Page 1 of 12
European Journal of Applied Sciences – Vol. 12, No. 3
Publication Date: June 25, 2024
DOI:10.14738/aivp.123.17014
Kitheka, J. M., Nyete, A. M., Moses, P. M., & Abungu, N. O. (2024). Optimal Power Flow on a 132-kV Line with Service Potential
Transformer Substations: A Case Study of Juja-Rabai Line. European Journal of Applied Sciences, Vol - 12(3). 312-323.
Services for Science and Education – United Kingdom
Optimal Power Flow on a 132-kV Line with Service Potential
Transformer Substations: A Case Study of Juja-Rabai Line
Joel Mwithui Kitheka
Department of Electrical and Information Engineering University of Nairobi
Abraham Mutunga Nyete
Department of Electrical and Information Engineering University of Nairobi
Peter Musau Moses
Department of Electrical and Electronic Engineering South Eastern Kenya
University
Nicodemus O. Abungu
Department of Electrical and Electronic Engineering Machakos University
ABSTRACT
Most growing countries in Africa are facing serious challenge of high-power
demand which is not matched with expansion of power generating units, power
transmission network and Power distribution lines. This trend has led to frequent
power outages due to over stressed transmission and distribution networks. Most
countries have resorted to increase the number of thermal power plants to
address the growing power demand. These power plants are highly reliable and
secure but are faced by the ever-increasing fuel prices. In order to maintain
constant power supply and minimize the frequent power outages, its important to
carryout optimal power flow in power system networks. Optimal power flow is an
optimization method used to determine the most economical load flow in
transmission lines that can address the existing power demand. In this research,
minimization of fuel cost was used as the objective function. The generator power
limits, voltage level limits and loadability limits of the transmission line were used
as the constraints. The gradient method and co-ordination equations were used in
determining the optimal power flow in the network that was adequate to address
the power demand. A case study of Juja-rabai line was used in this analysis. The
Rabai thermal power plant, Kipevu thermal power plant and Thika thermal power
plant were used to supply the loads.The research considered existing loads along
the trans mission line, currently being supplied by existing conventional
substations. The typical transmission line parameters were used in this study.
Economic load dispatch neglecting line losses was f irst calculated followed by
economic load dispatch considering transmission line losses. The power network
was later modeled and simulated in PowerWorld software. This study revealed
that generator one should supply 20 MW, generator two 37.5 Mw and generator
three 12.5 MW. The study revealed the loadability limit of the line under economic
load dispatch.
Page 2 of 12
313
Kitheka, J. M., Nyete, A. M., Moses, P. M., & Abungu, N. O. (2024). Optimal Power Flow on a 132-kV Line with Service Potential Transformer
Substations: A Case Study of Juja-Rabai Line. European Journal of Applied Sciences, Vol - 12(3). 312-323.
URL: http://dx.doi.org/10.14738/aivp.123.17014
Keywords: Optimal power flow, Economic load dispatch, Trans mission line,
Conventional Substation, Service Potential transformer Substation, load.
INTRODUCTION
The increased interconnection of power networks has led to energy crisis in the world and the
continuous rise in fuel prices has made the situation even worse. In this aspect, means of
reducing the running charges of power plants must be re-evaluated. One way of reducing the
running cost is by reducing the fuel consumption for meeting a particular load demand [1].
Fast developing countries in Africa are facing Peter Musau Moses Department of Electrical
and Electronic Engineering South Eastern Kenya University pemosmusa@gmail.com
Nicodemus O. Abungu Department of Electrical and Electronic Engineering Machakos
University abunguodero@gmail.com a serious challenge of high-power demand [2]. This has
led to rapid construction of thermal power plants to address the demand. The existing high
voltage lines and distribution lines are being used to evacuate power to load centres. The
phenomenon has resorted to recurrent power outages due to over stressed power lines.
