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BS EN IEC 60071-2:2018 – TC:2020 Edition

BS EN IEC 60071-2:2018 – TC:2020 Edition

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Tracked Changes. Insulation co-ordination – Application guidelines

Published By Publication Date Number of Pages
BSI 2020 359
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IEC 60071-2:2018 is now available as /2 which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.

IEC 60071-2:2018 constitutes application guidelines and deals with the selection of insulation levels of equipment or installations for three-phase electrical systems. It gives guidance for the determination of the rated withstand voltages for ranges I and II of IEC 60071-1 and to justify the association of these rated values with the standardized highest voltages for equipment. It covers three-phase systems with nominal voltages above 1 kV. It has the status of a horizontal standard in accordance with IEC Guide 108. This edition includes the following significant technical changes with respect to the previous edition: a) the annex on clearance in air to assure a specified impulse withstand voltage installation is deleted because the annex in IEC 60071-1 is overlapped; b) 4.2 and 4.3 on surge arresters are updated; c) 4.3.5 on very-fast-front overvoltages is revised. Annex J on insulation co-ordination for very-fast-front overvoltages in UHV substations is added; d) Annex H on atmospheric correction – altitude correction is added. e) Annex I on evaluation method of non-standard lightning overvoltage shape is added.

PDF Catalog

PDF Pages PDF Title
199 undefined
203 English
CONTENTS
209 FOREWORD
211 1 Scope
2 Normative references
212 3 Terms, definitions, abbreviated terms and symbols
3.1 Terms and definitions
3.2 Abbreviated terms
3.3 Symbols
217 4 Representative voltage stresses in service
4.1 Origin and classification of voltage stresses
218 4.2 Characteristics of overvoltage protection devices
4.2.1 General remarks
4.2.2 Metal-oxide surge arresters without gaps (MOSA)
220 4.2.3 Line surge arresters (LSA) for overhead transmission and distribution lines
4.3 Representative voltages and overvoltages
4.3.1 Continuous (power-frequency) voltage
221 4.3.2 Temporary overvoltages
224 4.3.3 Slow-front overvoltages
226 Figures
Figure 1 – Range of 2 % slow-front overvoltages at the receiving end due to line energization and re-energization
227 Figure 2 – Ratio between the 2 % values of slow-front overvoltages phase-to-phase and phase-to-earth
230 4.3.4 Fast-front overvoltages
234 4.3.5 Very-fast-front overvoltages [13]
Figure 3 – Diagram for surge arrester connection to the protected object
235 5 Co-ordination withstand voltage
5.1 Insulation strength characteristics
5.1.1 General
236 5.1.2 Influence of polarity and overvoltage shapes
237 5.1.3 Phase-to-phase and longitudinal insulation
5.1.4 Influence of weather conditions on external insulation
238 5.1.5 Probability of disruptive discharge of insulation
239 5.2 Performance criterion
240 5.3 Insulation co-ordination procedures
5.3.1 General
241 5.3.2 Insulation co-ordination procedures for continuous (power-frequency) voltage and temporary overvoltage
5.3.3 Insulation co-ordination procedures for slow-front overvoltages
242 Figure 4 – Distributive discharge probability of self-restoring insulation described on a linear scale
Figure 5 – Disruptive discharge probability of self-restoring insulation described on a Gaussian scale
243 Figure 6 – Evaluation of deterministic co-ordination factor Kcd
244 Figure 7 – Evaluation of the risk of failure
246 5.3.4 Insulation co-ordination procedures for fast-front overvoltages
Figure 8 – Risk of failure of external insulation for slow-front overvoltages as a function of the statistical co-ordination factor Kcs
247 6 Required withstand voltage
6.1 General remarks
6.2 Atmospheric correction
6.2.1 General remarks
6.2.2 Altitude correction
248 Figure 9 – Dependence of exponent m on the co-ordination switching impulse withstand voltage
249 6.3 Safety factors
6.3.1 General
6.3.2 Ageing
6.3.3 Production and assembly dispersion
6.3.4 Inaccuracy of the withstand voltage
250 6.3.5 Recommended safety factors (Ks)
7 Standard withstand voltage and testing procedures
7.1 General remarks
7.1.1 Overview
7.1.2 Standard switching impulse withstand voltage
251 7.1.3 Standard lightning impulse withstand voltage
7.2 Test conversion factors
7.2.1 Range I
252 7.2.2 Range II
7.3 Determination of insulation withstand by type tests
7.3.1 Test procedure dependency upon insulation type
Tables
Table 1 – Test conversion factors for range I, to convert required SIWV to SDWV and LIWV
Table 2 – Test conversion factors for range II to convert required SDWV to SIWV
253 7.3.2 Non-self-restoring insulation
7.3.3 Self-restoring insulation
7.3.4 Mixed insulation
254 7.3.5 Limitations of the test procedures
Figure 10 – Probability P of an equipment to pass the test dependent onthe difference K between the actual and the rated impulse withstand voltage
Table 3 – Selectivity of test procedures B and C of IEC 60060-1
255 7.3.6 Selection of the type test procedures
