Application - ABB 615 series Technical Manual

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1MAC059074-MB A

615 series ANSI

Technical Manual

Low trip value

End section 1

GUID-295E8CB1-B4A0-4207-A1B2-F542C5D1DF94-ANSI V1 EN

Operating characteristic for the stabilized stage of the generator

differential protection function

Application

The differential protection works on the principle of calculating the differential current at

the two ends of the winding, that is, the current entering the winding is compared to the

current exiting the winding. In case of any internal fault, the currents entering and exiting

the winding are different, which results in a differential current, which is then used as a

base for generating the trip signal. Due to this principle, the differential protection does not

trip during external faults. However, it should be noted that interturn faults in the same

phase are usually not detected unless they developed into some other kind of fault.

The short circuit between the phases of the stator windings normally causes large fault

currents. The short circuit creates a risk of damages to the insulation, windings and stator

core. The large short circuit currents cause large current forces which can damage other

components in the machine. The short circuit can also initiate explosion and fire. When a

short circuit occurs in a machine, there is a damage that has to be repaired. The severity

and the repair time depend on the degree of damage, which is highly dependent on the fault

time. The fast fault clearance of this fault type is of greatest importance to limit the

damages and the economic loss.

To limit the damages in connection to the stator winding short circuits, the fault clearance

time must be as short as possible (instantaneous). The fault current contributions from

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Protection functions

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