Sel 551 - Page 51

3.13
Date Code 20110408 Instruction Manual SEL-551 Relay
Relay Elements and Logic
Time-Overcurrent Elements
The following is an example of 51P1T element operation; the other time-
overcurrent elements operate similarly:
Torque Control Setting
SELOGIC control equations setting 51P1TC (torque control for phase time-
overcurrent element 51P1T) controls the input of current I
P
into the pickup
comparator and the curve timing/reset timing function.
If 51P1TC = logical 1 and I
P
> pickup setting 51P1P, then:
Relay Word bit 51P1 (pickup indication) = logical 1
and
curve timing takes place if element 51P1T is not already timed-out.
If 51P1TC = logical 1 and I
P
≤ pickup setting 51P1P, then:
Relay Word bit 51P1 (pickup indication) = logical 0
and
reset timing takes place if element 51P1T is not already reset.
If 51P1TC = logical 0, then:
Relay Word bit 51P1 (pickup indication) = logical 0 at all times.
Also, no current I
P
goes into the curve timing/reset timing function—no
curve timing takes place [effectively, the magnitude of I
P
as seen by the
curve timing/reset timing function is zero (0), and reset timing takes place
if the element is not already reset].
Example Torque Control Settings
Note in SHO Command (Showset) on page 5.16 that the factory settings for
51P1TC and the other time-overcurrent element torque control settings are set
equal to 1:
51P1TC = 1
Thus, the time-overcurrent elements are enabled all the time, and they behave
as detailed previously for 51P1TC = logical 1.
Other Torque Control Setting Ideas
51P1TC = IN1 apply nominal control voltage to optoisolated input IN1,
resulting in 51P1TC = logical 1; remove nominal control voltage to
optoisolated input IN1, resulting in 51P1TC = logical 0
51P1TC = LB2 assert local bit LB2 via the front-panel pushbuttons/display,
resulting in 51P1TC = logical 1; deassert local bit LB2 via the front-
panel pushbuttons/display, resulting in 51P1TC = logical 0
Many other torque control setting ideas are available with the flexibility of
SEL
OGIC control equations.
NOTE: Torque control equation
settings cannot be set directly to
logical 0.