MI 3109 EurotestPV Lite
Appendix E
– PV measurements – calculated values
75
Insulation measurements of PV modules and strings
The first insulation method described in the standard IEC 62446 results in two values:
R
OC+
insulation resistance between positive output and earth
R
OC-
insulation resistance between negative output and earth
The second method described in the standard returns only one value:
R
SC
insulation resistance between short circuit outputs and earth
To get comparable results both values of the first method must be converted to a single
value result. This can be done using the bellow equation, which is based on the
electrical substitute model of PV modules and returns the same or close value to the
insulation resistance measured by the second method.
To get accurate results care must be taken, when performing insulation measurements.
PV module or string can have a significant capacitive nature therefore the duration of
the measurement must be long enough, that the result is stable. Therefore the user has
to set up the duration of the measurement, which can be up to one minute. If the
measurement time is too short and the displayed value is not stable the final result must
be treated only as informational.
