: Electric and magnetic circuits IEC 15 1: The following values for the fictitious resistances RGfmay be used for the calculation of the peak short- circuit current with sufficient accuracy. It is only necessary to choose the branches which carry partial short-circuit currents at the nominal voltage corresponding to the 69009-4 location and branches with transformers adjacent to the short-circuit location.
Sequential short circuits are not considered.
IEC-60909 Short-Circuit in EasyPower
You can modify these values as needed in the short circuit options. Asymmetrical currents are calculated as the root mean square of the symmetrical and dc components. Voltage Factors c The voltage factor 660909-4 is used to scale the equivalent voltage source in the calculations to account for variations in the system voltage.
The values of p in equation 70 apply if synchronous machines are excited by rotating exciters or by static converter exciters provided, for static exciters, the minimum time delay tminis less than 0,25 s and the maximum excitation voltage is less than 1,6 times rated load excitation-voltage. Earth ground trip functions for low voltage circuit breakers or relays use the symmetrical earth ground current.
EasyPower uses the equivalent voltage source at the short-circuit location, symmetrical components impedance network, and the voltage factor c as described in section 2.
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The factors m and n first appeared as Figures 12a and 12b of IEC and are identical to them. Thus the network feeder in figure 4a is represented by its internal impedance Zot, transferred to the LV-side of the transformer see 3. Any branch may be a series combination of several impedances. Figure 16 can be used also for compound excited low-voltage generators with a minimum time delay tminnot greater than 0,1 s. Short-circuit duty results displayed in the single line drawing Table 5: You can obtain the following values of short-circuit currents at the fault location for both maximum and minimum short circuit currents:.
Iiec Center Find new research papers in: High voltage circuit breaker data comes with the DC time constant.
This method applies the 1. That is why it is not possible to give an easy method 60099-4 calculating i, and id. Then they contribute only to the initial symmetrical short-circuit current I: The upstream circuit breakers do not trip instantaneously whereas the most downstream circuit breaker trips fast, enabling selective coordination.
IEC Short-Circuit in EasyPower
This part of IEC deals with the calculation of short-circuit currents in the case of balanced or unbalanced short circuits. The initial line-to-earth short-circuit current Iil in figure 3d shall be calculated by: In the case of a near-to-generator short circuit, the short-circuit current can be considered as the sum of the following two components: For simplification of the calculation, groups of motors ief their connection cables may be combined to a single ic motor see motor M4 in figure 9.
Figure 1 gives schematically the general course of the short-circuit current in the case of a far-fiom- generator short circuit. Electrical equipment may be overstressed due to the short-circuit duration.
The deviation depends on the configuration of the network. This is admissible, because the impedance correction factor KTfor network transformers is introduced. Short circuits may have one or more sources, as shown in figures 11, 12, and Synchronous Generator Impedance Correction Factor The synchronous generator impedance correction factor K G for generators without unit transformers is calculated as follows per section 3.
For remote buses and branches across transformers, a phase angle shift is applied accordingly by the short circuit calculations. This figure is useful for information but should not be used instead of I calculation. For the short-circuit impedances of synchronous generators in the ice system, the following applies with KG from equation 1 8: You can insert tick marks arrows in the TCC plot to indicate the short-circuit current through the device.
Shunt admittances for example, line capacitances and passive loads are not to be considered when calculating short-circuit currents in accordance with figure 4b.