BS EN IEC 60071-2:2023

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Insulation co-ordination – Application guidelines

Published By	Publication Date	Number of Pages
BSI	2023	190

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Categories: 29.080.30 - Insulation systems, BSI

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Description

This part of IEC 60071 constitutes application guidelines and deals with the selection of insulation levels of equipment or installations for three-phase a.c. systems. Its aim is to give 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. This association is for insulation co-ordination purposes only. The requirements for human safety are not covered by this document. This document covers three-phase a.c. systems with nominal voltages above 1 kV. The values derived or proposed herein are generally applicable only to such systems. However, the concepts presented are also valid for two-phase or single-phase systems. This document covers phase-to-earth, phase-to-phase and longitudinal insulation. This document is not intended to deal with routine tests. These are to be specified by the relevant product committees. The content of this document strictly follows the flow chart of the insulation co-ordination process presented in Figure 1 of IEC 60071-1:2019. Clauses 5 to 8 correspond to the squares in this flow chart and give detailed information on the concepts governing the insulation coordination process which leads to the establishment of the required withstand levels. This document emphasizes the necessity of considering, at the very beginning, all origins, all classes and all types of voltage stresses in service irrespective of the range of highest voltage for equipment. Only at the end of the process, when the selection of the standard withstand voltages takes place, does the principle of covering a particular service voltage stress by a standard withstand voltage apply. Also, at this final step, this document refers to the correlation made in IEC 60071-1 between the standard insulation levels and the highest voltage for equipment. The annexes contain examples and detailed information which explain or support the concepts described in the main text, and the basic analytical techniques used.

