Short Duration Undervoltage Disturbance Ride-Through Test Procedure

A. No. This test procedure only needs to be completed for inverters that have been tested and comply with AS/NZS 4777.2:2015. Any inverters that have been updated and are compliant with AS/NZS 4777.2:2020 will have the capabilities outlined in this test procedure and therefore do not need to undertake additional testing. 

A. Yes, the VDRT test is an additional test procedure that is not captured in the current AS/NZS 4777.2:2015 test.  

A. Once the test has been completed, results must be sent to the South Australian Office of the Technical Regulator (OTR) via otr.invertertestresults@sa.gov.au. More details of the submission process can be found on the OTR’s Voltage Ride Through page. The full list of inverters can be found on the OTR’s Voltage Ride Through page. 

From 31 March 2021 the listing of compliant inverters will be taken over by Clean Energy Council through the products listing process. The CEC is currently reviewing and recording inverter VDRT test results. Therefore results should also be submitted to products@cleanenergycouncil.org.au 

A. The AS/NZS 4777.2:202X will supersede the Voltage Disturbance Ride Through test procedure once published and applied (which includes a 12-month grace period to allow for development and testing of products). However, it is important that inverters to be installed in South Australia complete the VDRT test procedure in order to meet the South Australian requirements in the interim. Once the revised AS/NZS 4777.2:202X is published and applied all inverters will need to meet these requirements in full. 

A. Certification practices for the VDRT test procedure will remain consistent with the current application of AS/NZS 4777.2:2015. So, if the series of inverters are able to receive the same AS/NZS 4777.2:2015 certificate to be listed on the product listing then the same would apply for this test, otherwise they would require two separate certificates. 

A. The difference between the two tests is described below: in AS/NZS 4777.2:2015 Appendix G2.2 and the test described in of the AEMO test procedure is: 

1. The AEMO test Section 2.2 the intent is to identify the response following a fast duration voltage dip (“step Voltage down to 177.5 V (2.5V below 180V) with the step change completed within 2 ms”) as would be experienced for a transmission level voltage disturbance. As per the Step (b)  
2. The AS/NZS4777.2:2015 Appendix G2.2 the intent is to identify the response following a slow voltage sag (“the voltage shall then be decreased in steps less than 1 V to 177.5 V. The dwell time at each voltage step shall be 5s”).

Through field observations and bench testing, AEMO have identified that the response of inverters to voltage events does appear to differ based on the speed of voltage event (i.e. some inverters are able to stay connected for events that appear for less than 1 second where the voltage is stepped down gradually but not when the voltage is rapidly decreased). It is therefore also necessary to also confirm the converse, that is, that the inverter does disconnect for an islanding event even if the voltage dip is rapid (as a worst case, the inverter might remain connected through a fast voltage event greater than 1 second which is not desired either). 

A. The intention of test report is to identify the subset of inverters that already have the voltage ride-through capability and is not intended to trigger inverter redesign or upgrades. If changes to firmware or design are required, the inverter should undertake compliance testing against AS/NZS4777.2:2015 again to ensure that the full suite of requirements are maintained.

AEMO has identified that whilst this is an immediate risk in South Australia, if it is addressed rapidly it would not require retrospective changes to the existing inverter fleet. AEMO is able to undertake other actions such as procuring additional contingency FCAS or applying new constraints in the meantime.  

Further, retrospective changes applied through an unmanaged firmware upgrade carries risks that could have unintended consequences across the fleet of inverters. 

The changes are intended to apply to all new and replacement inverters, other than warranty replacements, for both PV and battery systems. Off-grid inverters do not impact system security and therefore do not form part of the scope of this test procedure.

While testing will incur a cost to inverter manufacturers, this should be minimal (approximately $1000-3000/inverter certificate). The intention of this scheme is to identify the subset of inverters with the capability already built in, and not to trigger inverter manufacturers to redesign or rebuild their inverters to achieve this. So, there should be no additional cost to existing inverters on the market, it may, however, impact the number of available inverters in the market.