I
b2
I
d1
I
d2
I
b3
I
d3
100
200
300
100
200
300
400
500
End section 2
End section 1
Low trip value
Section 1
Section 2
Section 3
I
b
[%In]
I
d
[%In]
GUID-295E8CB1-B4A0-4207-A1B2-F542C5D1DF94-ANSI V1 EN
Figure 290:
Operating characteristic for the stabilized stage of the generator
differential protection function
4.3.5.5
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
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
575
Technical Manual
Содержание Relion 615 series
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