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Distribution Network Performance
Recent Network Performance
| Period | 1/7/07 - 30/06/08 |
| Energy received for delivery | 1,364,987,000 kWh |
| Energy not delivered, due to forced or planned interruption* | 272,822 kWh |
| Resultant delivery rate | 99.800% |
| Quality-failure payments** this period | $61,717 (relating to supply to 1171 connections) |
| Voltage complaints unresolved at period-end | 10 (out of 80,000 network connections) |
* Calculated for all interruptions based on the load that would have been delivered.
** Aurora introduced quality-failure payments in 1992. These are paid by Aurora to its customers - electricity retailers. Whether individual electricity consumers receive quality-failure payments is a matter for each retailer.
Performance Over Time
New Zealand's electricity distribution businesses are required to publicly disclose a large number of financial and operational parameters. Aurora's performance over time, and compared to like networks, has been as follows:
Comparison over time
| Year ended 31 March | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 |
|---|---|---|---|---|---|---|
| Return On Investment* | 9.3% | 31.6%(2) | 8.1% | 15.0% | 10.7% | 12.4% |
| Total Cost (1) | 1.04 | 0.99 | 1.02 | 1.04 | 1.09 | 1.35 |
| SAIDI (3) | 89 | 96 | 81 | 83 | 97 | 129 |
(1) As defined by the Information Disclosure regulations.
(2) Affected for all companies by overdue increase in the Commerce Commission's asset value handbook.
(3) System Average Interruption Duration Index (average total duration of interruptions, per consumer, per annum).
Performance Comparison with similar Networks
Comparison of the performance of different distribution networks is made difficult by the different external variables they operate under. However, it is generally acknowledged that consumer-density is the primary variable in New Zealand. Comparison of Aurora's performance with the four networks with closest consumer-density(4) is as follows:
Comparison with like distribution networks(4) (y.e. 31 March '08)
| 1 | 2 | Aurora | 3 | 4 | NZ Average | |
|---|---|---|---|---|---|---|
| Consumers per km of HV lines | 28.2 | 22.0 | 21.4 | 20.7 | 17.3 | 22.1 |
| Price effective distribution charge(5) | 5.3 | 5.0 | 4.6 | 4.8 | 5.5 | |
| SAIDI | 80 | 118 | 129 | 168 | 329 | 137 |
| Return on Investment | 13.8% | 10.1% | 12.4% | 10.6% | 10.6% |
(4) In consumer density - consumers per kM of high voltage line
(5) excludes transmission and includes the cost of distribution losses @ 6 c/kWh
Reliability Performance
According to customer surveys, the two most annoying dimensions of power interruptions are their frequency and their duration. Two standard international measures express these:
SAIFI - System Average Interruption Frequency Index. The number of consumers affected in each interruption is added up for all interruptions in a year and the total is divided by the average number of consumers during the year. The result is the number of interruptions that the average consumer experiences, which for Aurora consumers is 1.8 per year. This measure is most directly affected by equipment failure, and accordingly is a measure of asset quality and maintenance practices.
CAIDI - Consumer Average Interruption Duration Index. The number of consumers affected in each interruption is multiplied by the duration of the interruption and the consumer-minutes result is added up for all interruptions in a year. The total consumer-minutes for the year is then divided by the average number of consumers during the year. The result is the average length of each interruption experienced by the average consumer during the year, which for Aurora consumers is 56 minutes. This measure is most directly affected by fault response - the ability of the network operator to respond faster, and whether alternative supply routes are provided to restore supply until the faulty equipment is repaired.
Customer surveys also reveal that some consumers are more annoyed by frequency of interruption, and others by duration. If average frequency (SAIFI) is multiplied by average duration (CAIDI) the result is the total minutes of interruption per annum for the average consumer. This is called the System Average Interruption Duration Index (SAIDI) and is a good overall indicator of how reliable the electricity supply is.
Aurora's SAIDI has varied between 75 and 195 minutes over recent years, principally due to varying weather. The combined wind & snow storm of July 1999 caused the 195 minutes result to March 2000. The trend has been for a reduction in interruptions of 3.0% per annum compared to the national trend of 1.4% reduction.
The average SAIDI for New Zealand electricity distribution businesses, weighted by consumer numbers, is around 175 minutes, down from around 180 minutes of a decade ago, but up from the 120 minutes achieved a few years ago. Most distributors are planning to improve reliability of supply, such that the NZ average in 2012 is expected to be around 112 minutes.
Aurora's average SAIDI has been less than 100 minutes for most of the past decade, and thus is considerably better than both the current NZ average and the expected average in 2012. Aurora's consumer-density is very close to the NZ average so that such simple comparison is appropriate.