7.3.7 Selection of the type test voltages
256 8 Special considerations for overhead lines
8.1 General remarks
8.2 Insulation co-ordination for operating voltages and temporary overvoltages
8.3 Insulation co-ordination for slow-front overvoltages
8.3.1 General
257 8.3.2 Earth-fault overvoltages
8.3.3 Energization and re-energization overvoltages
8.4 Insulation co-ordination for lightning overvoltages
8.4.1 General
8.4.2 Distribution lines
258 8.4.3 Transmission lines
9 Special considerations for substations
9.1 General remarks
9.1.1 Overview
9.1.2 Operating voltage
9.1.3 Temporary overvoltage
Figure 11 – Example of a schematic substation layout used for the overvoltage stress location
259 9.1.4 Slow-front overvoltages
9.1.5 Fast-front overvoltages
9.2 Insulation co-ordination for overvoltages
9.2.1 Substations in distribution systems with Um up to 36 kV in range I
260 9.2.2 Substations in transmission systems with Um between 52,5 kV and 245 kV in range I
261 9.2.3 Substations in transmission systems in range II
262 Annexes
Annex A (informative) Determination of temporary overvoltages due to earth faults
263 Figure A.1 – Earth fault factor k on a base of X0/X1 for R1/X1 = R = 0
Figure A.2 – Relationship between R0/X1 and X0/X1 for constant values of earth fault factor k where R1 = 0
264 Figure A.3 – Relationship between R0/X1 and X0/X1 for constant values of earth fault factor k where R1 = 0,5 X1
Figure A.4 – Relationship between R0/X1 and X0/X1 for constant values of earth fault factor k where R1 = X1
265 Figure A.5 – Relationship between R0/X1 and X0/X1 for constant values of earth fault factor k where R1 = 2X1
266 Annex B (informative) Weibull probability distributions
B.1 General remarks
267 B.2 Disruptive discharge probability of external insulation
268 Table B.1 – Breakdown voltage versus cumulative flashover probability –Single insulation and 100 parallel insulations
269 B.3 Cumulative frequency distribution of overvoltages
271 Figure B.1 – Conversion chart for the reduction of the withstand voltage due to placing insulation configurations in parallel
272 Annex C (informative) Determination of the representative slow-front overvoltage due to line energization and re-energization
C.1 General remarks
C.2 Probability distribution of the representative amplitude of the prospective overvoltage phase-to-earth
C.3 Probability distribution of the representative amplitude of the prospective overvoltage phase-to-phase
274 C.4 Insulation characteristic
276 C.5 Numerical example
278 Figure C.1 – Example for bivariate phase-to-phase overvoltage curves with constant probability density and tangents giving the relevant 2 % values
279 Figure C.2 – Principle of the determination of the representative phase-to-phase overvoltage Upre
280 Figure C.3 – Schematic phase-phase-earth insulation configuration
Figure C.4 – Description of the 50 % switching impulse flashover voltage ofa phase-phase-earth insulation
281 Figure C.5 – Inclination angle of the phase-to-phase insulation characteristicin range “b” dependent on the ratio of the phase-phase clearance Dto the height Ht above earth
282 Annex D (informative) Transferred overvoltages in transformers
D.1 General remarks
283 D.2 Transferred temporary overvoltages
D.3 Capacitively transferred surges
285 D.4 Inductively transferred surges
287 Figure D.1 – Distributed capacitances of the windings of a transformer and the equivalent circuit describing the windings
288 Figure D.2 – Values of factor J describing the effect of the winding connections on the inductive surge transference
289 Annex E (informative) Lightning overvoltages
E.1 General remarks
E.2 Determination of the limit distance (Xp)
E.2.1 Protection with arresters in the substation
290 E.2.2 Self-protection of substation
Table E.1 – Corona damping constant Kco
291 E.3 Estimation of the representative lightning overvoltage amplitude
E.3.1 General
E.3.2 Shielding penetration
292 E.3.3 Back flashovers
294 E.4 Simplified method
295 Table E.2 – Factor A for various overhead lines
296 E.5 Assumed maximum value of the representative lightning overvoltage
297 Annex F (informative) Calculation of air gap breakdown strength from experimental data
F.1 General
F.2 Insulation response to power-frequency voltages
298 F.3 Insulation response to slow-front overvoltages
299 F.4 Insulation response to fast-front overvoltages
301 Table F.1 – Typical gap factors K for switching impulse breakdown phase-to-earth (according to [1] and [4])
302 Table F.2 – Gap factors for typical phase-to-phase geometries
303 Annex G (informative) Examples of insulation co-ordination procedure
G.1 Overview
G.2 Numerical example for a system in range I (with nominal voltage of 230 kV)
G.2.1 General
304 G.2.2 Part 1: no special operating conditions
310 Table G.1 – Summary of minimum required withstand voltages obtained for the example shown in G.2.2
311 G.2.3 Part 2: influence of capacitor switching at station 2
312 Table G.2 – Summary of required withstand voltages obtained for the example shown in G.2.3
313 G.2.4 Part 3: flow charts related to the example of Clause G.2
