What is CHM?

Circuit Health Monitor (CHM) technology provides continuous monitoring and assessment of events and conditions on electric circuits. CHM applies sophisticated signal processing, pattern recognition, and other digital techniques to high-fidelity line voltage and current waveforms from conventional current and potential transformers (CTs and PTs), typically located at a substation.

The CHM system consists of two principal components: a fleet of CHM devices, typically applied one per circuit, and a centralized master station that manages the fleet, retrieves circuit condition information from the fleet of devices, and provides a central portal for users to access that information. Most algorithmic processing is done by the devices, not the centralized master station. The CHM system uses secure communications techniques between the fleet of devices and the master station.

Background of CHM technology

Researchers at the Texas A&M Engineering Experiment Station (TEES) have created technologies to improve operational visibility of power systems, by monitoring conventional current and potential transformer (CT and PT) waveforms, of high fidelity, and continuously applying sophisticated algorithms to those waveforms to detect circuit events, including low-current events that typically are “invisible” to conventional technologies, such as protective relays, power quality meters, and advanced metering infrastructure (AMI) systems.

Early research focused on the long-standing industry problem of HiZ* faults. In contrast with conventional system protection, which operates by detecting gross variations in current amplitude, HiZ technology analyzes spectral and temporal content of high-fidelity current waveforms to detect HiZ faults of small current amplitude. HiZ technology was licensed for commercial use by General Electric/Multilin.

Researchers subsequently tackled the broader problem of detecting a wider variety of system events, including apparatus pre-failures and other undesirable circuit operating conditions. This effort, initially funded primarily by the Electric Power Research Institute (EPRI), began with the sole focus of anticipating faults and thus became known as Distribution Fault Anticipation (DFA). The DFA moniker has gained some industry recognition, and it persists, although DFA technology has capabilities well outside a conventional definition of “fault anticipation.”

HiZ and DFA technologies share similar requirements, including input signal requirements, but historically were practiced as separate technologies in separate platforms. An upgraded platform, scheduled for late 3Q2014, for the first time advantageously combines these two complementary technologies in a comprehensive Circuit Health Monitor (CHM) system. A sample of the types of events and conditions CHM can detect are described on a separate web page.

* High-impedance faults typically occur when an overhead line breaks, falls to the ground, and arcs, but draws too little current to trip conventional system protection systems. High-impedance faults can persist indefinitely and present shock and fire hazards. Various terms are used interchangeably for high-impedance, downed-conductor faults. TEES has adopted the term HiZ, but terms such as Downed Conductor Detection (DCD) should be taken as synonymous.