A machine in which mechanical energy is converted to electrical energy. Generators are made in a wide range of sizes, from very small machines with a few watts of power output to very large central-station generators providing 1000 MW or more. All electrical generators utilise a magnetic field to produce an output voltage which drives the current to the load. The electric current and magnetic field also interact to produce a mechanical torque opposing the motion supplied by the prime mover. The mechanical power input is equal to the electric power output plus the electrical and mechanical losses.