ABB Relion 670 series - Principle of operation; Full scheme measurement; Impedance characteristic

6.4.2 Principle of operation
6.4.2.1 Full scheme measurement
The execution of the different fault loops within the IED are of full scheme type, which
means that each fault loop for phase-to-ground faults and phase-to-phase faults are
executed in parallel.
The use of full scheme technique gives faster operation time compared to switched
schemes which mostly uses a phase selector element to select correct voltages and
current depending on fault type. So each distance protection zone performs like one
independent distance protection function with six measuring elements.
6.4.2.2 Impedance characteristic
The distance function consists of five instances. Each instance can be selected to be
either forward or reverse with positive sequence polarized mho characteristic
alternatively self polarized offset mho characteristics with reverse offset. The operating
characteristic is in accordance to figure
117 where zone 5 is selected offset mho.
Zs=0
R
jx
Mho, zone4
Mho, zone3
Mho, zone2
Mho, zone1
Offset mho, zone5
IEC09000143_2_en.vsd
X
R
Zs=Z1
Zs=2Z1
IEC09000143 V2 EN
Figure 117: Mho, offset mho characteristic and the source impedance influence on the mho characteristic
1MRK505222-UUS C Section 6
Impedance protection
241
Technical reference manual