Identification; Application - ABB Relion 670 Series Applications Manual

1MRK 511 358-UUS A
7.4.1

Identification

Function description
Four step residual overcurrent
protection
7.4.2

Application

The four step residual overcurrent protection EF4PTOC (51N_67N) is used in several applications in
the power system. Some applications are:
• Ground-fault protection of feeders in effectively grounded distribution and subtransmission
systems. Normally these feeders have radial structure.
• Back-up ground-fault protection of 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.
• Ground-fault protection of different kinds of equipment connected to the power system such
as shunt capacitor banks, shunt reactors and others.
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 is most commonly used, but alternatively current polarizing where currents in
transformer neutrals providing the neutral source (ZN) is used to polarize (IN · 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
different overcurrent protections is normally enabled by co-ordination between the operate time
of the different protections. To enable optimal co-ordination all overcurrent protections, to be co-
ordinated against each other, should have the same time characteristic. Therefore a wide range of
standardized inverse time characteristics are available: IEC and ANSI.
Application manual
IEC 61850 IEC 60617
identification identification
EF4PTOC
4(IN>)
4
alt
4
TEF-REVA V2 EN-US
Current protection
ANSI/IEEE C37.2
device number
51N_67N
Section 7
M14881-1 v5
M12509-12 v9
137