Application of Australia's New Harmonic Standard to a Long MV Feeder

Australia has just adopted AS/NZS 61000.3.6 1 as a standard for harmonics in MV and HV power systems. This standard accounts for time-variation by applying limits to 95% probability values of current or voltage. Stage 2 of the standard gives a method for allocating harmonic current limits to individual customers. The method is straightforward to apply for short feeders (Test 1) but is poorly specified for the more common situation when feeders are sufficiently long that there is a significant change in fault level away from the zone substation (Test 3). This paper develops a detailed approach for Test 3 consistent with the general guidelines of the standard. Some approximations need to be made to give a method that does not require an impracticably large amount of system data. The application of the method is illustrated by an example case study.