6.6.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Four step residual overcurrent
protection, zero or negative sequence
direction
EF4PTOC
2
IEC11000263 V1 EN
51N/67N
6.6.2
Application
The four step residual overcurrent protection, zero or negative sequence direction
EF4PTOC is used in several applications in the power system. Some applications are:
•
Earth-fault protection of feeders in effectively earthed distribution systems.
Normally these feeders have radial structure.
•
Back-up earth-fault protection of subtransmission and transmission lines.
•
Sensitive earth-fault protection of transmission lines. EF4PTOC can have better
sensitivity to detect resistive phase-to-earth-faults compared to distance
protection.
•
Back-up earth-fault protection of power transformers with earth source at
substation.
•
Earth-fault protection of different kinds of equipment connected to the power
system such as shunt capacitor banks, shunt reactors and others.
•
Negative sequence direcitonal earth-fault protection of feeders with PTs
connected in Open Delta connection from which it is not possible to derive Zero
sequence voltage.
•
Negative sequence directional earth-fault protection of double-circuit medium or
long transmission lines with significant mutual coupling.
In many applications several steps with different current operating levels and time
delays are needed. EF4PTOC can have up to four, individual settable steps. The
flexibility of each step of EF4PTOC is great. The following options are possible:
Non-directional/Directional function: In some applications the non-directional
functionality is used. This is mostly the case when no fault current can be fed from the
protected object itself. In order to achieve both selectivity and fast fault clearance, the
directional function can be necessary. This can be the case for earth-fault protection
in meshed and effectively earthed transmission systems. The directional residual
overcurrent protection is also well suited to operate in teleprotection communication
schemes, which enables fast clearance of earth faults on transmission lines. The
directional function uses the polarizing quantity as decided by setting. Voltage
polarizing (3U
0
or U
2
) is most commonly used, but alternatively current polarizing
(3I
0
or I
2
) where currents in transformer neutrals providing the neutral (zero sequence)
source (ZN) is used to polarize (IPol · ZN) the function. Dual polarizing where the sum
of both voltage and current components is allowed to polarize can also be selected.
Section 6
1MRK 505 291-UEN A
Current protection
116
Application manual
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