Schweitzer Engineering Laboratories SEL-300G - Protection Element Selection Guidelines

Relay Element Settings 2-5
SEL-300G Instruction Manual Date Code 20020206
PROTECTION ELEMENT SELECTION GUIDELINES
The SEL-300G Relay provides protection elements suitable for applications protecting many
different generators. Use Table 2.1 to help select the protection elements to enable for specific
applications.
Table 2.1: Recommended Protection Elements by Generator Grounding Method
Element/Function
High-
Impedance
Grounded
Resistance
Grounded
Solidly
Grounded
21 Backup Mho Phase Distance
Element
Available
3
Available
3
Available
3
24 Volts/Hertz Element Recommended Recommended Recommended
27 Undervoltage Optional Optional Optional
32 Reverse/Low-Forward Power Recommended Recommended Recommended
40 Loss-of-Field Recommended Recommended Recommended
46 Negative-Sequence Overcurrent Recommended Recommended Recommended
50N/51N Neutral Overcurrent Suggested
1
Suggested
1
Recommended
50P Phase Overcurrent
Not
Recommended
Not
Recommended Recommended
51C/51V Voltage-
Controlled/Voltage-Restrained Time-
Overcurrent
Available
3
Available
3
Available
3
59 Overvoltage Optional Optional Optional
64G 100% Stator Ground Elements Recommended Suggested
2
Not
Recommended
78 Out-of-Step Recommended Recommended Recommended
81 Over-/Underfrequency Elements Recommended Recommended Recommended
81 AC Abnormal Frequency Scheme Available Available Available
87 Current Differential Elements
(Available with Models 0300G1 and 0300G3)
Suggested for
large machines
Optional Optional
87N Ground Differential Element
(Available with Models 0300G0 and 0300G2)
Not
Recommended
Suggested
1
Suggested
1
1
If neutral CT is available.
2
If neutral PT is available.
3
Select no more than one of 21, 51C, or 51V elements for backup protection.