Biddle MEGGER - Page 33

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FIGURE
37.
"Major"
Megger
Facsimile
Scale
Cat.
No.
21159.
Operating Time
A
very
important
consideration
in
making
insulation
resist-
ance
tests
is
the
time
required
for
the
reading
of
insulation
resistance
to
reach
a
maximum.
The
time
required
to
charge
the
geometric
capacitance
is
very
short—usually
no
more
than
a
few
seconds—and
that
which
causes
further
delay
in
reach-
ing
full
“charge”
is
a
dielectric
absorption
effect.
It
may
be
a
matter
of
minutes
or
even
hours,
for
this
electrification
time
to
be
completed,
and
for
the
pointer
to
reach
an
absolute
maximum.
' Short-Time Readings
`
For
short-time
readings
of
insulation
resistance,
operate
the
instrument
for
a
definite
length
of
time—either
30
seconds
or
1
minute,
and
read
at
the
end
of
that
time.
Continue
cranking
steadily
at
slip
speed
until
the
reading
has
been
taken.
Make
future
tests
with
the
same
length
of
operating
time.
Time-Resistance
Method
_
When
using
a
hand-cranked
instrument,
operate
continu-
|
ously
for
1
minute.
Take
a
reading
at
the
end
of
the
first
30
'
seconds
and
another
reading
at
the
end
of
the
minute.
When
using
a
motor-driven
or
rectifier-operated
instrument,
the
time
intervals
are
usually
1
minute
and
10
minutes
from
the
time
the
testing
voltage
is
applied.
Or,
time-resistance
curves
may
be
taken
over
a
period
of
10
to
30
minutes,
or
longer.
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