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PDF Pages	PDF Title
2	undefined
5	Annex ZA (normative)Normative references to international publicationswith their corresponding European publications
6	English CONTENTS
13	FOREWORD
15	1 Scope 2 Normative references
16	3 Terms, definitions, abbreviated terms and symbols 3.1 Terms and definitions 3.2 Abbreviated terms
17	3.3 Symbols
22	4 Concepts governing the insulation co-ordination
23	5 Representative voltage stresses in service 5.1 Origin and classification of voltage stresses 5.2 Characteristics of overvoltage protection devices 5.2.1 General remarks
24	5.2.2 Metal-oxide surge arresters without gaps (MOSA)
26	5.2.3 Line surge arresters (LSA) for overhead transmission and distribution lines 5.3 General approach for the determination of representative voltages and overvoltages 5.3.1 Continuous (power-frequency) voltage 5.3.2 Temporary overvoltages
30	5.3.3 Slow-front overvoltages
32	Figures Figure 1 – Range of 2 % slow-front overvoltages at the receiving end due to line energization and re-energization [27]
33	Figure 2 – Ratio between the 2 % values of slow-front overvoltages phase-to-phase and phase-to-earth [28], [29]
36	5.3.4 Fast-front overvoltages
40	5.3.5 Very-fast-front overvoltages Figure 3 – Diagram for surge arrester connection to the protected object
41	5.4 Determination of representative overvoltages by detailed simulations 5.4.1 General overview 5.4.2 Temporary overvoltages
42	5.4.3 Slow-front overvoltages
43	5.4.4 Fast-front overvoltages
46	Figure 4 – Modelling of transmission lines and substations/power stations
47	5.4.5 Very-fast-front overvoltages
48	6 Co-ordination withstand voltage 6.1 Insulation strength characteristics 6.1.1 General
49	6.1.2 Influence of polarity and overvoltage shapes
50	6.1.3 Phase-to-phase and longitudinal insulation
51	6.1.4 Influence of weather conditions on external insulation 6.1.5 Probability of disruptive discharge of insulation
53	6.2 Performance criterion 6.3 Insulation co-ordination procedures 6.3.1 General
54	6.3.2 Insulation co-ordination procedures for continuous (power-frequency) voltage and temporary overvoltage
55	6.3.3 Insulation co-ordination procedures for slow-front overvoltages Figure 5 – Distributive discharge probability of self-restoring insulation described on a linear scale
56	Figure 6 – Disruptive discharge probability of self-restoring insulation described on a Gaussian scale Figure 7 – Evaluation of deterministic co-ordination factor Kcd
57	Figure 8 – Evaluation of the risk of failure
59	6.3.4 Insulation co-ordination procedures for fast-front overvoltages Figure 9 – Risk of failure of external insulation for slow-front overvoltages as a function of the statistical co-ordination factor Kcs
60	6.3.5 Insulation co-ordination procedures for very-fast-front overvoltages 7 Required withstand voltage 7.1 General remarks 7.2 Atmospheric correction 7.2.1 General remarks
61	7.2.2 Altitude correction
62	7.3 Safety factors 7.3.1 General Figure 10 – Dependence of exponent m on the co-ordination switching impulse withstand voltage
63	7.3.2 Ageing 7.3.3 Production and assembly dispersion 7.3.4 Inaccuracy of the withstand voltage 7.3.5 Recommended safety factors (Ks)
64	8 Standard withstand voltage and testing procedures 8.1 General remarks 8.1.1 Overview 8.1.2 Standard switching impulse withstand voltage 8.1.3 Standard lightning impulse withstand voltage
65	8.2 Test conversion factors 8.2.1 Range I 8.2.2 Range II Tables Table 1 – Test conversion factors for range I, to convert required SIWV to SDWV and LIWV
66	8.3 Determination of insulation withstand by type tests 8.3.1 Test procedure dependency upon insulation type 8.3.2 Non-self-restoring insulation 8.3.3 Self-restoring insulation Table 2 – Test conversion factors for range II to convert required SDWV to SIWV
67	8.3.4 Mixed insulation Table 3 – Selectivity of test procedures B and C of IEC 60060-1
68	8.3.5 Limitations of the test procedures 8.3.6 Selection of the type test procedures 8.3.7 Selection of the type test voltages Figure 11 – Probability P of an equipment to pass the test dependent on the difference K between the actual and the rated impulse withstand voltage
69	9 Special considerations for apparatus and transmission line 9.1 Overhead line 9.1.1 General
70	9.1.2 Insulation co-ordination for operating voltages and temporary overvoltages 9.1.3 Insulation co-ordination for slow-front overvoltages
71	9.1.4 Insulation co-ordination for fast-front overvoltages
72	9.2 Cable line 9.2.1 General 9.2.2 Insulation co-ordination for operating voltages and temporary overvoltages 9.2.3 Insulation co-ordination for slow-front overvoltages
73	9.2.4 Insulation co-ordination for fast-front overvoltages 9.2.5 Overvoltage protection of cable lines
74	9.3 GIL (gas insulated transmission line) / GIB (Gas-insulated busduct) 9.3.1 General 9.3.2 Insulation co-ordination for operating voltages and temporary overvoltages 9.3.3 Insulation co-ordination for slow-front overvoltages
