Contributions towards the development of the Technical Report IEC/TR 61000-3-13 on voltage unbalance emission allocation

Although voltage unbalance is a well understood concept, its presence as a power quality problem in electricity transmission and distribution networks has continued to be an issue of concerns primarily due to difficulties found by some network service providers in maintaining acceptable levels. This emphasises the lack of recommendations on engineering practices governing voltage unbalance that would facilitate the provision of adequate supply quality to connected customers. The International Electrotechnical Commission (IEC) has recently released the Technical Report IEC/TR 61000-3-13 which provides guiding principles for coordinating voltage unbalance between various voltage levels of a power system through the allocation of emission limits to installations. Although the IEC report is based on widely accepted basic concepts and principles, it requires refinements and original developments in relation to some of the key aspects. This thesis primarily focuses on making contributions for further improvements to the IEC report so as to present a more comprehensive voltage unbalance allocation procedure. Similar to the counterpart IEC guidelines for harmonics (IEC 61000-3-6) and flicker (IEC 61000-3-7) allocation, IEC/TR 61000-3-13 also apportions the global emission allowance to an installation in proportion to the ratio between the agreed apparent power, and the total available apparent power of the system seen at the busbar where it is connected. However, noting that voltage unbalance at a busbar can arise as a result of both load and system (essentially lines) asymmetries, IEC/TR 61000-3-13 applies an additional factor which is referred to as ‘Kue’ to the apportioned allowance. This factor Kue represents the fraction of the global emission allowance that can be allocated to customers, whereas the factor K ′ue (= 1−Kue) accounts for voltage unbalance which arises as a result of line asymmetries. Although

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