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.
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 differential current is limited to 1.0 × In.
When the differential current I_DIFF is in the operating region, the FAIL output is activated.
The function is internally blocked if any phase current is higher than the set Max operate current. When the internal blocking activates, the FAIL output is deactivated immediately. The internal blocking is used for avoiding false operation during a fault situation when the current transformers are saturated due to high fault currents.
The value of the differential current is available in the monitored data view on the LHMI or through other communication tools. The value is calculated with the equation.
The Start value setting is given in units of ×In of the phase current transformer. The possible difference in the phase and reference current transformer ratios is internally compensated by scaling I_REF with the value derived from the Primary current setting values. These setting parameters can be found in the Basic functions section.
The activation of the BLOCK input deactivates the FAIL output immediately.
Timer
The timer is activated with the FAIL signal. The ALARM output is activated after a fixed 200 ms delay. FAIL needs to be active during the delay.
When the internal blocking is activated, the FAIL output deactivates immediately. However, the ALARM output deactivates after a fixed delay of three seconds.
The function resets when the differential current is below the start value and the highest phase current is more than 5 percent of the nominal current (0.05 × In).
If the current falls to zero when the FAIL or ALARM outputs are active, the deactivation of these outputs is prevented.
The activation of the BLOCK input deactivates the ALARM output.