Electrical Power Systems

250 Electrical Power Systems
Unbalanced ault Analysis
10.1 INTRODUCTION
10
Chapters 8 and 9 were devoted to the treatment of symmetrical faults and symmetrical
components in a power system. In the case of symmetrical faults analysis, system remains
balanced during such faults and the analysis could conveniently be carried out on a single phase
basis. In the present chapter, we shall deal with unbalanced (unsymmetrical) faults, Different
types of unbalanced faults that occur in a power systems are: (a) Shunt Type aults (b) Series
Type aults.
Shunt aults are of three types:
1. Single Line to Ground (L–G) fault.
2. Line to Line (L–L) fault.
3. Double Line to Ground ( L–L–G) fault.
Example of series type fault is open conductor fault.
Unbalanced fault analysis is very important for relay setting, single-phase switch and system
stability studies. The method of symmetrical components explained in Chapter–9 is powerful
tool for the study of unbalanced faults–and will be applied in this chapter.
10.2 SINGLE LINE TO GROUND AULT
igure 10.1 shows a three phase generator with neutral grounded through impedance Z n.
ig. 10.1: L–G fault on phase a.