Telephone: +41 22 02 11 Telefax: +41 22 03 00 E-mail: [email protected] Web: INTERNATIONAL. STANDARD. IEC. Third edition. This part of IEC identifies the requirements for power transformers to sustain without damage the effects of overcurrents originated by external short. IEC. Second edition. This English-language version is As from 1 January all IEC publications are issued with a designation in the.
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In order to consider the transformer as having passed the short-circuit test, the following conditions shall be fulfilled: NOTE The mounting of accessories having no influence on the behaviour during short circuit e. Consolidated editions The IEC is now publishing consolidated versions of its publications. Large power transformers sometimes cannot be tested according to this standard due, for example, to testing limitations.
NOTE 1 At the end of the tests, if the windings are provided with tapping, the reactance must be measured for all the tapping positions at which the short-circuit tests have been carried out.
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U is the rated voltage U r of the winding under consideration, in kilovolts; Z t is the short-circuit impedance of the transformer referred to the winding under consideration; it is calculated as follows: In such cases, the overcurrent level must be limited by appropriate means, such as series reactors or, in some instances, fuses.
The short-circuiting of the winding may either follow post-set short circuit or precede pre-set short circuit the application of the voltage to the other winding of the transformer 4. If this is not the case, a single-phase supply, as described below, may be used.
Information relating to this publication, including its validity, is available in the IEC Catalogue of publications see below in addition to new editions, amendments and corrigenda.
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Particular requirements and ifc for safety isolating transformers and power supply units incorporating safety isolating transformers. NOTE In the case of winding in zigzag connection, the single-line-to-earth fault current may reach values higher than the three-phase short-circuit current.
However, the 6076-5 tap-changer is not required to be capable of switching the short-circuit current. Delta-connected stabilizing windings of three-phase transformers shall be capable of withstanding the overcurrents resulting from different forms of system faults that can arise in service associated with relevant system earthing conditions.
Particular requirements and tests for auto transformers and power supply units incorporating auto transformers IEC Safety of power transformers, 600766-5 supply units and similar Part IEC Series moving and fixed: NOTE It may not be irc to design auxiliary windings to withstand short circuits on their terminals.
NOTE Equations 4 and 5 are based on adiabatic conditions and are valid for only a short time duration, not exceeding 10 s. IEC Power transformers Part 5: The oscillograph can be set to record the phase currents.
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NOTE 2 For star-connected windings with non-uniform insulation, it is necessary to check whether or not the insulation of the neutral is sufficient for single-phase testing. In this context, a check of the axial compression of the windings could be useful.
With this test arrangement, it might be convenient to mutually connect the corresponding terminals of the phases not submitted to test in order to better control their voltage, provided that this is feasible and circuitry correct. The two windings 600776-5 be supplied either from the same power source or from two separate and synchronized power sources.
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Guidance for the identification of a similar transformer is given in annex A. Documents Flashcards Grammar checker. CombiFinder Discover how to find in thousands configurations, the Combination unit for you. The factor k accounts for the initial offset of the test current and to-r. However, these high values are limited, in the two limbs concerned, to a half of the coil and furthermore the currents in the other star-connected winding are lower than for a three-phase short circuit.
When a short-circuit test is selected, it shall be regarded as a special test, see 3. Table of physical and chemical constants — Kay and Laby — 15 edition, Longmans, Unless otherwise specified, the nine tests on a three-phase transformer with tappings are made in different positions of the tap changer, i.
Safety of power transformers, power suply units and similar Part 2: Particular requirements for isolating transformers for the supply of medical locations IEC Safety of power transformers, power supplies, reactors and similar products Part For all transformers, excluding the case given in 3. For transformers of category III, an agreement between the manufacturer and the purchaser is always needed with regard to the number of tests and the position of the tap-changer.
This increase in current should be taken into consideration when calculating the temperature rise of the zigzag winding. External short circuits are not restricted to three-phase short circuits; they include line-to-line, double-earth and line-to-earth faults.
When available testing facilities require the supply to be connected to the inner winding, special precautions shall be taken, for example, pre-magnetization of the core, to prevent the inrush of magnetizing current. If the windings are provided with tappings, the reactance and, if required, the resistance also have to be measured for the tapping positions at which short-circuit tests will be carried out.
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 categories I and II three-phase transformers, the total number of tests shall be nine, i. This procedure requires that the voltage of the test supply is suitably adjusted with respect to the rated voltage of the transformer.
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