How does the technology work? – The Circuit Health Monitoring system detects and reports faults, circuit component pre-failures (i.e., incipient failures), and other circuit events by applying sophisticated digital signal processing, pattern recognition, and other techniques to high-fidelity electrical waveforms acquired from CTs and PTs.
How was the technology developed? Texas A&M researchers have performed more than two decades of applied research to characterize electrical waveforms associated with faults, failures, and other events. These efforts involved cooperation with more than a dozen utilities who purchased and installed equipment on their circuits and provided field feedback that enabled correlation of specific waveform “fingerprints” with specific apparatus failures. The resulting system uses automated processes to monitor waveforms 24×7, characterize anomalies, and report specific events.
What types of events can the system detect? – A separate page provides a list of detectable events, some specifically related to wildfire mitigation and others related more generally to system visibility, reliability, operational efficiency, and improved work processes.
What are the major components of the system? – The CHM system has three major components.
- A fleet of substation-based CHM devices, each intended to monitor a single circuit, by: acquiring high-fidelity current and voltage waveforms on a 24×7 basis; detecting and analyzing anomalies in those waveforms; and creating actionable reports.
- A master station, to retrieve, store, and disseminate reports and data from the fleet of CHM devices and to manage that fleet. The master station is an off-the-shelf server computer loaded with custom software.
- A web site to provide a central portal for password-protected access to reports and data.
What is required to install substation-based CHM devices? – The form factor of the CHM device is similar to that of a modern digital relay. Each CHM device consists of a 19” rack-mount enclosure and has terminals for inputs from three conventional 5AAC CTs, three conventional 120VAC PTs, a 12VDC unit power supply, and twisted-pair RJ45 Ethernet/Internet. All terminals are on the rear of the device enclosure.
What kind communication is required? – Each substation-based CHM device communicates with the master station to deliver reports. Each device establishes and maintains an encrypted Internet connection to the master station, to enable bidirectional communication with the master station. Utility companies have provided these Internet connections in a variety of ways, including DSL, cable modem, cellular modem, and radio. Each CHM device can be configured with either a static or dynamic (DHCP) IP address.
What kind of distributed sensing and communication are required? None. Algorithms in the substation-based field devices use variations in substation-measured waveforms to detect events, including faults, component pre-failures, and operations of unmonitored reclosers and switched capacitor banks, along the length of the circuit, without communicating with those circuit devices.
How much data will I have to analyze every day? – The technology automates the analysis of data and requires minimal human effort or specialized knowledge. The system collects a large amount of data each day, but sophisticated analytics, in the substation-based device, analyze the data to generate actionable reports. Waveform files are available for viewing and manual analysis, if desired, assuming that the master station has been configured to retrieve them from the CHM devices.
How does the CHM system integrate with my other systems? – Utility companies have used information reported by the CHM system to locate some kinds of faults and component pre-failures, by manually integrating the CHM information with existing distribution information systems, fault-current studies, load studies, etc. Automating the process of integrating CHM-provided information with other utility systems is an area of research interest.
Can I apply CHM analytics to waveforms from my PQ meter or relay? – Although such devices may have the same CT and PT inputs as the CHM system, they do not sample CT and PT waveforms with sufficient fidelity to support CHM functions. Pre-failure of a line switch, for example, produces a unique electrical signature detectable in CT and PT waveforms, but the magnitude of the signature is too small to be detected by current models of PQ meters and relays.
Does the CHM system provide DFR and PQ recordings? – The CHM system provides high-fidelity DFR (digital fault recorder) recordings of analog quantities (i.e., current and voltage waveforms). It also records waveforms suitable for PQ analysis and performs basic PQ computations.
Can I use unconventional sensors, instead of CTs and PTs? – Circuit component pre-failures and other events produce electrical signatures having substantial current components at non-fundamental frequencies. Texas A&M performed field tests of common models of line post sensors and found that they either heavily filtered or heavily distorted those non-fundamental current components and therefore do not provide signals appropriate for CHM analysis. Texas A&M has not had opportunity to test other unconventional sensors and therefore does not know their suitability, but, in the absence of specific testing, does not recommend the use of sensors other than conventional CTs and PTs, for this project and this technology.
Can I apply one monitoring device per bus, instead of one per feeder? – Application of the technology at the bus level is discouraged. A bus supplies more current than an individual feeder, thereby increasing the difficulty of detecting low-magnitude waveform signatures caused by component pre-failures. In addition, it becomes more difficult to locate pre-failures and faults that cause momentary operations of unmonitored mid-point reclosers, because the faulted circuit cannot be determined from bus-level measurements. Finally, limited testing with bus-level installations indicates that, for a given fault, the bus sees an unpredictably different level of fault current than does the faulted circuit itself, and this difference increases the uncertainty in location methods based on current or impedance. Fault current measured at the bus differs from that measured on the faulted circuit, because, at least in part, a fault on one circuit affects bus voltage, thereby affecting current on each circuit on the bus, in turn affecting total bus current.
Does the technology “learn” over time? – System design anticipates algorithm enhancements over time. All levels of the system, including the substation-based CHM devices, anticipate and support deployment of new or updated algorithms.
At what voltages does the technology work? – The technology was developed and has hundreds of circuit-years of demonstration on distribution circuits ranging from 4kV to 35kV. Early work has been conducted and shows promise on low-voltage (120/208V) grid networks and on transmission circuits (>100kV). The CHM hardware takes inputs from conventional 5A current transformers and 120V potential transformers, so it can be applied across a wide range of circuit voltages. The same CHM devices and system hierarchy are appropriate to any voltage level, but current algorithms are targeted to the detection and characterization of phenomena common at distribution voltages.