4.3
Date Code 20080213 Instruction Manual SEL-351A Relay
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Loss-of-Potential Logic (Not in the SEL-351A-1)
Setting ELOP = Y
Additionally, if setting ELOP = Y and a loss-of-potential condition occurs
(Relay Word bit LOP asserts to logical 1), overcurrent elements set direction
forward (see Note 2) are enabled (see Figure 4.15, Figure 4.16, and
Figure 4.22). These direction forward overcurrent elements effectively
become nondirectional and provide overcurrent protection during a loss-of-
potential condition.
As detailed previously, voltage-based directional elements are disabled during
a loss-of-potential condition. Thus, the overcurrent elements controlled by
these voltage-based directional elements are also disabled. However, this
disable condition is overridden for the overcurrent elements set direction
forward if setting ELOP = Y.
NOTE 2: When global setting VSCONN = 3V0, the various ground-
directional elements that rely on zero-sequence voltage quantities (ORDER
settings V, S, P, and U) are not affected by a loss-of-potential condition on
relay inputs VA, VB, and VC, because these elements use the 3V
0
zero-sequence
voltage that comes directly from voltage input VS, rather than the zero-
sequence voltage calculated from voltage inputs VA, VB, and VC (wye-
connected PTs). This difference is shown in Figure 4.15 and Figure 4.16,
where Relay Word bit 3V0 is combined with Relay Word bits 32NE and 32VE
to create a block signal for the loss-of-potential signal. When LOP is asserted
and setting ELOP = Y1, the relay will not force an enable of the ground
elements that are set direction-forward when Relay Word bit 3V0 is asserted
(= logical 1) and one of the zero-sequence voltage-polarized ground
directional element enables (32VE or 32NE) is asserted. Refer to Settings for
Voltage Input Configuration on page 9.36.
Setting ELOP = N
If setting ELOP = N, the loss-of-potential logic still operates (Relay Word bit
LOP asserts to logical 1 for a loss-of-potential condition) but does not disable
any voltage-based directional elements (as occurs with ELOP = Y or Y1) or
enable overcurrent elements set direction forward (as occurs with ELOP = Y).
Courtesy of NationalSwitchgear.com
To Next Page
Loading...