- 62 -
000024DG
5 - Installation
S
election of differential protection downstream of the inverter
All ABB string inverters marketed in Europe are equipped with a device for
protection against ground faults in accordance with the safety standard
IEC 62109-2, sections 4.8.2 and 4.8.3 of the Standard (equivalent to
Standard DIN V VDE V 0126-1:2006, section 4.7). In particular, ABB
inverters are equipped with a redundancy on the reading of the ground
leakage current sensitive to all components of both direct and alternating
current. Measurement of the ground leakage current 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
disconnection 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
respectively 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
parts. The max. tripping times are progressively shortened as the speed
of change in the fault current increases and, starting from the 300 msec/
max for the 30 mA/sec change, they are shortened respectively to 150
msec and 40 msec for 60 mA and 150 mA changes.
It should in any case be noted that the integrated device only protects the
system against ground faults that occur upstream of the AC terminals of
the inverter (namely towards the DC side of the photovoltaic system and
consequently towards the photovoltaic modules). The leakage currents
that can occur in the AC section between the draw/feed and the inverter
are not detected and require an external protection device.
For protection of the AC line
, on the basis of the information above with
regard to the differential protection integrated in
ABB
inverters,
it is not
necessary to install a type B differential switch
.
In accordance with article 712.413.1.1.1.2 of Section 712 of IEC Standard 64-8/7, we hereby
declare that, because of their construction, ABB inverters do not inject ground fault direct
currents.
The use of an AC type circuit breaker with differential thermal magnetic protection with tripping
current of 300 mA is advisable so as to prevent false tripping, due to the normal capacitive
leakage current of photovoltaic modules.
In the case of systems which consist of several inverters connected to a single switch with
differential protection it is recommended that a device is installed which allows the adjustment
of the tripping value and the tripping time.
