oSIST prEN IEC 60076-4:2023
(Main)Power transformers - Part 4: Guide to the lightning impulse and switching impulse testing - Power transformers and reactors
Power transformers - Part 4: Guide to the lightning impulse and switching impulse testing - Power transformers and reactors
Leistungstransformatoren - Teil 4: Leitfaden zur Blitz- und Schaltstoßspannungsprüfung von Leistungstransformatoren und Drosselspulen
Transformateurs de puissance - Partie 4: Guide pour les essais au choc de foudre et au choc de manoeuvre - Transformateurs de puissance et bobines d'inductance
Močnostni transformatorji - 4. del: Vodilo za testiranje impulza strele in preklopnega impulza - Močnostni transformatorji in dušilke
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
oSIST prEN IEC 60076-4:2023
01-september-2023
Močnostni transformatorji - 4. del: Vodilo za testiranje impulza strele in
preklopnega impulza - Močnostni transformatorji in dušilke
Power transformers - Part 4: Guide to the lightning impulse and switching impulse testing
- Power transformers and reactors
Leistungstransformatoren - Teil 4: Leitfaden zur Blitz- und Schaltstoßspannungsprüfung
von Leistungstransformatoren und Drosselspulen
Transformateurs de puissance - Partie 4: Guide pour les essais au choc de foudre et au
choc de manoeuvre - Transformateurs de puissance et bobines d'inductance
Ta slovenski standard je istoveten z: prEN IEC 60076-4:2023
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
oSIST prEN IEC 60076-4:2023 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
oSIST prEN IEC 60076-4:2023
---------------------- Page: 2 ----------------------
oSIST prEN IEC 60076-4:2023
14/1109/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 60076-4 ED2
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2023-07-07 2023-09-29
SUPERSEDES DOCUMENTS:
14/1060/CD, 14/1061C/CC
IEC TC 14 : POWER TRANSFORMERS
SECRETARIAT: SECRETARY:
United Kingdom Ms Stephanie Lavy
OF INTEREST TO THE FOLLOWING COMMITTEES: PROPOSED HORIZONTAL STANDARD:
Other TC/SCs are requested to indicate their interest, if any,
in this CDV to the secretary.
FUNCTIONS CONCERNED:
EMC ENVIRONMENT QUALITY ASSURANCE SAFETY
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
The attention of IEC National Committees, members of
CENELEC, is drawn to the fact that this Committee Draft for
Vote (CDV) is submitted for parallel voting.
The CENELEC members are invited to vote through the
CENELEC online voting system.
This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of which
they are aware and to provide supporting documentation.
Recipients of this document are invited to submit, with their comments, notification of any relevant “In Some Countries”
clauses to be included should this proposal proceed. Recipients are reminded that the CDV stage is the final stage for
submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).
TITLE:
Power transformers - Part 4: Guide to the lightning impulse and switching impulse testing - Power
transformers and reactors
PROPOSED STABILITY DATE: 2026
Copyright © 2023 International Electrotechnical Commission, IEC. All rights reserved. It is permitted to download this
electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions.
You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without
permission in writing from IEC.
---------------------- Page: 3 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 2 –
NOTE FROM TC/SC OFFICERS:
---------------------- Page: 4 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 3 –
1 POWER TRANSFORMERS
2
3 Part 4: Lightning impulse and Switching impulse Tests
4 of Power Transformers and Reactors
5
6 FOREWORD
7 1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising all national
8 electrotechnical committees (IEC National Committees). The object of the IEC is to promote international co-operation on
9 all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities,
10 the IEC publishes International Standards. Their preparation is entrusted to technical committees; any IEC National
11 Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and
12 non-governmental organizations liaising with the IEC also participate in this preparation. The IEC collaborates closely with
13 the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between
14 the two organizations.
15 2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an international
16 consensus of opinion on the relevant subjects since each technical committee has representation from all interested
17 National Committees.
18 3) The documents produced have the form of recommendations for international use and are published in the form of
19 standards, technical specifications, technical reports or guides and they are accepted by the National Committees in that
20 sense.
