GE L30 Instruction Manual page 602

OVERVIEW
The current chosen is expressed as:
This current is then processed with the slope (S
restraint term for the local current as follows. For two-terminal systems, we have:
For three-terminal systems we have:
The final restraint current sent to peers and used locally in differential calculations is as follows:
where
MULT is a multiplier that increases restraint if CT saturation is detected (see CT Saturation Detection for details)
A
I is an adaptive restraint term (see Online Estimate Of Measurement Error for details)
LOC_ADA_A
The squared restraining current is calculated as a sum of squared local and all remote restraints:
The fault severity for each phase is determined by following equation:
where P is the pickup setting.
This equation is based on the adaptive strategy and yields an elliptical restraint characteristic. The elliptical area is the
restraint region. When the adaptive portion of the restraint current is small, the restraint region shrinks. When the adaptive
portion of the restraint current increases, the restraint region grows to reflect the uncertainty of the measurement. The
computed severity increases with the probability that the sum of the measured currents indicates a fault. With the
exception of "Restraint," all quantities are defined in previous sections. "Adaptive Restraint" is a restraint multiplier,
analogous to the slope setting of traditional differential approaches, for adjusting the sensitivity of the relay.
Raising the restraint multiplier corresponds to demanding a greater confidence interval and has the effect of decreasing
sensitivity while lowering it, equivalent to relaxing the confidence interval and increases sensitivity. Thus, the restraint
multiplier is an application adjustment that is used to achieve balance between sensitivity and security. The computed
severity is zero when the operate phasor is on the elliptical boundary, is negative inside the boundary, and positive outside
the boundary. Outside of the restraint boundary, the computed severity grows as the square of the fault current. The
restraint area grows as the square of the error in the measurements.
10
10-4
and S ) and breakpoint (BP) settings to form a traditional part of the
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L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CHAPTER 10: THEORY OF OPERATION
Eq. 10-6
Eq. 10-7
Eq. 10-8
Eq. 10-9
Eq. 10-10
Eq. 10-11