The vector shift detection also protects synchronous generators from damaging due to
islanding or loss-of-mains. To detect loss-of-mains with vector shift function, the
generator should aim to export or import at least 5...10% of the generated power to the
grid, in order to guarantee detectable change in loading after islanding or loss-of-mains.
Multicriteria Loss of Mains
Apart from vector shift, there are other passive techniques which are used for detecting
Loss of Mains. Some of these passive techniques are over/under voltage, over/under
frequency, rate of change of frequency, voltage unbalance, rate of change of power and so
on. These passive methods use voltage and frequency to identify Loss of Mains. The
performance of these methods depends on the power mismatch between local generation
and load. The advantage of all these methods is that, they are simple and cost effective, but
each method has a non detectable zone. To overcome this problem, it is recommended to
combine different criteria for detecting Loss of Mains.
Two or more protection functions run in parallel to detect Loss of Mains. When all criteria
are fulfilled to indicate Loss of Mains, an alarm or a trip can be generated. Vector shift and
rate of change of frequency are two parallel criteria typically used for detection of Loss of
Mains.
Chosen protection criteria can be included in the Application Configuration tool to create
multicriteria loss of mains alarm or trip.
4.5.8.6
Signals
Table 572:
78V Input signals
Name
Type
Default
Description
V_A_AB
SIGNAL
0
Phase-to-ground voltage A or phase-to-phase voltage
AB
V_B_BC
SIGNAL
0
Phase-to-ground voltage B or phase-to-phase voltage
BC
V_C_CA
SIGNAL
0
Phase-to-ground voltage C or phase-to-phase voltage
CA
BLOCK
BOOLEAN
0=False
Block signal for activating the blocking mode
Table 573:
78V Output signals
Name
Type
Description
TRIP
BOOLEAN
Trip
INT_BLKD
BOOLEAN
Protection function internally blocked
Section 4
1MAC059074-MB A
Protection functions
670
615 series ANSI
Technical Manual
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