21 4) In order to promote international unification, IEC National Committees undertake to apply IEC International Standards
22 transparently to the maximum extent possible in their national and regional standards. Any divergence between the IEC
23 Standard and the corresponding national or regional standard shall be clearly indicated in the latter.
24 5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment
25 declared to be in conformity with one of its standards.
26 6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent
27 rights. The IEC shall not be held responsible for identifying any or all such patent rights.
28 International Standard IEC 60076-4 has been prepared by IEC technical committee 14: Power
29 transformers.
This International Standard cancels and replaces the first edition published in 2002 and constitutes a
technical revision of that document.
30 This edition includes the following technical changes with respect to the previous
edition:
• Lightning impulse tests in presence of a relative overshoot value of 5% and higher (Clause 7.1.2).
• Test voltage function when performing chopped wave (Clause 7.2.1.1).
• Switching impulse tests on 3 phase transformers, test connections (Figure 5 and Figure 6)
• Glaninger circuit, clause A.3 (Annex A).
• New Annex C. Examples of oscillograms with peak voltage overshoot.
31 The text of this standard is based on the following documents:
FDIS Report on voting
32 Full information on the voting for the approval of this standard can be found in the report on voting
33 indicated in the above table.
34 This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.
35 Annexes A, B and C are informative only.
36
---------------------- Page: 5 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 4 –
37 IEC 60076 consists of the following parts, under the general title Power transformers:
38 Part 1: General
39 Part 2: Temperature rise
40 Part 3: Insulation levels, dielectric tests and external clearances in air
41 Part 4: Lightning impulse and Switching impulse Tests – Power Transformers and Reactors
42 Part 5: Ability to withstand short-circuit
43 Part 8: Application guide
44 Part 10: Determination of sound levels
45 Part xx: to be update by TC14 secretary
46 The committee has decided that the contents of this publication will remain unchanged until 20xx. At this
47 date, the publication will be
48 • reconfirmed;
49 • withdrawn;
50 • replaced by a revised edition, or
51 • amended.
52
53
---------------------- Page: 6 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 5 –
54 POWER TRANSFORMERS
55
56 Part 4: Lightning impulse and Switching impulse Tests
57 Power Transformers and Reactors
58
59
60
61
62 1 Scope
63 This part of IEC 60076 gives guidance and explanatory comments on the existing procedures for lightning
64 and switching impulse tests of power transformers to supplement the requirements of IEC 60076-3. It is
65 also generally applicable to the testing of reactors (see IEC 60076-6), modifications to power transformer
66 procedures being indicated where required.
67 Information is given on waveforms, test circuits including test connections, earthing practices, failure
68 detection methods, test procedures, measuring techniques and interpretation of results.
69 Where applicable, the test techniques are as recommended in IEC 60060-1 and IEC 60060-2.
70 2 Normative references
71 The following documents are referred to in the text in such a way that some or all of their content
72 constitutes requirements of this document. For dated references, only the edition cited applies. For
73 undated references, the latest edition of the referenced document (including any amendments) applies.
74
75 IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements
76 IEC 60060-2, High-voltage test techniques – Part 2: Measuring systems
77 IEC 60076-3, Power transformers – Part 3: Insulation levels, dielectric tests and external clearances in
78 air
79 IEC 60076-6, Reactors
80 IEC 61083-1, Instruments and software used for measurement in high-voltage impulse tests – Part 1:
81 Requirements for instruments
82 IEC 61083-2, Digital recorders for measurements in high-voltage impulse tests – Part 2: Evaluation of
83 software used for the determination of the parameters of impulse waveforms
TM
84 IEEE Std C57.98 -2011, IEEE Guide for Transformer Impulse Tests
TM
85 IEEE Std 4 -2013, IEEE Standard for High-Voltage Testing Techniques
86
87
---------------------- Page: 7 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 6 –
88 3 General
89 This standard is primarily based on the use of conventional impulse generators for both lightning and
90 switching impulse tests of transformers and reactors. The practice of switching impulse generation with
91 discharge of a separate capacitor into an intermediate or low-voltage winding is also applicable.
