It's a Gold Rail Series Thomas. They were released in 1993 in the US. Bandai also made them too for Japan known as the Thomas Engine Collection Series (shortened to TECS) for a longer period. Both ranges had a series of sets too, but I think only one, the Roundhouse, was in both ranges.
The switch on the engine activates the magnets, so when you want to uncouple from trucks, you just flick the switch and they pull apart.
The switch on the engine activates the magnets, so when you want to uncouple from trucks, you just flick the switch and they pull apart.