The
different properties the surface the insulating materials and
contamination from the surroundings promote this process..6.2 Creepage Distances
Creepage paths for surface currents can form the surface insulation
materials.6)
- Insulation group
- Degree pollution (see 4.4.2.1.6.
Deterioration increases during the time which currentflows. flashover can result complete connection made. direct
164 ____________________________________________________________
.6.
4.] does not exist. Under these conditions many the materials
may exhibit two, even all three the characteristics stated. The following behaviour insulation materials the presence of
surges can occur:
- decomposition the insulating material;
- the wearing away insulating material action electrical
discharges (electrical erosion);
- the progressive formation conductive paths which are produced on
the surface solid insulating material due the combined effects of
electric stress and electrolytic contamination the surface (tracking)
NOTE: Tracking erosion will occur when
- liquidfilm carrying the surface leakage current breaks, and
- the applied voltage sufficient break down the small gap formed
when thefilm breaks, and
- the current sufficient provide sufficient energy locally thermally
decompose the insulating material beneath the contamination. The
behaviour the insulating material under various contaminants and
voltages extremely complex.
A method classification for insulating materials [.4)
The creepage distance the shortest distance along the surface insulation
material between two conductive parts..1 Insulation material groups
Extract from IEC 60664-1
Comparative tracking index (CTI)
Insulating materials can roughly characterized according the damage
they suffer from concentrated release energy during surges when a
surface leakage current interrupted due drying the contaminated
surface. The following
are the major criteria for determining the creepage distances:
- Rated voltage (see 4