92 However, the method which employs an additional inductance in series with the capacitor to provide
93 slightly damped oscillations transferred into the high-voltage winding is not applicable.
94 Alternative means of switching impulse generation or simulation such as d.c. current interruption on an
95 intermediate or low-voltage winding or the application of a part-period of power frequency voltage are
96 not discussed since these methods are not as generally applicable.
97 Different considerations in the choice of test circuits (terminal connections) for lightning and switching
98 impulse tests apply for transformers and reactors. On transformers, all terminals and windings can be
99 lightning impulse tested to specific and independent levels. In switching impulse test, however, because
100 of the induced voltage transferred, a specified test level may only be obtained on one winding (see IEC
101 60076-3).
102 Whilst, on reactors, lightning impulse tests is similar to that on transformers, i.e., all terminals can be
103 tested separately, different considerations apply and different problems arise in switching impulse tests.
104 Hence, in this standard, lightning impulse tests are covered by a common text for both transformers
105 and reactors whilst switching impulse test is dealt with separately for the two types of equipment.
106 4 Specified waveforms
107 The voltage waveforms to be used normally during lightning and switching impulse tests of
108 transformers and reactors are given in IEC 60076-3, IEC 60076-6 and the methods for their
109 determination are given in IEC 60060-1.
110 5 Test circuit
111 The physical arrangement of test equipment, test object and measuring circuits can be divided into
112 three major circuits:
113 – the main circuit including the impulse generator, additional waveshaping components and the test
114 object;
115 – the voltage measuring circuit;
116 – the chopping circuit where applicable.
117 This basic arrangement is shown in Figure 1.
118 The following parameters influence the impulse waveform;
119 a) the effective capacitance C , and inductance of the test object, L ; C is constant for any given design
t t t
120 and any given waveform, L is also a constant for any given design. The effective L , however, may
t t
121 be influenced by the terminal treatment. It varies between the leakage inductance L for short-
s
122 circuited terminals and L for open-circuited terminals. More details in this respect are given in 7.1
o
123 and 7.3 and in annex A;
124 b) the generator capacitance C ;
g
125 c) waveshaping components, both internal and external to the generator, R , R , R , C (plus, where
si se p L
126 applicable, the impedance of a voltage divider Z );
1
127 d) the stray inductance and capacitance of the generator and the complete test circuit;
128 e) chopping equipment, where applicable.
---------------------- Page: 8 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 7 –
129 f) Non-linear elements in the transformer, which can cause differences between impulses at different
130 voltage levels
131 The front time T is determined mainly by combination of the effective surge capacitance of the test
1
132 object, including C , and the generator internal and external series resistances.
L
133 The time to half-value T is, for lightning impulses, primarily determined by the generator capacitance,
2
134 the inductance of the test object and the generator discharge resistance or any other parallel resistance.
135 However, there are cases, for example, windings of extremely low inductance, where the series
136 resistance will have a significant effect also on the wavetail. For switching impulses, other parameters
137 apply; these are dealt with in clause 8.
138 The test equipment used in lightning and switching impulse applications is basically the same.
139 Differences are in details only, such as values of resistors and capacitors (and the terminal connections
140 of the test object).
141 To meet the different requirements of the waveform for lightning and switching impulses, due
142 consideration has to be given to the selection of the impulse generator parameters, such as capacitance
143 and series and discharge (parallel) resistances. For switching impulses, large values of series resistors
144 and/or load capacitors may be necessary, which will result in significant reduction of the efficiency.
145 While the output voltage of the impulse generator is determined by the test levels of the windings with
146 respect to their highest voltage for equipment U for the test object, the required energy storage
m
147 capability is essentially dependent on the inherent impedances of the test object.
148 A brief explanation of the principles of waveform control is given in Annex A.
149 The arrangement of the test plant, test object and the interconnecting cables, earthing strips, and other
150 equipment is limited by the space in the test room and, particularly, the proximity effect of any
151 structures. During impulse tests, zero potential cannot be assumed throughout the earthing systems
152 due to the high values and rates of change of impulse currents and voltages and the finite impedances
153 involved. Therefore, the selection of a proper reference earth is important.
