Network harmonics

Network harmonics are a problematic by-product of many customer devices being connected to the electricity network. Typically referred to as 'grid pollution', technically network harmonics are non-sinusoidal currents or voltages produced by non-linear loads created by customer equipment.

Non linear loads such as those produced by Variable Speed Drives (VSD's) inject harmonic currents into the electricity distribution network. These harmonic currents couple with the system impedances creating voltage distortion at various points on the network. As a result, equipment such as computers, transformers, electric motors, cables, capacitors, electronic controls etc. connected to the same point can malfunction or even fail completely.

As harmonics are produced by the end user equipment, it is important that these harmonics are controlled at the end user terminal. This is considered a good practice, as by controlling the emission levels of individual sources of harmonics, the flow of harmonics into the network is restricted at the PCC. This in-turn limits widespread effects of harmonics across the entire network. 

Refer to our Rural Network Harmonics Standard and other documentation for further details about your obligations.

Customers with Variable Speed Drives

The Rural Network Harmonics Standard affects all customers that have connections with a cumulative VSD load exceeding 20kW.  

The Standard was revised and updated during January 2014. In addition to new installations of Variable Speed Drives (VSD's), effective from 20 January 2014, all existing connections with a cumulative VSD load exceeding 20kW were required to have a harmonic filter installed (or similar mitigation).