6 VIDAR ZP-BR01E BR0150GE
2 INTRODUCTION
2
Introduction
2.1 General
The VIDAR vacuum tester is used to test the ability of
the breaking chamber in a vacuum circuit breaker to
inhibit flashover. The rugged, lightweight, compact
and portable VIDAR is ideal for field work.
The vacuum bottles in vacuum breakers do not last
forever. Leakage starts after years or decades and the
bottles fill with air making the breaker unreliable. In
most cases the leakage process is rapid once it has
started. In addition to leakage, dirt on the poles and
on the exterior surface of the bottle can make it un-
safe during operation. The mechanics of the breaker
can become misaligned so that the distance between
the poles no longer is adequate. Vidar, introduced in
1985, uses high voltage DC to test the integrity of
vacuum breakers. There are some 2000 units of Vidar
in field service all over the world that perform daily
tests on the integrity of vacuum breakers.
2.2 Flashover threshold
voltage
The curve shown in Fig. 1 illustrates the relationship
between a vacuum chamber’s internal pressure and
its ability to inhibit flashover. This relationship permits
the vacuum to be checked indirectly by measuring
the voltage threshold. One special advantage of this
method is that you do not need to disassemble the
circuit breaker in order to test it.
The voltage shall be selected so that test point A (see
diagram) is sufficiently far from point B (when the
chamber is filled with air). However the electric stress in
the chamber must not be too high. In normal situations
the pressure is less than 10
-2
mbar.
For guidance on test voltage refer to IEC 694 and
ANSI C37-06 standards.
p ~10 mbar
p
-2
p
o
B
A
U
p
log p
log U
d
Fig. I. Flashover threshold voltage plotted against pressure in
vacuum chamber.
p : chamber pressure
p
o
: atmos. pressure
p
p
: max. pressure on passing voltage test
u
d
: breakdown voltage
u
p
: test voltage
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