Proposed amendment to IEC/TR 61000.3.6:2008 for harmonic allocation to loads in transmission systems

Ensuring harmonic voltage distortion levels in transmission systems remain below acceptable levels relies on appropriate allocations of emissions to customer loads and bulk supply points. A number of practical issues have been identified with the existing harmonic allocation method for transmission systems in the technical report IEC/TR 61000-3-6:2008, Ed.2: the method to assess the total available power of a busbar, a key component to harmonic allocations, is not intuitive and there is a lack of clarity in the report; the method for sharing planning levels also does not allow unused spare capacity at a busbar to be shared with other busbars in the network to increase their global contribution; and the method for allocation of individual limits does not account for the size and harmonic emission of existing loads connected to a busbar. This paper analyses these issues in detail and proposes some clarification and amendments required for the existing allocation method. A simplified transmission network is provided to clarify how total available power can be assessed, how individual limits can be allocated for multiple loads connected to the same busbar, and to demonstrate that a significant increase in global contribution and subsequently higher individual limits can be achieved.