Reliability Measures and Standards

The Queensland Electricity Industry Code details Minimum Service Standard (MSS) to be achieved for network reliability. The MSS are prescribed in the Code to provide a standard against which a distribution entity’s feeder performance can be assessed across the network and from year to year. Two reliability measures are defined as follows:

 System Average Interruption Duration Index (SAIDI) limits; and

 System Average Interruption Frequency Index (SAIFI) limits.

SAIDI indicates the total minutes, on average, that customers are without electricity during the relevant period. By contrast, SAIFI indicates the average number of occasions each customer’s supply is interrupted during the relevant period. Both indices are inclusive of both planned and unplanned events.

The Code prescribes that Energex must use its best endeavours to ensure that it does not exceed the SAIDI and SAIFI limits set out in the code for the relevant financial year.

Circumstances beyond the distribution entity’s control are generally excluded from the calculation of SAIDI and SAIFI metrics. In particular, the Code excludes the following events from the MSS calculations:

 An interruption of a duration of one minute or less (momentary);

 An interruption resulting from load shedding due to a shortfall in generation;

 An interruption resulting from a direction by AEMO, a system operator or any other body exercising a similar function under the Electricity Act, National Electricity Rules or National Electricity Law;

 An interruption resulting from automatic shedding of load under the control of under-frequency relays following the occurrence of a power system under-under-frequency condition described in the power system security and reliability standards;

 An interruption resulting from failure of the shared transmission grid (Powerlink);

 An interruption resulting from a direction by a police officer or another authorised person exercising powers in relation to public safety;

 An interruption to the supply of electricity which commences on a major event day;

and

 An interruption caused by a customer’s electrical installation or failure of that electrical installation.

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The MSS limits for 2013/14 and 2014/15 are presented in Section 10.1.1, along with Energex’s performance against these limits. The 2013/14 limits are in accordance with the Electricity Industry Code.

As part of the Queensland Government’s reform of the reliability standards, from 1 July 2014 the MSS provisions will be removed from the Electricity Industry Code and inserted into Energex’s Distribution Authority, with systemic failures to meet these standards to be considered a breach of Authority conditions. The MSS limits for 2014/15 and beyond will reflect the adoption of the IDC recommendation to flat-line MSS at the 2010/11 levels. This will mean a relaxation in the MSS for Urban and Rural customers.

Also under the Government reforms, Energex is required to continue to monitor Worst Performing Feeders (WPF) and report on their performance. A summary of the performance of Energex’s 2013/14 worst performing feeders is presented in Section 10.5 and a full report is contained in Volume 2 Section 11 of this Distribution Annual Planning Report.

Under the recent Queensland Competition Authority (QCA) review of the MSS, no additional measures were recommended for inclusion. However the AER does include the Momentary Average Interruptions Frequency Index (MAIFI) measure in its annual RINs and in the measures that may be applied in the STPIS. At this stage there is no requirement for Energex to report momentary interruptions MAIFI due to accuracy reasons. Energex’s preference is for reporting momentary interruptions by event MAIFIe rather than MAIFI, which is consistent with reporting in other jurisdictions. Energex is currently able to report MAIFIe to within an accuracy of around 95%. Energex investment programs presently do not include projects to deliver accurate reporting of MAIFI. Beyond reporting MAIFIe, the possible inclusion of MAIFIe in STPIS in the next regulatory period will require further improvement of data capture and reporting systems.

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10.1.1 Reliability Performance in 2013/14

The normalised results in Table 18 highlight a favourable performance against MSS for all of Energex’s network categories.

Table 18 – Performance Compared to the MSS Normalised Reliability

10.1.2 Reliability Compliance Processes

Due to inherent statistical variability in reliability performance from year to year, mainly due to adverse weather, simply aiming for the MSS would lead to regular non-compliances. To minimise the risk of non-compliance to less than once in 10 years, Energex has set its internal target to 10-15% below the stated MSS. These targets are based on a Monte Carlo simulation of the past five years of SAIDI and SAIFI performance data. Under the government reforms to the reliability standards, Energex will need to go beyond ‘best endeavours’ to ensure there is no systemic breaches of the MSS, defined to be an exceedance of the MSS limits in three consecutive years. Energex is now considering the appropriate internal targets to minimise this risk.

A forecast of network performance for each category is then carried out based on analysis of the three key components of planned outages, non-storm unplanned outages and storm unplanned outages. These forecasts are then adjusted to allow for both decreases in reliability (due to factors such as asset ageing), and expected improvements under Energex’s existing capital and operating expenditure program. These adjusted forecasts are then compared to the internal reliability targets to determine if a gap exists where the forecast performance is unfavourable to any of the targets.

If gaps in performance prevail, further network analysis is undertaken and programs are implemented to target those areas where the maximum reliability benefit can be achieved for

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minimum capital expenditure. Historically, the majority of these reliability programs have been made up of reliability improvements to specific 11 kV feeders, as Energex’s 11 kV network is the highest contributor to its SAIDI and SAIFI results. By creating projects around individual 11 kV feeders, the performance of each feeder can be analysed, and the improvement works can then be targeted to the specific issues on each feeder.

In conjunction with carrying out reliability improvement works aimed at the feeders that have the highest contribution to SAID and SAIFI, Energex is also proposing to complete reliability projects to address the feeders that have the poorest individual performance. The works proposed under these projects will also be targeted to address the specific issues on each feeder. Additional information on the worst performing feeders can be found in Section 10.5 and Volume 2 Section 11.

10.1.3 Reliability Non-compliance Corrective Actions

As shown in Table 18 above, Energex complied with its reliability standards for 2013/14 and is expecting to be compliant in 2014/15.