A Study on the New Zealand North Island Power System Resilience
Momen Bahadornejad (presenter), Jiatao Linweee
Electrical Engineering Department
School of Computing, Electrical and Applied Technology Unitec Institute of Technology
Unitec Research Symposium Auckland, New Zealand 8-9 December 2022
Introduction
o Worldwide the frequency of extreme events (e.g., hurricanes, earthquakes, and floods) and man-made attacks (cyber and physical attacks) has
increased dramatically in recent years
o These events have severely impacted power systems ranging from long outage times to major equipment (substations, transmission lines, and power plants) destructions
o This calls for developing control and operation methods and planning strategies to improve grid resilience against such events.
o Currently, there are several power system resilience definitions, metrics, and evaluation methods but non of them has been universally accepted or standardized
Examples of extreme events, where M denotes the number of customers without power in million
Introduction
o Resilience vs Reliability: resilience is applied to the events with low
probability and high impacts (LPHI), while reliability is applied to the events with high probability and low impacts (HPLI)
o Power system resilience can be enhanced before, during, and after a system accident
o It is necessary to strengthen the infrastructure of power systems to avoid more serious consequences when natural disasters occur.
o Overhead power lines need to be protected from short circuits caused by touching tree branches
o If these solutions are not effective, the consideration for relocating power facilities to appropriate sites is necessary
Introduction
o
Only 90% customer’s power was restored, 10 days after the Christchurch earthquake on 22 February 2011.
o
In that event, 50% of 66kV, 15% of 11kV and 1% of LV cable, 4 substations, control centre were damaged
o
The consequence of Christchurch earthquake implies the importance of power system resilience in New Zealand.
o
The stress on the transmission lines due to the power flow should also be considered when assessing the resilience of the system.
o
In this presentation, the findings of a study on the New Zealand North
Island power system resilience are highlighted
New Zealand Power System Overview o Hydroelectric is currently 53% of
the total generation capacity of the New Zealand power system.
o The majority of this generation is located in the South Island and is exported to the North Island
o 32% of this generation is installed in the lower South Island (LSI) region
o The surplus power flows from South to North via a 1200 MW 350 kV HVDC link
o Loosing the HVDC link is the biggest risk to the NI power system resilience
(Dernier, G., 2014)
NI Frequency Event– 12 Nov 2013 (Source: Transpower)
New Zealand AUFLS system has 2 blocks of load shedding each 16%. These large blocks of AUFLS may create the risk of a frequency ‘over-shoot’ which may lead to a blackout.
o The power generation capacity in NI should increase to reduce the load shedding o Adding geothermal is a better option compared to the wind farm
o Changes in AUFLS are required to minimise this risk
New Zealand North Island backbone diagram (Transpower,2019)
Dynamic Simulation Case 1
Daily demand
Dynamic Simulation Case 2
Huntly Unit5 and Stratford gas generator out of service.
StratfordG5 HuntlyG5
AUFLS 16%
Distributed generation will improve the NI power system resilience
Dynamic Simulation Case 3
Wairakei single line to ground fault (Rfault=16Ω)
L-G SC Disconnected from grid
Re-connected to grid
Static Simulation Case 1
Adding Pakuranga and Brownhill road busbars in model
Static Simulation Case 1
Power Loss difference
Transmission Line Loading Difference
Static Simulation Case 2
Changing transmission line voltages for Brownhill road and Otahuhu busbar
Static Simulation Case 2
Power Loss difference
Transmission Line Loading Difference
Conclusion
o New Zealand North Island (NI) power system resilience was studied using different simulations on the backbone of the NI power system.
o DigSILENT PowerFactory was used to simulate some contingencies and also the impacts of some suggested improvements on the NI power system
o It was shown that the suggested changes may improve resilience of the NI power system
o Also, increasing the generation capacity in the NI and using the distributed generation will improve the resilience of the system
o To improve the resilience, adding geothermal generation is a better option compared to the wind farm
References
o Bhusal, N., Abdelmalak, M., Kamruzzaman, M., & Benidris, M. (2020). Power system resilience:
Current practices, challenges, and future directions. IEEE Access, 8, 18064-18086.
o Dernier, G. (2014, December). Increasing transmission capacity in the New Zealand power system through smart grid technology. In 2014 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC) (pp. 1-5). IEEE.
o Huang, C. L., Wu, Y. K., & Li, Y. Y. (2021, September). A Review on the Resilience Assessment of Power Systems under Disasters. In 2021 7th International Conference on Applied System
Innovation (ICASI) (pp. 71-74). IEEE.
o Massie, A., & Watson, N. R. (2011). Impact of the Christchurch earthquakes on the electrical power system infrastructure. Bulletin of the New Zealand Society for Earthquake Engineering, 44(4), 425- 430.
