An Advanced Protection Scheme to Avert Blackouts due to Transmission Network Overload

Abstract

The Uganda power network has suffered various transformer overloads which have reduced power availability and utility income generation. Although frequency monitoring ensures system stability and calls for the Under Frequency Load Shedding scheme, other conditions that threaten power system stability like the loss of a tie line, overload trip of a power transformer, and overload trip of a transmission line need to be automated as well. This will not only improve reliability and continuity of service but also fast decision making, reduce the blackout zone, unnecessary load shedding, and minimal downtime. This paper presents a load management scheme that performs automatic load monitoring and feeder restoration by strictly following the set threshold values using PCM600, an ABB tool. The 11KV feeder load shedding hierarchy was strictly selected according to utility income-priority, strategic supply and safety. The logic configuration from PCM600 was validated and the Generic Object Oriented Substation Events (GOOSE) report was published. The Configured IED Description (CID) file from each IED (in PCM600) was saved in Substation Configuration Language (SCL) format and imported into IEDScout to simulate the IEC61850 communication. The simulation using IEDScout achieved a 500ms GOOSE messaging sequence and the traffic on the Ethernet cable was captured and analyzed using WireShark, a graphic user interface network protocol. A cost benefit ratio of 1.647 (greater than 1) was obtained to declared economically acceptable. This design caters for emergencies, i.e. very rare, non-continuous but possible and very catastrophic occurrences on the power system. Therefore this research provides an efficient solution to transmission line and transformer overload by automating downstream load-shedding and load restoration.