ABB RER670 Applications Manual page 487

1MRK 506 375-UEN A
Railway application RER670 2.2 IEC
Application manual
I The rated secondary CT current (A)
sr
I The rated current of the protection IED (A)
r
R The secondary resistance of the CT (Ω)
ct
R The resistance of the secondary wire and additional load (Ω). The loop resistance
L
containing the phase and neutral wires shall be used.
S The burden of a REx670 current input channel (VA). S
R
1 A and S
R
In substations with breaker-and-a-half or double-busbar double-breaker
arrangement, the fault current may pass two main phase CTs for the restricted earth
fault protection without passing the power transformer. In such cases and if both
main CTs have equal ratios and magnetization characteristics the CTs must satisfy
Requirement 86 and the Requirement 87:
I
³ = ×
sr
E E I
al alreq ef
I
pr
EQUATION2239 V2 EN-US
Where:
I Maximum primary fundamental frequency phase-to-earth fault current that passes two
ef
main CTs without passing the power transformer neutral (A)
Neutral CTs and phase CTs for impedance earthed transformers
The neutral CT and phase CTs must have a rated equivalent limiting secondary
e.m.f. E that is larger than or equal to the required rated equivalent limiting
al
secondary e.m.f. E below:
alreq
I
³ = × ×
E E 3 I
al alreq etf
I
EQUATION2240 V2 EN-US
Where:
I Maximum primary fundamental frequency phase-to-earth fault current that
etf
passes the CTs and the power transformer neutral (A)
I The rated primary CT current (A)
pr
I The rated secondary CT current (A)
sr
I The rated current of the protection IED (A)
r
R The secondary resistance of the CT (Ω)
ct
R The resistance of the secondary wire and additional load (Ω). The loop
L
resistance containing the phase and neutral wires shall be used.
S The burden of a REx670 current input channel (VA). S
R
I = 1 A and S
r
= 0.150 VA / channel for IR = 5 A
æ ö
S
× + +
R
R R
ç ÷
ct L
2
I
è ø
r
æ ö
S
× + +
sr R
R R
ç ÷
ct L
2
I
è ø
pr
r
= 0.150 VA / channel for I
R
Section 22
Requirements
=0.020 VA / channel for IR =
R
(Equation 88)
GUID-FA79C943-A19B-47E2-BFC5-C9D01347302A v3
(Equation 89)
= 0.020 VA / channel for
R
= 5 A
r
481