Symmetrical components analyze unbalanced three-phase systems: positive sequence (balanced, normal operation), negative sequence (balanced but reverse rotation, causes motor heating), and zero sequence (in-phase, linked to earth faults).

VTs use electromagnetic induction for voltage measurement, suited for systems up to 132 kV. CVTs combine capacitive division with electromagnetic transformation, offering higher stability and accuracy, ideal for high-voltage applications.

Earth fault protection differs in isolated and resistance-grounded systems: isolated systems use VTs in open-delta to detect voltage displacement (59N relay), enabling fault detection without tripping; resistance-grounded systems allow controlled fault current for reliable relay operation (50N/50G).

Motor protection relays detect electrical, thermal, and mechanical faults using ANSI codes: 49 (thermal overload), 50/51 (phase overcurrent), 50N/51N (earth fault), 46 (unbalance), 47 (phase failure), 48 (locked rotor).