4224 NEW ZEALAND GAZETTE No. 162

Part 6

Reliability Performance Measures To Be Disclosed By Transpower

(Disclosure Under Regulation 22)

1. Total number of unplanned interruptions.......................................... 62 110 103 164
   Resulting from 50 loss of supply incidents in 1999-2000*

2. Electricity customer interruptions in system minutes................................ 4.9 9.7 5.1 13.6
   **
   planned.................................................................... 2.8 2.7 2.1 2.1
   unplanned................................................................ 2.1 7.1 2.9 11.5

3. Underlying electricity customer interruptions in system minutes*.................... 4.9 7.3 5.1 6.9
   Underlying interruptions are those interruptions of 1 system minute or less duration*

   planned.................................................................... 2.8 1.7 2.1 2.1
   unplanned................................................................ 2.1 5.6 2.9 4.8

4. Average supply reliability........................................................ 99.9986% 99.9972% 99.9985% 99.9959%
   Measured by the energy supplied divided by the sum of the energy supplied and not supplied

5. Uneconomic generation due to planned and unplanned transmission system unavailability... - - - 0.55%
   Uneconomic generation relates to the amount of electricity generated from any source other than the most economic source

6. Uneconomic generation due to HVDC system unavailability............................... - - - 0.47%

7. Uneconomic generation due to unplanned transmission system unavailability............. - - - 0.12%

8. Planned interruption restoration performance....................................... 100% 94.4% 90.5% 72%

9. Unplanned interruption response.................................................... 100% 100% 98.1% 100%

The information compiled using estimated information includes Part 6 sections 2, 3 and 4. The methodology used to calculate the estimated information is documented and available from Transpower upon request.

Uneconomic generation (Part 6 sections 5, 6 and 7) is not relevant in the market environment because scheduling is now based on offered price, not economic cost. In the market, 'offers to generate' are made after taking constraints into account and it is not possible to predict what a generator would have offered if the constraint was not present. As a result data is not available to allow a calculation for 1999/2000 and a null entry has been returned. The values which appeared in the 1999 Quality Performance Report for 1997/98 and 1998/99 were prepared using the prescribed method, and these have been updated in this issue for the same reason.

• Where two supply voltages, or two customers, at the same station are both interrupted this is counted as two interruptions.

** Any minor differences between the total and the sum of planned and unplanned are due to rounding. System minutes of interruptions are not counted if energy is made up by backfeed from another point of supply or by embedded generation within a customers network.

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