Sel 751A - Figure 4.25 Power Factor Elements Logic; Table 4.21 Power Factor Settings

4.45
Date Code 20100129 Instruction Manual SEL-751A Relay
Protection and Logic Functions
Voltage-Based Protection
The power elements are not supervised by any relay elements other than the
minimum voltage check shown in Figure 4.23. If the protection application
requires overcurrent protection in addition to the power elements, there may
be a race condition, during a fault, between the overcurrent element(s) and the
power element(s) if the power element(s) are still receiving sufficient
operating quantities. Use the power element time delay setting to avoid such
race conditions.
Power Factor
Elements
If the measured power factor falls below the leading or lagging level for longer
than the time-delay setting, the relay can issue a warning or trip signal. The
power factor elements are enabled 55DLY seconds after Relay Word 52A is
asserted (breaker closed), however when 55DLY := 0 the element is always
enabled irrespective of the 52A status. Figure 4.25 shows the logic diagram
for the power factor elements. These elements can be used to detect
synchronous motor out-of-step or loss-of-field conditions. Refer to Figure 5.1
for the relay power measurement convention.
Figure 4.25 Power Factor Elements Logic
Table 4.21 Power Factor Settings
Setting Prompt Setting Range
Setting Name :=
Factory Defau lt
PF LAG TRIP LEVL OFF, 0.05–0.99 55LGTP := OFF
PF LD TRIP LEVEL OFF, 0.05–0.99 55LDTP := OFF
PF TRIP DELAY 1–240 sec 55TD := 1
PF LAG WARN LEVL OFF, 0.05–0.99 55LGAP := OFF
PF LD WARN LEVEL OFF, 0.05–0.99 55LDAP := OFF
PF WARN DELAY 1–240 sec 55AD := 1
PF ARMING DELAY 0–5000 55DLY := 0
Measured
Power Factor
52A
PF Leading
55LDAP
55LGAP
55A
0
55AD
Relay
Word
Bits
Relay
Word
Bit
Settings
55LDTP
55LGTP
55T
0
55TD
0
55DLY