Phase Current - GE Multilin G650 Manual

5.4 PROTECTION ELEMENTS
The G650 Phase current menu incorporates the following overcurrent elements:
Phase time overcurrent (51PH/51PL)
Phase instantaneous overcurrent (50PH)
Generator Thermal Model (49S)
5.4.3.1 PHASE TIME DELAYED OVERCURRENT ELEMENTS – PHASE HIGH/LOW (51PH/51PL)
The phase overcurrent element (51P) operates in a time period that depends on the applied current and on the set curve.
The phase current input may be selected as fundamental phasor magnitude or total waveform RMS magnitude as required
by the application. The element reset can be selected between Instantaneous and Linear (timed according to the
corresponding equation).
If the element timing is set as Definite Time, then the TD Multiplier setting will be use to define both the Operation time and,
in case of selecting Linear reset,. the Reset time of the element.
The element incorporates independent block inputs for each phase. When the element is blocked, the tripping time counter
is reset to 0. This feature allows the use of this input to instantaneously reset the protection element timing. The PICKUP
setting of the element can be dynamically reduced by a VOLTAGE RESTRAINT feature. Possible outputs for the protection
element logic are the pickup and tripping signals independent for each phase, and the general element pickup and tripping
signals.
The pickup current magnitude can be dynamically reduced depending on the existing voltage value. This is done using the
Voltage Restraint setting. The pickup current level is proportional to the phase-to-phase voltage measured according to a
5
coefficient shown on Figure 5–4:.This is accomplished via the multipliers (Mvr) corresponding to the phase-phase voltages
of the voltage restraint characteristic curve; the pickup level is calculated as 'Mvr' times the 'Pickup' setting. In the figure,
Vpp is the phase-to-phase voltage, and VT Nominal is the rated voltage set under General settings (please refer to section
5.3.1)
5-40
Figure 5–4: VOLTAGE RESTRAINT CHARACTERISTIC
G650 Generator Protection & Control System
5 SETTINGS

5.4.3 PHASE CURRENT

GEK-113285A