GE 845 Instruction Manual page 21

CHAPTER 1: INTRODUCTION
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
GROUND DIRECTIONAL OVERCURRENT (67G)
Directionality:........................................................Co-existing forward and reverse
Polarizing: ...............................................................Voltage, Current, Dual
Polarizing Voltage:..............................................V_0 or VX
Polarizing Current: ..............................................Isg
Operating Current: .............................................Ig
Level Sensing: .......................................................Ig, Isg
Characteristic Angle:.........................................-90º to 90º in steps of 1°
Limit Angle: ............................................................40º to 90º in steps of 1°, independent for forward and
Angle Accuracy:...................................................±2º
Pickup Level:..........................................................0.050 to 30.000 x CT in steps of 0.001
Dropout Level: ......................................................97 to 98%
Operate Time (no direction transition):.....< 12 ms typical at 3 x Pickup at 60 Hz
RESTRICTED GROUND (EARTH) FAULT (87G)
Operating Parameter:.......................................Ia, Ib, Ic and Ig (Fundamental Phasor Magnitude)
Pickup Level:..........................................................0.050 to 30.000 x CT in steps of 0.001 x CT (phase CT)
Ground Supervision Level:..............................0.050 to 30.000 x CT in steps of 0.001 x CT (ground CT)
Dropout Level: ......................................................97 to 98% of Pickup
Slope Range: .........................................................0 to 100% in steps of 1%
Pickup Delay:.........................................................0.000 to 6000.000 s in steps of 0.001 s
Level Accuracy:....................................................For 0.1 to 2.0 x CT: ±0.5% of reading or ±0.4% of rated,
Operate Time:.......................................................<25 ms at 1.1 x slope x Imax at 60 Hz, typically
Timing Accuracy: ................................................±3% of delay setting or ± ¼ cycle (whichever is greater) from
reverse
< 15 ms typical at 3 x Pickup at 50 Hz
whichever is greater
For > 2.0 x CT: ± 1.5% of reading
<30 ms at 1.1 x slope x Imax at 50 Hz, typically
pickup to operate
SPECIFICATIONS
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