"Both of these events are unlikely," Transpower said.
"The industry is being prudent and making preparations now, so that should action be needed, there are appropriate plans in place to address any shortfall in hydro generation."
Discussions on the issue had been going on for some time and preparations could be put in place so that if action was needed it could be implemented quickly. The initiatives were escalating.
They included discussions with large electricity users about demand side initiatives, effectively receiving a financial incentive for reducing electricity use, or running their own generation at specified times.
A buy back scheme could be implemented for commercial customers, where they received payment to cut back electricity usage when asked to so. That scheme could be extended to all users.
"An electricity savings programme is also being looked at - however this is a last resort and would be the final step in the process should action need to be taken," Transpower said.
The demand side initiatives would need to be implemented if it did not rain at all in the hydro catchment areas by the end of the month, even if all large generating plants stayed in service.
If a large generating plant unexpectedly went out of service, which was "very rare", implementation of the first stage would need to happen at that point.
Transpower issued its statement after Electricity Commission figures out today showed current hydro levels had dropped below a measure called the Minzone.
The Minzone is an analytical tool based on 77 years of hydro inflow information.
When hydro levels dropped below the Minzone it indicated the generating system needed careful management, Transpower said.
"When storage is at or below the Minzone, all thermal plants need to be running as much as possible and all hydro generators need to be conserving water to the maximum extent possible. This is already being done at present."
Transpower chief executive Patrick Strange said New Zealand had experienced drought this year in both the North and South Islands, resulting in very low inflows into the hydro lakes.
"In the case of Lake Taupo, the seasonal inflows are the lowest ever recorded," he said.
"We also had the unexpected closure of the New Plymouth thermal generating plant; the Stratford plant out for a scheduled mid-life maintenance; a unit out at Huntly and Huntly also experiencing some constraints due to river temperature.
"All of these have meant that the generators had to use more hydro to power the system, and this has put pressure on storage," Mr Strange said.
"Provided that the severe drought doesn't extend beyond autumn, and there is no failure at a large thermal plant, which is rare, the situation will be okay," he said.
"The industry is working well together to ensure that the power system remains secure this coming winter.
"It is important to note that, although we are initiating planning measures now, there is still plenty of time for it to rain - and rain will help the situation - before we need to implement any of the demand side initiatives."
- NZPA
