Customer Connection Points Research Articles

Ensuring public safety through proper earthing in low-voltage networks

Electrical network should have proper earthing (grounding) system for its reliable operation and for the safety of operating personnel and connected customers. Good earthing provides a suitable return path for the fault current when a short circuit occurs in the network. In a low-voltage (LV) network mainly terra-terra (TT) and terra-neutral (TN) type network configurations are commonly used. Depending on the agreement between the network operator and the customer, earthing at a customer's point of connection (POC) is provided by a dedicated earth conductor, combined network cable (PEN conductor), or via a separate earth electrode. When an earth retour path is broken or interrupted, it will not be able to provide earth retour circuit and can cause dangerous fault voltage at various exposed parts of the conducting circuit. In this paper, various LV network configurations are discussed. Further, a practical monitoring based case study is presented to analyze the diversity of earth resistance values for different LV network configurations. Also, guiding rules are given to define safe value of circuit impedance and earth resistance path for various configurations. Finally, a proposal is given to optimize the safety needs at a customer's POC.

Smart charging for electric vehicles to minimise charging cost

This paper assumes a smart grid framework where the driving patterns for electric vehicles are known, time variations in electricity prices are communicated to householders, and data on voltage variation throughout the distribution system are available. Based on this information, an aggregator with access to this data can be employed to minimise electric vehicles charging costs to the owner whilst maintaining acceptable distribution system voltages. In this study, electric vehicle charging is assumed to take place only in the home. A single-phase Low Voltage (LV) distribution network is investigated where the local electric vehicles penetration level is assumed to be 100%. Electric vehicle use patterns have been extracted from the UK Time of Use Survey data with a 10-min resolution and the domestic base load is generated from an existing public domain model. Apart from the so-called real time price signal, which is derived from the electricity system wholesale price, the cost of battery degradation is also considered in the optimal scheduling of electric vehicles charging. A simple and effective heuristic method is proposed to minimise the electric vehicles’ charging cost whilst satisfying the requirement of state of charge for the electric vehicles’ battery. A simulation in OpenDSS over a period of 24 h has been implemented, taking care of the network constraints for voltage level at the customer connection points. The optimisation results are compared with those obtained using dynamic optimal power flow.

Network Power-Flow Analysis for a High Penetration of Distributed Generation

Summary form only given. The connection of large numbers of small or micro-generators to low voltage distribution networks may put at risk traditional network designs. Such designs are based on traditional assumptions such as historical diversity factors and other simplifying assumptions that may no longer be appropriate. This paper describes on-going research, based on a detailed examination of a typical low voltage distribution system with increasing penetrations of distributed generation, mostly in the form of micro-generators (micro-clip, building integrated wind, and building integrated photovoltaics) connected at domestic properties. Modelling techniques have been developed that are applicable to complete distribution feeders: from primary substations, through medium and low-voltage networks to individual single-phase customer connection points. The modelling uses accurate unbalanced power-flow analysis (load-flow) and 1-minute time-series load data. Provisional results show that statistically, in terms of voltage quality and line limits, higher than expected penetrations of distributed generation can be accommodated without modifications to the distribution system. System evolution is discussed with even higher penetrations in mind.