Operating Condition Characteristics; Description - GE L90 Instruction Manual

9.2 OPERATING CONDITION CHARACTERISTICS

9.2OPERATING CONDITION CHARACTERISTICS
Characteristics of differential elements can be shown in the complex plane. The operating characteristics of the L90 are
fundamentally dependant on the relative ratios of the local and remote current phasor magnitudes and the angles of
I as shown in the Restraint Characteristics figure.
rem
The main factors affecting the trip-restraint decisions are:
1. Difference in angles (+ real represents pure internal fault when currents are essentially in phase, – real represents
external fault when currents are 180° apart).
2. The magnitude of remote current.
3. The magnitude of the local current.
4. Dynamically estimated errors in calculations.
5. Settings.
The following figure also shows the relay's capability to handle week-infeed conditions by increasing the restraint ellipse
when the remote current is relatively small (1.5 pu). Therefore, uncertainty is greater when compared with higher remote
currents (3 pu). The characteristic shown is also dependant on settings. The second graph shows how the relay's trip-
restraint calculation is made with respect to the variation in angle difference between local and remote currents. The char-
acteristic for 3 terminal mode is similar where both remote currents are combined together.
9
9-16 L90 Line Current Differential System
9 THEORY OF OPERATION

9.2.1 DESCRIPTION

I
loc
GE Multilin
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