ABB Relion 670 series, Technical Reference Manual

Page: 137 / 1232

When a fault is classified as internal by the negative sequence fault discriminator, a trip
is issued under the condition that the dual slope restrained function has been picked
up , while a classification as external fault results in an increase of the restrained
characteristic trip values
IdMinHigh .
For all differential functions it is the common trip that shall be used to
initiate a trip of a breaker. The separate trip signals from the different
parts lacks the safety against maloperation. This will in some cases
result in a 6 ms time difference between, for example restrained trip is
issued and common trip is issued. The separate trip signals shall only
be used for information purpose of which part that has caused the trip.
With reference to figure 51 , the outputs from the three analysis blocks are fed to the
output logic. Figure 54 shows a simplified block diagram of this output logic where
only trip commands and no alarm signals are shown for simplicity.
1MRK505222-UUS C
Section 5
Differential protection
131
Technical reference manual