Power Line Phenomena Detectable with Intelligent Monitoring (Partial List)

The TEES Circuit Health Monitoring system detects multiple types of circuit apparatus failures and pre-failures, including downed conductors and other potential fire-ignition sources, thus enabling proactive response to some failures and quicker response to others. By providing greater visibility of circuit health and events, it enables improved reliability, operational efficiency, and safety. The technology achieves these benefits by using sophisticated signal processing analytics to process high-fidelity current and voltage waveforms that are measured passively from conventional current and potential transformers typically available in substations.

Power line tear-down, including those caused by off-ROW trees – This is a common cause of wildfires. It often can be detected only after it occurs, rather than proactively, but potential for fire spread can be reduced by detecting the resulting downed conductor more quickly. An AMI system or a customer call may alert the utility that an outage has occurred, but does not distinguish downed conductor events from routine outages and therefore cannot elevate the response to an emergency-priority event. The TEES CHM system detects downed conductors and other arcing faults.

Conductor slap – This is a common cause of wildfires. When power line conductors slap together, they eject molten, possibly burning particles capable of igniting ground-level vegetation and other fuels. Each incident also progressively erodes the circuit conductors, weakening them and raising the potential for a broken conductor. Spans susceptible to slap tend to experience it repetitively, but long periods of time may pass between incidents and, as a result, the condition often is never recognized. Location and repairs generally are straightforward, but possible only if the condition is detected. TEES CHM has detected and helped locate conductor slap in multiple locations on circuits of multiple utility companies. The utilities seldom had any other notice of the condition.

Failing bushings and other circuit apparatus – A failing bushing often causes multiple flashover faults, over the course of days or weeks. Experience shows that customers are not a reliable source from which to learn of the momentary interruptions caused by these flashovers, even after multiple interruptions. Each incident creates a high-temperature power arc and may eject molten, possibly burning particles, which are potential ignition sources. Each incident also progressively erodes the affected conductors, weakening them and potentially leading to broken, downed conductors. Flashovers to the housing of a transformer or other circuit equipment also can breach the housing, allowing moisture ingress and the potential for a catastrophic failure involving explosion of the equipment and expulsion of burning insulating oil. Detecting these failures reduces the number of flashover faults, the number of incidents that eject particles, the degree of conductor erosion, the potential for broken conductors, and the potential for other catastrophic failures. The CHM system detects and helps locate failing bushings and other conditions that cause repetitive flashover faults.

Arcing inside capacitor banks – Capacitor banks can develop internal arcing that can last for an extended period of time and eventually breach the capacitor housing, eject burning oil, and create ignition sources for pole top and ground-level fires. TEES CHM detects capacitor arcing, which otherwise may occur for hours to days to weeks before the utility becomes aware of it.

Failing clamps and line switches – Hotline clamps and line switches commonly experience a failure mode in which their mechanical jaws degrade, creating low-level arcing in the jaws, further eroding the jaws and the attached power line conductors. This is a known cause of pole top fires and broken conductors. The failure is a progressive one. TEES CHM often detects these failures hours, days, or weeks before they escalate to cause fires, outages, or other condition that gets the attention of the utility company or customers.

Routine capacitor bank failures – Switched capacitor banks frequently experience failures, such as loss of a phase. The periodic testing and maintenance that are intended to detect these failures are expensive and inefficient, and even may be deferred in times of tight budgets or overworked crews. Further, testing and maintenance typically occur only annually, so capacitors may remain in a failed state for months. With substation-only monitoring, and without communicating with the capacitors, TEES CHM reports inoperative phases of switched feeder capacitors, enabling the creation of work lists to address failures as they occur, rather than waiting for an arbitrarily long routine maintenance interval.

Non-routine capacitor bank defects – Periodic maintenance detects some types of capacitor failures, including blown phases. It does not detect other types of failures and pre-failures, however, including switches that bounce when closing or restrike when opening. These conditions occur intermittently and can cause difficult-to-diagnose power quality problems that affect sensitive customer equipment. Periodic maintenance also may not detect capacitor controller problems that have been documented to switch banks too frequently, perhaps dozens of times per day, but only under certain operating conditions. The CHM system detects and reports these and other non-routine capacitor bank defects. (Also see closely related item above, on “Arcing inside capacitor banks.”)

Primary cable failures and pre-failures – Failing primary cables sometimes produce detectable pre-failure electrical signatures hours to weeks in advance of failure. Also, when cables experience final failure, they sometimes produce unique electrical behavior. TEES CHM system detects these conditions.

Diagnosis of fault cause – Some apparatus failures create fault signatures unique to the type of failure. Crews responding to outages or other trouble can respond more effectively if they know the fault cause before they begin their search. Some failure-specific signatures currently are known. In the future, it is anticipated that these signatures will be added to the CHM system, which accepts new or refined software analytics, without change of hardware.

Oversight of unmonitored reclosers and sectionalizing switches – Many circuits, in particular the long circuits typical of rural service territories, use numerous unmonitored reclosers and automatic sectionalizing switches to limit outage extent when faults occur. The CHM system reports fault sequences involving these devices, enabling detection of proper and improper operation. This has been demonstrated to detect reclosers that are operating incorrectly (e.g., incorrect sequences or too many shots without lockout) and conversely to validate correct operation of otherwise-suspect reclosers.

Fault location– The CHM system reports fault current and other fault-location information for operations of substation feeder breakers and also for fuse blows and line recloser operations. These values can be put into system models to provide fault location.