ABB REG650 Technical Manual page 100

Section 5
Differential protection
94
respective block signals, a restrained trip TRIPRES and common trip TRIP are
issued
3. If a start signal is issued in a phase, and the fault has been classified as
internal, then any eventual block signals are overridden and a unrestrained
negative-sequence trip TRNSUNR and common trip TRIP are issued without
any further delay. This feature is called the unrestrained negative-sequence
protection.
4. The sensitive negative sequence differential protection is independent of any
start signals. It is meant to detect smaller internal faults, such as turn-to-turn
faults, which are often not detected by the traditional differential protection.
The sensitive negative sequence differential protection starts whenever both
contributions to the total negative sequence differential current (that must be
compared by the internal/external fault discriminator) are higher than the value
of the setting IMinNegSeq. If a fault is positively recognized as internal, and
the condition is stable with no interruption for at least one fundamental
frequency cycle the sensitive negative sequence differential protection
TRNSSENS and common trip TRIP are issued. This feature is called the
sensitive negative sequence differential protection.
5. If a start signal is issued in a phase (see signal STL1), even if the fault has
been classified as an external fault, then the instantaneous differential current
of that phase (see signal IDL1) is analyzed for the 2
contents (see the blocks with the text inside: 2nd Harmonic; Wave block and
5th Harmonic). If there is less harmonic pollution, than allowed by the settings
I2/I1Ratio, and I5/I1Ratio, (then the outputs from the blocks 2nd harmonic and
5th harmonic is 0) then it is assumed that a minor simultaneous internal fault
must have occurred. Only under these conditions a trip command is allowed
(the signal TRIPRESL1 is = 1). The cross-block logic scheme is automatically
applied under such circumstances. (This means that the cross block signals
from the other two phases L2 and L3 is not activated to obtain a trip on the
TRIPRESL1 output signal in figure 39)
6. All start and blocking conditions are available as phase segregated as well as
common (that is three-phase) signals.
IDL1 MAG
a
a>b
I Diff Alarm
b
IDL2 MAG
a
a>b
I Diff Alarm
b
IDL3 MAG
a
a>b
I Diff Alarm
b
IEC06000546 V1 EN
Figure 43: Differential current alarm logic
1MRK 502 034-UEN -
nd
and the 5
tAlarm Delay
&
t
th
harmonic
IDALARM
en06000546.vsd
Technical Manual