A power system includes an engine including an exhaust line, a turbine in the exhaust line, a bypass line connected to the exhaust line upstream of the turbine and comprising a controllable bypass valve, and a controller arranged to control opening of the bypass valve to bypass the turbine when, for example, the engine is operated such that power is transmitted from the crankshaft to the turbine shaft, and/or at least one of an engine load, an engine speed, and an exhaust line pressure are below predetermined levels. A method of operating a power system is also disclosed.