Breaker Failure Protection - ABB REG670 Applications Manual

Section 24
Requirements
24.1.6.3
24.1.6.4
754

Breaker failure protection

The CTs must have a rated equivalent limiting secondary e.m.f. E
or equal to the required rated equivalent limiting secondary e.m.f. E
I
³ = × ×
sr
E E 5 I
al alreq op
I
pr
EQUATION1380 V2 EN
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 rated current of the protection IED (A)
r
R The secondary resistance of the CT (W)
ct
R
The resistance of the secondary cable and additional load (W). The loop resistance containing
L
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 The burden of an IED current input channel (VA). S
R
VA/channel for I =5 A
r
Restricted earth fault protection (low impedance differential)
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
The neutral CT and the phase CTs must have a rated equivalent limiting secondary
e.m.f. E that is larger than or equal to the maximum of the required rated equivalent
al
limiting secondary e.m.f. E
³ = × ×
E E 30 I
al alreq rt
EQUATION2237 V2 EN
³ = × ×
E E 2 I
al alreq etf
I
EQUATION2238 V2 EN
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
æ ö
S
× + +
R
R R
ç ÷
ct L
2
I
è ø
r
below:
alreq
æ ö
I S
× + +
sr R
R R
ç ÷
ct L
2
I I
è ø
pr r
æ ö
I
S
× + +
sr R
R R
ç ÷
ct L
2
I
è ø
pr
r
1MRK 502 071-UEN -
that is larger than
al
alreq
=0.020 VA/channel for I =1 A and S
R r
Application manual
below:
(Equation 305)
=0.150
R
(Equation 306)
(Equation 307)