Non-Directional Inverse Time Delayed Phase And Residual Overcurrent Protection - ABB REC650 Applications Manual

Section 16
Requirements
16.1.6.3
350
Non-directional inverse time delayed phase and residual overcurrent
protection
The requirement according to Equation
if the high set instantaneous or definitive time stage is used. In this case Equation
only necessary requirement.
If the inverse time delayed function is the only used overcurrent protection function the
CTs must have a rated equivalent secondary e.m.f. E
required secondary e.m.f. E
I
×
³ = ×
E E 20 I s n
op
a l a lre q
I
pn
EQUATION1679 V1 EN
where
I The primary current set value of the inverse time function (A)
op
I The rated primary CT current (A)
pn
I The rated secondary CT current (A)
sn
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
L
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 The burden of an IED current input channel (VA). S
R
and S
Independent of the value of I
following:
I
×
³ =
E E I
s n
k ma x
a l a lre q ma x
I
pn
EQUATION1680 V1 EN
where
I Maximum primary fundamental frequency current for close-in faults (A)
kmax
96 and Equation
below:
alreq
æ ö
S
× + +
R R R
ç ÷
CT L
2
è I ø
n
=0.250 VA/channel for I =5 A
R r
the maximum required E
op
æ ö
S
× + +
R R
R
ç ÷
CT L
2
I
è ø
n
1MRK 511 286-UUS A
97 does not need to be fulfilled
that is larger than or equal to the
al
=0.010 VA/channel for I
R
is specified according to the
al
Application manual
95 is the
(Equation 96)
=1 A
r
(Equation 97)