ABB RER670 - Restricted Earth Fault Protection (Low Impedance Differential)

sr
R
al alreq op ct L
2
pr
r
I
S
E E 5 I R R
I
I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION1380 V2 EN-US (Equation 85)
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
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
22.1.6.2 Restricted earth fault protection (low impedance differential)
GUID-AFAFC587-6986-4FF4-A5E1-6F5DC0A72A6B v1
The requirements are specified separately for solidly earthed and impedance
earthed
transformers. For impedance earthed transformers the requirements for the
phase CTs are depending whether it is three individual CTs connected in parallel or
it is a cable CT enclosing all three phases.
Neutral CTs and phase CTs for solidly earthed transformers
GUID-7CD7512F-F7BD-479E-B7B6-0D5DF22869D4 v3
The neutral CT and the phase CTs must have a rated equivalent limiting secondary
e.m.f. E
al
that is larger than or equal to the maximum of the required rated
equivalent limiting secondary e.m.f. E
alreq
below:
2
30
sr
R
al alreq rt ct L
pr
r
I
S
E E I R R
I
I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION2237 V2 EN-US (Equation 86)
2
2
sr
R
al alreq etf ct L
pr
r
I
S
E E I R R
I
I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION2238 V2 EN-US (Equation 87)
Where:
I
rt
The rated primary current of the power transformer (A)
I
etf
Maximum primary fundamental frequency phase-to-earth fault current that passes
the CTs and the power transformer neutral (A)
I
pr
The rated primary CT current (A)
Table continues on next page
Section 22 1MRK 506 375-UEN A
Requirements
480 Railway application RER670 2.2 IEC
Application manual