For faults far from the generator faults in three phase systems, each type of fault the symmetrical short-circuit current I" k is given by:. Typically both a maximum fault level used for rating equipment , and minimum level used for protections settings are calculated. When evaluating the maximum and minimum, the following condtions are taken into account:. Presently, in myCableEngineering we use the conductor operating temperature as the reference for both maximum and minimum fault levels. Knowledge Base.
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Short-circuit current of a far-from-generator short circuit with constant a. Short-circuit current of a near-to-generator short circuit with decaying a. Characterization of short circuits and their currents Short-circuit impedances of a three-phase a. System diagram and equivalent circuit diagram for network feeders Three-winding transformer example Phasor diagram of a synchronous generator at rated conditions Example for the estimation of the contribution from the asynchronous motors in relation to the total short-circuit current Short-circuit currents and partial short-circuit currents for three-phase short circuits between generator and unit transformer with or without on-load tap.
Example of a meshed network fed from several sources Factor p for calculation of short-circuit breaking current 1, Factor q for the calculation of the symmetrical short-circuit breaking current of asynchronous motors Linand il,,, factors for cylindrical rotor generators Factors ;Iminand il,,,for salient-pole generators Transformer secondary short circuits.
Factor m for the heat effect of the d. Factor n for the heat effect of the a. Voltage factor c Calculation of short-circuit currents of asynchronous motors in the case of a short circuit at the terminals see 4. The object of the IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work.
International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization for Standardization ISO in accordance with conditions determined by agreement between the two organizations.
Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter.
The IEC shall not be held responsible for identifying any or all such patent rights. This first edition cancels and replaces IEC published in and constitutes a technical revision.
Annex A forms an integral part of this standard. At this date, the publication will be 0 reconfirmed; 0 withdrawn; 0 replaced by a revised edition, or 0 amended. Systems at highest voltages of kV and above with long transmission lines need special consideration. This part of IEC establishes a general, practicable and concise procedure leading to results, which are generally of acceptable accuracy.
For this calculation method, an equivalent voltage source at the short-circuit location is introduced. This does not exclude the use of special methods, for example the superposition method, adjusted to particular circumstances, if they give at least the same precision. The superposition method gives the short-circuit current related to the one load flow presupposed. This method, therefore, does not necessarily lead to the maximum short-circuit current.
This part of IEC deals with the calculation of short-circuit currents in the case of balanced or unbalanced short circuits. This fault is beyond the scope of, and is therefore not dealt with in, this standard. For currents during two separate simultaneous single-phase line-to-earth short circuits in an isolated neutral system or a resonance earthed neutral system, see IEC Short-circuit currents and short-circuit impedances may also be determined by system tests, by measurement on a network analyzer, or with a digital computer.
In existing low-voltage systems it is possible to determine the short-circuit impedance on the basis of measurements at the location of the prospective short circuit considered. In general, two short-circuit currents, which differ in their magnitude, are to be calculated: the maximum short-circuit current which determines the capacity or rating of electrical equipment; and the minimum short-circuit current which can be a basis, for example, for the selection of fuses, for the setting of protective devices, and for checking the run-up of motors.
NOTE The current in a three-phase short circuit is assumed to be made simultaneously in all poles. Investigations of non-simultaneous short circuits, which may lead to higher aperiodic components of short-circuit current, are beyond the scope of this standard.
This standard does not cover short-circuit currents deliberately created under controlled conditions short-circuit testing stations. This part of IEC does not deal with the calculation of short-circuit currents in installations on board ships and aeroplanes. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply.
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.
For undated references, the latest edition of the normative document referred to applies. The calculation of the three-phase peak short-circuit current i, applies to the line conductor and to the instant at which the greatest possible short-circuit current exists.
Sequential short circuits are not considered. ILR highest symmetrical r. This is the only active voltage of the network 1.
The values are given in table 1 NOTE The introduction of a voltage factor c is necessary for various reasons. These are: - voltage variations depending on time and place, - changing of transformer taps, - neglecting loads and capacitances by calculations according to 2. It does not take into account adjustable time delays of tripping devices. The symbols represent physical quantities possessing both numerical values and dimensions that are independent of units, provided a consistent unit system is chosen, for example the international system of units SI.
E" Subtransient voltage of a synchronous machine f Frequency 50 Hz or 60 Hz Ib Symmetrical short-circuit breaking current r. Ik Steady-state short-circuit current r. IkP Steady-state short-circuit current at the terminals poles of a generator with compound excitation Initial symmetrical short-circuit current r.
