15
On screen warning codes
Breakdown detection
If insulation breakdown is detected,
the unit aborts the test and flashes
“brd” and the final test result
alternately in the main digital
display. This display is disabled
when in burn mode as the unit will
continue the test without aborting.
The instrument detects breakdown
in terms of a rapid drop in test
voltage commensurate with that caused by an arc across or though the
insulation under test.
Noise detection
Excessive noise during test
In environments such as HV switch yards or substations electrical noise
levels can be high enough to effect insulation test measurements. This
noise takes the form of induced currents in the measurement circuit.
The noise current is either picked up by test leads or induced directly
in the item under test. The S1-552/2 and S1-1052/2 are all capable of
accurate measurements with up to 3 mA of induced noise current. The
S1-554/2 and S1-1054/4 are design for very high noise environments and
can provide accurate measurements with up to 4 mA of noise current
present.
A level of noise exceeding the instruments specified capability will be
indicated by an alternating sine wave on the display. The test continues
while displaying the noise. If the noise drops back down the normal
display is resumed.
The effects of noise can be reduces significantly with the use of high
quality Megger screened test leads.
The picture displayed on the right
shows the expected screen result
of an IR test on with a 5000 V test
voltage after 2 minutes 9 seconds.
The black and grey waveforms are
displayed alternately while the noise
is present. When the noise is removed
the wave form is replaced by the
correct reading.
Test aborted due to extremely high
noise
Should an extremely high level of
noise be present, particularly at the
start of a test, the instrument will
indicate nSE (Noise). The instrument
will require switching off and on again to reset.
In certain rare circumstances breakdown of the circuit under test may
interfere with the sensitive current measuring circuit. In this event the
unit stops and also displays nSE. The instrument will again require
switching off and on again to reset.
