Load Avoidance - GE MiCOM P40 Agile Technical Manual

Chapter 7 - Distance Protection
Remote Zone 2 Reach = line impedance of Green Valley to Blue River + 50% line impedance from
Green valley to Tiger Bay
= (100 + 40) x 0.484
Ð 79.4° W secondary
= 8.13
³ (8.13 Ð 79.4° x 120%) - 5.81 Ð 79.4°
Zone 4 Reach
Ð 79.4° W secondary
= 3.95
This is the minimum Zone 4 Reach setting, so:
Set Z4 Ph. Reach and Z4 Gnd. Reach = 3.96 W
●
● Set Z4 Ph. Angle and Z4 Gnd. Angle = 80°
7.11.8

LOAD AVOIDANCE

The maximum full load current of the line can be determined from the calculation:
I = [(Rated MVAFLC) / (
FLC
The settings must allow for a level of overloading, typically a maximum current of 120% I
system transmission lines. Also, for a double circuit line, during the auto-reclose dead time of fault clearance on
the adjacent circuit, twice this level of current may flow on the healthy line for a short period of time. Therefore the
circuit current loading could be 2.4 x I
With such a heavy load flow, the system voltage may be depressed, typically with phase voltages down to 90% of
Vn nominal.
Allowing for a tolerance in the measuring circuit inputs (line CT error, VT error, protection accuracy, and safety
margin), this results in a load impedance which might be 3 times the expected rating.
To avoid the load, the blinder impedance needs to be set:
£ (Rated phase-ground voltage Vn) / (I
Z
= (115/√3) / (I
FLC
Set the V< Blinder voltage threshold at the recommended 70% of Vn = 66.4 x 0.7 = 45 V.
7.11.9 QUADRILATERAL RESISTIVE REACH SETTINGS
If applying Quadrilateral characteristics, as well as the Impedance Reaches, the Resistive Reaches also need to be
considered. The Resistive reaches of the phase-fault elements must be set to cover the maximum expected phase-
to-phase fault resistance. The Resistive reaches of the earth-fault elements should take into account the arc-
resistance and the tower footing resistance.
Phase-Fault Elements
Ideally, the Resistive reach should be set greater than the maximum fault arc resistance for a phase-phase fault
(Ra), calculated in terms of the minimum expected phase-phase fault current, the maximum phase conductor
separation, according to the formula developed by (van) Warrington as:
Ra = (28710 x L)/If x 1.4
where:
If = Minimum expected phase-phase fault current (A)
●
L = Maximum phase conductor separation (m)
●
Typical figures for Ra are given, for different values of minimum expected phase fault currents, in the following
table:
204
Ð 79.4° x 0.12
Ö 3 x Line kV)]
.
FLC
x 3)
x 3)
FLC
P543i/P545i
prevailing on the
FLC
P54x1i-TM-EN-1