Compliance Bulletin No 6 (TO BE REVIEWED IN 2018-19) - Instrument transformer testing

Compliance bulletin
Release date: 
6 December 2011


Chapter 7 of the National Electricity Rules has been substantially amended and renumbered with effect from 1 December 2017. Under these changes, Responsible Persons have been replaced by a new type of registered participant, a Metering Coordinator.

Nevertheless the discussion in Compliance Bulletin No. 6 regarding instrument transformer testing has ongoing relevance to Metering Coordinators. Metering Coordinators should test instrument transformers every 10 years for accuracy, unless an alternate test plan has been approved by the Australian Energy Market Operator (AEMO).  Following the amendments to Chapter 7 of the National Electricity Rules, references in the compliance bulletin to obligations of the Responsible Person should be read as references to obligations of the Metering Coordinator.  The table below sets out the equivalent provisions in the amended rules for several provisions that are discussed in the compliance bulletin.

Description Rules before 1 December 2017 Rules in effect from 1 December 2017
Ensuring accuracy and testing of metering installations Clause 7.2.5(d)(2) Clause 7.3.2(e)(2)
Testing to the required class accuracy S7.3.1(a) S7.6.1(a)
Maximum period between tests Table S7.3.2 Table S7.6.1.2
Testing in accordance with the rules requirements or under an asset management strategy S7.3.1(c) S7.6.1(c)
Metering installation components 7.3.1 7.8.2
Responsibility for testing 7.6.1(a) 7.9.1(a)

The Australian Energy Regulator (AER) will review Compliance Bulletin No. 6 once metering contestability has been in place for sufficient time for us to assess whether the bulletin remains relevant under metering contestability, and whether new compliance issues are emerging.  Metering Coordinators that require clarification of their instrument transformer testing obligations should contact AEMO’s metering team in the first instance.


The AER released its sixth compliance bulletin in 2011. This compliance bulletin relates to instrument transformer testing.

The National Electricity Rules (Electricity Rules) require instrument transformers to be tested every 10 years for accuracy, unless an alternate test plan has been approved by the Australian Energy Market Operator (AEMO). In 2011, the AER was made aware of a failure by industry to test instrument transformers in accordance with the Electricity Rules. The AER was also notified by AEMO that industry had formed a Current Transformer Testing working group (CTTWG) to identify an acceptable sample testing approach.

The AER is concerned by the potential harm untested instrument transformers may have on the National Electricity Market (NEM). If an instrument transformer is inaccurate, this can affect the overall accuracy of the metering installation. However, given the work of the CTTWG and the current lack of industry guidance on testing methodologies, the AER has chosen to issue a compliance bulletin. The AER is seeking that industry demonstrate a willingness to comply by testing a sample of their instrument transformers over 12 months.