Internal fault
region
0 deg
180 deg
90 deg
270 deg
120 deg
Angle could not be
measured. One or both
currents too small
NegSeqROA
(Relay Operate Angle)
IminNegSeq
Internal /
external fault
boundary.
Default ± 60 deg
External fault
region
The characteristic is defined by the
settings:
IMinNegSeq and NegSeqROA
en06000433-2.vsd
IEC06000433 V2 EN-US
Figure 69: NegSeqROA: NegSeqROA determines the boundary between the
internal- and external fault regions
7.3.3.4 Open CT detection
M15266-340 v5
The Generator differential function has a built-in, advanced open CT detection feature.
This feature can block the unexpected operation created by the Generator differential
function in case of open CT secondary circuit under normal load condition. An alarm
signal can also be issued to station operational personnel to make remedy action once
the open CT condition is detected.
The following setting parameters are related to this feature:
• Setting parameter OpenCTEnable enables/disables this feature
• Setting parameter tOCTAlarmDelay defines the time delay after which the alarm
signal will be given
• Setting parameter tOCTReset defines the time delay after which the open CT
condition will reset once the defective CT circuits have been rectified
• Once the open CT condition has been detected, then all the differential protection
functions are blocked except the unrestraint (instantaneous) differential protection
The outputs of open CT condition related parameters are listed below:
1MRK 502 071-UUS A Section 7
Differential protection
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 183
Application manual
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