ABB RED650, Applications Manual

Page: 93 / 454

IBase set in primary Amp
M12541-95 v3
Set a common IBase in Global base for the protected line (circuit). Most current
settings for the protection function are then related to the IBase . The setting of
IBase is normally made so that it corresponds to the maximum rated CT in any of
the line terminals. For example, if all CTs used in a protected circuit are 1000A/1A,
that is, the primary current rating is 1000 A, then IBase = 1000 A is a good choice.
NoOfUsedCTs
M12541-98 v8
NoOfUsedCTs indicates to the function the number of three-phase CT sets included
in the protected circuit. Note that one IED can process one or two local current
terminals of the protected circuit. This is the case, for example, in 1½ breaker
configurations in the line bay, where one of the two CT sets will be represented as
one separate current terminal. A two-terminal line with 1½ breaker configurations
at one line end must consequently have
NoOfUsedCTs = 3 .
Current terminals
IEC15000450-2-en.vsdx
IED
IED
IEC15000450 V2 EN-US
Figure 38: Example when setting NoOfUsedCTs = 3 in 1½ breaker
configurations
6.1.3.2 Percentage restrained differential operation
M12541-104 v4
Line differential protection is phase-segregated where the operate current is the
vector sum of all measured currents taken separately for each phase. The restrain
current, on the other hand, is considered the greatest phase current in any line end
and it is common for all three phases. Observe that the protection may no more be
phase-segregated when there is an in-line power transformer included in the
protected circuit. These are usually of the Dy or Yd type and the three phases are
related in a complicated way. For example, a single-phase earth fault on the wye
side of the power transformer is seen as a two-phase fault on the delta side of the
transformer.
Operation : Line differential protection function is switched on or off with this
setting. If the parameter Operation is set to Off this IED is switched over to Slave
mode and trip is initiated by the remote end IED.
The characteristic of the restrained differential function is shown in Figure 39 . The
restrained characteristic is defined by the settings:
1MRK 505 393-UEN B
Section 6
Differential protection
Line differential protection RED650 2.2 IEC 87
Application manual