Relay Element Settings 2-7
SEL-300G Instruction Manual Date Code 20020206
Select a curve shape and time-dial that allow this element to coordinate with the system primary
protection.
3.0051CTD
U251CC
=
=
Electromechanical reset emulation should be applied if the system phase overcurrent relays are
induction disk relays; otherwise, electromechanical reset emulation is not necessary.
N51CRS =
By definition, this element should be torque controlled by an undervoltage element. To prevent
misoperation if a potential transformer fuse blows, the element is also torque controlled by the
!60LOP Relay Word bit.
!60LOP27PP51CTC ∗=
To enable and set the phase-to-phase undervoltage element, set
voltsVNOM•0.827PP
YE27
=
=
With the settings above, the 51C element is enabled whenever generator phase-to-phase voltage
is less than 80% of nominal, as long as there is not a simultaneous loss-of-potential condition.
You may wish to use a different undervoltage element pickup setting.
Voltage-Restrained Time-Overcurrent Settings
When using the 51V element, set the 51VP pickup setting greater than the maximum generator
phase current expected under full voltage, nonfault conditions. Divide this current by the phase
current transformer ratio, CTR, to find the element pickup current in secondary amps.
amps
CTR
current loadmax
51VP ≤
Select a curve shape and time-dial that allow this element to coordinate with the system primary
protection.
3.001VTD
U251VC
=
=
Electromechanical reset emulation should be applied if the system phase overcurrent relays are
induction disk relays; otherwise, electromechanical reset emulation is not necessary.
N51VRS =
Because this element reduces its pickup setting automatically as generator voltage decreases, the
element should not be permitted to operate if there is a blown potential transformer fuse
condition. To prevent misoperation if a potential transformer fuse blows, the element is torque
controlled by the !60LOP Relay Word bit.
LOP60!VTC51 =
With the settings above, the 51V element is enabled as long as there is not a loss-of-potential
condition.
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