ABB Relion 670 Series Applications Manual page 104

Section 6
Differential protection
• In two-zone busbar differential protections, it is freely settable by using the setting CheckZoneSel at
each bay function block.
• In six-zone busbar differential protection, the currents of all active feeder bays are measured
unconditionally by the check zone, if the check zone is able to operate. By an active feeder, we
mean a feeder bay which is not deactivated, that is, neither its operMode is Off nor it is out of
service.
And the check zone supervises differential protection zones. Exactly which differential protection zones
shall be supervised by the operation of the check zone also varies, depending on the version of the IED
used:
• In two-zone busbar differential protections, freely settable by using a setting CheckZoneSup at each
zone function block,
• In six-zone busbar differential protection, all active protection zones are supervised unconditionally
by the check zone, if the check zone is able to operate. By an active protection zone, we mean a
zone which both is enabled and used/connected to at least one CT.
Moreover, there are some additional features only available for six-zone busbar differential protection, for
example, the possibilities to externally block the check zone operation.
Please also refer to "Check zone protection" in Technical reference manual, for more details about the
check zone.
6.1.3.4 Switch status monitoring
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 62, 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 Switch
Status 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.
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:
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1MRK 505 370-UUS Rev. K
M12107-3 v4
SEMOD127523-5 v3
Busbar protection REB670
Application manual