Schweitzer Engineering Laboratories SEL-351-5, Инструкция по эксплуатации, Страница: 131 / 706

3.51
Date Code 20070117
Instruction Manual SEL-351-5, -6, -7 Relay
Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements
Voltage Sag, Swell, and Interruption Elements (Available in Firmware Version 7)
Voltage Sag, Swell, and Interruption Elements
(Available in Firmware Version 7)
The SEL-351-7 has three types of elements to detect voltage disturbances.
These elements detect voltage sags, swells, and interruptions (abbreviated as
“VSSI” or “SSI”). These elements are enabled by group setting ESSI = Y and
controlled by the VINT, VSWELL, and VSAG settings.
Enter the VSSI element threshold settings VSAG, VSWELL, and VINT in
percentage units, which relate to the Positive-Sequence Reference Voltage:
Vbase. The use of percentage settings instead of absolute voltage limits allows
the SSI elements to perform better in systems that have a range of nominal
voltages, with no need to adjust settings for seasonal loading or to set them far
apart to accommodate the action of a tap-changing transformer. The SSI
elements respond to phase-to-neutral voltages when the relay is wye
connected, and phase-to-phase voltages when the relay is delta connected, as
determined by Global setting PTCONN.
The Positive-Sequence Reference Voltage is discussed in its own subsection.
The Voltage Sag, Swell, Interruption Recorder automatically uses the SSI
elements. These elements are also available as Relay Word bits, so they can be
used in any SEL
OGIC
control equation. See Sag/Swell/Interruption (SSI)
Report (Available in Firmware Version 7) on page 12.34 .
Voltage Sag Elements
As shown in Figure 3.32 , if the magnitude of a voltage drops below the
voltage sag pickup threshold for one cycle, the corresponding SAG Relay
Word bit for that phase (or phase-to-phase pair) asserts (SAGA, SAGB, or
SAGC, wye connected; SAGAB, SAGBC, SAGCA, delta connected). If all
three SAG
p elements assert, an additional Relay Word bit asserts—SAG3P.
The SAG elements remain asserted until the magnitude of the corresponding
voltage rises and remains above the sag dropout threshold for one cycle.
The sag pickup and dropout thresholds depend on Vbase and the VSAG
setting.
Figure 3.32 Voltage Sag Elements
Voltage Swell
Elements
As shown in Figure 3.33 , if the magnitude of a voltage rises above the voltage
swell pickup threshold for one cycle, the corresponding SW Relay Word bit
for that phase (or phase-to-phase pair) asserts (SWA, SWB, or SWC, wye
connected; SWAB, SWBC, SWCA, delta connected). If all three SW
p
elements assert, an additional Relay Word bit asserts—SW3P. The SW
elements remain asserted until the magnitude of the corresponding voltage
drops and remains below the swell dropout threshold for one cycle.
Set
p = A, B, or C (Wye)
or
p = AB, BC, or CA (Delta)
Output
Reset
|Vp|
(Vbase • VSAG) =
Pickup Threshold
(Vbase • [VSAG + 1%]) =
Dropout Threshold
1.00
0.00
Cycles
1.00
0.00
Cycles
ESSI = Y
VSAG
≠
OFF
SAGp
Relay
Word
Bits
Group
Settings