Biddle MEGGER - Page 37

nected
to
the
Line
and
Earth
terminals
of
the
Megger
instru-
ment
with
Terminals
3,
1
and
2
respectively
connected
to
the
instrument
Guard
terminal.
R’
is
the
value
of
the
ballast
re-
sistance
in
megohms
of
the
instrument
in
use.
In
making
these
three
measurements
do
not
connect
the
Line
terminal
of
the
instrument
to
the
grounded
terminal
of
the
network,
as
any
leakage
over
the
instrument
case
between
the
Earth
terminal
and
ground
will
shunt
the
resistance
being
measured.
ADDED.
CONDUCTOR OF APPARATUS
BEING TECTED a RESISTANCE
THROUGH INSULATION.
FIGURE 42a
RESISTANCE BETWEEN `
4 H.V. WINDING 8 CORE.
RESISTANCE BETWEEN
H.V a L.V WINDINGS.~_ œ
I}, RESISTANCE BETWEEN
X Ὁ LY. WINDING 8 CORE.
FIGURE 42b
As a Source of Direct Current
With
connections
from
the
Earth
and
Guard
terminals,
the
“Megger”
Insulation
Tester
serves
as
a
convenient
source
of
d-c voltage. This is used:
For
Dielectric
Strength
Tests
and
for
breaking
down
high
resistance
faults.
For
Operating
Wheatstone
Bridges
at
high
potential.
This
is
frequently
done
in
telephone
work
for
locating
high
resist-
ance
faults.
The
instrument
is
substituted
for
the
Wheatstone
Bridge
battery,
with
a
corresponding
increase
in
sensitivity
of
the
Bridge.
In
a
hand-cranked
instrument,
an
overload
or
a
breakdown
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