State of the art servo-electric technology brings advantages in front of conventional servo-hydraulic systems being more energy-efficient, maintenance-free, cleaner, and noiselessly.

Either linear, torsion or rotary loads may be applied:

• Linear by means of ball-screw electromechanical cylinders or linear motors (permanent-magnet-excited synchronous linear motors).

• Torsion by means of torque motors (high-pole permanent-magnet-excited synchronous motors).

• Rotary low-pole either asynchronous (three-phase squirrel-cage) or synchronous (permanent-magnet) high power density motors.

Thanks to the 4-quadrant operation of those electric machines (motor-generator) in combination with the inverters (IGBT power semiconductors):

• On torsional fatigue tests the energy applied on the load-increasing part of the cycle (which is stored as elastic deformation into the specimen) is recovered on the load- decreasing part of the cycle and therefore up to 80% electrical power cost savings may be expected in comparison with servo-hydraulic technology.

• Meanwhile on rotary multi-motor testing systems they are coupled through a common DC link allowing the energy to be exchanged between motors that are motoring and generating. In this way, energy is saved, the line infeed is relieved and line harmonics reduced.