318 G.3 Numerical example for a system in range II (with nominal voltage of 735 kV)
G.3.1 General
G.3.2 Step 1: determination of the representative overvoltages – values of Urp
319 G.3.3 Step 2: determination of the co-ordination withstand voltages – values of Ucw
320 G.3.4 Step 3: determination of the required withstand voltages – values of Urw
321 G.3.5 Step 4: conversion to switching impulse withstand voltages (SIWV)
G.3.6 Step 5: selection of standard insulation levels
322 G.3.7 Considerations relative to phase-to-phase insulation co-ordination
323 G.3.8 Phase-to-earth clearances
G.3.9 Phase-to-phase clearances
324 G.4 Numerical example for substations in distribution systems with Um up to 36 kV in range I
G.4.1 General
G.4.2 Step 1: determination of the representative overvoltages – values of Urp
325 G.4.3 Step 2: determination of the co-ordination withstand voltages – values of Ucw
326 G.4.4 Step 3: determination of required withstand voltages – values of Urw
327 G.4.5 Step 4: conversion to standard short-duration power-frequency and lightning impulse withstand voltages
G.4.6 Step 5: selection of standard withstand voltages
328 G.4.7 Summary of insulation co-ordination procedure for the example of Clause G.4
329 Table G.3 – Values related to the insulation co-ordination procedure for the example in G.4
330 Annex H (informative)Atmospheric correction – Altitude correction
H.1 General principles
H.1.1 Atmospheric correction in standard tests
331 H.1.2 Task of atmospheric correction in insulation co-ordination
Figure H.1 – Principle of the atmospheric correction during test of a specified insulation level according to the procedure of IEC 60060-1
332 Figure H.2 – Principal task of the atmospheric correctionin insulation co-ordination according to IEC 60071-1
333 H.2 Atmospheric correction in insulation co-ordination
H.2.1 Factors for atmospheric correction
H.2.2 General characteristics for moderate climates
334 H.2.3 Special atmospheric conditions
Figure H.3 – Comparison of atmospheric correction δ × kh with relative air pressure p/p0 for various weather stations around the world
335 H.2.4 Altitude dependency of air pressure
336 H.3 Altitude correction
H.3.1 Definition of the altitude correction factor
Figure H.4 – Deviation of simplified pressure calculation by exponential function in this document from the temperature dependent pressure calculation of ISO 2533
337 H.3.2 Principle of altitude correction
Figure H.5 – Principle of altitude correction: decreasing withstand voltage U10 of equipment with increasing altitude
338 H.3.3 Standard equipment operating at altitudes up to 1 000 m
H.3.4 Equipment operating at altitudes above 1 000 m
339 H.4 Selection of the exponent m
H.4.1 General
H.4.2 Derivation of exponent m for switching impulse voltage
341 Figure H.6 – Sets of m-curves for standard switching impulse voltage including the variations in altitude for each gap factor
342 H.4.3 Derivation of exponent m for critical switching impulse voltage
Figure H.7 – Exponent m for standard switching impulse voltage for selected gap factors covering altitudes up to 4 000 m
343 Figure H.8 – Sets of m-curves for critical switching impulse voltage including the variations in altitude for each gap factor
Figure H.9 – Exponent m for critical switching impulse voltage for selected gap factors covering altitudes up to 4 000 m
344 Figure H.10 – Accordance of m-curves from Figure 9 with determination ofexponent m by means of critical switching impulse voltage for selected gap factors and altitudes
Table H.1 – Comparison of functional expressions of Figure 9 with the selected parameters from the derivation of m-curves with critical switching impulse
345 Annex I (informative) Evaluation method of non-standard lightning overvoltage shape for representative voltages and overvoltages
I.1 General remarks
I.2 Lightning overvoltage shape
I.3 Evaluation method for GIS
I.3.1 Experiments
346 I.3.2 Evaluation of overvoltage shape
I.4 Evaluation method for transformer
I.4.1 Experiments
I.4.2 Evaluation of overvoltage shape
348 Figure I.1 – Examples of lightning overvoltage shapes
349 Figure I.2 – Example of insulation characteristics with respect to lightning overvoltages of the SF6 gas gap (Shape E)
Figure I.3 – Calculation of duration time Td
Table I.1 – Evaluation of the lightning overvoltage in the GIS of UHV system
350 Figure I.4 – Shape evaluation flow for GIS and transformer
351 Figure I.5 – Application to GIS lightning overvoltage
Figure I.6 – Example of insulation characteristics with respect to lightning overvoltage of the turn-to-turn insulation (Shape C)
352 Figure I.7 – Application to transformer lightning overvoltage
Table I.2 – Evaluation of lightning overvoltage in the transformer of 500 kV system
353 Annex J (informative) Insulation co-ordination for very-fast-front overvoltages in UHV substations
J.1 General
J.2 Influence of disconnector design
354 J.3 Insulation co-ordination for VFFO
355 Figure J.1 – Insulation co-ordination for very-fast-front overvoltages
356 Bibliography

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BS EN IEC 60071-2:2018 - TC
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