Instrument transformer is the collective name given to CTs and VTs. Instrument transformers are designed to transform the voltages or currents present in the high voltage transmission and distribution systems to lower values that can be utilised by metering devices. If an instrument transformer is inaccurate, this can affect the overall accuracy of the metering installation which in turn can impact on customer billing and market settlement.

Yurika as your Metering Coordinator (MC) is required to collect and retain details of the currency of test certificates of all its customers and provide this information to the Australian Energy Regulatory (AER), as and when requested.

Failure to conduct regular tests may result in adverse financial outcomes if the HV CT/VTs are recording inaccurate metering data. If the HV CT/VT is over-recording consumption, your electricity bill will be higher than it should. Testing could also identify when a transformer is faulty or otherwise damaged.

Yes, to ensure the safety of all involved, an outage of the HV feed into your site in which the CTs/VTs are installed will be required. This requires coordination between you as the customer, the local network service provider (LNSP) and the electrical contractor conducting the testing to schedule the outage. Whether a total site outage is required will depend on how the feeders come into the site. Some sites can switch between feeders or may be able to switch to on-site back-up generation to avoid shutting down plant.

A 12-hour outage is scheduled to ensure all circumstances are covered. However, the actual outage time is dependent on the site and the characteristics of each set of CTs and VTs.

Meter testing: the metering device is tested for accuracy and can be isolated from supply without any power interruptions to the customer’s site.
CT/VT testing: testing of the HV current and voltage measuring instruments (transformers) connected to the meter which are located in substations or on power poles.

To demonstrate to the AER, Yurika must comply with its obligations as a Metering Coordinator — all testing must be undertaken by either an AEMO accredited Metering Provider, or by a NATA accredited facility.

NATA Accreditation is a high-level process of recognising collective, specific and demonstrated competencies. The core of NATA Accreditation is the third party, objective, peer assessment process at a scientific and technical level that provides assurance of the laboratory’s capability to produce reliable data from particular measurements. Not all NATA certified companies can test to all relevant standards. Any company engaged to perform the testing must be registered as accredited for the particular testing standards. The nameplate of the CT and VT will outline the standard to which the instrument was built, and the testing must align with this Australian Standard.

At any point a large customer may appoint a new MC, but this will not remove the requirement to conduct the CT/VT testing or change the timeframe for testing. The new MC will simply take over responsibility for keeping a record of the currency of test certificates.

In some cases, the CT/VTs in relation to a site may belong to the LNSP. Where this is the case, it is not your responsibility to arrange and pay for testing.