Symmetrical locked-rotor current of an asynchronous motor Rated current of electrical equipment Thermal equivalent short-circuit current d. Nominal system voltage, line-to-line r. Rated voltage, line-to-line r. Rated short-circuit voltage of a transformer in per cent Short-circuit voltage of a short-circuit limiting reactor in per cent Rated resistive component of the short-circuit voltage of a transformer in per cent Rated reactive component of the short-circuit voltage of a transformer in per cent Positive-, negative-, zero-sequence voltage Reactance, absolute respectively relative value Synchronous reactance, direct axis respectively quadrature axis Fictitious reactance of a generator with compound excitation in the case of steady-state short circuit at the terminals poles Xd resp.
Xq Subtransient reactance of a synchronous machine saturated value , direct 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.
Figure 1 - Short-circuit current of a far-from-generator short circuit with constant a. Depending on the application of the results, it is of interest to know the r. In meshed networks there are several direct-current time constants. That is why it is not possible to give an easy method of calculating i, and id. Special methods to calculate i, with sufficient accuracy are given in 4. Figure 2 - Short-circuit current of a near-to-generator short circuit with decaying a.
This is admissible, because the impedance correction factor KTfor network transformers is introduced. 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. For balanced and unbalanced short circuits as shown in figure 3, it is useful to calculate the short-circuit currents by application of symmetrical components see 2.
When calculating short-circuit currents in systems with different voltage levels, it is necessary to transfer impedance values from one voltage level to another, usually to that voltage level at which the short-circuit current is to be calculated. For per unit or other similar unit systems, no transformation is necessary if these systems are coherent, i. The impedances of the equipment in superimposed or subordinated networks are to be divided or multiplied by the square of the rated transformation ratio t,.
Voltages and currents are to be converted by the rated transformation ratio t,. The equivalent voltage source is the only active voltage of the system. All network feeders, synchronous and asynchronous machines are replaced by their internal impedances see clause 3.
In all cases it is possible to determine the short-circuit current at the short-circuit location F with the help of an equivalent voltage source. 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.
Figure 3 - Characterization of short circuits and their currents Figure 4 shows an example of the equivalent voltage source at the short-circuit location F as the only active voltage of the system fed by a transformer without or with on-load tap-changer. All other active voltages in the system are assumed to be zero.
Thus the network feeder in figure 4a is represented by its internal impedance Zot, transferred to the LV-side of the transformer see 3. Shunt admittances for example, line capacitances and passive loads are not to be considered when calculating short-circuit currents in accordance with figure 4b.
O 1 marks the positive-sequence neutral reference. The impedance of the network feeder and the transformer are related to the LV-side and the last one is also corrected with KT see 3.
This postulates that the electrical equipment has a balanced structure, for example in the case of transposed overhead lines. The results of the short-circuit current calculation have an acceptable accuracy also in the case of untransposed overhead lines. Using this method, the currents in each line conductor are found by superposing the currents of the three symmetrical component systems: - positive-sequence current L l ; - negative-sequence current L 2 ; - zero-sequence current L o.
The following types of unbalanced short circuits are treated in this standard: - line-to-line short circuit see figure 3b , - line-to-line short circuit with earth connection see figure 3c , - line-to-earth short circuit see.
For the purpose of this standard, one has to make a distinction between short-circuit impedances at the short-circuit location F and the short-circuit impedances of individual electrical equipment.
The positive-sequence short-circuit impedance z , at the short circuit location F is obtained according to figure 5a, when a symmetrical system of voltages of positive-sequence phase order is applied to the short-circuit location F, and all synchronous and asynchronous machines are replaced by their internal impedances.
IEC-60909 Short-Circuit in EasyPower
For this calculation method, an equivalent voltage source at the short-circuit location is introduced. This does not exclude the use of special methods, for example the superposition method, adjusted to particular circumstances, if they give at least the same precision. The superposition method gives the short-circuit current related to the one load flow presupposed. This method, therefore, does not necessarily lead to the maximum short-circuit current. Short-circuit currents and short-circuit impedances may also be determined by system tests, by measurement on a network analyser, or with a digital computer.
BS EN 60909-0:2016
EasyPower offers a complete and accurate solution to short-circuit calculations in three-phase AC systems using the IEC standard. You can enter equipment data and parameters via user friendly interface. The IEC standard terminology is used in the user interface and reports. You can obtain the following values of short-circuit currents at the fault location for both maximum and minimum short circuit currents:.