**5. Conclusion**

158 Electrical Generation and Distribution Systems and Power Quality Disturbances

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Load X/R

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Load X/R

As the X/R ratio of the line increases the index accuracy did not decrease homogeneously. Between the values of 0.3 and 0.5 for load X/R an area of decreased inaccuracy can be observed. This is due to the scaling factor setting being 1.6 for the entire range of line X/R ratios investigated. The accuracy of the index is within acceptable margins as the largest deviation is within 2.5% (Polycarpou & Nouri, 2009). The index is within acceptable

Comparing Figure 11 to Figure 13, it is concluded that as the X/R ratio of the line increases, any load increment has more severe impact on the receiving end voltage due to the impedance magnitude of the line. The CVI deviation corresponding to this investigation

M5

M1

M2

M3

M4 M5

M4 M3

M2

M1

0.8 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 1

case can be seen in Figure 14.

0

0.005

0.01

0.015

CVI Dev

accuracy limits.

0.02

0.025

0.03

Fig. 13. Ur for load X/R variation whilst line X/R=1

Fig. 14. CVI deviation for load X/R variation whilst line X/R=1

Ur(pu)

The first part of this chapter presents various statistical voltage sag indices proposed by electrical association organisations and indices suggested by recent researchers. These indices are used to characterise any voltage sag, according to the individual index point of view. The procedure to evaluate the quality of supply, reference to non-rectangular events and equipment compatibility issues are also presented. To demonstrate the theory of equipment compatibility, with the use of System Average RMS Variation Frequency Index, various power acceptability curves were used.

Furthermore the formulation defining a set of Mathematical voltage sag indices, leading to the Combined Voltage Index, is presented. Various motor power factors and loading levels are used in order to establish the behavior of the index for a wide range of loads. Mathematical description of voltage angle characteristics, relating to line X/R ratio variation is also illustrated. A relationship is established between the slope of ζ and the range of accuracy for each solution of the quadratic index. The CVI has proven to be easy to assess, accurate and representative of the disturbance it characterizes at distribution level. If better accuracy is required for distribution system applications, the scaling factor can be varied to achieve it. The described CVI index can be used in conjunction with optimization techniques for power quality improvement as well as power system operation optimization. The index is adaptable to incorporate future changes in technology and system parameters. This enables its implementation into the next generation of power system planning software.