Kenya is one of the growing countries with rich resources of power sources to address its
power demand. These power plants include geothermal power plants from OLkaria, wind
power from Turkana power plants, hydro power plants from Kiambere (168MW), kindaruma
(72MW), Gitaru (225MW) Sondu Miriu (61MW) and Masinga (40MW) dams, thermal power
plants in Rabai (90Mw), Kipevu I (60Mw),Kipevu III (115MW), Iberafrica 1(56MW), Iberafrica
2(52.5MW),Athi River Gulf (80MW), Triump (83MW), Thika power (87MW), Embakasi gas
turbine 1 (27MW) and Embakasi gas turbine 2 (27MW) among others[3][4]. Despite the
extensive sources of power generating power plants, the transmission lines have remained at
the same state for some times. This makes them inadequate to evacuate power to address the
growing power demand. This has been the key sources of national blackouts in Kenya. Voltage
stability analysis methods and transient stability analysis methods have been employed in
Kenyan power networks in attempt to address the frequent power outages [2][5]. The
Stability analysis methods are not enough. Optimal power flow analysis should be employed
to ascertain whether the generated power is being economically evacuated to address the
ever-growing power demand. Renewable energy has been used to address the power demand
in rural areas and in towns. The use of Service Potential Transformer substation (SPT) is the
current trend of addressing lack of electricity in villages near high voltage (HV) lines [6][7].
This paper aimed at determining whether optimal power flow would address the power
demand in the society, minimize power outages and bring annual savings from fuel costs.
LITERATURE REVIEW
Service Potential Transformer Substations
SPT refers to modified instrument transformer, specifically a voltage transformer capable of
stepping down high voltages like 132kV, 220kV, 440kV to low voltages like 240 volts with
distribution capabilities. These static machines have a capability of supplying single phase
loads [8]. Originally SPTs were used in substations to step down voltage from transmission
lines to low voltages to provide power in the control rooms [9]. Kenya has a wide spread
transmission network, transverse most parts of its rural areas which are not supplied with
electricity. SPT substation tap power using high voltage connectors without interrupting the
power flow along the transmission line. In addition, only a single disconnection switch and
circuit breaker is required.
Page 3 of 12
Services for Science and Education – United Kingdom 314
European Journal of Applied Sciences (EJAS) Vol. 12, Issue 3, June-2024
Figure 1 shows an SPT used to step 132 kV to 240 Volts to supply single phase loads in
households whereas a conventional substation used three transformers to step voltage from
132 kV to 66 kV, from 66 kV to 33 kV and from 33 kV to 11 kV [10]. An SPT substation was
designed and installed to supply villages near the line in Congo. This technology is secure and
operational upto date [8]. This technology was implemented in a rural village in Congo to
supply electricity as captured in Figure 2.
Fig. 1: SPT versus conventional substation.
Optimal Power Flow on a Power Network
In a practical power system, the power plants are located at different distances from the load
centre and their fuel prices are different. In addition to that, the generated power is supposed
to be more than the total load power demand plus transmission line losses. In an
interconnected power system, the main aim is to determine the real and reactive power of
each generating unit with an objective of minimizing fuel cost. In this case the real and
reactive power of a power plant is allowed to vary within certain limits so as to meet a
particular load demand using minimum fuel cost. This is known as optimal power flow (OPF).
The OPF is used to optimize the power flow solutions of large interconnected systems. This is
achieved by minimizing the objective function while maintaining an acceptable system
performance in terms of generator capability limits and outputs of compensating devices [11].
A research was carried out to validate the effectiveness of PowerWorld simulator in carrying
out OPF and unit commitment scheduling over time in competitive electric power markets
using Matlab software [12]. Matlab Matlab simulator tool box contains functions like linear
programming, quadratic programming, binary integer programming, nonlinear optimization,
nonlinear least square, multi objective optimization and system of nonlinear equations [13].
The above functions provided a fast and accurate approach for validation of PowerWorld
simulator-based model. The comparison was based on whether an optimal solution obtained
using PowerWorld simulator was consistent with results obtained using Matlab, whether
piece wise linear simplification in PowerWorld affects it’s accuracy. The comparison revealed
that, the results generated by Matlab and PowerWorld were very close demonstrating the
effectiveness of using PowerWoorld to solve the optimal Power dispatch problem for
interconnected networks [11]. This paper carried out optimal power flow analysis on Juja-