ABB 615 Series ANSI, Техническое руководство

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1MAC050144-MB C
Section 4
Protection functions
615 series ANSI 327
Technical Manual
Figure 155: Positive direction of current
Unrestrained Differential (High Stage)
The differential protection includes an Unrestrained Differential high stage. The
instantaneous stage operates and the OPR_HS output is activated when the amplitude of
the fundamental frequency component of the differential current exceeds the set
High trip
value or when the instantaneous peak values of the differential current exceed 2.5 · High
trip value . The factor 2.5 (= 1.8 ·
√
2) is due to the maximum asymmetric short circuit
current.
The TRIP output is always activated when the OPR_HS output activates.
The internal blocking signals of the function block do not prevent the operation of the
instantaneous stage. When required, the trip signal due to instantaneous operation can be
blocked by the binary inputs BLK_OPR_HS or BLOCK.
4.6.1.5 Application
The differential protection, works on the principle of calculating the differential current at
two ends of the winding i.e. the current entering the winding is compared with the current
going out of the winding. In case of any internal fault the current entering and leaving the
winding will be different resulting into differential current, which is use as base for
generating trip signal. Due to this principle differential protection do not trip during
external faults. However it should be noted that inter-turn faults in the same phase are
usually not detected unless they are developed into some other kind of fault.
Short circuit between the phases of the stator windings causes normally very large fault
currents. The short circuit gives risk of damages on 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 are dependent on the degree of damage, which is highly dependent on the
fault time. Fast fault clearance of this fault type is therefore of greatest importance to limit
the damages and thus the economic loss.
External fault
ID_A = 0
I_A2 I_A1
I_A2 I_A1
M