Date Code 20000421 Specifications 2-7
SEL-251, -2, -3 Instruction Manual
FUNCTIONAL SPECIFICATIONS
Note: Overcurrent Elements: Values shown are for 5-amp nominal current input models. (Divide
current values by five for 1-amp nominal current input models.)
Phase Overcurrent Elements for Phase and Three-Phase Faults - See Figure 2.18 and
Figure 2.21
51T Phase Time-Overcurrent Element
• Curve families: moderately inverse, inverse, very inverse, extremely inverse
• Time dial: 0.5 to 15.00 in 0.01 steps
• Pickup (51P): 1 to 12 A ±2% of setting ±0.1 A secondary
• Time delay or 1-cycle reset time
• Timing: ±5% and ±1 cycle for currents between 2 and 20 multiples of pickup
• Internally and externally torque controllable
50LT Phase Definite-Time Overcurrent Element
• Pickup (50L): 0.5 to 100 A ±2% of setting ±0.1 A secondary
• Time delay: 0 to 16,000 cycles in 1-cycle steps
• Internally and externally torque controllable
50H Phase Instantaneous Overcurrent Element
• Pickup: 0.5 to 100 A ±2% of setting ±0.1 A secondary
• Internally and externally torque controllable
50C Phase Instantaneous Overcurrent Element
• Pickup: 0.5 to 100 A ±2% of setting ±0.1 A secondary
• Can be used to override voltage control through TCI setting choice
Negative-Sequence Overcurrent Elements for Phase-to-Phase Faults - See Figure 2.19
51QT Negative-Sequence Time-Overcurrent Element
• Element measures 3 I
2
negative-sequence current
• Curve families: moderately inverse, inverse, very inverse, extremely inverse
• Time dial: 0.5 to 15.00 in 0.01 steps.
• Pickup (51QP): 1 to 12 A ±3% of setting ±0.18 A secondary
• Time delay or 1-cycle reset time
• Timing: ±5% and ±1 cycle for currents between 2 and 20 multiples of pickup
• Externally torque controllable
50QT Negative-Sequence Definite-Time Overcurrent Element
• Element measures 3 I
2
negative-sequence current
• Pickup (50Q): 0.5 to 100 A ±3% of setting ±0.18 A secondary
• Time delay: 0 to 16,000 cycles in 1-cycle steps
• Externally torque controllable
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