Tractional Load; Sensitivity Issues - GE L60 Instruction Manual

CHAPTER 8: APPLICATION OF SETTINGS DISTANCE/BACKUP SUPERVISION
Figure 8-4: Using FlexElements for harmonics detection
The typical pickup setting for THD is 10 to 25%. THD measurements are available per source. As such, for breaker-and-a-
half applications, the source used to sum the CT currents can be used.

8.2.6 Tractional load

Where tractional load is tapped from the line protected by the L60, significant and variable negative-sequence current can
exist on the line, thereby not allowing sensitive FDL and FDH settings. On such lines, it is beneficial to detect faults based
on change in the sequence components of the currents. Again, FlexElements can be used for such an application.
Figure 8-5: Using FlexElements to detect changes in current sequence components
8
The figure depicts FlexElements programmed to detect changes in the positive, negative, and zero-sequence currents two
times per power cycle on a 50 Hz system. The FlexElement outputs are assigned to the and
87PC FDL AUX 87PC FDH AUX
settings to start phase comparison when a change in the current components is detected. These FlexElements are
immune to slow increases of the current components, but operate for step changes of the operating quantities.

8.2.7 Sensitivity issues

Phase comparison is fundamentally dependent on the coincidence of local and remote squares to ensure a correct
tripping decision. However, ensure correct starting by the FDL detector and arming action by the FDH detector, to allow the
coincidence detector operate correctly. Therefore, some precautions are necessary when choosing settings for FDL and
FDH or assigning auxiliary elements to compliment those detectors.
L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL 8-7