Schweitzer Engineering Laboratories SEL-351 - Overvoltage Element Operation Example; Undervoltage Element Operation Example; Voltage Elements Used in POTT Logic

Date Code 20001006 Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements 3-37
SEL-351 Instruction Manual
Undervoltage Element Operation Example
Refer to Figure 3.21 (top of the figure).
Pickup setting 27P1P is compared to the magnitudes of the individual phase voltages V
A
, V
B
, and
V
C
. The logic outputs in Figure 3.21 are the following Relay Word bits:
27A1 = 1 (logical 1), if V
A
< pickup setting 27P1P
= 0 (logical 0), if V
A
≥ pickup setting 27P1P
27B1 = 1 (logical 1), if V
B
< pickup setting 27P1P
= 0 (logical 0), if V
B
≥ pickup setting 27P1P
27C1 = 1 (logical 1), if V
C
< pickup setting 27P1P
= 0 (logical 0), if V
C
≥ pickup setting 27P1P
3P27 = 1 (logical 1), if all three Relay Word bits 27A1, 27B1, and 27C1 are asserted
(27A1 = 1, 27B1 = 1, and 27C1 = 1)
= 0 (logical 0), if at least one of the Relay Word bits 27A1, 27B1, or 27C1 is
deasserted (e.g., 27A1 = 0)
Overvoltage Element Operation Example
Refer to Figure 3.21 (bottom of the figure).
Pickup setting 59P1P is compared to the magnitudes of the individual phase voltages V
A
, V
B
, and
V
C
. The logic outputs in Figure 3.21 are the following Relay Word bits:
59A1 = 1 (logical 1), if V
A
> pickup setting 59P1P
= 0 (logical 0), if V
A
ó pickup setting 59P1P
59B1 = 1 (logical 1), if V
B
> pickup setting 59P1P
= 0 (logical 0), if V
B
ó pickup setting 59P1P
59C1 = 1 (logical 1), if V
C
> pickup setting 59P1P
= 0 (logical 0), if V
C
ó pickup setting 59P1P
3P59 = 1 (logical 1), if all three Relay Word bits 59A1, 59B1, and 59C1 are asserted
(59A1 = 1, 59B1 = 1, and 59C1 = 1)
= 0 (logical 0), if at least one of the Relay Word bits 59A1, 59B1, or 59C1 is
deasserted (e.g., 59A1 = 0)
Voltage Elements Used in POTT Logic
Refer to Figure 3.21 and Figure 3.22 for wye-connected voltage inputs. Note that voltage elements
27A1, 27B1, 27C1, and 59N1 are also used in the weak-infeed portion of the POTT logic, if the
weak-infeed logic is enabled (see Figure 5.6).
Refer to Figure 3.23 and Figure 3.24 for delta-connected voltage inputs. Note that voltage
elements 27AB1, 27BC1, 27CA1, and 59Q1 are also used in the weak-infeed portion of the POTT
logic, if the weak-infeed logic is enabled (see Figure 5.6).
Courtesy of NationalSwitchgear.com