Siemens 7SR12 Argus - Page 379

7SR11 & 7SR12 Applications Guide
©2017 Siemens Protection Devices Limited Chapter 7 Page 23 of 48
I
F
I
L
I
01
I
02
I
03
Feeder
1
Feeder 2
Feeder
3
Resonant
coil
Figure 2.8-2 Earth fault current distribution in Compensated network
Three methods are commonly employed to detect the wattmetric current. The 7SR12 relay has customer settings
that can be configured to provide each of these methods.
I
RES
V
RES
I
RES
V
RES
Faulted circuit
Healthy circuit during fault
Figure 2.8-3 Earth fault current direction in compensated network
(i) The directional boundary can be used to discriminate between healthy and faulted feeders. The characteristic
angle is set to approximately 0º and the boundary at +90º used to detect the direction of the resistive component
within the residual current. Setting of the boundary is critical to discriminate between faulted and unfaulted
circuits. Setting ‘67SEF Compensated Network’ to ‘Enabled’ will set the directional boundaries to ±87º around the
characteristic angle, fine adjustment of the boundary may be necessary using the characteristic angle setting.
Faulted
V
RES
Characteristic Angle
Healthy
Figure 2.8-4 Adjustment of Characteristic Angle
(ii) The element measuring circuit can be subjected to only the cosine component of residual current i.e. to directly
measure the real (wattmetric) current due to losses. The current I
RES
Cos(θ-Ø) is calculated where θ is the
measured phase angle between residual current and voltage and Ø is the characteristic angle. This option is
selected by setting ‘Ires Select’ to ‘Ires Real’. The characteristic angle should be set to 0º.