6.2.2
Function block
Figure 467: Function block
6.2.3
Functionality
The current circuit supervision function CCSPVC is used for monitoring current
transformer secondary circuits.
CCSPVC 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.
CCSPVC 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.
6.2.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of CCSPVC can be described with a module diagram. All the modules
in the diagram are explained in the next sections.
Figure 468: Functional module diagram
Differential current monitoring
Differential current monitoring supervises the difference between the summed
phase currents I_A, I_B and I_C and the reference current I_REF.
The current operating characteristics can be selected with the
Start value setting.
When the highest phase current is less than 1.0 × In, the differential current limit is
defined with
Start value. When the highest phase current is more than 1.0 × In, the
differential current limit is calculated with the equation.
1MRS757644 H
Supervision functions
620 series
Technical Manual
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