Development of techniques for assessing customer accountability for harmonic distortion across a ring main network

Abstract

Modern power systems consist of non-linear loads and high integration of renewable energy sources (RES). The conventional power system is not designed to accommodate new smart grid technologies. This causes challenges for power quality, which can no longer be ignored by both utilities and customers. There are several power quality issues that the utilities have to monitor and manage in real-time. One of the most important is the level of harmonic distortion. A certain percent of harmonic distortion at the Point of Common Coupling (PCC) as prescribed by national and international standards is allowed by power utilities. However, the challenge experienced is that the harmonic distortion from the distinctive individual points to the PCC sometimes exceeds the standard harmonic limits. This harmonic distortion can originate either from upstream through the background harmonics (utility side responsibility) or downstream through the non-linear loads and renewable energy sources (customer’s responsibility). There are multiple customers connected at the PCC, thus it is challenging to identify the harmonic source between customers and utility. Hence this research work proposes a practical and commercial method to quantify the harmonic contribution between the power utility and different customers. This method will enable the engineers to assess the accountability of the harmonic distortion measured at the PCC. This research is based on the modified direction of active power flow. This is because this method is generally used by the industrial power quality measurement instruments which the power utility uses for power quality analysis. Harmonic active power is considered when the harmonic source detection methodology is set. A new technique is developed to detect the source of harmonic distortion. Most methods in literature only highlight harmonic detection between the utility and the customer. The research undertaken below highlights the direction of active power at the fundamental and harmonic frequency. A proposed new formula is presented for total active power at a combined frequency (fundamental and harmonic frequencies). The known Norton and Thevenin equivalent circuits are adapted by deriving a mathematical model that accommodates the multiple customers connected at the PCC. To monitor and manage the harmonic distortion during the initial stage of the electricity supply agreement, a harmonic monitoring management system is proposed. Different case studies were modelled in the DIgSILENT software package to validate the proposed methods. The industrial simulation case study is validated by the measurement taken from the NamPower network for six months. It was concluded that the new adapted equivalent circuits be used for power system analysis but not recommended for harmonic source detection. If the proposed harmonic monitoring management system is implemented by the utility, the challenge of harmonic source detection will be minimised. The direction of the active power flow method is proved to be a practical and commercially viable method of harmonic source detection.