Areva MiCOM P441, Техническое руководство

Страница: 149 / 636

Relay Description P44x/EN HW/E33
MiCOM P441/P442 & P444 Page 21/44
The model for the current Ifault circulating in the fault I
αβ
.
V
AB
= 2Z
1
.D
fault
.I
AB
+ R
fault
.I
fault
V
BC
= 2Z
1
.D
fault
.I
BC
+ R
fault
.I
fault
V
CA
= 2Z
1
.D
fault
.I
CA
+ R
fault
.I
fault
= 3 phase-to-phase loops are continuously monitored and computed for each sample.
V
αβ
= 2Z
1
.D
fault
.I
αβ
+ R
fault
.I
fault
V
αβ
= 2(R
1
+ j. X
1
).D
fault
.I
αβ
+ R
fault
.I
fault
V
αβ
= 2R
1
.D
fault
.I
αβ
+ 2j. X
1
.D
fault
.I
αβ
+ R
fault
.I
fault
V
αβ
= 2R
1
.D
fault
.I
αβ
+ 2X
1
.D
fault
.
dI
αβ
dt
+ R
fault
.I
fault
V
AB
= R
1
.D
fault
.(I
A
– I
B
) + (L
AA
–L
AB
).D
fault
.
dI
A
dt
+ (L
AB
–L
BB
).D
fault
.
dI
B
dt
+ (L
AC
–L
BC
).D
fault
.
dI
C
dt
+
R
fault
2
.I
fault
V
BC
= R
1
.D
fault
.(I
B
– I
C
) + (L
AB
–L
AC
).D
fault
.
dI
A
dt
+ (L
BB
–L
BC
).D
fault
.
dI
B
dt
+ (L
BC
–L
CC
).D
fault
.
dI
C
dt
+
R
fault
2
.I
fault
V
CA
= R
1
.D
fault
.(I
C
– I
A
) + (L
AC
–L
AA
).D
fault
.
dI
A
dt
+ (L
BC
–L
AB
).D
fault
.
dI
B
dt
+ (L
CC
–L
AC
).D
fault
.
dI
C
dt
+
R
fault
2
.I
fault
Impedance measurement algorithms work with instantaneous values (current and voltage).
Derivative current value (dI/dt) is obtained by using FIR filter.
4.2 "Deltas" Algorithms
The patented high-speed algorithm has been proven with 10 years of service at all voltage
levels from MV to EHV networks. The P440 relay has ultimate reliability of phase selection
and directional decision far superior to standard distance techniques using superimposed
algorithms. These algorithms or delta algorithms are based on transient components and
they are used for the following functions:
Detection of the fault
By comparing the superimposed values to a threshold which is low enough to be crossed
when a fault occurs and high enough not to be crossed during normal switching outside of
the protected zones.
Establishing the fault direction
Only a fault can generate superimposed values; therefore, it is possible to determine
direction by measuring the transit direction of the superimposed energy.
Phase selection
As the superimposed values no longer include the load currents, it is possible to make high-
speed phase selection.
4.2.1 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.