Energy and Utilities Virtual Conference

Proceedings

Keeping New Zealand's Lights On

Heidi Heath, Transpower

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Transpower owns and operates the electricity grid in New Zealand, keeping energy flowing to 4 million residents. The New Zealand power system is long and skinny, with the major generation centres in the bottom of the South Island and the major load centre at the top of the North Island. As such, the system is very susceptible to frequency deviations and oscillations when a generator or large load unexpectedly trips off.

Transpower uses MATLAB to calculate how much spinning reserve and interruptible load must be scheduled during each half hour trading period to ensure that, in the event of a large disturbance, the system frequency doesn’t deviate to the point where it could cause cascading outages, voltage stability issues, or blackout. Detailed models of each generator and governor are built in Simulink, along with models of the HVDC link between the two islands and some basic load models. All of the detailed models are combined into a large Simulink model of the New Zealand power system. Run in conjunction with other MATLAB code files, this tool, called the Reserve Management Tool or RMT, calculates how much spinning reserve is required under a variety of conditions.

During every half hour period, RMT uses MATLAB to calculate what the largest risk to the system will be (a large generator or the HVDC link), how fast the frequency will fall if the calculated unit trips, how much load will be shed under certain contingencies due to the last-resort Automatic Under-Frequency Load Shedding scheme, what the expected governor response will be from dispatched generators, and the system inertia. It uses these parameters to calculate a final figure of how much spinning reserve and interruptible load must be scheduled for the given conditions.