Phase Selection; Fault Modelling; Network Status Monitoring; Prefault And Fault Inception Value - GE MiCOM P40 Agile Technical Manual

P44x/EN AP/Hb6
(AP) 5-16

Phase selection

As the superimposed values no longer include the load currents, it is possible to make high-
speed phase selection.
2.2.1

Fault Modelling

Consider a stable network status-the steady-state load flow prior to any start. When a fault
occurs, a new network is established. If there is no other modification, the differences
between the two networks (before and after the fault) are caused by the fault. The network
after the fault is equivalent to the sum of the values of the status before the fault and the
values characteristic of the fault. The fault acts as a source for the latter, and the sources act
as passive impedance in this case.
Figure 4:

Prefault and fault inception value

Network Status Monitoring

The network status is monitored continuously to determine whether the "Deltas" algorithms
can be used. The network must be "healthy". This is characterised by the following:
• The circuit breaker(s) should be closed just prior to fault inception (2 cycles of healthy
pre-fault data should be stored) – the line is energised from one or both ends,
• The source characteristics should not change noticeably (there is no power swing or
out-of-step detected).
V I
R R
R F
Z
Z
S
Relay
V
= Voltage at Relay Location
R
I
= Current at Relay Location
R
Unfaulted Network (steady state prefault conditions)
' '
V I
R R
R F
Z Z
S L
Relay
' Voltage at Relay Location
V
=
R
'
I
Current at Relay Location
=
R
Faulted Network (steady state)
V I
R R
R F
Z Z
S L
Relay
= Voltage at Relay Location
V
R
=
I Current at Relay Location
R
Z
L L
V
F (prefault voltage)
Z
L
R
F
Z
L
-V
F
R
F
Fault Inception
Application Notes
MiCOM P40 Agile P442, P444
V I
R R
R F
Z
R
Relay
' '
V I
R R
R F
Z
R
Relay
V I
R R
R F
Z
R
Relay
P3033ENa