154 The current return path between the test object and the impulse generator should be of low impedance.
155 It is good practice to firmly connect this current return path to the general earth system of the test room,
156 preferably close to the test object. This point of connection should be used as reference earth and to
157 attain good earthing of the test object it should be connected to the reference earth by one or several
158 conductors of low impedance (see IEC 60060-2).
159 The voltage measuring circuit, which is a separate loop of the test object carrying only the measuring
160 current and not any major portion of the impulse current flowing through the windings under test, should
161 also be effectively connected to the same reference earth.
162 In switching impulse tests, since the rates of change of the impulse voltages and currents are much
163 reduced compared with those in a lightning impulse test and no chopping circuit is involved, the
164 problems of potential gradients around the test circuit and with respect to the reference earth are less
165 critical. Nevertheless, it is suggested that, as a precaution, the same earthing practices should be
166 followed as used for lightning impulse tests.
167 Electromagnetic compatibility (EMC):
168 Power transformers are more and more fitted with control and protection devices, which are sensitive
169 in regard of overvoltage, caused by (fast) transients.
---------------------- Page: 9 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 8 –
170 Potential differences, caused by special groundings at lightning and switching impulse tests the
171 different grounding of the control-and protection device (in regard of safety) can damage electronic
172 parts.
173 Examples of affected device:
174 - Mainly large transformers are fitted with (computerized) condition monitoring systems.
175 - Cooling equipment (fans, pumps) is driven in dependence of transformer load and transformer noise.
176 Such an operation is controlled by electronic device etc.
177 During impulse tests it is recommended to disconnect all electric and electronic equipment installed on
178 the transformer.
179 6 Verification of the impulse voltage measuring system before a test
180 It is not the intention of this standard to give any recommendation on measuring systems or their
181 calibration but, of course, the apparatus which is used should be approved in accordance with IEC
182 60060. Before a test, an overall check of the test circuit and the measuring system may be performed
183 at a voltage lower than the reduced voltage level. In this check, voltage may be determined by means
184 of a sphere gap or by comparative measurement with another approved device. When using a sphere
185 gap, it should be recognized that this is only a check and does not replace the periodically performed
186 calibration of the approved measuring system. After any check has been made, it is essential that
187 neither the measuring nor the test circuit is altered except for the removal of any devices for checking.
188 Information on types of voltage dividers, their applications, accuracy, calibration and checking is given
189 in IEC 60060-2.
190 7 Lightning impulse tests
191 7.1 Waveforms
192 7.1.1 General
193 The values of waveform specified may not always be obtainable. In the impulse tests of large power
194 transformers and reactors, of low winding inductance and/or high surge capacitance, wider tolerances
195 may have to be accepted.
196 7.1.2 Front time T1
197 The surge capacitance of the transformer under test being constant, the series resistance may have to
198 be reduced in an attempt to obtain the correct front time T or rate of rise, but the reduction should not
1
199 be to the extent that oscillations on the crest of the voltage wave become excessive. If it is considered
200 desirable to have a short front time (preferably within the specified limits) then oscillations and/or
201 overshoots may have to be accepted. In such an event, a compromise between the extent of allowable
202 oscillations and the obtainable front time is necessary. In general, the test circuit should be arranged
203 in such way, that the overshoot/oscillation is minimal.
204 If the relative overshoot (ß’) exceeds 5% here are the tests options (ref. IEC 60076-3 Edition 3.0 2013-
205 07; clause 13.2.1) :
206 • For windings receiving chopped wave(s) lightning impulse tests, T1 can be increased up to 2.5
207 µs to reduce the overshoot (ß).
208 • During the tests, if the relative overshoot (ß’) exceed 5% at full voltage level, the test voltage
209 function should be applied in accordance with IEC 60060-1 to determine the test voltage value.
