Non-Adaptive Protection Coordination for Radial Distribution Feeder with Distributed Generation

Abstract

The connection of Distributed Generations (DGs) into a power systems distribution network improves the network’s voltage profile, power quality and enhances voltage stability hence the distribution networks can withstand higher loading conditions reducing the network’s overdependence on the main grid in improving its security and reliability. However, DG connection into a radial distribution network causes an increase on the network’s short circuit current levels with the increase in the short circuit current levels creating a miss-coordination amongst the Over-Current Protective Devices (OCPDs) during a fault hence affecting the reliability of the over-current protection schemes implemented to protect the distribution network. In this research a conventional Fuse-Fuse over-current protection scheme was modelled to protect a radial test feeder from faults and the fuses coordinated while clearing the single line to ground (SLG) faults occurring at the feeder nodes without DGs connected. While clearing faults occurring in the test feeder, coordination is achieved if the upstream fuse minimum melting time (MMT) characteristics and the downstream fuse total clearing time (TCT) characteristics have a time coordination margin not less than 0.025 seconds between them. When Wind Turbine Generators (WTGs) were connected into the radial test feeder, the short circuit current levels increased; the network sequence reactance reduced; and the fuse-fuse time coordination margins reduced to levels less than the 0.025 seconds minimum threshold. Diminishing Fuse-Fuse time coordination margins to levels less than 0.025 seconds due to the increase in the networks’ short circuit current levels upon WTG connection rendered the Fuse-Fuse over-current protection scheme inadequate and insufficient in protecting the radial test feeder from short circuit faults.This research considered the use of Fault Current Limiters (FCLs) to improve on the problem of diminishing fuse-fuse time coordination margins introduced by the WTGs by reducing the prospective fault currents in the test feeder to lower manageable levels not to cause further Fuse-Fuse miss-coordination. Series Current Limiting Reactors (CLRs) were introduced as additional impedances into the feeder to increase the feeder sequence reactance which had reduced due to WTGs connection. Once the WTGs were coupled into the radial test feeder using the CLRs, the feeder short circuit current levels reduced, the network sequence reactance increased and the diminishing time coordination margins between the fuses increased to levels above 0.025 seconds which is the minimum threshold for Fuse-Fuse coordination. CLRs reduced the prospective fault currents contribution from the WTGs to lower manageable levels not to cause further diminishing fuse-fuse time coordination margins thus restoring Fuse-Fuse coordination hence improving on the Fuse-Fuse over-current protection scheme reliability and efficiency in protecting the feeder.