Important Questions of Unsymmetrical Fault:

1. What is a 3-Φ unsymmetrical fault ? Discuss the different types of unsymmetrical faults that can occur on

a 3-Φ system.

2. Discuss the ‘symmetrical components method’ to analyse an unbalanced 3-Φ system.

3. Express unbalanced phase currents in a 3-Φ system in terms of symmetrical components.

4. What do you understand by positive, negative and zero sequence impedances ? Discuss them with reference to synchronous generators, transformers and transmission lines.

5. Derive an expression for fault current for single line-to-ground fault by symmetrical components method.

6. Derive an expression for fault current for line-to-line fault by symmetrical components method.

7. Derive an expression for fault current for double line-to-ground fault by symmetrical components method,

8. What do you understand by sequence networks ? What is their importance in unsymmetrical fault calculations ?

9. Write short notes on the following :

(i) Positive sequence network

(ii) Negative sequence network

(iii) Zero sequence network

10. Why is 3-Φ symmetrical fault more severe than a 3-Φ unsymmetrical fault ?

11. In a 3-Φ system, it has been found that negative sequence components and zero sequence components are What do you conclude from it ?

12. Do the sequence components physically exist in a 3-Φ system ?

13. Why do we prefer to analyse unsymmetrical faults by symmetrical components method ?

14. The positive sequence network of a power system is similar to the negative sequence network. What do you infer from it ?