Alstom MiCOM P546 - 3.2.10 Load avoidance; 3.2.11 Additional settings for quadrilateral applications; 3.2.11.1 Phase fault resistive reaches (Rph)

P54x/EN AP/La4 Application Notes
(AP) 6-58 MiCOM P543, P544, P545 & P546
AP
Remote Zone 2 reach = (Blue River-Green Valley) line impedance +
50%n (Green Valley-Tiger Bay) line
impedance
= (100+40) x 0.484 79.4 x 0.12
= 8.13 79.4  secondary
Z4  ((8.13 79.4) x 120%) - (5.81 79.4)
= 3.95 79.4
Minimum zone 4 reverse reach setting = 3.96 80 ohms secondary
3.2.10 Load avoidance
The maximu
m full load current of the line can be determined from the calculation:
I
FLC
= [(Rated MVA
FLC
) / (3 x Line kV)]
In practice, relay settings must allow for a level of overloading, typically a maximum current
of 120% IFLC prevailing on the 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 IFLC.
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, relay
tolerance, 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:
Z  (Rated phase-ground voltage Vn) / (IFLC x 3)
= (115/√3) / (IFLC x 3)
Set the V< Blinder voltage threshold at the recommended 70% of Vn = 66.4 x 0.7 = 45 V.
3.2.11 Additional settings for quadrilateral applications
3.2.11.1
Phase fault resistive reaches (Rph)
In prima
ry impedance terms, RPh reaches must be set to cover the maximum expected
phase-to-phase fault resistance. Ideally, RPh must be set greater than the maximum fault
arc resistance for a phase-phase fault, calculated as follows:
Ra = (28710 x L)/If
1.4
Where:
If = Minimum expected phase-phase fault current (A);
L = Maximum phase conductor separation (m);
Ra = Arc resistance, calculated from the van Warrington formula ().
Typical figures for Ra (primary ) are given in the table below, for different values of
minimum expected phase fault current.
Conductor spacing
(m)
Typical system voltage
(kV)
If = 1 kA If = 2 kA If = 3 kA
4 110 - 132
7.2  2.8  1.6 
8 220 - 275
14.5  5.5  3.1 
11 380 - 400
19.9  7.6  4.3 