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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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. It is recommended that the tolerance on the agreed test current values and the duration of the tests are in line with those prescribed for two-winding transformers and that the test sequence is selected according to the expected increase of electrodynamic forces.
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.
Unless otherwise specified, the three tests on a single-phase transformer with tappings are made in a different position of the tap-changer, i. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply.
General requirements and tests. NOTE At the zigzag connected windings, the short-circuit current for a single-line-to-earth fault may reach considerably higher values than at the three-phase fault. If the post-set short circuit is used, the voltage shall not exceed 1,15 times the rated voltage of the winding, unless otherwise agreed between the manufacturer and the purchaser.
Safety of power transformers, power supply units and similar Part One of the methods of determining the factor k is by switching on during the preliminary adjustment tests at a maximum of the line-to-line voltage. NOTE 3 Temporary sparks over tank joints may occur at the energizing stage and internal sparking at the frame joints at the energizing and short-circuit stages. The testing arrangements, the current values, the sequence and the number of tests are always subject to agreement between the manufacturer and the purchaser.
There may be also a certain change of reactance with time after the tests. Electrodynamic hazard to 60067-5 winding assembly may be higher either at three- or single-phase short circuit depending on the winding design.
The results of the short-circuit reactance measurements and the oscillograms taken during the different stages of the tests shall be examined for any isc of possible anomalies during the tests, especially any indications of change in the short-circuit reactance.
Missing page numbers correspond to the Frenchlanguage pages. Reference number IEC GSM based remote monitoring of 8 parameters of transformer.
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The winding closer ied the core is to be short-circuited in order to avoid saturation of the magnetic core which could lead to an excessive magnetizing current superimposed on the short-circuit current during the first few cycles. Particular requirements for separating transformers for general use.
U and Z t are defined as follows: The IEC collaborates closely with the International Organization for Standardization ISO in accordance with conditions determined by agreement between the two organizations. This circumstance is not significant for the ability of the transformer to withstand short-circuit unless combustible gas is found 600076-5 the relay.
The single-phase voltage during the test shall be equal to voltage between phases during the three-phase test. Account shall be taken of the different forms of system faults that can arise in service, for example line-to-earth faults and line-to-line faults associated with the relevant system and transformer earthing conditions; see IEC External short circuits are not restricted to three-phase short circuits; they include line-to-line, double-earth and line-to-earth faults.
These characteristics shall be specified by the purchaser in his enquiry. In this context, a check of the axial compression of the windings could be useful. Another method for determining the phase current in a delta-connected winding is by suitably interconnecting the secondary windings of the current transformers measuring the line currents. The IEC shall not be held responsible for identifying any or all such patent rights. Protection accessories, such as a gas-and-oil-actuated relay and pressure relief device, shall be mounted on the transformer during the test.
Active Obsolete All Text: Table 2 — Short-circuit apparent power of the system Highest voltage for equipment, U m Short-circuit apparent power kV MVA Current European practice 7,2; 12; 17,5 and 24 36 52 and 72,5 and and 1 3 6 10 20 30 35 40 60 83 Current North American practice 1 5 15 15 25 30 35 40 60 83 NOTE If not specified, a value between 1 and 3 should be considered for the ratio of zero-sequence to positive-sequence impedance of the system.
When a short-circuit test is selected, it shall be regarded as a special test, see 3.
INTERNATIONAL STANDARD IEC
In this case, the factor k is found from oscillograms of the line currents. However, for transformers of category I, the repetition of the routine tests with the exception of the dielectric tests may be omitted.
Particular requirements and tests for isolating transformers and power supply units incorporating isolating transformers. Ability to withstand short circuit This English-language version is derived from the original bilingual publication by leaving out all French-language pages.
In this case, provision should be made by the purchaser to limit the overcurrent to the maximum value determined by the manufacturer and stated on the rating plate. Unless otherwise specified, the nine tests on a three-phase transformer with tappings are made in different positions of the tap changer, i. NOTE In connection with the economical impact of the cost of a transformer of category III and the cost implication of any thorough visual inspection extended to the inner parts of the unit, it is recommended that a series of photographs be taken of the position of the winding leads, taps, alignment of spacers and configuration of the end insulation components, etc.
Safety of power transformers, power supplies, reactors and similar products Part 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. Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter. 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: However, in order to simulate as closely as possible the effects of repetitive short-circuit events likely to occur in service, to allow a better monitoring of the behaviour of the unit under test and to permit a meaningful judgement in connection with possible variations of the measured short-circuit impedance, it is recommended that the number of tests is as follows: With regard to tap-changer position and test sequence, the same procedure as described for transformers of categories I and II is recommended.
The oscillograph can be set to record the phase currents. NOTE 2 In case of single-phase units connected to form a three-phase bank, the value of rated power applies to three-phase bank rating.
Safety of transformers, reactors, power supply units and similar products for supply voltages up to 1 V Part 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 600766-5 the short-circuit tests have been carried out.