A computer-based voltage control experiment for advanced power system operation teaching

International Journal of Electrical Engineering Education, Jul 2001 by Chung, T S

Abstract This paper presents the development of a computer-based electrical power system control experiment for advanced undergraduate students in Electrical Power Engineering. Using the experiment the student is trained in understanding power system voltage performance in operation and the control measures in abnormal conditions. The computer-based experiment method could enhance student appreciation of concepts and offer a cost-effective solution to the problem of expensive conventional hardware experimental setups. Simulation examples with test power systems and discussions of users' feedback are presented to show the effectiveness of the method.

Keywords security analysis; sensitivity matrix; voltage control

In advanced undergraduate teaching of Electrical Power Systems, it is well recognised that hardware laboratory experiments simulating power system control are difficult to implement and perform Hence there is a real need to develop computer-based models to assist power system teaching in this area. In this context, a PC-based model in power system voltage control is developed.

In power system operation, voltage control may be achieved by injecting reactive power into the system. The controllers adjust both generation and flow of reactive power. In this way, an appropriate node voltage profile can be obtained. The following control measures are commonly used to adjust reactive power and bus voltage of the power system:1,2

1 Synchronous condenser and capacitor compensation

2 Transformer tap change

3 Change of the generator terminal voltages

4 Load shedding

Methodology

The methodology of the voltage control effects is based on the application of sensitivity technique to power system control. Sensitively technique is widely used to analyse linear systems. It represents the relationship between the control actions and their effects. As the power system is actually a non-linear system, the sensitivity factor between a reactive control measure and the bus voltages cannot be a constant value over a large range. However, the first-order sensitivity function may be used for small incremental changes. This implies that the sensitivity technique can be used to analyse the reactive power and voltage control problem. For an N bus power system with M control measures, the relationship between the bus voltages and the control measures can be represented as shown in Fig. 1.

Theoretical analysis and mathematical justification may be found in Refs 3 and 4.

Conclusion

This paper presents a power system voltage control computer-based experiment to supplement the teaching of advanced power systems subjects. The experiment allows learners to visualise the results of contingency analysis and the possible remedial action. The programme provides a better understanding of voltage control and remedial action in power system operation without the need to perform hardware experiments which are time consuming and expensive to set up. Simulation studies with sample power systems show the effectiveness of the model. Feedback surveys from students and teaching staff also support the method positively.

References

I David Tzouh-Wei Sun and Raymond R. Shoults, 'A preventive strategy method for voltage and reactive power dispatch', IEEE Trans. PAS, 104 (1985), 1670-1676.

2 G. Huang, `Reactive and real power control for computationally effective voltage and thermal management', IEEE Trans. PAS, 104 (1985), 1728-1738.

3 R. Mota-Palomino and V. H. Quintana, `Sparse reactive power scheduling by a penalty function-linear programming technique', IEEE PWRS-1 (1986), 31-39.

4 C. C. Liu and K. Tomsovic, `An expert system assisting decision-making of reactive power/ voltage control', IEEE PWRS-1, 3 (1986), 195-201.

5 K. R. C. Mamandur, `Emergency Adjustment to Var. Control Variables to Alleviate Overvoltages, Under-voltages, and Generator Var. Limit Violations', IEEE Trans. PAS, 101 (1982).

T. S. Chung

Department of Electrical Engineering, The Hong Kong Polytechnic University, Hong Kong E-mail: eetschun@polyu.edu.hk