This International Standard describes a method for calculating the minimum approach distances for live working, at maximum voltages between 72,5 kV and 800 kV. This standard addresses system overvoltages and the working air distances or tool insulation between parts and\/or workers at different electric potentials.<\/p>\n
The required withstand voltage and minimum approach distances calculated by the method described in this standard are evaluated taking into consideration the following:<\/p>\n
workers are trained for, and skilled in, working in the live working zone;<\/p>\n<\/li>\n
the anticipated overvoltages do not exceed the value selected for the determination of the required minimum approach distance;<\/p>\n<\/li>\n
transient overvoltages are the determining overvoltages;<\/p>\n<\/li>\n
tool insulation has no continuous film of moisture or measurable contamination present on the surface;<\/p>\n<\/li>\n
no lightning is seen or heard within 10 km of the work site;<\/p>\n<\/li>\n
allowance is made for the effect of conducting components of tools;<\/p>\n<\/li>\n
the effect of altitude, insulators in the gap, etc, on the electric strength is taken into consideration.<\/p>\n<\/li>\n<\/ul>\n
For conditions other than the above, the evaluation of the minimum approach distances may require specific data, derived by other calculation or obtained from additional laboratory investigations on the actual situation.<\/p>\n
| PDF Pages<\/th>\n | PDF Title<\/th>\n<\/tr>\n | ||||||
|---|---|---|---|---|---|---|---|
| 5<\/td>\n | English CONTENTS <\/td>\n<\/tr>\n | ||||||
| 7<\/td>\n | 1 Scope 2 Terms, definitions and symbols 2.1 Terms and definitions <\/td>\n<\/tr>\n | ||||||
| 9<\/td>\n | 2.2 Symbols used in the normative part of the document <\/td>\n<\/tr>\n | ||||||
| 10<\/td>\n | 3 Methodology <\/td>\n<\/tr>\n | ||||||
| 11<\/td>\n | 4 Factors influencing calculations 4.1 Statistical overvoltage 4.2 Gap strength <\/td>\n<\/tr>\n | ||||||
| 12<\/td>\n | 4.3 Calculation of electrical distance DU 4.3.1 General equation 4.3.2 Factors affecting gap strength <\/td>\n<\/tr>\n | ||||||
| 13<\/td>\n | Table 1 \u2013 Average ka values <\/td>\n<\/tr>\n | ||||||
| 14<\/td>\n | Figure 1 \u2013 Illustration of two floating conductive objects of different dimensions and at different distances from the axis of the gap <\/td>\n<\/tr>\n | ||||||
| 15<\/td>\n | Table 2 \u2013 Floating conductive object factor kf <\/td>\n<\/tr>\n | ||||||
| 16<\/td>\n | Figure 2 \u2013 Typical live working tasks <\/td>\n<\/tr>\n | ||||||
| 17<\/td>\n | 5 Evaluation of risks <\/td>\n<\/tr>\n | ||||||
| 18<\/td>\n | 6 Calculation of minimum approach distance DA Annexes <\/td>\n<\/tr>\n | ||||||
| 19<\/td>\n | Annex\u00a0A (informative)Ergonomic distance <\/td>\n<\/tr>\n | ||||||
| 21<\/td>\n | Annex\u00a0B (informative)Overvoltages Table B.1 \u2013 Classification of overvoltages according to IEC\u00a060071-1 <\/td>\n<\/tr>\n | ||||||
| 23<\/td>\n | Figure B.1 \u2013 Ranges of ue2 at the open ended line due to closing and reclosing according to the type of network (meshed or antenna) with and without closing resistors and shunt reactors <\/td>\n<\/tr>\n | ||||||
| 25<\/td>\n | Annex\u00a0C (informative)Dielectric strength of air <\/td>\n<\/tr>\n | ||||||
| 27<\/td>\n | Annex\u00a0D (informative)Gap factor kg <\/td>\n<\/tr>\n | ||||||
| 28<\/td>\n | Table D.1 \u2013 Gap factors for some actual phase\u00a0to\u00a0earth configurations <\/td>\n<\/tr>\n | ||||||
| 29<\/td>\n | Annex\u00a0E (informative)Allowing for atmospheric conditions <\/td>\n<\/tr>\n | ||||||
| 31<\/td>\n | Table E.1 \u2013 Atmospheric factor ka for different reference altitudes and values of U90 <\/td>\n<\/tr>\n | ||||||
| 33<\/td>\n | Annex\u00a0F (informative)Influence of floating conductive objects on the dielectric strength <\/td>\n<\/tr>\n | ||||||
| 36<\/td>\n | Figure F.1 \u2013 Influence of the length of the floating conductive objects \u2013 phase to earth rod-rod configuration \u2013 250 \u00b5s \/2 500 \u00b5s impulse <\/td>\n<\/tr>\n | ||||||
| 37<\/td>\n | Figure F.2 \u2013 Influence of the length of the floating conductive objects \u2013 phase to phase conductor-conductor configuration \u2013 250 \u00b5s \/2 500 \u00b5s impulse <\/td>\n<\/tr>\n | ||||||
| 38<\/td>\n | Figure F.3 \u2013 Reduction of the dielectric strength as a function of the length D for constant values of \u03b2 \u2013 Phase\u00a0to\u00a0earth rod-rod configuration Figure F.4 \u2013 Reduction of the dielectric strength as a function of the length P for constant values of \u03b2 \u2013 Phase\u00a0to\u00a0phase conductor-conductor configuration <\/td>\n<\/tr>\n | ||||||
| 41<\/td>\n | Annex\u00a0G (informative)Live working near contaminated, damaged or moist insulation <\/td>\n<\/tr>\n | ||||||
| 42<\/td>\n | Table G.1 \u2013 Example of maximum number of damaged insulators calculation(gap factor 1,4) <\/td>\n<\/tr>\n | ||||||
| 43<\/td>\n | Table G.2 \u2013 Example of maximum number of damaged insulators calculation(gap factor 1,2) <\/td>\n<\/tr>\n | ||||||
| 44<\/td>\n | Figure G.1 \u2013 Strength of composite insulators affected by simulated conductive and semi-conductive defects <\/td>\n<\/tr>\n | ||||||
| 46<\/td>\n | Bibliography Figures Tables <\/td>\n<\/tr>\n<\/table>\n","protected":false},"excerpt":{"rendered":" Live working. Minimum approach distances for a.c systems in the voltage range 72,5 kV to 800 kV. A method of calculation<\/b><\/p>\n |