ABB REB650 - Non-Directional Inverse Time Delayed Phase and Residual Overcurrent Protection

18.1.6.3 Non-directional inverse time delayed phase and residual overcurrent
protection
M11339-3 v5
The requirement according to Equation
44 and Equation 45 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 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:
sr
R
al alreq op ct L
2
pr
r
I
S
E E 20 I R R
I
I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION1076 V2 EN-US (Equation 44)
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
r
The rated 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 earthed systems. The resistance of a single secondary wire should be
used for faults in high impedance earthed 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
Independent of the value of I
op
the maximum required E
al
is specified according to
the following:
sr
R
al alreq max k max ct L
2
pr
r
I
S
E E I R R
I
I
æ ö
³ = × × + +
ç ÷
è ø
EQUATION1077 V2 EN-US
(Equation 45)
where
I
kmax
Maximum primary fundamental frequency current for close-in faults (A)
1MRK 505 388-UEN B Section 18
Requirements
Busbar protection REB650 2.2 IEC 299
Application manual