Mitigation for floating neutral in distribution systems.

Abstract

The rollout of electrification programme in deep rural communities has significantly improved the quality of life for people of South Africa, some who never anticipated that they would have access to electricity. Most rural community members start saving and buy electrical appliances like refrigerators and televisions as soon as they become aware that they are going to have aces to electricity in the following year. A broken neutral conductor in the electrical network always leaves a devastating impact to the customers connected to that network especially in poor rural communities. The resultant damage to their electrical appliances is regrettable especially considering that the majority of electrification beneficiaries cannot afford to install their own protection devices. An engineering solution integrated to the current protection philosophy was required to mitigate against such type of network failures. The main aim of the study was to have a better understanding of the current network protection philosophy of the electrification projects, protection capabilities of the current installed devices and equipment and recommend improvements to address gaps identified with the purpose of improving customer’s experience of the services that some waited for lifetime to receive. The literature review and laboratory experiments conducted revealed that the current protection philosophy focused more on protection against over current and earth leakage faults. There was minimal effort on overvoltage and under-voltage protection on the customer’s point of supply. Over voltage and under voltage are normally the fault conditions experienced by customers when the neutral conductor in the distribution system is broken. The current protection philosophy and practice in distribution were tested against the regulatory and statutory requirements. The philosophy and practices complied with the regulatory and statutory requirements. However, the compliance does not take way the impact the fault have on customers. A responsible supply authority can go an extra mile to protect the customer’s equipment they supply from network faults though it is not a minimum requirement. Considering the social status of the electrification beneficiaries, the provision of the overvoltage and under voltage protection to distribution customers will be a social contribution of a responsible supply authority and a minimal cost to the company compared to the consequential damage that floating neutral have on customers. Current available technology in the market as well as simulations conducted on Multisim and PSIM demonstrated that there are implementable viable solutions to mitigate and minimize the risk of damage against broken neutral conductor faults. The analysis of the results obtained during the study confirmed that current protection is not adequate and that there is a need to relook at the protection requirements to cover over voltage and under voltage protection. Refinements in the current minimum protection requirements were recommended for implementation.