ABB RELION 620 Series Technical Manual page 603

1MAC504801-IB E
6.4.2
6.4.3
6.4.4
620 series ANSI
Technical Manual
Function block
GUID-6EDF2732-697A-4770-AF30-A957E20E7054-ANSI V1 EN
Figure 305: Function block
Functionality
The CT secondary circuit supervision function MCS 3I, I2 is used for monitoring the
current transformer secondary circuit where a separate reference current transformer input
for comparison is not available or where a separate voltage channel for calculating or
measuring the zero-sequence voltage is not available. MCS 3I, I2 can be used for detecting
the single-phase failure on the current transformer secondary for protection application
involving two or three sets of the three-phase current transformers.
MCS 3I, I2 detects a fault in the measurement circuit and issues an alarm which can be
used for blocking the protection functions, for example, differential protection, to avoid
unwanted tripping.
MCS 3I, I2 is internally blocked in case of a transformer under no-load condition or if a
current in any one phase exceeds the set maximum limit.
Operation principle
The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
The operation of the CT secondary circuit supervision function can be described with a
module diagram. All the modules in the diagram are explained in the next sections.
Section 6
Supervision functions
597