This calculation is based on IEC (, c), “Short-circuit currents in three-phase a.c. systems – Part 0: Calculation of currents” and. EasyPower offers a complete and accurate solution to short-circuit calculations in three-phase AC systems using the IEC standard. You can enter. IEC Edition INTERNATIONAL. STANDARD. NORME. INTERNATIONALE. Short-circuit currents in three-phase a.c. systems –.
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When an impedance is present between the starpoint of the generator and earth, the correction factor KG shall not be applied to this impedance.
Ied is not necessary for the product 1, The type of short circuit which leads to the highest short-circuit current depends on the values of the positive-sequence, negative-sequence, and zero-sequence short-circuit impedances of the system. 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.
The initial short-circuit current at the short-circuit location F is the phasor sum of the individual partial short-circuit currents see figure EasyPower offers a complete and accurate solution to short-circuit calculations in three-phase AC systems using the IEC standard.
Regardless of the time of short-circuit occurrence, the discharge current of the shunt capacitors may be neglected for kec calculation of the peak short-circuit current. Lec impedances are used for rotating machines with the impedance correction factors. In the calculation of short-circuit currents, those medium-voltage and low-voltage motors may be neglected, provided that, according to the circuit diagram interlocking or to the process reversible drivesthey are not switched in at the same lec.
Factor q may also be obtained from figure Short-circuit current of a near-to-generator short circuit with decaying a. In this case the Joule integral is determined from the characteristic of the current-limiting device. For breaking current you can choose from 0.
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However, parties 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. The generator impedance shall be transferred to the high-voltage side using the kec transformation ratio t.
This can lead to a situation where the partial short-circuit currents are too small to operate any further protection device, particularly in the case of minimum short-circuit currents. Asymmetrical values can be used with protective devices that respond to the asymmetrical currents. Factor m for the heat effect of the d.
I,, is the rated current of the generator transferred to the high-voltage side see 4. Single-fed short circuits supplied by a transformer according to figure 4, may a priori be regarded as far- from-generator short circuits if X, 2 Ur, with XQ, calculated in accordance with 3. The short-circuit current through any protective device can be used to clip the TCC curve of the device.
Thus the network feeder in figure 4a is represented by its internal impedance Zot, transferred to the LV-side of the transformer see 3. NOTE Equivalent circuits of the positive-sequence and the zero-sequence system are given in IECtable Iitem 4 to 7 for different cases of starpoint earthing.
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IEC standard specifies clock number notation and their respective phase angle shift for transformers. 609909 of short circuits and their currents If not, they are subject to additional considerations.
The text of this standard is based on the following documents: In this case special considerations beyond the iiec and procedure given in this standard have to be taken into account see for instance 2. Factor p for calculation of short-circuit breaking current 1, The superposition method gives the short-circuit current related to ie one load flow presupposed. For other ,values of minimum time delay, linear interpolation between curves is acceptable.
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Short Circuits in Power Systems: A Practical Guide to IEC 60909-0, 2nd Edition
IEC TR2- lire: Low-voltage motors are to be taken into account in auxiliaries of power stations and in industrial and similar installations, for example in networks of chemical and steel industries and pump- stations. Short-circuit currents and partial short-circuit currents for three-phase short circuits between generator and unit transformer with or without on-load tap. Xq Subtransient reactance of a synchronous machine saturated valuedirect axis respectively quadrature axis xd Unsaturated synchronous reactance, relative value xd sat Saturated synchronous reactance, relative value, reciprocal of the saturated no-load short-circuit ratio Impedance, absolute respectively relative value Short-circuit impedance of a three-phase a.
Asymmetrical Currents Asymmetrical currents for the initial and the four breaking time intervals are also calculated for use in protective device coordination. For simplification, it is permitted to use the same value for as for the three- phase short circuit.
High voltage circuit breaker data comes with the DC time constant. Short-circuit duty results displayed in the single line drawing Table 5: Figure 21 – Factor m for the heat effect of the d.
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.
Earth ground trip functions for low voltage circuit breakers or relays use the symmetrical earth ground current. This will display the curve only up to the maximum current the device will see. If the Joule integral or the thermal equivalent short-circuit current shall be calculated for unbalanced short circuits, replace I: For dated references, subsequent amendments to, or revisions of, any of these publications do not apply.