3.3
Date Code 20080213 Instruction Manual SEL-351A Relay
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Instantaneous/Definite-Time Overcurrent Elements
Pickup Operation
The phase instantaneous/definite-time overcurrent element logic begins with
Figure 3.1 and Figure 3.2. The pickup settings for each level (50P1P–50P6P)
are compared to the magnitudes of the individual phase currents I
A
, I
B
, and I
C
.
The logic outputs in Figure 3.1 and Figure 3.2 are Relay Word bits and
operate as follows (Level 1 example shown):
Note that single-phase overcurrent elements are not available in Levels 5 and 6
(see Figure 3.2).
Ideally, set 50P1P > 50P2P > 50P3P > 50P4P so that instantaneous
overcurrent elements 50P1–50P4 will display in an organized fashion in event
reports (see Figure 3.3 and Table 12.3).
50A1 = 1 (logical 1), if I
A
> pickup setting 50P1P
= 0 (logical 0), if I
A
≤ pickup setting 50P1P
50B1 = 1 (logical 1), if I
B
> pickup setting 50P1P
= 0 (logical 0), if I
B
≤ pickup setting 50P1P
50C1 = 1 (logical 1), if I
C
> pickup setting 50P1P
= 0 (logical 0), if I
C
≤ pickup setting 50P1P
50P1 = 1 (logical 1), if at least one of the Relay Word bits 50A1,
50B1, or 50C1 is asserted (e.g., 50B1 = 1)
= 0 (logical 0), if all three Relay Word bits 50A1, 50B1, and
50C1 are deasserted (50A1 = 0, 50B1 = 0, and 50C1 = 0)
Courtesy of NationalSwitchgear.com
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