IEC 61865 pdf download – Overhead lines – Calculation of the electrical component of distance between live parts and obstacles – Method of calculation
1Scope
This International Standard provides guidance for the calculation of electrical distancesbetween live and earthed parts required to prevent air-gap breakdown which may endangermembers of the public who legitimately come close to live parts. lt is applicable only tooverhead lines designed to operate at more than 45 kV phase-to-phase a.c. It deals with theelectrical component of distances between conductors and movable objects – vehicles on theground, vessels on water, persons on top of objects or on the ground,wildlife on the ground(but not airborne), etc.
This standard does not deal with the following public and worker safety aspects:
stationary objects – structures beneath or next to lines，trees，ground contours，etc.These，in general,require consideration as to whether the structure can be climbed on,the extent to which the tree will grow, etc;
minimum approach distance for live working, which is dealt with in lEC 61472;
capacitive coupling or magnetic induction by overhead lines，such as voltages induced invehicles under a line, or in pipelines buried alongside it;
currents flowing in the ground that originate from lines and result in step and touchvoltages around structures during line faults or lightning strikes;
flashover of line insulators or spark gaps,or a phase-to-phase discharge，resulting inaudible and electrical noise and intense arcs;
dielectric breakdown of the air between the conductors and the ground due to large firesbeneath conductors;
minimum electrical distances required to prevent discharge to adjacent overhead power orcommunication circuits.
This standard does not give the electrical distance requirements for the design of overheadline structures. Neither does it give the distance requirements for overhead line structureswhich need to be accessible to workers while the line is energized (for example, distances toline workers or painters). Distances between conductors and the structure of the tower arenormally chosen to meet the required operating reliability of the line. lt is possible that thisdistance may not always be adequate to allow live working or，in some cases, access forworkers to parts of the structure near to live conductors.
2Normative references
The following normative documents contain provisions which，through reference in this text,constitute provisions of this International ‘Standard. For dated references，subsequentamendments to, or revisions of， any of these publications do not apply. However,parties toagreements based on this International Standard are encouraged to investigate the possibilityof applying the most recent editions of the normative documents indicated below.For undatedreferences,the latest edition of the normative document referred to applies.Members of lECand lso maintain registers of currently valid lnternational Standards.
IEC 60050(601):1985,International Electrotechnical Vocabulary (IEV) – Chapter 601:Generation,transmission and distribution of electricity – General
IEC 60050(604):1987,International Electrotechnical Vocabulary (IEV) – Chapter 604:Generation, transmission and distribution of electricity -Operation
IEC 60060-1:1989，High-voltage test techniques – Part 1: General definitions and testrequirements
IEC 60071-1:1993,Insulation co-ordination – Part 1 : Definitions,principles and rulesIEC60071-2:1996,Insulation co-ordination – Part 2: Application guide
IEC 61472:1998,Live working – Minimum approach distances – Method of calculation
3Terms, definitions and symbols
For the purposes of this International Standard, certain definitions from IEC 60050(601) andIEC 6o050(6o4) as well as the following definitions apply.
3.1Definitions
3.1.1
nominal voltage of a system
suitable approximate value of voltage used to designate or identify a system[IEV 601-oi-21]
NOTE See also lEv 601-01-29: phase-to-phase voltage.
3.1.2
highest voltage of a system vs
highest value of operating voltage which occurs under normal operating conditions at any timeand any point in the system
[IEv 601-01-23]
NOTE 1 See also IEv 601-01-29: phase-to-phase voltage.
NOTE 2 Transient overvoltages due, for example,to switching operations and abnormal operation， as well asabnormal temporary variations of voltage,are not taken into account.
3.1 .3
temporary overvoltage
oscillatory overvoltage (at power frequency) at a given location, of relatively long duration and which is undamped or weakly damped
[IEV 604-03-1 2, modified]
IEC 61865 pdf download – Overhead lines – Calculation of the electrical component of distance between live parts and obstacles – Method of calculation
