Sel 551 - Overcurrent Elements

1.6
SEL-551 Relay Instruction Manual Date Code 20110408
Introduction and Specifications
Overcurrent Elements
Section 1
Introduction and Specifications
Overcurrent Elements
The OFF setting disables the overcurrent element.
Time-Overcurrent
Element
Specifications
See Section 4: Setting the Relay for complete setting range information.
Instantaneous
Overcurrent Element
Specifications
See Section 4: Setting the Relay for complete setting range information.
Instantaneous
Overcurrent Element
Pickup and Reset
Time Curves
Figure 1.4 and Figure 1.5 show pickup and reset time curves applicable to all
the instantaneous overcurrent elements in the SEL-551 (60 Hz or 50 Hz
relays). These times do not include output contact operating time and, thus,
are accurate for determining element operating time for use in internal
SEL
OGIC control equations. See Output Contacts on page 1.4 for information
on output contact operating times (pickup/dropout time). Output contact
operating time has to be added to the pickup time given in Figure 1.4 to
calculate the overall instantaneous overcurrent element tripping time.
Table 1.1 Overcurrent Elements
Instantaneous Time-Overcurrent
Phase 50P1–50P6 51P1T, 51P2T
Single-Phase 50A, 50B, 50C
Neutral Ground
a
a
The neutral ground overcurrent elements (50N1, 50N2, and 51N1T) operate from the separate
neutral current input channel IN. All other overcurrent elements (including the residual ground
overcurrent elements) operate from the phase current input channels IA, IB, and IC.
50N1, 50N2 51N1T
Residual Ground 50G1, 50G2 51G1T
Negative-Sequence (3I2)
b
b
IMPORTANT: See Appendix F: Setting Negative-Sequence Overcurrent Elements for information
on setting negative-sequence overcurrent elements
50Q1, 50Q2 51Q1T, 51Q2T
Setting Range,
5 A nominal
c
c
The available current channel ratings (5 A or 1 A) for phase (IA, IB, and IC) and neutral (IN) are
specified separately-refer to the ordering information sheets for the SEL-551.
OFF, 0.5–80.0A OFF, 0.5–16.0A
Setting Range,
1 A nominal
c
OFF, 0.1–16.0A OFF, 0.1–3.2A
Pickup Accuracy: ±0.10 A secondary and ±5% of setting
(5 A nominal channel)
±0.02 A secondary and ±5% of setting
(1 A nominal channel)
Curve Timing Accuracy: ±1.5 cycles, and ±2% (I
nom
/I
sec
), and ±4% of curve time for
currents between (and including) 2 and 30 multiples of
pickup
Curves operate on definite-time for currents above 30 multi-
ples of pickup or 16 times nominal current.
Transient overreach: <5% of pickup
Pickup Accuracy: ±0.10 A secondary and ±5% of setting
(5 A nominal channel)
±0.02 A secondary and ±5% of setting
(1 A nominal channel)
Transient overreach: <5% of pickup