## IEC 60909 1 PDF

IEC Short-Circuit Current Calculation in Three-Phase A.C. Systems Part 1: Factors for the Calculation of Short-Circuit Currents in Three-Phase A.C. Part 1: Factors for the calculation of short-circuit currents according to IEC 0. Numéro de référence. Reference number. CEI/IEC/TR The International Electrotechnical Commission (IEC) is the leading global IEC TR , Short-circuit currents in three-phase a.c. systems – Part 1: .

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Voltages and currents are to be converted by the rated transformation ratio t. The effective resistance of the stator of synchronous machines lies generally much below the given values for RGf. 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.

I librarian researcher I design engineer safety engineer ci Q7 Please assess the standard in the I following categories, using testing engineer ci the numbers: It is not necessary for the product 1, The results of the short-circuit current calculation have an acceptable accuracy also in the case of untransposed overhead lines.

Characterization of short circuits and their currents 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.

Electric and magnetic devices IEC When calculating the partial short-circuit current I: For grounded systems the influence of motors on the line-to-earth short-circuit current cannot be neglected.

This occurs in the case of a far-from-generator short circuit. 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.

Q5 This standard meets my needs: 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.

I 660909 not at all ci This procedure is not allowed when calculating the peak short-circuit current i. 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. This part of IEC deals with the calculation of short-circuit currents in the case of balanced or unbalanced short ifc.

For higher temperatures than 20 OC, see equation 3. The values of p in equation 70 apply if synchronous machines 06909 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.

NOTE The following values for resistivity may be used: The correction factor Kso 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.

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. The impedance of the auxiliary transformer AT in figure 13 is to be corrected with KT from 3.

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The effect of series capacitors can be neglected in the calculation of short-circuit currents, if they are equipped with voltage-limiting devices in parallel, acting if a short circuit occurs. As a result, reversible static converter-fed drives are treated iwc the calculation of short-circuit currents in a similar way as asynchronous motors.

Shunt admittances for example, line capacitances and passive loads are not to be considered when calculating short-circuit currents in accordance with figure 4b. Xk may be neglected.

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. This is the only active voltage of the network 1. Short-circuit impedances of a three-phase a.

Figure 16 can be used also for compound excited low-voltage generators with a minimum time delay tminnot greater than 0,1 s.

Rated voltage, line-to-line r. 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 zero-sequence short-circuit impedance at the short-circuit location F is obtained according to figure isc, if an a.

Calculations are simplest for balanced short circuits on radial systems, as the individual contributions to a balanced short circuit can be evaluated separately for each source figures 12 or The calculation of the minimum steady-state short-circuit current in the case of a near-to- generator short circuit, fed by one or’ several similar and 60990 working generators with compound excitation, is made as follows: For the calculation of the partial short-circuit current I L 2 feeding into the short-circuit location F2, for example at the connection to the high-voltage side of the auxiliary transformer AT in figure 13, it is sufficient to take: For simplification, it is permitted to use the same value for IC as for the three- phase short circuit.

This part of IEC does not deal with the calculation of short-circuit currents in installations on board ships and aeroplanes.

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Synchronous machines generators, motors, or compensators with terminal-fed static exciters do not contribute to I k in the case of a short-circuit at the terminals of the machine, but they contribute to l k if there is an impedance between the terminals and the short-circuit location. 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 unit.

International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. O 1 marks the positive-sequence neutral reference. Normally, the steady-state short-circuit current Ik is smaller than the symmetrical short-circuit breaking current 1. 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.

For the short-circuit impedance of synchronous generators in the zero-sequence system, the following applies with KG from equation 1 8: I education ci military ci I other 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. Short-circuit current-limiting reactors shall be treated as a part of the short-circuit impedance.