ABB RELION REX640 Technical Manual page 647

1MRS759142 C
REX640
Technical Manual
has most certainly occurred in the area protected by the differential protection relay.
The internal blocking signals of the biased stage are inhibited.
The operation of the differential protection is based on the fundamental frequency
components. The operation is accurate and stable: the DC component and harmonics
of the current do not cause unwanted operations.
Instantaneous high stage
Instantaneous high stage can be enabled or disabled with the Enable high set setting.
The corresponding parameter values are "True" and "False".
The operation of Instantaneous high stage is not biased. 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 operation value High
operate value or when the instantaneous value of the differential current exceeds 2.5 ⋅
High operate value. The value 2.5 (=1.8 ⋅ √2) is due to the maximum asymmetric short
circuit current.
If the biasing current is small compared to the differential current, or if the phase angle
between the currents of the two windings with the highest phase current is close to zero
(normally, the phase difference is 180 degrees) or the phase angle between the
compared phase currents (in case of a two-winding transformer) is close to zero, a
fault has occurred in the area protected by the differential protection. The operating
value set for the instantaneous stage is automatically halved and the internal blocking
signals of the biased stage are inhibited.
Id/Ir
High operate value
OPERATE
AREA (LS)
Slope
section 2
Low operate value
End section 1
GUID-FBF24381-99FC-48C2-BA3E-FB4F39F4EB8F V1 EN
Figure 354: Operating characteristics of the protection. LS stands for the biased
low stage and HS for the instantaneous high stage.
The OPERATE output is always activated with the OPR_HS output. The internal
blocking signals of the differential function do not prevent the trip signal of the
instantaneous differential current stage from being activated. When required, the
operating outputs of Instantaneous high stage can be blocked by the external control
signals BLK_OPR_HS or BLOCK.
OPERATE
AREA (HS)
Slope
section 3
NON-OPERATE
AREA (LS & HS)
End section 2
Section 4
Protection functions
NON-OPERATE
AREA (LS)
Ib/Ir
641