In directly grounded network the amplitude of single phase fault current is similar to amplitude of short
circuit current. Directly or small impedance grounded network schemes are normal in transmission,
distribution and in industry.
Phase angle setting of the trip area is adjustable as is the base direction of the area (angle offset).
Broad range mode with multi-criteria detection for unearthed and compensated
networks
When protecting compensated long-distance cables and overhead lines it is in some cases dif cult to
distinguish between healthy- and faulty feeder. Merely measuring the angle and magnitude of residual
voltage and currents is not always enough, but changes in symmetrical components of phase currents
and voltages are also needed. Also, when protecting feeders from earth faults two modes are used
depending on the network status (ungrounded or compensated). When changing between these two
statuses setting group must be changed and especially in case of distributed compensation the
change may be dif cult or impossible to arrange. Lastly, in a compensated network protection, the
relay with traditional algorithms may sporadically detect an earth-fault in a long healthy feeder due to
CT errors. For all these reasons, Arcteq has developed an improved alternative to these traditional
directional earth fault protections.
Figure. 5.4.5. - 42. Angle tracking of DEF function. Broadrange mode.
New broad range mode is capable of detecting earth-fault directionally in both ungrounded and
compensated networks not only by just combining the two stages together but using a new multi-
criteria detection. This optional additional tripping condition for compensated networks uses Arcteq’s
patented, high-resolution intermittent earth-fault algorithm with added symmetrical component
calculation of phase currents and voltages. If this mode is activated the tripping criteria comprises of a
measured residual current in the fourth quadrant and the symmetrical components of voltages and
currents detecting a fault. No extra parameterization is required compared to traditional method. Multi-
criteria algorithm can be tested with COMTRADE les supplied by Arcteq. Function requires
connection of 3-phase currents, residual current and residual voltage to operate correctly.
To avoid unnecessary trips encroachment area against I0 CT errors in compensated long healthy lines
can be added.
AQ-F255
Instruction manual
Version: 2.00
79
© Arcteq Relays Ltd
