ABB Relion REQ650, Applications Manual

Page: 324 / 340

it is advisable to check the actual unwanted residual current during the
commissioning.
16.1.6 Rated equivalent secondary e.m.f. requirements
With regard to saturation of the current transformer all current transformers of high
remanence and low remanence type that fulfill the requirements on the rated
equivalent limiting secondary e.m.f. E
al
below can be used. The characteristic of the
non remanence type CT (TPZ) is not well defined as far as the phase angle error is
concerned. If no explicit recommendation is given for a specific function we therefore
recommend contacting ABB to confirm that the non remanence type can be used.
The CT requirements for the different functions below are specified as a rated
equivalent limiting secondary e.m.f. E
al
according to the IEC 61869-2 standard.
Requirements for CTs specified according to other classes and standards are given at
the end of this section.
16.1.6.1 Breaker failure protection
The CTs must have a rated equivalent secondary e.m.f. E
al
that is larger than or equal
to the required secondary e.m.f. E
alreq
below:
sn
R
al alreq op CT L
2
pn r
I S
E E 5 I R R
I
I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION1380 V1 EN
(Equation 80)
where:
I
op
The primary operate value (A)
I
pn
The rated primary CT current (A)
I
sn
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
=0.010 VA/channel for I
r
=1 A and S
R
=0.250
VA/channel for I
r
=5 A
16.1.6.2 Non-directional instantaneous and definitive time, phase and residual
overcurrent protection
The CTs must have a rated equivalent secondary e.m.f. E
al
that is larger than or equal
to the required secondary e.m.f. E
alreq
below:
Section 16
1MRK 505 291-UEN A
Requirements
318
Application manual