Section 6 Current protection
6.1 Instantaneous phase overcurrent protection 3-phase
output PHPIOC
6.1.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Instantaneous phase overcurrent
protection 3-phase output
PHPIOC
SYMBOL-Z V1 EN
50
6.1.2 Application
Long transmission lines often transfer great quantities of electric power from
production to consumption areas. The unbalance of the produced and consumed
electric power at each end of the transmission line is very large. This means that a fault
on the line can easily endanger the stability of a complete system.
The transient stability of a power system depends mostly on three parameters (at
constant amount of transmitted electric power):
• The type of the fault. Three-phase faults are the most dangerous, because no
power can be transmitted through the fault point during fault conditions.
• The magnitude of the fault current. A high fault current indicates that the decrease
of transmitted power is high.
• The total fault clearing time. The phase angles between the EMFs of the
generators on both sides of the transmission line increase over the permitted
stability limits if the total fault clearing time, which consists of the protection
operating time and the breaker opening time, is too long.
The fault current on long transmission lines depends mostly on the fault position and
decreases with the distance from the generation point. For this reason the protection
must operate very quickly for faults very close to the generation (and relay) point, for
which very high fault currents are characteristic.
The instantaneous phase overcurrent protection 3-phase output PHPIOC can operate
in 10 ms for faults characterized by very high currents.
1MRK 505 291-UEN A Section 6
Current protection
85
Application manual
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