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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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