ABB RELION REX640 Technical Manual page 1206

Protection and control

Hide thumbs Also See for RELION REX640:

Table of Contents

Protection related functions

Figure 688: Definition of a physical fault point resistance in different fault loops

Steady-state asymmetry and load compensation

Power systems are never perfectly symmetrical. The asymmetry produces steady-

state quantities in the form of zero-sequence and negative-sequence voltages and

currents. If not compensated, these are error sources for fault distance calculation

especially in case of earth faults. All earth-fault distance calculation algorithms of

SCEFRFLO use the delta quantities which mitigate the effects of the steady-state

The load current is another error source for fault distance calculation. Its influence

increases with higher fault resistance values. SCEFRFLO employs independent load

compensation methods for each fault type to achieve optimal performance. The

purpose of load compensation is to improve the accuracy of the fault distance

calculation models by estimating the actual fault current in the fault location. Delta-

quantities are used for this to mitigate the effect of load current on fault distance

For earth faults, the load compensation is done automatically inside the fault

distance calculation algorithm. For short circuit faults, load compensation is

enabled with setting

parameter should be set to "Disabled" only if the ratio between the expected fault

current and load current is high or when the fault distance estimate for the short

circuit fault is required for each shot of an autoreclosing sequence.

The delta quantity describes the change in measured signal due to the fault.

Result quality indicator

The quality of the estimated fault distance is judged and reported in recorded

data as the Flt Dist quality together with the fault distance estimate. The Flt Dist

quality is a bit vector indicating detected sources of inaccuracy in the fault distance

estimate. If Flt Dist quality equals 1, the result is not affected by error sources. This

results in good quality for the fault distance estimate. If factors affecting negatively

Load Com PP loops . The default value is "Enabled". The

Signal value during fault

Signal value during healthy state just before fault

1MRS759142 F

(Equation 305)

Technical Manual