ABB RELION 670 Series Applications Manual page 104

Section 6
Differential protection
6.1.3.4 Zone selection (CT switching)
The so-called CT switching (that is, zone selection) is required in situation when one particular
circuit (that is, bay) can be connected to different busbars by individual disconnectors. Typical
example is a station with double busbars with or without transfer bus as shown in figure
figure 61, where any feeder bay can be connected to any of the two buses. In such cases the status
of all busbar disconnectors and all transfer disconnectors shall be given to the busbar protection.
Traditionally, the CT switching has been done in CT secondary circuits. However, with REB670 this
is not the case. All necessary zone selection (that is, CT switching) is done in software. Therefore,
the CT secondary circuits are always intact and without any auxiliary relay contacts.
To provide proper zone selection (that is, busbar replica) the position information from all relevant
primary switches (that is, disconnectors and/or circuit breakers) must be given to the IED. This is
typically done by connecting two auxiliary contacts (that is, normaly open and normaly closed aux
contacts) from each primary switch to the IED binary inputs (that is, optocouplers). In REB670
configuration one SwitchStatus function block shall be associated with each primary switching
device. This block is then used internally to derive the primary object status and then pass this
information to the busbar protection internal Zone Selection logic.
6.1.3.5 Auxiliary contact requirement and evaluation
Auxiliary contact requirements for disconnectors and circuit breakers
The position of the primary switching object is typically obtained via two auxiliary contacts of the
primary apparatus. The first auxiliary contact indicates that primary device is closed. In protection
literature it is called by different names as stated below:
• Normally open auxiliary contact
• "a" contact (that is, 52a)
• "closed"
The second auxiliary contact indicates that primary device is open. In protection literature it is
called by different names as stated below:
• Normally closed auxiliary contact
• "b" contact (that is, 52b)
• "open"
Typically both contacts are used to provide position indication and supervision for busbar
protection.
6.1.3.6 Minimum contact requirements
The minimum requirement for the busbar replica is the record of the disconnector position by
using just one auxiliary contact, either NO or NC type. However recording a pair of auxiliary
contacts, representing the OPEN and CLOSE position, offer additional features which can improve
the reliability of the bus replica including supervision possibilities.
6.1.3.7 Auxiliary contact evaluation logic
Two logic schemes can be found.
98
1MRK 505 337-UUS A
M12107-3 v3
68 and
SEMOD127523-5 v2
SEMOD127523-18 v1
SEMOD127523-21 v2
Application manual