210 • Irrespective of the overshoot value, it is permissible to apply the requirements of IEC 60060-1
211 Annex B to evaluate the parameters of the lightning impulse.
212 In case of a ß’ higher than 5 %, it is allowed to proceed with the test when the test voltage function is
213 enabled.
---------------------- Page: 10 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 9 –
214 NOTE 1: When the manufacturer does not have the software with the test voltage function according to IEC 60060-1, the
215 second option of IEC 60076-3 with a larger front time, less overshoot and additional chopped wave test should be chosen.
216 Examples of oscillograms having overshoot are shown in Annex C.
217 NOTE 2: In case of high beta value and an overshoot with frequency above 500 kHz, the test voltage function significantly
218 reduces the test voltage value U compared to the peak value of the recorded curve U . This may lead to higher electrical
t e
219 stress and possible breakdown of the insulation system.
220 In general, manual evaluation of the test voltage is unreliable for lightning impulse tests of
221 transformers. If the manufacturer does not have the software with the test voltage function
222 according to IEC 60060-1, the buyer should be informed of this at the offer stage.
223 7.1.3 Non-linear elements
224 In some cases, the active parts of power transformers are protected with non-linear elements (surge
225 arresters). These components can cause different waveforms, depending on the voltage level of the
226 impulse. The required test sequences are defined in IEC 60076-3. Generally, it must be clarified: The
227 parameters of the waveform of an impulse have to be adjusted at the reference voltage level. Further
228 adjustments on 100 % voltage level are not allowed, if there are changes in the shape of the curve,
229 this has to be accepted.
230 NOTE: As specified in 60076-3, 3 references impulses are recommended prior the 100% full waves impulses. These
231 impulses are:
232 1. Impulse reference between 50% and 60% of the full test wave.
233 2. Impulse reference between 60% and 75% of the full test wave.
234 3. Impulse reference between 75% and 90% of the full test wave.
235
236 7.1.4 Time to half-value T2
237 For large power transformers and particularly the intermediate and low-voltage windings thereof, the
238 may not be achievable within the value set by the tolerance. The inductance
virtual time to half-value T
2
239 of such windings may be so low that the resulting waveform is oscillatory. This problem may be solved
240 to some extent by the use of large capacitance within the generator, by parallel stage operation, by
241 adjustment of the series resistor or by specific test connections of the terminals of windings not under
242 test or, in addition, of the non-tested terminals of windings under test.
243 If lightning impulse tests are carried out on phase-terminals of a delta-winding, the not-tested terminals
244 of that winding can be resistance earthed.
245 If the neutral of a star-connected winding is tested, the phase-terminals can be resistance earthed.
246 If the phase terminals of a star-connected winding are tested, the neutral-terminal has to be solidly
247 grounded or grounded through a low-ohmic shunt.
248 When resistance earthing of any non-tested line terminal is employed, it is necessary to ensure that the
249 voltage to earth appearing on any non-tested terminal does not exceed
250 – 75 % of the rated lightning withstand voltage of that terminal for star-connected windings;
251 – 50 % of the rated lightning withstand voltage of that terminal for delta-connected windings (because
252 of the undershoot voltages to earth on the delta terminals – see also 7.4).
253 When the waveform is oscillatory due to extremely low inductance and/or small impulse generator
254 capacitance, the amplitude of the undershoot should not exceed 50 % of the test voltage. With this
255 limitation, guidance for selecting impulse generator capacitance and adjusting waveforms is given in
256 annex A.
---------------------- Page: 11 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 10 –
257 7.2 Impulses chopped on the tail
258 7.2.1 Time to chopping
259 Different times to chopping T (as defined in IEC 60060-2), will result in different stresses (voltage and
c
260 duration) in different parts of the winding(s) depending on the winding construction and arrangement
261 employed. Hence, it is not possible to state a time to chopping which is the most onerous either in
262 general or for any particular transformer or reactor. The time to chopping should be between 3 µs and
263 6 µs. A time, between 2 µs and 6 µs can be accepted, provided that the peak value of the lightning
264 impulse wave is achieved before the chop, as required by IEC 60076-3, clause 13.3.1.
