P44x/EN AP/Hb
MiCOM P40 Agile P442, P444
(AP) 5-
2 DISTANCE ALGORITHMS
The operation is based on the combined use of two types of algorithms:
• "Delta" algorithms, also called High Speed algorithms, using the superimposed current
and voltage values that are characteristic of a fault. These are used for phase
selection and directional determination. The fault distance calculation is performed by
the "impedance measurement algorithms” using Gauss-Seidel.
• "Conventional" algorithms using the impedance values measured while the fault
occurs. These are also used for phase selection and directional determination.
The fault distance calculation is performed by the "impedance measurement
algorithms" using Gauss-Seidel.
The fastest algorithm gives the immediate directional decision.
2.1 Distance and Resistance Measurement
MiCOM P44x distance protection is a full scheme distance relay. To measure the distance
and apparent resistance of a fault, the following equation is solved on the faulted loop:
(n).Z
L
Relay
P3030ENa
R
F
Z
SL
I
L
Local
Source
(1-n).Z
L
Z
SR
I
R
I
F
= I + I'
Remote
Source
V
L
= (Z
L
x I x D) + R
F
x I
F
= ((r
+jx) x I x D) + R
F
x I
F
where
V
L
V
L
= local terminal relay voltage
r = line resistance (ohm/mile)
x =
=
=
=
line reactance (ohm/mile)
current measured by the relay on the faulty phase
current flowing into the fault from local terminal
=
current flowing into the fault from remote terminal
=
fault location (permile or km from relay to the fault)
current flowing in the fault (I + I')
I
F
I
I'
R
F
Assumed Fault Currents:
For Phase to Ground Faults (ex., A-N),
For Phase to Phase Faults (ex., A-B),
I
F
= 3
I
0
I
A
for 40ms, then
after 40 ms
I
F
=
I
AB
Relay
V
R
D
=
fault resistance
=
apparent fault resistance at relay; R x (1 + I'/I)
R
Figure 1: Distance and fault resistance estimation
The impedance measurements are used by High Speed and Conventional Algorithms.
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