Abstract
In power system planning, the general concern is the ability of a power system to supply
increasing loads without undervoltages. Nonetheless, decrease in loads can also occur in
power systems, e.g., when mines are decommissioned leading to shrinkage in load.
Depending on the scale of the load reduction, problem of steady overvoltages can arise.
This study proposes an investigation of using of step-down transformers to reduce steady
state overvoltages in a lightly loaded network comprising of long corridors. The
investigation evaluates the proposal of installing transformers at both ends of the length
network, forming a ring of transformers to derate the operating voltage of the derated
network. The load flow simulation studies are initially carried out manually by scaling
the load down using the Power System Software for Engineers (PSS/E). The load flow
studies for the lowest load served without violations are carried out for the case without
transformers and the derated case with transformers.
The study further proposed the use of Python program to automate the studies through
scaling the load down until the voltage limits are reached by sending commands to
PSS/E using Python syntax. In addition to this, the use of Tabu Search (TS) algorithm is
proposed for optimally selecting a combination of lines to accommodate the least load
within the voltage limits. The load is scaled down automatically in PSS/E using Python
program with the least load served as an objective function and the constraints being the
voltage limits.
The study found that the use of step-down transformers can successfully reduce the
steady state overvoltages in a lightly loaded network. The introduction of Python
program to automate the studies was successful. Lastly, intelligence of Tabu Search
algorithm can successfully select the optimal combination of lines to serve the least load
without voltage violations.
M.Phil. (Electrical and Electronic Engineering)