by disturbances and in particular, by changes in the
operating point (M. Wadi, 2017). The problem of coordinating protective relays in power system networks
consists of selecting their suitable settings such that
their fundamental protective function is met under the
requirements of sensitivity, selectivity, reliability, and
speed. In a modern power system, abnormal conditions
can frequently occur to cause interruption to the supply, and may damage the equipment connected to the
power system, which allows us to note the importance
of designing a reliable protective system (Mancer N,
2015). The power system is the interconnection of
more than one control areas through tie lines. The
generators in a control area always vary their speed
together (speed up or slow down) for the maintenance
of the frequency and relative power angles to the predefined values in both static and dynamic conditions.
If any sudden load change occurs in a control area
of the interconnected power system then there will be
frequency deviation as well as tie line power deviation (Behera, 2019). The cascade outages that occurred
in Rwanda from 2018 to 2020 mostly proved severe
and very significant. It has been reported that during
the power outages about 5 million people have been
affected in 5 districts from the Northern region and
7 districts from the Western region, and 70 MW of
load were lost, which was about 27% of the total load.
Some other major cascade events began when lightning and overloading caused the tripping of a major
transmission line between the Western and Northern
grids. Research work in these two regions aimed to
predict voltage collapse and voltage overload with a
view to controlling and reducing its occurrence on
power system networks (Weiss R. 2020). Electrical
energy is a primary prerequisite for economic growth.
The demand for electrical energy has greatly increased
due to large-scale industrialization. A modern power
system operates under stressed conditions because of
the growth in demand and the deregulation of electric
power system. This leads to many problems associated with the operation and control of power systems.
The economics of power generation has been a major
concern for the power utilities (P. K. Modi, 2006).
Power systems are becoming heavily stressed due to
the increased loading of the transmission lines and
due to the difficulty of constructing new transmission
systems as well as the difficulty of building new generating plants near the load centers.All of these problems
lead to the voltage stability problem in the power system (Z. Osman, 2006). The effective power system in
Rwanda relies heavily on the ability of engineers to
ensure a continuous and reliable service in cascade
outages. In the ideal case, the load feeding should be
at a constant frequency of 50 Hz and voltage. For reasonable operation of consumer devices, voltage and
frequency should be maintained and secured within
tolerable limits in practical applications. A voltage
decrease from 10% to 15% or a reduction in frequency of system can cause stalling of the device loads
(Tanwani, 2013). The first requirement of this is the
maintenance of parallel operation of the synchronous
generator with the necessary ability to grip the load
condition. Because, if synchronism between the generator and the systems is missing at any time, it will affect
the voltage and current instability and system relays
will disconnect the supply at faulty sections (Naresh
K. Tanwani, 2014). The load frequency control problems are denoted by regulating the active power output
to generate units responding to the disturbances in system frequency and load power interchanges within the
prescribed ranges (Congzhi Huang, 2017). The secure
operation of power systems with the variation of loads
has been a challenge for power system engineers since
the 1920s. (Steinmetz, 1920). The voltage and frequency instability in the short term is driven by fast
recovering load components that tend to restore power
consumption in the time frame of seconds after a voltage drop caused by a contingency. The PID controller
and Automatic Voltage Regulator have been shown to
be more effective for the enhancement and optimization of power system stability with better damping
under small and large disturbances when compared
with conventional excitation control (M. J. Hossain,
2009).
2 MATERIAL AND METHODS
2.1 Balanced state control system
In this research, the PID controllers for frequency load
control have been employed. The parameters and setting values of single and two area generation of hydroelectric power plants like the rated power load of 200
MW, load disturbance of 50 MW, turbine time constant
of 0.5 sec, governor time constant of 0.2 sec, generator
inertia constant of 5 sec, governor speed regulation of
0.05 p.u, power system time constant of 10 sec, and
motor load damping coefficient of 0.6 p.u have been
chosen and employed into Ntaruka and Nyabarongo
Hydroelectric power plants as shown in Figures 2, 3,
5, and 6 in the Northern and Western grids, which
have been controlled at Gikondo National Network
Dispatching and Control. The Northern electricity grid
has been monitored to check whether there were any
cascade blackouts or changing conditions during the
system normal operation. The system condition was
evaluated by computing the frequency load system
using PID controllers. These control schemes have
checked the frequency deviation and drips, demand–
supply power imbalance, and load change to ensure
the reliability and stability of the power system. When
the system was determined to be secure (not vulnerable), the monitoring system has continued in operating
condition. Otherwise, the vulnerable parts and conditions were identified. As the possible unbalanced
frequency and overload problems for those vulnerable conditions have occurred, they were predicted, and
suitable and corresponding control strategies to mitigate and prevent the power blackouts were identified
and activated whenever needed. The models and simulations of the scenarios have been computed using
52
operating point (M. Wadi, 2017). The problem of coordinating protective relays in power system networks
consists of selecting their suitable settings such that
their fundamental protective function is met under the
requirements of sensitivity, selectivity, reliability, and
speed. In a modern power system, abnormal conditions
can frequently occur to cause interruption to the supply, and may damage the equipment connected to the
power system, which allows us to note the importance
of designing a reliable protective system (Mancer N,
2015). The power system is the interconnection of
more than one control areas through tie lines. The
generators in a control area always vary their speed
together (speed up or slow down) for the maintenance
of the frequency and relative power angles to the predefined values in both static and dynamic conditions.
