Comparative Analysis of Transmission Lines Falling Conductor Protection Methods

An energized overhead conductor may break and fall to the ground or on surrounding objects due to several reasons such as conductor aging, hardware failures, pole knock-over, severe weather conditions, and natural disasters. When an energized conductor falls to the ground or other grounded objects, this may cause a ground fault or arcing. This poses a risk to utility personnel, public safety, equipment, and may ignite wildfires. Traditional broken conductor detection or Falling Conductor Protection (FCP) is typically based on the current unbalance calculated as the ratio of negative sequence current (I2) to positive sequence (I1), with an I2/I1 detection slope set to 20%-30%. However, detecting broken conductor events during lightly-loaded operating conditions may be challenging. Also, it may be challenging to distinguish between broken conductor events and asymmetrical faults within and outside of the zone of protection. The mechanics of a conductor separation depends on the type of hardware failures and may be sudden or gradually evolving over a period of time. This affects the electrical parameters that are continuously measured by Intelligent Electronic Devices (IEDs) and may result in the misoperation of traditional FCP methods. This paper evaluates the effectiveness of existing FCP methods for broken-conductor detection in transmission lines. The FCP methods evaluated include current-based (using the conventional I2/I1 and the modified I2/I1 methods) and impedance-based methods. The performance of these FCP methods is validated using field events playback and hardware-in-the-loop simulations using the Real-Time Digital Simulator (RTDS). Extensive testing using in-zone and out-of-zone broken conductor events, in-zone and out-of-zone fault events, and transient events were tested for an actual transmission system. Lessons learned from the testing and evaluation of the FCP methods are also discussed.