Protection coordination is the proof that the correct device clears each fault within equipment limits while healthy sections remain energised. It requires more than visually separated time-current curves. Learning objectives Build coordination cases, include measurement and breaker delays and document…
Voltage measurement can come from inductive VTs, capacitive or resistive sensors, and low-power instrument transformers. Each technology has different burden, interface, failure and test requirements. Learning objectives Select a measurement technology, design safe secondary circuits and preserve accuracy from primary…
A protection CT must reproduce fault current accurately enough for the relay to make the correct decision during the required time. Ratio and nominal burden alone do not describe transient saturation. Learning objectives Build the CT secondary circuit, calculate burden…
Trip-circuit supervision detects loss of the electrical path needed to open a breaker. It monitors a circuit condition; it does not prove that the mechanism will move or that the breaker can interrupt current. Learning objectives Choose supervision coverage for…
Breaker-failure protection operates when a trip command is issued but the assigned breaker does not clear the current or reach the required open state. It must act fast enough to limit damage yet remain secure for normal breaker clearing. Learning…
Synchronism-check permits closing only when the electrical conditions on both sides of an open breaker are acceptable. It protects equipment from severe current and torque caused by out-of-phase closing. Learning objectives Set voltage, angle and slip limits, define dead/live bus…
Distance protection estimates apparent impedance from measured voltage and current. Because line impedance is broadly proportional to distance, zones can provide fast directional protection with time-graded backup. Learning objectives Set zone reach and delay from line impedance, account for fault…
Differential protection compares currents entering and leaving a defined zone. It is fast and selective for internal faults, but measurement errors, CT saturation and transformer phase shift must be stabilised. Learning objectives Draw the zone, form operate and restraint quantities…
Negative-sequence current creates a magnetic field rotating opposite to the positive-sequence field. In motors and generators this induces double-frequency rotor currents and can produce severe heating at modest phase-current unbalance. Learning objectives Calculate I2, distinguish unbalance causes and apply pickup…
Thermal protection estimates temperature from current and cooling conditions. It is fundamentally different from instantaneous overcurrent because the protected object stores heat and cools over time. Learning objectives Configure thermal capacity, heating and cooling constants, alarm/trip levels and restart inhibition…
