ABB RELION 620 Series Technical Manual page 455

1MAC504801-IB E
620 series ANSI
Technical Manual
F > K × I × (T × ×
ω
a r kmax dc
GUID-683C906B-2772-46F3-8BF3-F333E0915A2E V1 EN
I 10 (p.u.)
kmax
T 100 (ms)
dc
ω 100π (Hz)
T 10 (ms)
m
K 1
r
Re-energizing against a fault occurring further down in the network.
The protection must be stable during the re-energization against a fault on the line. In this
case, the existence of remanence is very probable. In this example, it is 40 percent.
The fault current is now smaller and since the ratio of the resistance to the reactance is
greater in this location, having a full DC offset is not possible. Furthermore, the DC time
constant (T ) of the fault current is now smaller, here 50 ms.
dc
Assuming a maximum fault current is 30 percent lower than in the bus fault and a DC
offset 90 percent of the maximum.
F > K × I × 0.9 (T ×
a r kmax dc
GUID-309A8E47-ABC4-4CED-B8C8-A1D8525B1BC0 V1 EN
I 0.7 x 10 = 7 (p.u.)
kmax
T 50 (ms)
dc
ω 100π (Hz)
T 10 (ms)
m
K 1/(1-0.4) = 1.6667
r
If the actual burden of the current transformer (S
enough to provide a sufficient value for F
situation.
• A current transformer with a higher rated burden S
a higher rated accuracy limit F
• A current transformer with a higher nominal primary current I1
burden) can be chosen.
-Tm / Tdc
(1 - e ) + 1) 40 ≈
-Tm / Tdc
× × (1 - e ) + 1) 40 ≈
ω
) in
a
, there are two alternatives to deal with the
a
) or
n
Section 4
Protection functions
Equation 49 cannot be reduced low
can be chosen (which also means
n
(but the same rated
n
(Equation 51)
(Equation 52)
449