Distributed Power Generation Units and Their Impact on the Power Network

1. Distributed Power Generation Units and Their Impact on the Power Network ABB Switzerland Ltd. Christoph Haederli

2. Large scale DG interconnection • System parameters • Protection • Stability • “Plug and Power” “Virtual DG” in small European town

3. Case Study with Small European Town • Study in CALPOS • Real network (ca. 1 km2) • “random” placing of DG • 5 MVA load / 7 MVA DG

4. Considered Network Configurations Meshed network configuration • Three MV lines • MV transformers connected on LV level (All LV lines connected in selected area). • Redundancy for MV lines Station to station (non meshed) network configuration • Three MV lines • No connection between MV transformers on LV level • No redundancy for MV lines

5. Voltage Profile • All these nodes are LV-nodes. In the MV-network, the voltage profile is in the admissible range for all calculated cases. • Load profiles applied • Admissible range: -10 / +6 % (Germany)

6. Voltage Rise in Station to Station LV-grid

7. Voltage Rise in meshed LV grid

8. Voltage Rise in Station to Station LV-grid

9. Loading of LV Network • All these lines are LV-lines.

10. Comparison of Network Configurations • Meshed LV grid with multiple MV strands • higher reliability • more balanced voltage profile • smaller voltage rise at load steps • lower equipment loading (in normal operation) • lower losses • can handle more DG without alterations in grid • Non-meshed LV grid with station to station supply • higher capacity with the same amount of resources • simple design, easier to plan and extend • Cheaper • No reverse power relays needed • Lower short circuit power

11. Impact on Protection • Qualitative • Reverse power flow • Additional functionality required (Loss of mains detection, etc.) • Quantitative • Relay parameter settings • Increased short circuit power Selective tripping schedule of distance protection relays with infeed effect

12. Reverse Power Relays MV Line 1 • DG may trip reverse power relay under normal operating conditions Reverse Power Relay Meshed LV grid Reverse Power Relay MV Line 2

13. Ik” Indicators on MV Line (Small Town Study) ( Ik” = short circuit current )

14. Stability: Inverter Based DG Configuration • DG-power conditioner

15. Stability: Equivalent Network with Multiple DG • Paralleling of inverters in LV grid • Line parameters from small town case study

16. Robust Stability Analysis • Robust stability analysis

17. Stability Analysis, Parallel Units • Number of units allowed for stable operation (Generic 100kW DG model used for calculations) • Stability depends very much on filter and control • Other configurations may allow higher numbers of parallel units

18. Conclusions • “Plug and power” for small units and small aggregated power. • Limited “Plug and power” for intermediate Power • No “Plug and power” for large units and a lot of aggregated power. • Advanced planning • Economical barriers • Important factors • Network configuration • DG type • Stability depends strongly on network impedance, filter design and control of DG • A significant share of power can be supplied locally by DG without reverse power flow into the network