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Electricity
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A key function of the Bureau is to monitor and promote continuous improvement in the performance of the electricity supply system. To achieve this Bureau uses internationally recognised performance indicators for the Distribution and Transmission network. The independent generation companies are incentivised by way of availability payments to ensure that their plant is available on a near-continuous basis (the companies achieve, on average, over 95% availability through the year).
In addition, the Bureau investigates major system incidents or outages which affect customers. These may include accidental tripping of equipment, failures of plant, widespread outages or incidents where the time to restore power was excessively long.
The new price control, commencing January 2006, includes a performance incentive scheme (PIS) for the Distribution and Transmission companies which provides annual bonuses for year on year improvements in the following key performance indicators:
Transco PIS indicators:
- Availability: = {total hours each transmission circuit or transformer is available} divided by {total number of circuits & transformers x hours in the year}
- Energy lost: = total MWh unsupplied due to unplanned incidents in a year (excluding incidents resulting from users of the transmission system)
Disco PIS indicators:
- SAIDI: System Average Interruption Duration Index = number of customer minutes lost in any one year, divided by the total number of connected customers (average for the year)
- SAIFI: System Average Interruption Frequency Index = total number of customer interruptions in any one year, divided by the total number of connected customers
[Note: for Disco indicators the term ‘Availability or Customer Minutes Lost (CML)’ is the same as SAIDI; the term ‘security or Customer Interruptions (CI)’ is equal to SAIFI x 100]
In addition to the above indicators the Bureau requires companies to report more detailed statistics on a monthly and annual basis. These are used to assess the impact on customer service levels and to work with the companies to enhance processes and systems which will improve customer satisfaction into the future.
The overall levels of network performance for the transmission and distribution companies are shown in the Bureaus Annual Reports under the Publications section
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