Common transformer faults include winding insulation breakdown, turn-to-turn shorts, bushing flashover, oil degradation, partial discharge, OLTC contact wear, cooling system failure, and core grounding faults. These issues originate from thermal aging, moisture ingress, overvoltage events, mechanical shocks, and contamination. Protection systems detect abnormalities through differential relays, sudden pressure relays, Buchholz relays, and thermal alarms.