265 Oscillograms or digital recordings of chopped waves, are only comparable up to the times to chopping.
266 7.2.1.1 Test voltage function when performing chopped wave
267 In general, for liquid immersed transformers the chopped wave is 110% of the full wave, while in dry
268 type transformers the chopped wave is 100%.The k-factor (test voltage function) evaluation of a
269 chopped wave of 110% of the full wave (as recommended in 60060-1, Annex B), should give a peak
270 value U of 110% of the full wave.
t
271 When the calculated test value Ut is inconsistent, the following steps are recommended:
272 a) Front chopped lightning impulse:
273 Not applicable to chopped waves on transformers.
274 b) Tail chopped lightning impulse with chopping time occurring after the peak value:
TM
275 Voltage reduction ratio Method (Ref. IEEE Std 4 -2013)
276 • Apply a reduced full wave (RFW).
277 • The test voltage function should provide the test voltage value U and the peak value U of
t e
278 the original recorded curve. If Ue is not available, it could be graphically determined on the
279 recorded oscillogram.
280 • Find the Voltage Reduction Ratio. Rv = U / U
t e
’
281 • Apply a full voltage chopped wave, having a recorded voltage U
e
’
282 • The calculated U t is defined as:
’ ’
283 U = Rv * U
t e
284 c) The value of front time T1 of the reduced full wave (RFW) is used to determine the T1 value of
285 the chopped wave.
286 7.2.1.2 Test voltage function and presentation of test results
287 When the test voltage function is enabled, the following test results should be displayed:
288 • U is the test voltage
t
289 • ß’ is the relative overshoot magnitude
290 The following optional value should be available for display:
291 • U the peak value of the original recorded curve
e
292 7.2.2 Rate of collapse and amplitude of reversed polarity of the chopped impulse
293 The characteristic events during chopping are largely dependent on the geometrical arrangement of the
294 chopping circuit involved and on the impedance of the chopping circuit and of the test object, all of
295 which determine both the rate of collapse and the amplitude of the undershoot.
296 In IEC 60076-3, the undershoot has been limited to 30 % of the amplitude of the chopped impulse. This,
297 in fact, represents a guideline for the arrangement of the chopping circuit and may entail the introduction
298 of additional impedance Z in this circuit to meet the limit (see Figure 1).
c
299 The chopping loop, however, should be as small as possible to obtain the highest rate of collapse, but the
300 undershoot should be limited to less than, or equal to 30 %. On multiple layer windings, the layer impedance
301 may damp the collapse normally to the extent that it does not oscillate around zero (see Figure B.20).
302 The recommendation in IEC 60076-3 to use a triggered-type chopping gap is made because of its
303 advantage in obtaining consistency of the time to chopping, thereby facilitating the comparison of
---------------------- Page: 12 ----------------------
oSIST prEN IEC 60076-4:2023
IEC CD 60076-4 IEC:2020 – 11 –
304 oscillograph or digital recordings not only before but also after chopping. The latter part will only be
305 comparable for reasonably identical times to chopping.
306 7.3 Terminal connections and applicable methods of failure detection
307 7.3.1 Terminal connections
308 It is essential that the terminal connections of the test object and the earthing practices employed relate
309 to the method of failure detection adopted.
310 Connections for impulse tests are detailed in IEC 60076-3 for transformers and in IEC 60076-6 for
311 reactors. Normally the non-tested terminals of the phase winding under test are earthed and the non-
312 tested phase windings are shorted and earthed. However, in order to improve the wavetail T ,
2
313 resistance earthing of the non-tested windings may be advantageous (see clause 5 and 7.1) and, in
314 addition, the non-tested line terminals of the winding under test may also be resistance earthed.
315 In addition to the methods of waveform adjustment in 7.1, the following factors have to be considered:
316 a) if a terminal has been specified to be directly earthed or connected to a low-impedance cable in
317 service, then that terminal should be directly earthed during the test or earthed through a resistor
318 with an ohmic value not in excess of the surge impedance of the cable;
319 b) earthing through a low-resistance shunt for the purpose of impulse current measurements may be
320 considered t
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.