Schweitzer Engineering Laboratories SEL-300G - Setting Calculation; Information Needed; Loss-Of-Field Protection Using a Negative Offset Zone 2; Recommendations

2-32 Relay Element Settings
Date Code 20020206 SEL-300G Instruction Manual
Setting Calculation
Information Needed
• Generator direct axis reactance, Xd, in secondary ohms
• Generator transient reactance, Xd', in secondary ohms
• Generator rated line-to-line voltage, in secondary volts (VNOM setting)
• Generator rated phase current, in secondary amps (INOM setting)
• When a positive Zone 2 offset is desired, you also need:
• Step-up transformer reactance, XT, in secondary ohms
• Generator rated power factor
Recommendations
Unless there is a requirement to match existing loss-of-field protection that uses a positive offset
Zone 2 element, use the negative offset setting recommendations below. Recommendations for
both setting methods are provided.
Loss-of-Field Protection Using a Negative Offset Zone 2
When setting Zone 2 with a negative offset, set the Zone 1 diameter equal to 1.0 per unit
impedance.
Ω
INOM•1.73
VNOM
40Z1P =
Set the Zone 1 offset equal to one-half the generator transient reactance, Xd', in secondary ohms.
Ω
−
=
2
'Xd
1XD40
Zone 1 loss-of-field tripping is typically performed with short or zero time delay.
seconds 0.040Z1D =
Set the Zone 2 diameter equal to the machine direct axis reactance, Xd, in secondary ohms.
Ω Xd40Z2P =
Set the Zone 2 offset equal the Zone 1 offset.
Ω
−
=
2
'Xd
2XD40