| dc.description.abstract | Economy and reliability of service are important considerations in power system operation
and planning. The primary objective in power system planning and operation is to minimise the cost
of meeting the power requirements of the system over some appropriate period of time and in a
manner consistent with reliable service.
The appropriate time could be short ( say afew minutes) or long ( say one year) depending
on the nature of the energy resources available to the system. Obviously, the aim in the utilization
of energy resources is to realise the greatest possible value during the period of operation in terms
of fuel usage. Thermal or gas stations rely on fossil fuels like coal, diesel, gas etc for their operation.
In addition to being expensive, fossil fuels are exhaustible and therefore thermal stations should be
set to operate with minimum cost so as to reduce fuel usage. Hydro and geothermal stations have
negligible operating costs but should nonetheless be operated efficiently if the available hydro and
geothermal resources are to be exploited to the maximum.
The limiting factor is of course system constraints like voltage levels, power flow on
transmission lines, generator output limits, etc., which should be maintained within an acceptable
operating range to ensure reliability of supply.
An optimal power flow problem formulates an appropriate objective function ( cost, real
power loss, load shedding etc.) which is then minimised subject to satisfying system constraints like
voltage levels, transformer taps, line flows etc. The solution can be obtained using several non -
linear programming techniques which include the steepest descent method, Quadratic Programming
Method ( QPM) and the Gradient Projection Method (GPM) among others. In this thesis, the
optimization problem is solved using the steepest descent method and targets the Kenya Power System.
The solution technique is based on the Newton Raphson load flow formulation, a first order
gradient adjustment algorithm for minimising the objective function and use of penalty functions to
account for violation of dependent variables. These include system security constraints such as
voltage levels on load buses and real and reactive power flows on transmission lines which, when
satisfied, ensure a reliable and secure supply of power. Only the short term operational problem is
addressed. The long term hydro-thermal co-ordination planning problem is recommended for future
research. | en |
