Abstract
Voltage unbalance (VU) in residential distribution networks (RDNs) is mainly caused by load unbalance in three phases, resulting from network configuration and load-variations. The increasing penetration of distributed generation devices, such as small wind turbines (SWTs), and their uneven distribution over the three phases have introduced difficulties in evaluating possible VU. This paper aims to provide a three-phase probabilistic power flow method, point estimate method to evaluate the VU. This method, considering the randomness of load switching in customers’ homes and time-variation in wind speed, is shown to be capable of providing a global picture of a network’s VU degree so that it can be used for fast evaluation. Applying the 2m + 1 scheme of the proposed method to a generic UK distribution network shows that a balanced SWT penetration over three phases reduces the VU of a RDN. Greater unbalance in SWT penetration results in higher voltage unbalance factor (VUF), and cause VUF in excess of the UK statutory limit of 1.3%.
Highlights
Voltage unbalance (VU) is a costly and potentially damaging phenomenon in electrical power systems
voltage unbalance factor (VUF) at the remote end of the low voltage (LV) cables are shown higher than the LV busbar
A probabilistic power flow method, point estimate method is applied to a generic UK LV network to evaluate voltage unbalance in residential distribution networks with small wind turbines
Summary
Voltage unbalance (VU) is a costly and potentially damaging phenomenon in electrical power systems. VU will affect network losses, the performance of transformers and induction motors, causing overheating, etc. VU is more common in residential distribution networks (RDNs), where a large number of single-phase loads are used. In RDNs, wherever possible, efforts are made to distribute the single-phase loads uniformly over the three-phase supply. It is recognised that it is unlikely that, at a given time instant, electrical loads are balanced in three phases because of the randomness of load switching in customers’ homes [1]. Load unbalance is the major cause of VU in existing RDNs [2,3]
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