ABB Relion 650 Series Applications Manual page 86

Section 7
Current protection
7.2 Four step residual overcurrent protection, zero, negative
sequence direction EF4PTOC (51N/67N)
7.2.1 Identification
Function description
Four step residual overcurrent
protection, zero or negative
sequence direction
7.2.2 Application
The four step residual overcurrent protection, zero or negative sequence direction EF4PTOC
(51N_67N) is used in several applications in the power system. Some applications are:
• Ground-fault protection of feeders in effectively grounded distribution systems. Normally
these feeders have radial structure.
• Back-up ground-fault protection of subtransmission and transmission lines.
• Sensitive ground-fault protection of transmission lines. EF4PTOC (51N_67N) can have better
sensitivity to detect resistive phase-to-ground-faults compared to distance protection.
• Back-up ground-fault protection of power transformers with ground source at substation.
• Ground-fault protection of different kinds of equipment connected to the power system such
as shunt capacitor banks, shunt reactors and others.
• Negative sequence direcitonal ground-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 ground-fault protection of double-circuit medium or long
transmission lines with significant mutual coupling.
In many applications several steps with different current pickup levels and time delays are needed.
EF4PTOC (51N_67N) can have up to four, individual settable steps. The flexibility of each step of
EF4PTOC (51N_67N) 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 ground-fault protection in meshed and effectively grounded
transmission systems. The directional residual overcurrent protection is also well suited to
operate in teleprotection communication schemes, which enables fast clearance of ground faults
on transmission lines. The directional function uses the polarizing quantity as decided by setting.
Voltage polarizing (3V
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.
Choice of time characteristics: There are several types of time characteristics available such as
definite time delay and different types of inverse time characteristics. The selectivity between
80
IEC 61850
identification
EF4PTOC
or V ) is most commonly used, but alternatively current polarizing (3I
0 2
© Copyright 2013 ABB. All rights reserved
IEC 60617 ANSI/IEEE C37.2
identification device number
51N/67N
2
IEC11000263 V1 EN-US
1MRK 505 287-UUS B
IP14509-1 v5
M14881-1 v4
M12509-12 v6
or I )
0 2
Busbar protection REB650
Application manual