Digital Input Module PFSK130 3BSE002616R1

Digital Input Module PFSK130 3BSE002616R1

Digital Input Module PFSK130 3BSE002616R1

A breakdown of the insulation between a transformer winding and the core or the tank may result in a large fault current which causes severe damage to the windings and the transformer core. A high gas pressure may develop, damaging the transformer tank. Fast and sensitive detection of earth faults in a power transformer winding can be obtained in solidly earthed or low impedance earthed networks by the restricted earthfault protection. The only requirement is that the power transformer winding is connected to earth in the star point (in case of star-connected windings) or through a separate earthing transformer (in case of delta-connected windings).

The low impedance restricted earth-fault protection REFPDIF is a winding protection function. It protects the power transformer winding against faults involving earth. Observe that single phase-to-earth faults are the most common fault types in transformers. A sensitive earth-fault protection is therefore desirable. A restricted earth-fault protection is the fastest and the most sensitive protection, a power transformer winding can have and will detect faults such as:

• earth faults in the transformer winding when the network is earthed through an impedance • earth faults in the transformer winding in solidly earthed network when the point of the fault is close to the winding star point. The restricted earth-fault protection is not affected, as a differential protection, with the following power transformer related phenomena:

• magnetizing inrush currents

• overexcitation magnetizing currents

• load tap changer

• external and internal phase faults which do not involve earth

• symmetrical overload conditions Due to its features, REFPDIF is often used as a main protection of the transformer winding for all faults involving earth.