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SEFELEC1500M Instructions
148
V1.06
16.
APPLICATION NOTES
16.1.
PURPOSE OF THE DIELECTRIC TESTS
The purpose of the dielectric strength tests is to:
Detect the manufacturing defects of a piece of electrical equipment,
Check the quality of the insulators of a piece of electrical equipment,
Check that the electrical installation was carried out correctly,
Check the insulation resistance of a piece of equipment or of an installation in order
to following the changes and the ageing of it.
These are based on insulation resistance measurements and on dielectric strength tests.
16.2.
TERMINOLOGY
MINIMUM CONDUCTOR SPACING
the smallest spacing, measured across the surface of an insulator between two conductors,
required to prevent tracking.
LEAKAGE CURRENT
current across or through an insulating medium or at a given voltage. The leakage current is
used to establish the insulation resistance of an insulating material.
BREAKDOWN
an instantaneous failure of the insulating properties of the insulating material. Breakdown re-
sults in more or less serious damage to the material. Breakdown tests can be destructive or
non-destructive.
INSULATION RESISTANCE
characteristic of an insulator that, subjected to a given voltage, has a resistance such that
the value of the leakage current that passes through it remains permissible.
DIELECTRIC STRENGTH
ratio between the voltage at which a dielectric rupture of the insulator occurs and the dis-
tance between the two points where the voltage is applied (generally expressed in kV/cm).
Depending on the nature of the insulator (solid, liquid or gas), dielectric rupture may be
caused by perforation, tracking or arcing.