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300 V
100 V
power
conditioning
200 V
100 V
(arc
voltage)
0 V
Figure 10.7. Open circuits in high voltage PV arrays can lead to arcing (©1981
IEEE Ross).
3. Earthing (grounding)—A number of sites in a photovoltaic system require
grounding to prevent possible electrocution:
x Frame grounding—prevents frames reaching unsafe voltages in case of
a ground fault.
x Circuit grounding—prevents the cell circuit from floating above ground
and overstressing primary insulation. One terminal or centre voltage point
is tied to ground.
Reference should be made to Standards Australia (2005) or local standards
for detailed advice.
10.5.1 Islanding
Grid-connected photovoltaic systems can continue to operate when the grid shuts
down, a phenomenon called ‘islanding’, if the injected real and reactive powers are
equal between production and consumption in the separated section of the grid
(Schmid & Schmidt, 2003). While this may appear to be an advantage in areas where
grid reliability is poor, it poses a serious problem for grid maintenance crews, who
may not be aware that lines are still energised. If the grid is reconnected during
islanding, transient over-currents can flow through the circuit breaker and the
photovoltaic system inverters (Kitamura et al., 1993).
There are two basic approaches to the control of islanding (Matsuda et al., 1993)—
via the inverter or via the distribution network. Inverter techniques involve detection
of either grid voltage and frequency variations or increases in harmonics, or
monitoring of grid impedance. The German safety code for single-phase grid-
connected systems smaller than 5 kW recommends two independent switching
systems, one including a mechanical switch, such as a relay, reliant on monitoring
grid impedance and frequency. In Australia, permitted methods for grid connection
are specified by a Standard (Standards Australia, 2002b).
Recent studies (Abella & Chenlo, 2004) have concluded that islanding is virtually
impossible where there is low PV penetration in the grid. Although high penetration
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