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Shift in current angle across delta-wye transformer Integration with Protective Device Coordination The IEC short-circuit results are integrated with the protective device coordination tools in EasyPower.
Click to learn more. Medical device software — Software life cycle processes. For minimum short-circuit calculations the motor contribution is excluded.
The following features are supported:. EasyPower supports the following four types of short-circuit conditions as per IEC of buses when voltage is below threshold Figure 7: You can display short-circuit marks for initial, breaking and steady state currents.
Take the smart route to manage medical device compliance. Capacitors and non-rotating loads are not included in the calculations. To download standard IEC Short-circuit currents in three-phase a. If the link fails, the document cannot be downloaded, please click on the Broken link to let us know.
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If your documents are loaded by many people. Click here for details. Your internet browser has disabled JavaScript. 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.
The values of positive-sequence and negative-sequence impedances can differ from each other only in the case of rotating machines. The zero-sequence short-circuit impedance at the short-circuit location F is obtained according to figure 5c, if an a. When calculating unbalanced short-circuit currents in medium- or high-voltage systems and applying an equivalent voltage source at the short-circuit location, the zero-sequence capacitances of lines and the zero-sequence shunt admittances are to be considered for isolated.
The capacitances of lines overhead lines and cables of low-voltage networks may be neglected in the positive-, negative- and zero-sequence system. 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.
The deviation depends on the configuration of the network. 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.
In this case, the three-fold zero-sequence current flows through the joint return. In the case of high-voltage feeders with nominal voltages above 35 kV fed by overhead lines, the equivalent impedance 2, may in many cases be considered as a reactance, i. 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.
In special cases the zero-sequence equivalent short-circuit impedance of network feeders may need to be considered, depending on the winding configuration and the starpoint earthing of the transformer.
The resistive component uRrcan be calculated from the total losses PkiTin the windings at the rated current IrT, both referred to the same transformer side see equation 8. For large transformers the resistance is so small that the impedance may be assumed to consist only of reactance when calculating short-circuit currents. The resistance is to be considered if the peak short-circuit current ip or the d. Zero-sequence impedance arrangements for the calculation of unbalanced short-circuit currents are given in IEC Additional information may be found in IEC This correction factor shall not be introduced for unit transformers of power station units see 3.
If the long-term operating conditions of network transformers before the short circuit are known for sure, then the following equation 12b may be used instead of equation 12a. The impedance correction factor shall be applied also to the negative-sequence and the zero- sequence impedance of the transformer when calculating unbalanced short-circuit currents. 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.
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.
With these impedances the corrected equivalent impedances LK, z B K and ZCKshall be calculated using the procedure given in equation i i. The three impedance correction factors given in equation 13 shall be introduced also to the negative-sequence and to the zero-sequence systems of the three-winding transformer.
Impedances between a starpoint and earth shall be introduced without correction factor. NOTE Equivalent circuits of the positive-sequence and the zero-sequence system are given in IEC , table I , item 4 to 7 for different cases of starpoint earthing. An example for the introduction of the correction factors of equation 13 to the positive-sequence and the zero-sequence system impedances of the equivalent circuits is given in 2.
The impedances and z o L of low-voltage and high-voltage cables depend on national techniques and standards and may be taken from IEC or from textbooks or manufacturer's data. For higher temperatures than 20 OC, see equation 3. Short-circuit current-limiting reactors shall be treated as a part of the short-circuit impedance. U, is the nominal voltage of the system; ur, is the rated voltage of the generator; ZGK is the corrected subtransient impedance of the generator; 2, is the subtransient impedance of the generator in the positive-sequence system:.
The following values for the fictitious resistances RGfmay be used for the calculation of the peak short- circuit current with sufficient accuracy. The influence of various winding-temperatures on RGf is not considered. These values cannot be used when calculating the aperiodic component id.
The effective resistance of the stator of synchronous machines lies generally much below the given values for RGf. In this case the manufacturer's values for RG should be used. For the short-circuit impedances of synchronous generators in the negative-sequence system, the following applies with KG from equation 1 8 : For the short-circuit impedance of synchronous generators in the zero-sequence system, the following applies with KG from equation 1 8 : When an impedance is present between the starpoint of the generator and earth, the correction factor KG shall not be applied to this impedance.
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