ABB Relion 670 Series Applications Manual page 140

Section 8
Current protection
8.2.1 Identification
Function description
Directional phase overcurrent
protection, four steps
8.2.2 Application
Directional phase overcurrent protection, four steps OC4PTOC (51_67) is used in several
applications in the power system. Some applications are:
• Short circuit protection of feeders in distribution and subtransmission systems. Normally
these feeders have a radial structure.
• Back-up short circuit protection of transmission lines.
• Back-up short circuit protection of power transformers.
• Short circuit protection of different kinds of equipment connected to the power system such
as; shunt capacitor banks, shunt reactors, motors and others.
• Back-up short circuit protection of power generators.
In many applications several steps with different current pickup levels and time delays are needed.
OC4PTOC (51_67) can have up to four different, individually settable steps. The following options
are possible:
Non-directional / Directional function: In most 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.
Choice of time delay characteristics: There are several types of time delay characteristics available
such as definite time delay and different types of inverse time delay characteristics. The selectivity
between different overcurrent protections is normally enabled by co-ordination between the
function time delays of the different protections. To enable optimal co-ordination between all
overcurrent protections, they should have the same time delay characteristic. Therefore, a wide
range of standardized inverse time characteristics are available for IEC and ANSI. It is also possible
to tailor make the inverse time characteristic.
Normally, it is required that the phase overcurrent protection shall reset as fast as possible when
the current level gets lower than the operation level. In some cases some sort of delayed reset is
required. Therefore, different kinds of reset characteristics can be used.
For some protection applications, there can be a need to change the current pick-up level for some
time. A typical case is when the protection will measure the current to a large motor. At the start
up sequence of a motor the start current can be significantly larger than the rated current of the
134
IEC 61850
identification
OC4PTOC
If VT inputs are not available or not connected, the setting parameter
x = step 1, 2, 3 or 4) shall be left to the default value Non-directional .
(
© Copyright 2017 ABB. All rights reserved
IEC 60617 ANSI/IEEE C37.2
identification device number
51_67
TOC-REVA V2 EN-US
1MRK 511 401-UUS F
M14885-1 v6
M15335-3 v9
DirModeSelx
Bay control REC670
Application manual