30 ELECTRIC.IE • The Magazine & Website for the Irish Electrical Industry • National Rules Figure 4 - - Typical Island Mode Earthing Arrangement PEI disconnections. The PEI must have sufficient local energy generation and/or storage to meet the installation's demand or have load shedding facilities in place to reduce demand to match supply capacity. Island mode can also be used for back-up power supply during grid outages. It necessitates the use of battery storage and usually standby generators. Provisions must be in place for safe transition to and from island mode. This is discussed throughout Section 8.82.6. Islandable PEI – Earthing (8.82.6) This section introduces the concept of Islandable PEIs and states that these must have a (i) “switching device for islanding” (SDFI) and (ii) a “system referencing conductor switching device”. There is no acronym suggested for the latter. If there were to be one it would be RCSD. It is basically a neutral earthing switch for the PEI when in island mode. Effectively you cannot have one without the other so, it is easier to refer to the combined unit as “an island mode switch”. This can be manual or automatic and operated locally or remotely. The SDFI and RCSD elements must be electrically and / or mechanically interlocked so that the two switches cannot be simultaneously closed. In its simplest form an island mode switch could be a normal I-O-II three position manual load transfer switch using double pole for single phase installations and four pole for three phase installations. The live conductors would be wired through the position “I” side while the neutral and earth of the PEI would be wired through the position “II” side. So in position “I” the utility supply switch is closed and the neutral earth contact is open i.e. the systems is in “Grid Connected” mode. In position “II” the utility supply is open and the neutral earth contact is closed i.e. the system is in “Island” mode. Similar arrangements can be achieved using contactors or motorised circuit breakers with appropriate mechanical and electrical interlocks. Unfortunately, the diagrams in the Standard are quite confusing. For example Figure 8.82.4 provides an example of an islandable PEI architecture showing the interlock between SDFI and RCSD / neutral earth switch. However it is a single line diagram and does not show how the neutral of the utility supply is connected to earth. Numerous other examples of Island mode switching are provided in the diagrams in Section 8.82.6. While these are multi-line drawings the switchgear devices are represented as boxes which again lack clarity. Annex 8.82D also provides diagrams for Island mode switching for dwellings. Unfortunately these are also single line diagrams and do not explain the requirements very well. Figure 4 below is a simplified multiline diagram showing a single phase PEI with the island mode switch as described above. It is loosely based on Figures 8.82.5 and 8.82D.5 in the Standard where the PEI operates in TN-C-S in grid-connected mode and becomes TN-S in island mode. The following is the legend to the diagram. 1. DSO network / transformer 2. DSO POC / Cut out with Neutral earth terminal 3. DSO Meter 4. Main protective Conductor 5. Earth Conductor 6. Earth Electrode 7. Solar PV 8. Solar PCE / Inverter with Neutral earth terminal 9. Battery 10. Customers Main distribution board with items 11-14 11. Main breaker – Double pole 12. Island Mode Switch including 2 pole SDFI and 1 pole RCSD 13. Solar input RCBO 100mA type B 14. Load protective devices 15. Load shed contactor for nonessential load 16. Essential Load fed from RCBO 17. Essential Load fed from MCB 18. Non-essential Load fed from RCBO
RkJQdWJsaXNoZXIy Mzk5MjA=