3.8
SEL-351A Relay Instruction Manual Date Code 20080213
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Instantaneous/Definite-Time Overcurrent Elements
Pickup and Reset Time Curves
See Figure 3.5 and Figure 3.6.
Neutral-Ground
Instantaneous/
Definite-Time
Overcurrent Elements
Four levels of neutral-ground instantaneous/definite-time overcurrent
elements are available. Two additional levels of neutral-ground
instantaneous overcurrent elements (Levels 5 and 6) are also available.
The different levels are enabled with the E50N enable setting, as shown in
Figure 3.8 and Figure 3.9.
NOTE: The definite-time elements
are not supported in the SEL-351A-1.
To understand the operation of Figure 3.8 and Figure 3.9, follow the
explanation given for Figure 3.1, Figure 3.2, and Figure 3.3 in Phase
Instantaneous/Definite-Time Overcurrent Elements on page 3.1,
substituting current I
N
(channel IN current) for phase currents and
substituting like settings and Relay Word bits.
50BC1 = 1 (logical 1), if I
BC
> pickup setting 50PP1P
= 0 (logical 0), if I
BC
≤ pickup setting 50PP1P
50CA1 = 1 (logical 1), if I
CA
> pickup setting 50PP1P
= 0 (logical 0), if I
CA
≤ pickup setting 50PP1P
Courtesy of NationalSwitchgear.com
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