4.12.2.3 Functionality
The current unbalance protection for shunt capacitor banks function CUBPTOC
is used to protect the double-Y-connected capacitor banks from internal faults.
CUBPTOC is suitable for the protection of internally fused, externally fused and
fuseless applications.
CUBPTOC has two stages of operation, that is, operation stage and alarm stage.
In the operating stage, CUBPTOC starts when the measured unbalance current
exceeds the set limit. The operation time characteristics can be selected to be
either definite time (DT) or inverse definite minimum time (IDMT). The operation
under alarm stage is either based on the DT characteristics or the faulty element
counter of a capacitor bank.
CUBPTOC has a blocking functionality. It is possible to block the function outputs,
timers or the function itself, if required.
4.12.2.4 Operation principle
The function can be enabled and disabled with the
Operation
setting. The
corresponding parameter values are “On” and “Off”. The current unbalance
protection for shunt capacitor banks operates on the DFT measurement mode.
The operation of CUBPTOC can be described by using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 411: Functional module diagram
Natural unbalance Compensation
A standard double-Y-connected shunt capacitor bank configuration is shown in
Figure 412
. The fundamental frequency component of an unbalance current is
measured on the common neutral connecting the two balanced parts of a shunt
capacitor bank, that is, between star point 1 and star point 2.
1MRS757644 H
Protection functions
620 series
Technical Manual
783
To Next Page
Loading...
