Schweitzer Engineering Laboratories SEL-351A, Manual, Page: 106 / 666

3.34
SEL-351A Relay Instruction Manual
Date Code 20080213
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Voltage Elements
Figure 3.26 Channel VS Voltage Elements (Wye- or Delta-Connected PTs)
Accuracy
Steady-State Pickup Accuracy:
±2 V and ±2% of setting (phase and synchronizing elements)
±2 V and ±4% of setting (negative-, positive-, and zero-sequence
elements, phase-to-phase elements)
Transient Overreach:
±5% of pickup
Voltage Element
Operation
Note that the voltage elements in Table 3.10 – Table 3.12 and Figure 3.22 –
Figure 3.26 are a combination of “undervoltage” (Device 27) and
“overvoltage” (Device 59) type elements. Undervoltage elements (Device 27)
assert when the operating voltage goes
below the corresponding pickup
setting. Overvoltage elements (Device 59) assert when the operating voltage
goes
above the corresponding pickup setting.
Undervoltage Element Operation Example
Refer to Figure 3.22 (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 3.22 are the following
Relay Word bits:
27S
59S1
59S2
27SP
V
S
59S1P
59S2P
Settings/
Voltages
Relay
Word
Bits
NOTE:
Does not apply to the
SEL-351A-1.
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)
Courtesy of NationalSwitchgear.com