Operations Preparatory To Pv Generator Connection; Checking The Correct Polarity Of The Strings; Checking Of Leakage To Ground Of The Photovoltaic Generator; Choice Of Differential Protection Downstream Of The Inverter - ABB TRIO-20.0/27.6-TL-OUTD Product Manual

O
perations preparatory to PV generator connection
C
hecking the correct polarity of the strings
Inversion polarity can cause serious damage
C
hecking of leakage to ground of the photovoltaic generator
Do not connect the strings if a leakage to ground has been found because the inverter might
not connect to the grid.
C
hoice of differential protection downstream of the inverter
Using a voltmeter, check that the voltage of each string observes the
correct polarity and falls within the input voltage limits accepted by the
inverter (see technical data).
If the voltage without load of the string is near the maximum value ac-
cepted by the inverter, it must be borne in mind that with low ambient
temperatures the string voltage tends to increase (in a different way ac-
cording to the photovoltaic module used). In this case, it is necessary to
carry out a check of the sizing of the system and/or a check on the con-
nections of the modules of the system (e.g.: number of modules in series
higher than the design number).
Measure the voltage present between positive and negative pole of each
string with respect to ground.
If a voltage is measured between an input pole and ground, it may be that
there is a low insulation resistance of the photovoltaic generator and the
installer will have to carry out a check to solve the problem.
All ABB string inverters marketed in Europe are equipped with a device
for protection against ground faults in accordance with the safety stand-
ard set in Germany by Standard VDE V 0126-1-1:2006-02 (please refer
to section 4.7 of the Standard).
In particular, ABB inverters are equipped with a redundancy on the read-
ing of the ground leakage current sensitive to all components of both
direct and alternating current. Measurement of the ground leakage cur-
rent is carried out at the same time and independently by 2 different
processors: it is sufficient for one of the two to detect an anomaly to trip
the protection, with consequent separation from the grid and stopping of
the conversion process.
There is an absolute threshold of 300 mA of total leakage current AC+DC
with protection tripping time at a max. of 300 msec.
In addition, there are another three tripping levels with thresholds re-
spectively at 30 mA/sec, 60 mA/sec and 150 mA/sec to cover the "rapid"
changes in fault current induced by accidental contact with leaking live
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5 - Installation