Non-Directional Inverse Time Delayed Phase And Residual Overcurrent Protection - ABB REC670 Applications Manual

1MRK 511 401-UUS A
24.1.6.3
Bay control REC670 2.2 ANSI
Application manual
I
×
³ = ×
E E 1.5 I s n
op
a l a lre q
I
pn
EQUATION1678 V1 EN-US
where:
I The primary operate value (A)
op
I The rated primary CT current (A)
pr
I The rated secondary CT current (A)
sr
I The nominal current of the protection IED (A)
n
R
The secondary resistance of the CT (W)
ct
R The resistance of the secondary cable and additional load (W). The loop resistance containing the
L
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 The burden of an IED current input channel (VA). S
R
VA/channel for I =5 A
r
Non-directional inverse time delayed phase and residual overcurrent
protection
The requirement according to Equation
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
CTs must have a rated equivalent limiting secondary e.m.f. E
equal to the required rated equivalent limiting secondary e.m.f. E
I
×
³ = ×
E E 20 I s n
op
a l a lre q
I
pn
EQUATION1679 V1 EN-US
where
I The primary current set value of the inverse time function (A)
op
I The rated primary CT current (A)
pr
I The rated secondary CT current (A)
sr
I The nominal current of the protection IED (A)
n
Table continues on next page
æ ö
S
× + +
R R R
ç ÷
CT L
2
I
è ø
n
R
130 and Equation
æ ö
S
× + +
R R R
ç ÷
CT L
2
I
è ø
n
Section 24
Requirements
=0.020 VA/channel for I =1 A and S
r
131 does not need to be
that is larger than or
al
below:
alreq
(Equation 129)
=0.150
R
M11339-3 v5
(Equation 130)
633