Test Mode Summary; Insulation Resistance 'Ir' Test; Breakdown Mode / Burn Mode; Alarm Limit Mode - Megger MIT520/2 User Manual

TEST MODE SUMMARY

Press the 'MODE' button to cycle through and select the test mode.
Modes of test to be chosen from include an insulation resistance 'IR' test, a
polarization index 'PI' test, a step voltage 'SV' test, and a dielectric
discharge 'DD' test. If timers T1 and T2 are set, the instrument will
automatically calculate the dielectric absorption ratio 'DAR' of the
insulation. PI, DAR, and IR values are automatically stored and displayed if
the data is available, irrespective of the selected test mode. At the end of a
test the instrument can be made to display either the insulation
resistances, insulation currents or ratios plus capacitance measurements by
using the 'Ω/I' toggle button. See section 'Ω/I button' for cycling through
results and toggling units.

Insulation Resistance 'IR' test

This is the default mode in which the instrument powers up. This test
mode measures insulation resistance continuously at the selected voltage.
The test voltage may be varied during an 'IR' test by pressing the test
voltage L or M buttons. The test duration can be set using the 'main
timer'. The test will finish automatically after this time has elapsed. On test
completion, insulation capacitance and the time constant associated with it
is calculated and displayed.
Time Constant (TC) = R
If timers T1 and T2 are set, the instrument will calculate and display the
DAR value under the segment 'DAR'. On completion of the test, the
instrument will display the insulation resistance measured at these times
under the segment symbols 'T1' and 'T2'. If the test runs for longer than
10 minutes, the instrument will calculate the 'polarisation index'. This
value will be displayed under the display segment symbol 'PI'. On
completion of the test, the instrument will display the insulation resistance
recorded at 1 minute and 10 minutes under the segment symbols '1m' and
'10m'.
x C
ins ins
Pressing the 'Ω/I' button toggles the display to show the insulation
resistances, insulation currents, DAR and PI ratios, and capacitance. The
resistances and currents will be displayed under the 'T1', 'T2', '1m' and
'10m' segment headings, the ratios under the 'DAR' and 'PI' segment
headings. The capacitance reading is indicated by its units of either 'nF' or
'µF'. Refer to section 'Ω/I button'.

Breakdown mode / burn mode

The insulation resistance 'IR' test operates in either the 'Burn' or
'Breakdown' mode of operation. The default mode is breakdown. To
change mode press and hold the function button, then press and release
the mode button repeatedly until the desired mode is indicated by the
flashing symbol on the display. Release the function button to select it.
In the breakdown mode the 'Breakdown Indicator' will be illuminated –
refer to page 6. In this mode the test will automatically terminate should
the insulation break down to prevent damage to the insulation under test.
In the burn mode the 'Burn Indicator' is illuminated – refer page 6. The
burn mode disables the normal breakdown detection and enables the
insulation test voltage to continue even after breakdown of the insulation.
This will enable the location of the failure to be seen and heard. Due to
the potential damage that could occur, the unit produces two long beeps
when starting a test with burn mode activated.

Alarm limit mode

The insulation resistance 'IR' test has an option of setting an alarm limit. If
this mode is selected, the instrument will beep should the resistance
reading exceed a user selectable threshold. To set the limit, hold down the
function button, then press and release the mode button repeatedly until
the 'A ↑' symbol is flashing on the display. Use the timer L and M buttons
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