NStar, a Northeast Utilities company that delivers electricity and natural gas to 1.4 million customers in Eastern and Central Massachusetts, said Monday that it has completed work on a three-year, $20 million project that aims to reduce the extent, frequency, and duration of customer outages.

In recent years, storms have put electricity systems in the region to the test, sometimes resulting in outages. A few years ago, the state fined NStar and National Grid for what officials called an inadequate performance in 2011 following Tropical Storm Irene and a Halloween snowstorm referred to as “Snowtober.”

One goal of the upgrade program that NStar refers to as a “self-healing project” is to modernize the electric distribution grid. The “self healing” system, NStar says, combines detection, assessment, decision support, and network control to automatically reroute power around outages, limiting households affected to those closest to the damaged equipment.

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About half the project’s funding came from the US Department of Energy, and the upgrade included the installation of hundreds of automated switches, NStar said.

The upgrades were implemented mostly outside of densely populated urban areas such as the Back Bay in Boston, where a widespread outage occurred in early 2012 after a cable-connection failure at a Scotia Street substation.

“NStar customers are already benefiting from the grid modernization investments made through our self-healing project,” NStar Electric president Craig Hallstrom said in a statement. “While we may not be able to control the weather in New England, we know that this technology enables our system to operate more efficiently than ever in all seasons.”