In the second book/movie, lightning strikes a tree at a regular time each day. Katniss shoots an arrow connected to a wire connected to the tree directly at the "sky" of the arena just as lightning strikes, and the electrical current shorts the entire system. She has already discovered that there are force fields surrounding the edges of the arena, and has learnt to recognize the tell-tale cracks. As she aims at the sky, we see the clouds swirl and it loses its verisimilitude, as a beehive pattern shows us the many sections of the huge forcefield. After the explosions, Katniss collapses, but is flown out of the arena by rebels and taken to safety.
In the book, we stay with Katniss's first person perspective, but in the movie version of this situation, we cut from the explosion to see President Snow muttering, "It's not possible" in disbelief. The television screens he is looking at flicker out. He walks to the game masters who are seated around the holographic model of the arena and we see it shut down. Somebody says, "We've lost power."