To use the load blinders you must set the Load Blinders setting to Enabled. You then set appropriate values for
the blinder impedance using the Z< Blinder Imp setting, the b value using the Load/B Angle setting, and the
undervoltage threshold using the Load Blinder V< setting.
4.9 CROSS COUNTRY FAULT PROTECTION
"Cross country fault" is a term that has been adopted to cover a fault scenario where two separate single-phase
faults occur on a system together. For example, where single-pole tripping is employed, if a single phase-to-earth
fault occurs, the voltages on the other phases can rise above normal. This may cause a breakdown elsewhere on
the system and result in another fault involving a different phase to the one on which the original fault occurred.
The distance protection in this product features cross-country override logic, which is built into the phase selector.
The logic is dedicated to providing Cross-Country fault protection for solidly-earthed systems. It ensures correct
operation a fault in Zone 1 that may evolve to involve a different phase. For isolated or compensated earthing
systems a settable phase preferential logic will be used for cross-country faults instead.
The cross-country override logic:
● Prevents possible false operation of the phase-phase distance elements whilst allowing the appropriate
Zone1 phase-earth element to trip.
● Acts when the distance protection makes a multiple phase selection (where more than one phase is
involved in the fault), but only one Zone 1 phase-earth element picks up. Only "on-angle" operation of the
Zone 1 phase-earth element can activate the logic. this prevents incorrect operation due to impedance
encroachment.
● Allows only one Zone 1 phase-earth element to operate. The operation of that element must match the
phase pick-up indication of the phase selector. For example, if the original phase selection indicated
involvement of only B and C phases, the logic could allow a BN trip or a CN trip to override the phase-phase
selection, but override by the AN element is not allowed.
● Does not apply if more than one forward Zone 1 element picks up. In this case the fault is considered multi-
phase and the protection trips three-pole.
Note:
Load blinding can be applied for phase and earth characteristics. Residual compensation is not applied. Phase characteristics
use phase-to-phase voltage and phase-to-phase current. Earth fault characteristics use phase-to-neutral voltage and phase-
to-neutral current.
P543i/P545i Chapter 7 - Distance Protection
P54x1i-TM-EN-1 175
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