Earthing system analysis to improve protection system performance in distribution networks

The objective of this paper is to provide a comprehensive analysis of earthing system to enhance protection system performance in distribution networks. Al Ain Distribution Company (AADC) is one of the subsidiary companies of Abu Dhabi Water and Electricity Authority (ADWEA) in the United Arab Emirates (UAE). AADC is responsible to operate and maintain the power distribution from voltage level of 0.4 kV up to and including 33 kV in the eastern region of Abu Dhabi emirate. AADC is always keen to provide safe and secure power supply to its customers. Network performance KPI's such as SAIFI, and SAIDI would be improved, if protection system isolates the fault correctly. The protection system can't operate independently, if the network components such as earthing system, equipments, OHL/Cable, etc. are not designed properly. AADC initiated a project in the year 2010 to study the existing earthing arrangement and standards in liaison with protection system to improve network performance. The study also included live line tests in 11kV system with different types of fault with different vendor in order to analyse performance of HiZ / BCP relays as HiZ faults are a great challenge in AADC due to nature of soil in eastern region of Abu Dhabi emirate. Trial earthing was also a part of the study which included different types of earthing grids in variant site conditions at different locations to analyse the nature of soil in order to improve earthing system in AADC network. AADC was the first utility company in the region (UAE as well as Gulf countries) to conduct the live line tests in 11 kV OHL. The test results and trial earthing lead to several conclusion in determining optimum earthing arrangements and selection of right protection application in AADC network. Thus, the study added additional advantage to improve protection system performance in distribution network. This paper also analyses the performance of multiple protection applications duly considering power transformer neutral earthing arrangement such as solid, resistor and reactor earthing, for safe and secure operation in distribution network level.