75	9.3.4 Insulation co-ordination for fast-front overvoltages 9.3.5 Overvoltage protection of GIL/GIB lines 9.4 Substation 9.4.1 General Figure 12 – Example of a schematic substation layout used for the overvoltage stress location
76	9.4.2 Insulation co-ordination for overvoltages
79	Annexes Annex A (informative) Determination of temporary overvoltages due to earth faults
80	Figure A.1 – Earth fault factor k on a base of X0/X1 for R1/X1 = Rf = 0 Figure A.2 – Relationship between R0/X1 and X0/X1 for constant values of earth fault factor k where R1 = 0
81	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
82	Figure A.5 – Relationship between R0/X1 and X0/X1 for constant values of earth fault factor k where R1 = 2X1
83	Annex B (informative) Weibull probability distributions B.1 General remarks
84	B.2 Disruptive discharge probability of external insulation
86	Table B.1 – Breakdown voltage versus cumulative flashover probability – Single insulation and 100 parallel insulations
87	B.3 Cumulative frequency distribution of overvoltages
89	Figure B.1 – Conversion chart for the reduction of the withstand voltage due to placing insulation configurations in parallel
90	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 Figure C.1 – Probability density and cumulative distribution for derivation of the representative overvoltage phase-to-earth
93	C.3 Probability distribution of the representative amplitude of the prospective overvoltage phase-to-phase
94	C.4 Insulation characteristic
97	C.5 Numerical example
98	Figure C.2 – Example for bivariate phase-to-phase overvoltage curves with constant probability density and tangents giving the relevant 2 % values
99	Figure C.3 – Principle of the determination of the representative phase-to-phase overvoltage Upre
100	Figure C.4 – Schematic phase-phase-earth insulation configuration Figure C.5 – Description of the 50 % switching impulse flashover voltage ofa phase-phase-earth insulation
101	Figure C.6 – Inclination angle of the phase-to-phase insulation characteristic in range “b” dependent on the ratio of the phase-phase clearance Dto the height Ht above earth
102	Annex D (informative) Transferred overvoltages in transformers D.1 General remarks
103	D.2 Transferred temporary overvoltages D.3 Capacitively transferred surges
105	D.4 Inductively transferred surges
107	Figure D.1 – Distributed capacitances of the windings of a transformer and the equivalent circuit describing the windings
108	Figure D.2 – Values of factor J describing the effect of the winding connections on the inductive surge transference
109	Annex E (informative) Determination of lightning overvoltages by simplified method E.1 General remarks E.2 Determination of the limit distance (Xp) E.2.1 Protection with arresters in the substation
110	E.2.2 Self-protection of substation Table E.1 – Corona damping constant Kco
111	E.3 Estimation of the representative lightning overvoltage amplitude E.3.1 General E.3.2 Shielding penetration
112	E.3.3 Back flashovers
114	E.4 Simplified approach
116	E.5 Assumed maximum value of the representative lightning overvoltage Table E.2 – Factor A for various overhead lines
118	Annex F (informative) Calculation of air gap breakdown strength from experimental data F.1 General F.2 Insulation response to power-frequency voltages
119	F.3 Insulation response to slow-front overvoltages
120	F.4 Insulation response to fast-front overvoltages
122	Table F.1 – Typical gap factors K for switching impulse breakdown phase-to-earth (according to [1] and [4])
123	Table F.2 – Gap factors for typical phase-to-phase geometries
124	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
125	G.2.2 Part 1: no special operating conditions
131	Table G.1 – Summary of minimum required withstand voltages obtained for the example shown in G.2.2
132	G.2.3 Part 2: influence of capacitor switching at station 2
133	Table G.2 – Summary of required withstand voltages obtained for the example shown in G.2.3
134	G.2.4 Part 3: flow charts related to the example of Clause G.2
139	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
140	G.3.3 Step 2: determination of the co-ordination withstand voltages – values of Ucw
141	G.3.4 Step 3: determination of the required withstand voltages – values of Urw
142	G.3.5 Step 4: conversion to switching impulse withstand voltages (SIWV)
143	G.3.6 Step 5: selection of standard insulation levels G.3.7 Considerations relative to phase-to-phase insulation co-ordination
144	G.3.8 Phase-to-earth clearances
145	G.3.9 Phase-to-phase clearances G.4 Numerical example for substations in distribution systems with Um up to 36 kV in range I G.4.1 General
146	G.4.2 Step 1: determination of the representative overvoltages – values of Urp G.4.3 Step 2: determination of the co-ordination withstand voltages – values of Ucw
147	G.4.4 Step 3: determination of required withstand voltages – values of Urw
148	G.4.5 Step 4: conversion to standard short-duration power-frequency and lightning impulse withstand voltages
149	G.4.6 Step 5: selection of standard withstand voltages G.4.7 Summary of insulation co-ordination procedure for the example of Clause G.4
150	Table G.3 – Values related to the insulation co-ordination procedure for the example in G.4
