Intelligent sensors are one of the fundamental building blocks of the smart grid, with their ability to provide data on the state or health of the grid in real time. [Engerati-Smart Grid Modernization – A Practical Guide]
As part of an initiative to build out a “predictive grid” for DTE Energy, Tollgrade Communications is aiming to benchmark the detection and response to power outages based on monitoring with smart grid sensors. The first set of data is now available in the first of what will be eight quarterly reports.
Building a predictive grid for the Motor City
DTE Energy and Tollgrade’s ‘Building a predictive grid for the Motor City’ initiative is intended as a comprehensive modernization of the grid in the Detroit metropolitan area, where the utility is headquartered.
The project, which is also a Clinton Global Initiative (CGI) Commitment to Action, involves deployment of Tollgrade’s LightHouse Predictive Grid platform starting in late 2013. The platform comprises medium voltage sensors and predictive grid analytics that communicates with the sensors to bring back the events that are captured into centralized software to classify grid conditions and assess the health of the network in real-time.
The deployment is being phased and beyond the sensor deployment and event classification phases, the final phases will cover tying events to the SCADA for faster restoration and outage prevention based on the classified events.
Based on six months of data, 86% of the events classified were line disturbances, which precede an outage but do not trip protection or typically raise alarms. Of the others, 10% were momentaries and just 4% were actual outages.
The data also indicated that line disturbances are closely related to outages by following a similar pattern, with most events occurring in the summer months then dropping off dramatically in October, with a slight uptick in the winter during the months of November and December. In the summer the most likely cause is leaves of trees hitting the power lines, while in winter causes include ice storms, cars hitting poles during ice storms and trees falling over among others.
By contrast, momentaries are the highest in the summer months, most likely due to lightning strikes, and dramatically drop off in the winter.
Power outage causes
Actual events that caused power outages on the DTE Energy network were found to include underground cable failure, wire contact and pole top transformer failure.
Each of these present a unique waveform, which has now been classified, enabling a proactive response before an outage occurs, or in the case of transformer failure a reduced power restoration time.
“Through our CGI commitment with Tollgrade, we have a goal to prevent 10 outages a year over the next two years in the DTE Energy service territory where the LightHouse system is deployed,” said Vince Dow, Vice President Distribution Operations at DTE Energy. “Not only does the solution help us to classify events that can prevent power outages, it will also help us to get vital information to our crews to restore power outages faster when they are unavoidable. This will positively impact the Detroit area economy.”
Among the lessons learned is the importance of viewing line disturbances as an early indicator to outages and, therefore, that they should be closely monitored and adopted as a new category essential to preventing future outages.
As an example the report also cites the case of a large northeastern utility in the US also using the Lighthouse platform, which discovered a failing voltage regulator and responded before its failure and what would have been a three-hour power outage affecting about 2,000 customers in December 2014.
According to Tollgrade, currently LightHouse is the only smart grid sensor to register line disturbances.
Other lessons learned:
• DTE Energy realized that adding sensors on the line near existing switching locations is preferable, as if a fault occurs on the line, the problem area can be isolated with almost immediate power restoration to the remaining customers.
• DTE Energy leadership wanted to leverage the existing investment in their ABB/Tropos advanced metering infrastructure (AMI) system for the communication path for LightHouse sensors, leveraging their smart metering investment into the distribution automation part of their network.
• DTE Energy is in the process of taking ownership of the city of Detroit’s electric grid which was previously run directly by the city. For a minimal investment, the company will be able to deploy Tollgrade sensors throughout the network and gain immediate visibility in a matter of weeks.
According to a Tollgrade statement, US businesses lose an estimated average $15,709 every 30 minutes during a power outage costing $104-164 billion annually. Another $15-20 billion is lost annually due to momentaries.