Relay Element Settings 2-45
SEL-300G Instruction Manual Date Code 20020206
Relay Word Bit Function Description Typical Applications
51G
Residual Time-Overcurrent Pickup Indication, Event Triggering,
SER Triggering, Testing
51GT
Residual Time-Overcurrent trip Tripping, SER Triggering
51GR
Residual Time-Overcurrent reset Testing
Neutral Overcurrent Setting Calculation
Information Needed
• Generator terminal ground fault current, In, A primary
• Generator grounding transformer ratio to 1 (in high-impedance grounded protection
applications)
• Neutral CT transformer ratio to 1
Recommendations
In all applications where a neutral current transformer is connected between the generator neutral
point and ground or in the secondary of the generator grounding transformer, you can apply the
neutral overcurrent elements 51N and 50N1 for stator ground fault detection.
Warning: Generator neutral overcurrent protection cannot detect stator winding faults at or near
the generator neutral point, nor is it effective while the generator grounding circuit is opened. In
resistance and high-impedance grounded generator applications, use this relay’s 100% stator
ground protection to ensure that all stator winding faults are detected.
Set the 51NP equal to or just greater than the element minimum pickup setting.
Α 0.551NP =
An inverse curve shape (U2) and time-dial of 3.0 provide 6.5 second tripping for 1.0 A secondary
faults.
3.051NTD
U251NC
=
=
Electromechanical reset emulation is not necessary and this element may be in service
continuously so the torque-control setting is logical 1.
151NTC
N51RS
=
=
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