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.
Highlights
The primary aim of an electric power system is to provide satisfactory uninterrupted electrical power supply to customers within the set limits of frequency and voltage, the power system must be able to remain secure without serious consequences to any contingencies [1]
While the under-frequency load shedding scheme on the transmission network monitors the system frequency and timely sheds-off load to maintain frequency within set limits, the overload condition on the transmission network has only been left to overcurrent relays and operators for monitoring and load shedding decisions [2]
This paper presents a design used to increase availability of the power components by smart downstream automatic feeder isolation and ensuring that load shedding sequences are initiated before the transmission line protection relays operate
Summary
The primary aim of an electric power system is to provide satisfactory uninterrupted electrical power supply to customers within the set limits of frequency and voltage (reliability), the power system must be able to remain secure without serious consequences to any contingencies (stability) [1]. The challenge with manual action is the lack of accuracy, isolating too much load or too little load which reduces the time taken to stabilize the power system, further, when the load-violation occurs very fast, the operator cannot make a very fast decision brownouts, blackouts or cascaded failures [4]. According to [3], operators should be able to monitor and quickly identify critically loaded components within the power system. This becomes even harder as the network expands into power pools, there is a need for smart operation of the power system [5]. This paper presents a design used to increase availability of the power components by smart downstream automatic feeder isolation and ensuring that load shedding sequences are initiated before the transmission line protection relays operate
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