a
This factor depends on the design of the protection function and can be a
function of the primary DC time constant of the close-in fault current.
k
This factor depends on the design of the protection function and can be a
function of the primary DC time constant of the fault current for a fault at the set
reach of zone 1.
The a- and k-factors have the following values for the different types of distance
function:
High speed distance: (ZMFPDIS and ZMFCPDIS)
Quadrilateral characteristic:
a = 1 for primary time constant Tp
£
400 ms
k = 3 for primary time constant Tp
£
200 ms
Mho characteristic:
a = 2 for primary time constant Tp
£
400 ms (For a = 1 the delay in operation
due to saturation is still under 1.5 cycles)
k = 3 for primary time constant Tp
£
200 ms
Quadrilateral distance: (ZMQPDIS, ZMQAPDIS and ZMCPDIS, ZMCAPDIS and
ZMMPDIS, ZMMAPDIS)
a = 1 for primary time constant Tp
£
100 ms
a = 3 for primary time constant Tp
>
100 and
£
400 ms
k = 4 for primary time constant Tp
£
50 ms
k = 5 for primary time constant Tp
>
50 and
£
150 ms
Mho distance: (ZMHPDIS)
a = 1 for primary time constant Tp
£
100 ms
a = 3 for primary time constant Tp
>
100 and
£
400 ms
k = 4 for primary time constant Tp
£
40 ms
k = 5 for primary time constant Tp
>
40 and
£
150 ms
25.1.6.3
Breaker failure protection
M11621-3 v5
The CTs must have a rated equivalent limiting secondary e.m.f. E
al
that is larger than
or equal to the required rated equivalent limiting secondary e.m.f. E
alreq
below:
s n
R
a l
a lre q
CT
L
2
pn
n
op
I
S
E
E
5 I
R
R
I
I
³
= ×
×
+
+
æ
ö
×
ç
÷
è
ø
EQUATION1677 V1 EN-US
(Equation 521)
where:
I
op
The primary operate value (A)
I
pr
The rated primary CT current (A)
I
sr
The rated secondary CT current (A)
I
n
The nominal current of the protection IED (A)
R
ct
The secondary resistance of the CT (
W
)
R
L
The resistance of the secondary cable and additional load (
W
). The loop resistance containing the
phase and neutral wires, must be used for faults in solidly grounded systems. The resistance of a
single secondary wire should be used for faults in high impedance grounded systems.
S
R
The burden of an IED current input channel (VA). S
R
=0.020 VA/channel for I
r
=1 A and S
R
=0.150
VA/channel for I
r
=5 A
Section 25
1MRK 504 163-UUS A
Requirements
990
Transformer protection RET670 2.2 ANSI
Application manual
Содержание RELION RET670
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