Power System Compensation Using Passive Compensators and Facts Controllers
Chapter One
Objective of the thesis
The study is aimed at using passive compensators and FACTS controllers to achieve
power system compensation.
The specific objectives of the study are:
· To obtain the load flow of the Northern Nigerian 330kV transmission grid
· To determine the voltage magnitudes at the various buses
· To identify the voltage violations
· To apply the passive compensators and FACTS controllers at the worst case scenarios of voltage violations and comparing the effects of the compensators.
CHAPTER TWO
LITERATURE REVIEW
The electric power generation-transmission-distribution in developing countries constitutes a large system that exhibits a range of dynamic phenomena [2]. Stabilities of these systems need to be maintained even when subjected to low probability disturbances so that the electricity can be supplied to consumers with high reliability. In the recent time, power demand has increased substantially while the expansion of power generation and transmission has been severely limited. Various controllers such as High voltage dc transmission, static var compensator, have
been developed over time to control the dynamic characteristics of power systems. Many of the controllers are on-off switches (circuit breakers) that can isolate short-circuited or malfunctioning equipment, or shed load or generation. Others are discrete controllers like tap changers in transformers or switching of capacitor/reactor banks. Still others are continuous Control like voltage controllers and power system stabilizers in rotating generators or the newer
Power electronic controls in FACTS devices (Flexible AC Transmission Systems refers to modern electronic devices like High Voltage DC Transmission or Static VAR Controllers that can control power flows or voltage). However, these controllers are local in that, their input and their control variables are in the same local substation [3].
Transmission System Compensation
It is of paramount importance to transmit as much power as possible through transmission lines and cables consistent with the requirement of stability and security of supply. Power transmission is limited mainly by thermal factors in cables, transformer, generator and short transmission lines, but in long lines and cables the variation of voltage and the maintenance of stability are constraints to power transmission [4]. The voltage profile and the stability of transmission lines and cables can be enhanced using reactive compensation. In the early days it
took the value of fixed value reactors and capacitors which are usually controlled by mechanical switchgear. Nowadays, power electronics equipment have been developed and applied to extend the range of the control with the variety of the methods and products. This is what brought about the FACTS concepts [5]. The FACTs devices are able to provide active and reactive power to the power grid rapidly. The power compensation achieved by FACTs devices could adjust the voltage of the whole system and the power flow could be satisfactorily controlled. Generally,
the FACTs devices and technology could be categorized as shown in the figure 2.1 below.
CHAPTER THREE
METHODOLOGY
The line data, generator data and the load data of the Northern Nigerian 330kV transmission grid were modeled in Power Systems Analysis Tool (PSAT) box environment.
Then Newton-Raphson A.C load flow was used to run the load flow and the voltage magnitudes are identified. The bus with low voltage violation is implemented with passive compensator and Unified Power Flow Controller after which comparison being made between them. The simulation was done with Newton- Raphson load flow owing to its accuracy and fast convergence. However, the results were found to be promising. The minimum and the maximum
voltage are set to 0.90pu and 1.1pu respectively. Moreover, UPFC is used in the work and its choice is due to its advantages over all other FACTS devices. The flow chart for the methodology is shown in fig3.1.
CHAPTER FOUR
SIMULATION AND RESULTS
The simulation was carried out by typing in the MATLAB command window “psat ” . After a splash window, the “Main GUI” appeared in our screen. We opened a data file to launch PSAT simulink model library to set up the one line diagram of Northern Nigerian 330Kv transmission grid. We clicked on the setting to set our frequency to 50Hz and power base to 100MVA. Thereafter, we loaded the system and carried out power flow. Sequel to carrying out the power flow analysis, Newton Raphson was selected on the option box. Moreover, the load flow study
for the network under consideration (Northern Nigerian 330kv line) was done with the NewtonRaphson method owing to its quick convergence. In addition, it converged after 0.34 seconds with 5 P and Q iterations. The data for the simulation was obtained from Table3.1 and 3.2 and was prepared using power systems tool box (PSAT). The load flow study was carried out to obtain the voltage magnitudes taking into assumption that voltage magnitudes should range between 0.90pu and 1.10pu in the simulations. And a bus whose voltage magnitude falls out of
the range suffers from voltage violation and is considered a critical case for power system compensation. The network model with static capacitor and UPFC are shown in figure 4.1 and
figure 4.2 respectively.
CHAPTER FIVE
CONCLUSION
Considering the rate of convergence of Newton Raphson method and the accuracy of its analysis, it can be opined that it has proven to be excellent in the load flow analysis of the 21-bus of the Northern Nigerian 330kV transmission grid. The load flow studies identified buses with low voltages as thus: Birnin-Kebbi (0.6245pu), Katampe (0.7237pu), Kaduna (0.6950pu), Kano (0.5713pu), Yola (0.8457pu), Gwagwalada (0.7013pu), Lokoja (0.8516pu), Ajaokuta (0.8045pu), Geregu (0.8854pu). The simulation of the network with passive compensator and FACTS controller substantially improved the voltages at Birnin-Kebbi (0.9531pu), Kano (0.9524pu), and Gwagwalada (0.9846pu) but FACTS controller proved to be more effective in the voltage enhancement from the following result Birnin-Kebbi (0.9531) , Kano (0.9524), and Gwagwalada (0.9846 ).
Suggestion for further study
We suggest that further study should look at the following:
· Minimization of the real power loss
· Optimal placement of the compensating devices at the affected transmission lines with losses
· Application of artificial intelligence to the power system network
· Cost implication of using the two types of the compensating devices
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