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Block Zones 1 - 4

V02779

IS/Comp EF

342

VN> Start

V< Start

Healthy Condition

First Fault

Evolving 3-phase fault

ZP AB Comp.

1326

ZP BC Comp.

ZP CA Comp.

1327

1328

VN> Start

V< Start

IN> Bias

Second Fault

1335

V< Start

VN> Start

IN>Bias – I2 check

Evolving 2P Fault (No Neutral Current)

VAB

VBC

VCA

V< Start

All poles dead

ZQ AB Comp.

1974

ZQ BC Comp.

ZQ CA Comp.

1975

1976

0.9*Vnom

890

Figure 91: Second earth fault detection logic

A second fault is detected if additionally there is a neutral overvoltage, imbalance in the voltage triangle (phase

undervoltage) and there is enough neutral overcurrent (a minimum of 50 mA for correct device operation).

6.3.4

PHASE PREFERENTIAL LOGIC

With double earth faults (cross-country faults), the aim is to isolate one of the fault locations and expect that the

fault at the other location will self-extinguish, or will be tripped manually after successful detection. To achieve this

for isolated or compensated systems, the distance protection must have a preference as to which phase-to-earth

loop to measure.

There are two types of priority criteria; acyclic and cyclic.

Acyclic criteria are such that one of the phases is always the lowest priority. For example, A(B) Acyclic logic means:

phase A is higher priority than phase B, phase B is higher priority than phase C, and phase C is the lowest priority

and will never be selected, therefore C has the lowest priority. Acyclic criteria are most commonly used for

distribution systems.

P543i/P545i Chapter 7 - Distance Protection

P54x1i-TM-EN-1 187

Brand	GE
Model	P24DM
Category	Control Unit
Language	English

GE P24DM User Manual

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