An Advanced protection scheme to avert blackouts due to transmission network overload.

Abstract

The transmission and distribution networks suffer various overloads which have reduced power availability and utility income generation. Some networks employ frequency monitoring with Under Frequency Load Shedding to ensure system stability. However, other conditions that threaten power system stability like the loss of a tie line, overload trip of power transformers, distribution and transmission lines need to be monitored and prevented by implementing protection schemes which automatically shed off the extra load. This will not only improve reliability and continuity of service but also fast decision making to reduce the blackout zone and downtime. This paper presents a load management scheme that performs automatic load shedding and feeder restoration by strictly following the set threshold values using PCM600, an ABB tool. The logic configuration from PCM600 was validated and the Generic Object Oriented Substation Events (GOOSE) report 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 developed model was applied to a case study on the Ugandan transmission network to achieve a 500ms GOOSE messaging sequence on the station bus. IEDScout demonstrated a station-bus traffic data flow rate of 2 kbps responsible for CB commands and status update. The traffic on the Ethernet cable was captured and analyzed using WireShark, a graphic user interface network protocol, two data packets were sent every second through the Ethernet cable and 464 k bytes of data packets were sent as messages on the station bus during the simulation. The model was tested and was able to send a CB open command with in 2ms of overload threshold violation and when the transformer load was reduced, CB close command for load re-connection was sent with in 2ms. A cost benefit ratio of 1.647 was obtained. This model caters for very rare, non-continuous but possible and very catastrophic occurrences on the power system. Therefore, this paper provides an efficient solution to transmission line and transformer overload by automating downstream load-shedding and load restoration.