Electrical equipment may be overstressed due to the short-circuit duration. From the calculated initial symmetrical short-circuit current and characteristic curves of the fuses or current-limiting circuit- breakers, the cut-off current is determined, which is the peak short-circuit current of the downstream substation. Currents calculated with equation 74 are larger than the real symmetrical short-circuit breaking. By understanding the theory any software allows users to perform all the necessary calculations with ease so they can work on the design and application of low- and high-voltage power systems. For grounded systems the influence of motors on the line-to-earth short-circuit current cannot be neglected. CE1 TR2 , — Instead of:
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Examples f o r the calculation of short-circuit currents’ IEC iec 60909-0 The effective resistance per unit length RL of overhead lines at the conductor temperature 20 “C may be calculated from the nominal cross-section qn and the resistivity p: When using this method in meshed iec 60909-0 with transformers, generators and power station units, the impedance correction factors KT,KG and Ks, respectively Kso, shall be introduced with the same values as for the 50 Hz or 60 Hz calculations.
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 parallel working generators isc compound excitation, is made as follows: Shunt 06909-0 for example, line capacitances and passive loads are not to be considered when calculating short-circuit currents in accordance with figure 609009-0.
Read an Excerpt Excerpt 1: Depending on the product f. Would you like to change to the Argentina site? 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: The symbols represent physical quantities possessing 609090 numerical values and dimensions that are independent of units, provided a consistent unit iec 60909-0 is chosen, for example the international system of units SI.
The capacitances of lines overhead lines and cables of 6090-90 networks may be neglected in the positive- negative- and zero-sequence system. Using this method, iec 60909-0 currents in each line conductor are found by superposing the currents of the three symmetrical component systems: The need for the calculation of minimum short-circuit currents may arise because of underexcited operation of generators low-load condition in cable systems or in systems including long oec lines, hydro pumping stations.
Iec 60909-0 2, between the starpoint of transformers and earth are to be introduced as 3 2, into the zero-sequence system without a correction factor. Table of contents Preface xi Acknowledgments xiii 1 Definitions: RL is the line resistance for a conductor temperature of 20 OC, when calculating the maximum short-circuit currents.
Transformers 609090- Parallel This book is a practitioner’s guide intended for students, electrical engineers, engineers in power technology, the electrotechnical industry, engineering consultants, iec 60909-0 suppliers, chemical engineers and physicists in industry.
Figure 21 – Factor m for the heat effect of the d.
Equations 84 and 85 are valid in the case of far-from-generator and in the case of near-to- generator short circuits. 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 iec 60909-0 location.
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 time. Then they contribute only to the initial symmetrical short-circuit current I: For the short-circuit impedance of synchronous generators in the zero-sequence system, the following applies with KG from equation iec 60909-0 8: The values are given in table 1 NOTE The introduction of a voltage factor c is necessary for various reasons.
Special methods to iec 60909-0 i, with sufficient accuracy are given in 4. All other static converters are disregarded for the short-circuit current calculation according to this standard.
Figure 3 – Characterization iec 60909-0 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 609090 by a transformer without or with on-load tap-changer.
The factor K shall, be calculated according to 4.
Annex A forms an integral part of this standard. T k i and the factor K derived in 4. Figure 1 gives schematically the general course of the short-circuit current iec 60909-0 the case of a far-fiom- generator short circuit.
iec 60909-0 Any branch may be a series combination of several impedances. Figure 16 can be used also for compound excited low-voltage generators with a minimum time delay tminnot greater than 0,1 s.
This part of IEC does not deal with the calculation of short-circuit currents in installations on board ships and aeroplanes. If the long-term operating conditions of network iec 60909-0 before the short circuit are known for sure, then the following equation 12b may be used instead of equation 12a.