1. ABB Switzerland Ltd. Christoph Haederli
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 Quantitative 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 Reverse Power Relay Meshed LV grid
DG may trip reverse power relay under normal operating conditions

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

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