If any sudden load change occurs in a control area
of the interconnected power system then there will be
frequency deviation as well as tie line power deviation (Behera, 2019). The cascade outages that occurred
in Rwanda from 2018 to 2020 mostly proved severe
and very significant. It has been reported that during
the power outages about 5 million people have been
affected in 5 districts from the Northern region and
7 districts from the Western region, and 70 MW of
load were lost, which was about 27% of the total load.
Some other major cascade events began when lightning and overloading caused the tripping of a major
transmission line between the Western and Northern
grids. Research work in these two regions aimed to
predict voltage collapse and voltage overload with a
view to controlling and reducing its occurrence on
power system networks (Weiss R. 2020). Electrical
energy is a primary prerequisite for economic growth.
The demand for electrical energy has greatly increased
due to large-scale industrialization. A modern power
system operates under stressed conditions because of
the growth in demand and the deregulation of electric
power system. This leads to many problems associated with the operation and control of power systems.
The economics of power generation has been a major
concern for the power utilities (P. K. Modi, 2006).
Power systems are becoming heavily stressed due to
the increased loading of the transmission lines and
due to the difficulty of constructing new transmission
systems as well as the difficulty of building new generating plants near the load centers.All of these problems
lead to the voltage stability problem in the power system (Z. Osman, 2006). The effective power system in
Rwanda relies heavily on the ability of engineers to
ensure a continuous and reliable service in cascade
outages. In the ideal case, the load feeding should be
at a constant frequency of 50 Hz and voltage. For reasonable operation of consumer devices, voltage and
frequency should be maintained and secured within
tolerable limits in practical applications. A voltage
decrease from 10% to 15% or a reduction in frequency of system can cause stalling of the device loads
(Tanwani, 2013). The first requirement of this is the
maintenance of parallel operation of the synchronous
generator with the necessary ability to grip the load
condition. Because, if synchronism between the generator and the systems is missing at any time, it will affect
the voltage and current instability and system relays
will disconnect the supply at faulty sections (Naresh
K. Tanwani, 2014). The load frequency control problems are denoted by regulating the active power output
to generate units responding to the disturbances in system frequency and load power interchanges within the
prescribed ranges (Congzhi Huang, 2017). The secure
operation of power systems with the variation of loads
has been a challenge for power system engineers since
the 1920s. (Steinmetz, 1920). The voltage and frequency instability in the short term is driven by fast
recovering load components that tend to restore power
consumption in the time frame of seconds after a voltage drop caused by a contingency. The PID controller
and Automatic Voltage Regulator have been shown to
be more effective for the enhancement and optimization of power system stability with better damping
under small and large disturbances when compared
with conventional excitation control (M. J. Hossain,
2009).
2 MATERIAL AND METHODS
2.1 Balanced state control system
In this research, the PID controllers for frequency load
control have been employed. The parameters and setting values of single and two area generation of hydroelectric power plants like the rated power load of 200
MW, load disturbance of 50 MW, turbine time constant
of 0.5 sec, governor time constant of 0.2 sec, generator
inertia constant of 5 sec, governor speed regulation of
0.05 p.u, power system time constant of 10 sec, and
motor load damping coefficient of 0.6 p.u have been
chosen and employed into Ntaruka and Nyabarongo
Hydroelectric power plants as shown in Figures 2, 3,
5, and 6 in the Northern and Western grids, which
have been controlled at Gikondo National Network
Dispatching and Control. The Northern electricity grid
has been monitored to check whether there were any
cascade blackouts or changing conditions during the
system normal operation. The system condition was
evaluated by computing the frequency load system
using PID controllers. These control schemes have
checked the frequency deviation and drips, demand–
supply power imbalance, and load change to ensure
the reliability and stability of the power system. When
the system was determined to be secure (not vulnerable), the monitoring system has continued in operating
condition. Otherwise, the vulnerable parts and conditions were identified. As the possible unbalanced
frequency and overload problems for those vulnerable conditions have occurred, they were predicted, and
suitable and corresponding control strategies to mitigate and prevent the power blackouts were identified
and activated whenever needed. The models and simulations of the scenarios have been computed using
52