Function Block - ABB 615 series Technical Manual

Section 6
Supervision functions
6.2.2
6.2.3
6.2.4
846

Function block

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Figure 434: Function block
Functionality
The current circuit supervision function CCM is used for monitoring current transformer
secondary circuits.
CCM calculates internally the sum of phase currents (I_A, I_B and I_C) and compares the
sum against the measured single reference current (I_REF).The reference current must
originate from other three-phase CT cores than the phase currents (I_A, I_B and I_C) and
it is to be externally summated, that is, outside the protection relay.
CCM detects a fault in the measurement circuit and issues an alarm or blocks the
protection functions to avoid unwanted tripping.
It must be remembered that the blocking of protection functions at an occurring open CT
circuit means that the situation remains unchanged and extremely high voltages stress the
secondary circuit.
Operation principle
The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
The operation of CCM can be described with a module diagram. All the modules in the
diagram are explained in the next sections.
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Figure 435: Functional module diagram
1MAC059074-MB A
615 series ANSI
Technical Manual