Directional Element Design for Protecting Circuits with Capacitive Fault and Load Currents
This paper, based on real world event data, introduces a state of the art directional element that has been proven to prevent many of the commonly reported mis-operations caused by traditional directional elements. Such examples include wind farm collector circuits where there have been a significant number of documented occurrences of false trips due to leading power factor loads caused by dynamic VAR controllers. To mitigate, several ‘work around’ solutions have been devised and published. These include creative yet cumbersome approaches that use load encroachment and reverse power functions, both of which have limitations since they were never intended for that purpose. There are also challenges using traditional directional elements for situations where the fault current is capacitive. Such examples include ground fault current in networks that can be operated as either isolated or compensated. All of these challenges can be overcome using an ‘easy to set’ flexible directional element design that allows for the phase angle operating characteristics to be extended or retracted through its minimum/maximum forward and reverse angle settings. For quick and efficient evaluation of study cases, specific directional element settings have been modeled in protection design software as they appear in the relay to ensure the relay will respond securely and reliably for all operating conditions (grounding methods), system variables and fault scenarios encountered. The paper provides test data and oscillography reports from event (COMTRADE) files to validate the directional element’s performance.