Relay Element Settings
2-61
SEL-300G Instruction Manual
Date Code 20060731
performance. Use the voltage-restrained element if your protection standards or preferences
require it.
Voltage-Controlled Time-Overcurrent Settings
Set the 51CP pickup setting less than the generator fault duty, calculated using the generator
steady-state reactance,
d
X (transient reactance
d
X
′
may be used if the generator excitation
system is able to support higher fault voltage and current). This value may safely be below
maximum load, as the element is only enabled during low-voltage fault conditions. Divide the
generator fault duty by the phase current transformer ratio, CTR, to find the element pickup
current in secondary amps.
CTR
IP
CP
51
≤
Select a curve shape and time-dial that allow this element to coordinate with the system primary
protection.
3.00
51CTD
U2
51CC
=
=
Electromechanical reset emulation should be applied if the system phase overcurrent relays are
induction disk relays; otherwise, electromechanical reset emulation is not necessary.
N
51CRS
=
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.
!60LOP
27PP1
51CTC
∗
=
To enable and set the phase-to-phase undervoltage element, set
volts
VNOM
•
0.8
27PP1
Y
E27
=
=
With the settings above, the 51C element is enabled whenever generator phase-to-phase voltage
is less than 80 percent 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
load
max
51VP
>
Summary of Contents for SEL-300G
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