SOUTH PORTLAND — The city said it will conduct an internal investigation to determine how firefighters on Tuesday damaged a new, $1.1 million ladder truck during a training exercise.

The city said three firefighters were training in the rear parking lot of the Cash Corner fire station when the truck’s aerial ladder made contact with power lines along Skillin Street, damaging portions of the truck’s electrical system.

The electrical surge also caused one of the truck’s front tires to catch fire.

The three firefighters were able to extinguish the flames. After Central Maine Power shut down electricity to Skillin Street, support staff from the truck manufacturer, Pierce, helped firefighters override systems on the truck to lower the ladder so the truck could be stored in an empty bay of the station.

Engineers from the manufacturer are expected to assist in troubleshooting the damage and determine a path moving forward, the city said. In the interim, the city will deploy its 1996 ladder truck.