Schweitzer Engineering Laboratories SEL-387E - Curve Shape Settings (51 Pnc, 51 Qnc, 51 Nnc, 51 PC1 C, 51 NC1 C); Electromechanical Reset Settings (51 Pnrs, 51 Qnrs, 51 Nnrs, 51 PC1 RS, 51 NC1 RS); Inverse-Time Element Pickups (51 Pnp, 51 Qnp, 51 Nnp, 51 PC1 P, 51 NC1 P); Time-Dial Settings (51 Pntd, 51 Qntd, 51 Nntd, 51 PC1 TD, 51 NC1 TD)

Date Code 20080110 Protection Functions 3-47
SEL-387E Instruction Manual
Inverse-Time Element Pickups (51PnP, 51QnP, 51NnP, 51PC1P, 51NC1P)
Range:
1 A: OFF, (0.1–3.2), A secondary, in 0.01 A steps
5 A: OFF, (0.5–16), A secondary, in 0.01 A steps
The pickup setting acts as a horizontal scaling factor for an inverse-time curve, because the curve
formula uses current multiple of pickup as an input.
Set pickups, and the following three settings defining the time overcurrent curve, to fit the
practices of your organization, coordinate with upstream and downstream devices such as fuses
and motors, and accommodate transient and fault conditions.
Curve Shape Settings (51PnC, 51QnC, 51NnC, 51PC1C, 51NC1C)
Range:
U1, U2, U3, U4, U5
C1, C2, C3, C4, C5
This setting defines a particular curve equation for an inverse-time curve from among five U.S.
(U1–U5) and five IEC (C1–C5) curves.
Time-Dial Settings (51PnTD, 51QnTD, 51NnTD, 51PC1TD, 51NC1TD)
Range:
US 0.5–15, IEC 0.05–1, in 0.01 steps
The time-dial setting acts to scale an inverse-time curve vertically, to vary the output timing for a
given multiple of pickup.
Electromechanical Reset Settings (51PnRS, 51QnRS, 51NnRS, 51PC1RS, 51NC1RS)
Range:
Y, N
This setting defines whether an inverse-time curve emulates an electromechanical disk and resets
slowly or instantaneously when current drops below pickup. A setting of Y causes the relay to
emulate an electromechanical disk. A setting of N causes full reset of the time-overcurrent
element one cycle after current drops below the element pickup setting.
Torque-Control Settings (50PnmTC, 50QnmTC, 50NnmTC, 51PnTC, 51QnTC, 51NnTC)
Range:
SEL OGIC control equation
Note: n = Winding 1, 2, or 3; m = Level 1, 2, 3, or 4.
The torque-control setting is an enable setting for which you have three options: a setting of
logical 0 disables the associated definite-time element, a logical 1 permits the element to operate,
and SEL
OGIC control equations allow conditional assertion of the element.
Application Guidelines
Transformer Overcurrent Protection
Instantaneous overcurrent elements typically provide high-speed protection for high-current,
internal transformer faults and coordinated backup protection for faults on the adjacent bus and/or