A hybrid working machine providing or receiving electrical power

A working machine comprises a combustion engine (101), an electromechanical power transmission chain (102) between the combustion engine and one or more actuators (109) of the working machine, an electrical connector system (103) for connecting to an external electrical power network (110), and an electronic power converter (104) for transferring electrical energy from the electromechanical power transmission chain to the external electrical power network and from the external electrical power network to the electromechanical power transmission chain. The working machine can be used as an auxiliary power plant for increasing reliability and capacity of power supply. On the other hand, the working machine can be energized merely by the external electrical power network when the capacity of the electrical power network is sufficient and when it is more cost-effective to use the electrical power network than to use the combustion engine.