151	Annex H (informative) Atmospheric correction – Altitude correction application example H.1 General principles H.1.1 Atmospheric correction in standard tests
152	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
153	Figure H.2 – Principal task of the atmospheric correction in insulation co-ordination according to IEC 60071-1
154	H.2 Atmospheric correction in insulation co-ordination H.2.1 Factors for atmospheric correction H.2.2 General characteristics for moderate climates
155	H.2.3 Special atmospheric conditions
156	H.2.4 Altitude dependency of air pressure Figure H.3 – Comparison of atmospheric correction δ × kh with relative air pressure p/p0 for various weather stations around the world
157	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
158	H.3.2 Principle of altitude correction
159	H.3.3 Altitude correction for standard equipment operating at altitudes up to 1 000 m Figure H.5 – Principle of altitude correction: decreasing withstand voltage U10 of equipment with increasing altitude
160	H.3.4 Altitude correction for standard equipment operating at altitudes above 1 000 m H.4 Selection of the exponent m H.4.1 General
161	H.4.2 Derivation of exponent m for switching impulse voltage
163	H.4.3 Derivation of exponent m for critical switching impulse voltage Figure H.6 – Sets of m-curves for standard switching impulse voltage including the variations in altitude for each gap factor Figure H.7 – Exponent m for standard switching impulse voltage for selected gap factors covering altitudes up to 4 000 m
164	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
165	Figure H.10 – Accordance of m-curves from Figure 10 with determination of exponent m by means of critical switching impulse voltage for selected gap factors and altitudes Table H.1 – Comparison of functional expressions of Figure 10 with the selected parameters from the derivation of m-curves with critical switching impulse
166	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
167	I.3.2 Evaluation of overvoltage shape I.4 Evaluation method for transformer I.4.1 Experiments
168	I.4.2 Evaluation of overvoltage shape Figure I.1 – Examples of lightning overvoltage shapes
169	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
170	Figure I.4 – Shape evaluation flow for GIS and transformer
171	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)
172	Figure I.7 – Application to transformer lightning overvoltage Table I.2 – Evaluation of lightning overvoltage in the transformer of 500 kV system
173	Annex J (informative) Insulation co-ordination for very-fast-front overvoltages in UHV substations J.1 General J.2 Influence of disconnector design
174	J.3 Insulation co-ordination for VFFO
175	Figure J.1 – Insulation co-ordination for very-fast-front overvoltages
176	Annex K (informative) Application of shunt reactors to limit TOV and SFO of high voltage overhead transmission line K.1 General remarks K.2 Limitation of TOV and SFO K.3 Application of the neutral grounding reactor to limit resonance overvoltage and secondary arc current
177	K.4 SFO and Beat frequency overvoltage limited by neutral arrester
178	K.5 SFO and FFO due to SR de-energization K.6 Limitation of TOV by Controllable SR K.7 Insulation coordination of the SR and neutral grounding reactor K.8 Self-excitation TOV of synchronous generator
179	Annex L (informative) Calculation of lightning stroke rate and lightning outage rate L.1 General L.2 Description in CIGRE [37]
180	L.3 Flash program in IEEE [49] L.4 [Case Study] Calculation of Lightning Stroke Rate and Lightning Outage Rate (Appendix D in CIGRE TB 839 [37]) L.4.1 Basic flow of calculation method Figure L.1 – Outline of the CIGRE method for lightning performance of an overhead line
182	Figure L.2 – Flowchart to calculate lightning outage rate of transmission lines
183	L.4.2 Comparison of Calculation Results with Observations Figure L.3 – Typical conductor arrangements of large-scale transmission lines Figure L.4 – Lightning stroke rate to power lines -calculations and observations-
184	Figure L.5 – Lightning outage rate -calculations and observations-
185	Bibliography

Additional information

Status	Definitive
Pages	190
Publication Date	2023-09-22
ISBN	978 0 539 03017 4
Standard Number	BS EN IEC 60071-2:2023
Title	Insulation co-ordination – Application guidelines
Identical National Standard Of	EN 60071-2 Ed.5.0, IEC 60071-2 Ed.5.0
Replaces	BS EN IEC 60071-2:2018
Descriptors	Stress, High-voltage installations, Selection, Statistical methods of analysis, Dielectric strength, Coordination, Electrical installations, Statistical distribution, Factor of safety, Three-phase current, Rated voltage, Protected electrical equipment, High-voltage equipment, Electrical equipment, Classification systems, Overvoltage protection, Withstand voltage, Mathematical calculations, Clearance distances, Overvoltage, Surge protection, Overhead power lines, Impulse voltages, Electrical insulation
Publisher	BSI
Committee	PEL/99
ICS Codes	29.080.30 - Insulation systems

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