Schweitzer Engineering Laboratories SEL-421-4 - Table 5.15 Voltage and Breaker Pole Correlation; Table 5.16 Frequency Estimation Outputs; Undervoltage Supervision Logic

5.17
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Undervoltage Supervision Logic
The single pole-open Relay Word bits SPOA, SPOB and SPOC control the cor-
relation. During an open-pole condition, the relay assigns a value of zero volts to
the phase associated with the open pole. For example, if the A-Phase of a single
pole breaker (BK1TYP = 1 or BK2TYP = 1) is open, SPOA asserts to indicate
the open-pole condition. When SPOA asserts, the relay substitutes zero volts for
the VF01 and VF11 values. If you selected VF01/VF11 = VAY, then the VF01/
VF11 voltages are set to zero when SPOA asserts. Likewise, if you selected
VF01/VF11 = VBY, then the VF01/VF11 voltages are still set to zero and not
VF02 and VF12. Take care to assign the appropriate phase voltages to match the
correlation shown in Table 5. 15 when using single-pole breakers.
Undervoltage Supervision Logic
Relay Word bit 27B81, the output of the logic shown in Figure 5.13, supervises
the frequency elements for system undervoltage conditions. In the logic, the com-
parator compares the absolute value of the alpha component voltage (Valpha)
against the 81UVSP setting value. Equation 5.1 shows the equation for calculat-
ing Valpha.
Equation 5.1
V F 0 2 L o c a l F r e q . S o u r c e 2 ( Z E RO , VAY, V B Y, V C Y, VA Z , V B Z , V C Z ) V B Y
V F 0 3 L o c a l F r e q . S o u r c e 3 ( Z E RO , VAY, V B Y, V C Y, VA Z , V B Z , V C Z ) V C Y
VF11 Alt. Freq. Source 1 (ZERO, VAY, VBY, VCY, VAZ, VBZ, VCZ) ZERO
VF12 Alt. Freq. Source 2 (ZERO, VAY, VBY, VCY, VAZ, VBZ, VCZ) ZERO
VF13 Alt. Freq. Source 3 (ZERO, VAY, VBY, VCY, VAZ, VBZ, VCZ) ZERO
Table 5.15 Voltage and Breaker Pole Correlation
Relay Word Bit Phase A Phase B Phase C
SPOA = 0 VF01/VF11 – –
SPOA = 10––
SPOB = 0 – VF02/VF12 –
SPOB = 1–0–
SPOC = 0 – – VF03/VF13
SPOC = 1––0
Table 5.16 Frequency Estimation Outputs
Name Description Type
FREQ Measured system frequency (40–65 Hz) Analog Quantity
FREQP Measured frequency (20–80 Hz) Analog Quantity
FREQOK Measured frequency is valid Relay Word bit
FREQFZ Measured frequency is frozen Relay Word bit
Table 5.14 Frequency Estimation (Sheet 2 of 2)
Label Prompt
Default
Value
Valpha VF01
VF02
2
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VF03
2
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