The initial line-to-earth short-circuit current Iil in figure 3d shall be calculated by: 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. Depending on the product f. Electric and magnetic devices IEC 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. Currents during two simultaneous single phase line-to-earth short circuits and partial short-circuit currentsflowing through earth IEC ,- Short-circuit current calculation in three-phase a. I cochez tout ce qui convient Je suis lehn: The short-circuit impedances for the examples in figures 1l b and 1I C are given by the following equations: For simplification of the calculation, groups of motors including their connection cables may be combined to a single equivalent motor see motor M4 in figure 9. The factor n in figure 22 is given by: In general, the calculation according to 4.

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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. Search results IEC Webstore Calculation of short-circuit currents of asynchronous motors in the case of a short circuit at the iev see 4. If the short circuit is a far-from-motor short circuit i. NOTE The current in a three-phase short circuit is assumed to be made simultaneously in all poles.

Annex A forms an integral part of this standard. CE1 TR—l read: Equations 84 and 85 are valid in the case of far-from-generator and in the case of near-to- generator short circuits. This is admissible, because the impedance correction factor KTfor network transformers is introduced. The total short-circuit current in F1 or F2 figure 13 is found by adding the partial short-circuit current IL,, caused by the medium- and low-voltage auxiliary motors of the power station oec.

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.

The need for the calculation of minimum short-circuit currents may arise because underexcited operation of generators low-load condition in cable systems or in systems including long overhead lines, hydro pumping stations. If Si is used in spite of this in connection with short-circuit calculations, for instance to calculate the internal impedance of a network feeder at the connection point Q, then the definition given should be ied in the following form: The generator impedance shall be transferred to the high-voltage side using the rated transformation ratio t.

I In the case of minimum steady-state short circuits introduce see 2. Factors ;Iminand il,,for salient-pole generators The initial short-circuit current at the short-circuit location F is the phasor sum of the individual partial short-circuit currents see figure That is why it is not possible to give an easy method of calculating i, and id. This is the only active voltage of the network 1.

They do not contribute to the symmetrical short-circuit breaking current I, and the steady-state short-circuit current I k. The effective resistance of the stator of synchronous machines lies generally much below the given values for RGf. I cochez tout ce qui convient Je suis lehn: 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 currents.

The equations 46 and 47 are given for the calculation of and in figure 3c: It is assumed that the operating voltage at the terminals of the generator is equal to UrG.

Electric and magnetic circuits IEC 15 1: Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter.

If underexcited operation of the power station unit is expected at some time for instance to a large extent especially in pumped storage plantsthen only when calculating unbalanced short- circuit currents with earth connection see figures 3c and 3d the application of Ks according to equation 22 may lead to results at the non-conservative side.

In the case of figure 4, for instance, to the LV side. The resistance is to be considered if the peak short-circuit current ip or the d. 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.

With respect to equation 99 in table 3 the steady-state short-circuit current of asynchronous motors is zero in the case of a three-phase short circuit at the terminals figure 12 and equation Linand il,, factors for cylindrical rotor generators The factor n in figure 22 is given by: For undated references, the latest edition of the normative document referred to applies.

The IEC shall not be held responsible for identifying any or all such patent rights. 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. The decaying aperiodic component id.

Factors for the calculation of short-circuit currents in three-phase a. Depending on the product f. RL is the line resistance for a conductor temperature of 20 OC, when calculating the maximum short-circuit currents. When an impedance is present between the starpoint of the generator and earth, the correction isc KG shall not be applied to this impedance.

The positive-sequence short-circuit impedance zat 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 factor p may also be obtained from figure 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. 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.

For grounded systems the influence of motors on the line-to-earth short-circuit current cannot be neglected. 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. 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.

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## IEC 60909 1 PDF

Nikinos You can display short-circuit tick marks for initial, breaking and steady state currents. Display of short-circuit currents You can view the currents in various formats such as phase currents for A, B and C phases or in symmetrical components: EasyPower provides the option of showing a warning when the short-circuit duty percent is above a user defined safety margin threshold but below the violation level. The correction factors for three-winding transformers with or without LTC are calculated using the following equations. Radiation protection instrumentation — Equipment for sampling and moni Motor contributions are excluded. Steady-state short-circuit current I k is calculated based on section 4.

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## IEC 60909-1 PDF

The Redline version provides you with a quick and easy way to compare all the changes between this standard and its previous edition. The Redline version is not an official IEC Standard, only the current version of the standard is to be considered the official document. IEC specifies procedures for calculation of the prospective short-circuit currents with an unbalanced short circuit in high-voltage three-phase a. The currents calculated by these procedures are used when determining induced voltages or touch or step voltages and rise of earth potential at a station power station or substation and the towers of overhead lines.

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