ABB REB670 - Non-Directional Inverse Time Delayed Phase and Residual Overcurrent Protection

sn
R
al alreq CT L
2
pn n
op
I
S
E E 1.5 I R R
I I
³ = × × + +
æ ö
×
ç ÷
è ø
EQUATION1678 V1 EN-US (Equation 94)
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
21.1.6.4 Non-directional inverse time delayed phase and residual overcurrent
protection
M11339-3 v5
The requirement according to Equation
95 and Equation 96 does not need to be
fulfilled if the high set instantaneous or definitive time stage is used. In this case
Equation is the only necessary requirement.
If the inverse time delayed function is the only used overcurrent protection function the
CT
s 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:
sn
R
al alreq CT L
2
pn n
op
I S
E E 20 I R R
I I
³ = × × + +
æ ö
×
ç ÷
è ø
EQUATION1679 V1 EN-US (Equation 95)
where
I
op
The primary current set value of the inverse time function (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)
Table continues on next page
Section 21 1MRK 505 370-UUS A
Requirements
530 Busbar protection REB670 2.2 ANSI
Application manual