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| GE Multilin Relay |
The main protection functions are listed below with a brief definition. They are listed in numerical order by ANSI Standard Device Numbers, ANSI/IEEE C37.2-2008.
ANSI code – Name of function – Definition
12 – Overspeed – Detection of rotating machine overspeed.
14 – Underspeed – Detection of rotating machine underspeed.
21 – Distance Protection – Impedance measurement detection.
21B – Underimpedance – Back-up phase-to-phase short-circuit protection for generators.
24 – Flux Control – Overfluxing check.
25 – Syncho-check – Check before paralleling two parts of the power system.
26 – Thermostat – Protection against overloads.
27 – Undervoltage – Protection for control of voltage sags.
27D – Positive sequence undervoltage – Protection of motor against operation with insufficient voltage.
27R – Remanent undervoltage – Check the disappearance of voltage sustained by rotating machines after the power supply is disconnected.
27TN – Third harmonic voltage – Detection of stator winding insulation earth faults (impedant neutral).
32P - Directional active overpower - Protection against active overpower transfer.
32Q - Directional reactive overpower - Protection against reactive overpower transfer.
37 – Phase undercurrent – 3 phase protection against undercurrent.
37P – Directional active underpower - Protection against active underpower transfer.
37Q - Directional reactive underpower - Protection against reactive underpower transfer.
38 - Bearing temperature monitoring – Protection against overheating of rotating machine bearings.
40 - Field Loss – Protection of synchronous machines against faults or field loss.
46 - Negative sequence / unbalance – Protection against unbalanced phase current.
47 - Negative sequence overvoltage – Negative sequence voltage protection and detection of reverse rotation of rotating machines.
48 - Excessive starting time and locked rotor – Protection of motors against starting with overloads or reduced voltage, and for loads that can block.
49 - Thermal overload – Protection against overloads.
49T - RTDs – Protection against overheating of machine windings.
50 - Instantaneous phase overcurrent – 3 phase protection against short circuits.
50BF – Breaker failure – Checking and protection if the circuit breaker fails to trip after a tripping order.
50G – Instantaneous earth fault – Protection against earth faults (residual current measured directly by a single sensor. By CT or core balance CT).
50N - Instantaneous earth fault – Protection against earth faults (residual current calculated or measured by 3 CT’s).
50V - Instantaneous voltage-restrained phase overvoltage – 3 phase protection against short circuit with voltage dependent threshold.
50/27 – Inadvertent generator energization – Detection of inadvertent generator enegization.
51 - Delayed phase overcurrent – 3 phase protection against overloads and short circuits.
51G - Delayed earth fault – Protection against earth faults (residual current measured directly by a single sensor. By CT or core balance CT).
51N – Delayed earth fault - Protection against earth faults (residual current calculated or measured by 3 CT’s).
51V - Delayed voltage-restrained phase overcurrent - 3 phase protection against short circuit with voltage dependent threshold.
59 - Overvoltage – Protection against excessive voltage or sufficient voltage detection.
59N – Neutral voltage replacement – Insulation fault protection.
63 - Pressure – Detection of transformer internal faults (gas, pressure).
64REF – Restricted earth fault differential – Earth fault protection for star connected 3 phase windings with earth neutral.
64G - 100% generator stator earth fault – Detection of stator winding insulation earth faults (impedant neutral power systems).
66 - Successive starts – Protection function that monitors the number of motor starts.
67 - Directional phase overcurrent – 3 phase short circuit protection according to current flow direction.
67N – Directional earth fault – Earth fault protection depending on current flow direction
67NC - Directional earth fault – Earth fault protection depending on current flow direction (Neutral compensated).
78 - Vector shift – Vector shift disconnection protection.
78PS – Pole slip – Detection of loss of synchronization of synchronous machines.
79 - Recloser – Automated device that recloses the circuit breaker after transient line fault tripping.
81H – Overfrequency – Protection against abnormally high frequency.
81L – Underfrequency – Protection against abnormally low frequency.
81R - Rate of change of frequency (ROCOF) – Protection for fast disconnection of two parts of the power system.
87B - Busbar differential – 3 phase protection against busbar internal faults.
87G - Generator differential – 3 phase protection against internal faults in AC generators.
87L - Line differential – 3 phase protection against line internal faults.
87M – Motor differential - 3 phase protection against internal faults in motors.
87T – Transformer differential – 3 phase protection against internal faults in transformers.
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