ABB RELION 620 Series Technical Manual page 789

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1MRS757644 F

Technical Manual

Function block

GUID-6447040F-55DC-4FA5-9111-0941695F8544 V1 EN

Function block symbol

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

CUBPTOC has a blocking functionality. It is possible to block the function outputs,

timers or the function itself, if required.

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.

Protection functions

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