SEL Falling Conductor Mitigation Solution

William O’Brien
San Diego Gas & Electric Company

Eric Udren
Quanta Technology, LLC

Kamal Garg, Dennis Haes, and Bala Sridharan
Schweitzer Engineering Laboratories, Inc.

ABSTRACT

When an overhead electric power distribution circuit conductor breaks—for example, when a car strikes a pole or a splice or clamp fails—the energized conductor falls to ground. The resulting high-impedance ground fault may be difficult or impossible to detect by relays located in the substation. In any case, no ground fault protection relay can operate until well after the time the fault has occurred—after the falling energized conductor has hit the ground and created a hazardous situation. For decades, utilities and equipment manufacturers have worked to develop methods for tripping these hazardous ground faults as quickly as possible. This paper describes a new falling conductor detection scheme that trips the affected circuit section in the narrow time window between the moment of the break and the time the conductor hits the ground. The affected circuit section is de-energized while the conductor is still falling, eliminating the risk of an arcing ground fault or energized circuits on the ground.

Jim Li
Anterix, Inc.

Henry Loehner and Tanushri Doshi
Schweitzer Engineering Laboratories, Inc.

ABSTRACT

The falling conductor protection (FCP) application developed by Schweitzer Engineering Laboratories, Inc. (SEL) depends upon reliable, low-latency broadband communications to de-energize broken distribution power lines as they fall, eliminating the risk of wildfire caused by arcing of live wires on the ground. This paper describes the test bed operation of the FCP application enabled by a private Long-Term Evolution (LTE) network using Anterix’s 900 MHz band spectrum. It reports that, in a range of network congestion and signal strength scenarios, the 900 MHz private LTE network successfully supports the FCP application to de-energize the affected circuit section within one second. This is less than the time it takes for a broken conductor to fall to the ground, typically a distance of 25 feet.

Charlie Cerezo and Caleb Murphy
San Diego Gas & Electric Company

Tanushri Doshi, Rohit Sharma, and Jay Lopes
Schweitzer Engineering Laboratories, Inc.

ABSTRACT

When an overhead distribution conductor breaks and the energized wire falls on the ground, it often creates a high-impedance ground fault, which may be difficult or nearly impossible to detect by traditional protective equipment in the substation. Even if conventional protective devices detect this high-impedance ground fault, it is important to remember that the detection and isolation process begins well after the energized conductor has been in contact with the ground, possibly for several seconds to several minutes. This condition presents wildfire risks and a public safety hazard.

San Diego Gas & Electric Company (SDG&E) has implemented a falling conductor protection (FCP) solution based on synchrophasor technology and high-speed IEC 61850 Generic Object-Oriented Substation Event (GOOSE) tripping. This solution detects and trips the affected circuit section within milliseconds of the break. The affected circuit section is de-energized before the conductor touches the ground, thereby eliminating the risk of safety hazards caused by an energized downed conductor. SDG&E has implemented this solution to date on multiple 12 kV circuits with traditional communications layouts using Ethernet radios. This paper discusses the first-of-its-kind FCP solution implemented on a 12 kV rural distribution circuit with a private Long-Term Evolution (LTE) network. The circuit has been commissioned and is in service under monitoring mode since June 2022.