ABB Relion 670 series, Technical Reference Manual, Page: 129 / 1232

IED
IED
IED
Communication Channel
Communication Channel
Communication Channel
Protected zone
ANSI05000040_2_en.vsd
ANSI05000040 V2 EN
Figure 47: Example of application on a three-terminal line with breaker-and-a-half
breaker arrangements
The current differential algorithm provides high sensitivity for internal faults, at the
same time as it has excellent stability for external faults. Current samples from all CTs
are exchanged between the IEDs in the line ends (master-master mode) or sent to one
IED (master-slave mode) for evaluation.
A restrained dual biased slope evaluation is made where the bias current is the highest
phase current in any line end giving a secure through fault stability even with heavily
saturated CTs. In addition to the restrained evaluation, an unrestrained high differential
current setting can be used for fast tripping of internal faults with very high currents.
A special feature with this function is that applications with small power transformers
(rated current less than 50 % of the differential current setting) connected as line taps
(that is, as "shunt" power transformers), without measurements of currents in the tap,
can be handled. The normal load current is here considered to be negligible, and
special measures need only to be taken in the event of a short circuit on the LV side of
the transformer. In this application, the tripping of the differential protection can be
time delayed for low differential currents to achieve coordination with down stream
over current IEDs.
1MRK505222-UUS C
Section 5
Differential protection
123
Technical reference manual