In a closed loop power flow test bench, all torque-loaded components form a mechanical closure system which is driven by an external drive unit such as motor providing necessary torque. Due to the gear engagement or bearing friction for friction, the closed power flow system generates power loss, but the power loss can be basically compensated by the external drive unit.
In a closed system, the torque is applied by a rotary actuator. If the built-in installation method is applied, the drive shaft should be divided into two parts and rotary actuator is installed in the cross section. If the cantilever installation method is applied, the rotary actuator is suspended at the end of the shaft.