Voltage distribution over a string of suspension insulators, I-t fuse characteristic. Measurement of symmetrical components in unbalanced systems; negative and zero sequence filters. Power and voltage relations at the ends of short and medium transmission lines. Grounding of power system neutrals: solid, resistive and inductive grounding. Characteristics of instantaneous overcurrent and under-voltage relays. Comparison of the characteristics of static, electromechanical, and numerical relays. Overcurrent time lag relays. O/C directional overcurrent relays. Differential protection schemes.