Outages - Prevention Better Than Cure

Smart grid sensors identified a ‘conductor slapping’ event that would otherwise have resulted in a major outage.
Published: Mon 11 Jan 2016

Outages are by far the most serious occurrence for utilities with a potentially major impact on customers and the wider economy as well as the company bottom line.

In the United States outages impact the average consumer about 90 minutes a year, compared with for example 70 minutes in the UK or 53 minutes in France. While many of the outages can be attributed to weather-related incidents, almost a quarter of them are due to ageing assets reaching their natural end-of-life. Non-storm related power outages are estimated to cost the country as much as US$200 billion. Identifying events before they turn into outages, and if an outage does occur, minimizing its impact and restoring power as fast as possible are critical for utility operations.

Such is the promise of smart grids with the potential of sensing and analytics to detect, identify and locate events on the network in near real-time. For outage situations with such monitoring many utilities could get a 10-15-minute advance notice, enabling them to take immediate preventive action.

An outage avoided

An example of an outage avoided is at a large US East Coast utility, which in early 2015 had rolled out Tollgrade Communications’s smart grid sensors on its circuits to improve system reliability and enhance electric service to its customers.

In October, a series of unusual momentary faults alarms were sent to the engineering team. When investigated with the accompanying waveforms, it was found that a tree falling on a power line had generated a large fault producing a massive amount of current going through the lines and causing them to swing (i.e. conductor slapping). This movement created a series of cascading faults that just kept repeating until the feeder would eventually have shut down and resulted in a power outage for the entire area with more than 10,000 customers.

“This type of event is extremely difficult for utilities and network operators to identify or locate if all three phases of the electric grid are not monitored in real-time. Even though the sensors were installed with a different application in mind, they uncovered an issue no one would have known existed,” comments David Maloney, Senior Sales Engineer at Tollgrade Communications.

With the areas where there was too much slack between the power lines identified, the company has been able to add spacer insulators to prevent a recurrence in the event of a fault.

Smart grid sensors help improve reliability

Tollgrade’s Lighthouse MV sensors and predictive grid analytics are currently deployed at over 30 utilities on three continents. Among these is the Detroit utility DTE Energy, where their use in power restoration following a substation fire has been demonstrated. [DTE Energy Improves Power Outage Management With Smart Grid Sensors]

As part of an initiative to develop industry benchmarks, findings over a 15-month period across six utilities are as follows:

• 84% of the events classified by sensors were line disturbances that often precede an outage

• 13% of the events were momentaries

• Just 3% percent of the events were actual power outages.

All of these have followed a similar pattern over the 15 months. Most events have occurred in the summer months, with a slight uptick entering the month of December and another increase in March. There was also a steep increase entering the summer months and more specifically with the number of line disturbances with a 25% increase in comparison to the winter season.

Summer months consistently display high frequency of events, mostly due to high loading on lines, equipment failures and being a storm season with heavy rain and winds. The winter months displayed little activity, until early Spring, when late-season cold temperatures and ice storms impacted a large section of North America and affected numerous customers. The steep increase for the summer season is explained by two factors – more sensors in the field and, therefore, more data collected and targeting of poor performing circuits.

The data also confirms earlier findings of a close correlation of line disturbances to outages, indicating the importance of viewing line disturbances as an early indicator to outages. Accordingly line disturbances should be carefully monitored and adopted by utilities and regulators as a new category essential to preventing future outages.

Further reading

Tollgrade Communications: Predictive Grid Quarterly Report. Volume  4, December 2015.