Setting Guidelines; General Settings - ABB RED650 Applications Manual

Section 6
Differential protection
6.1.3
6.1.3.1
86
CT signal disappears when all currents are again normal, or when all three currents
become zero.
• Setting parameter OpenCTEnable enables and disables this feature.
• Setting parameter OCTBlockEnenables and disables the blocking of
differential function once an open CT is detected. When OCTBlockEn is set to
OFF, only an alarm signal is issued.
• Setting parameter tOCTAlarmDelay defines the time delay after which the
alarm signal is given.
• Setting parameter tOCTResetDelay defines the time delay after which the open
CT condition resets once the defective CT circuits have been repaired.
• Once the open CT condition has been detected, all the differential protection
functions are blocked except the unrestrained (instantaneous) differential
protection. However, there is no guarantee that an unwanted disconnection of
the protected circuit can always be prevented.
• For applications where the currents from two CTs are summated and sent over
LDCM, the output OPENCT must be connected to CTFAIL on LDLPSCH
logic in order for the Open CT detection to operate properly. Observe that
summation of currents shall be avoided where possible.
The outputs of the open CT conditions are OPENCT and OPENCTAL.
• OPENCT: Open CT detected
• OPENCTAL: Alarm issued after the setting delay
Outputs (positive integer) for information on the local HMI:
• OPENCTIN: Open CT in CT group inputs (1 for input 1 and 2 for input 2)
• OPENCTPH: Open CT with phase information (1 for phase L1, 2 for phase L2,
3 for phase L3)

Setting guidelines

Line differential protection receives information about currents from all line
terminals and evaluates this information in three different analysis blocks. The
results of these analyses are then forwarded to an output logic, where the
conditions for trip or no trip are checked.
The three current analyses are:
• Percentage restrained differential analysis
•
nd th
The 2 and 5 harmonic analysis (only if there is a power transformer
included in the protected circuit)
• Internal/external fault discriminator

General settings

1MRK 505 393-UEN B
Line differential protection RED650 2.2 IEC
Application manual
SEMOD54832-1 v3
M12541-86 v4
M12541-93 v3