New Electric Superimposition Variable-Speed Drive

Germany-based specialist in drive technology Renk is presenting a new mechanical variable-speed drive with a superimposition low-voltage induction electric motor to control the speed of compressors or pumps: RECOVAR-E. The name stands for Renk ECOnomic VARiator, the E indicating the electric superimposition drive.

For most compressors and pumps above 3 MW using variable-frequency drives (VFD) with medium-voltage electric motors, RECOVAR-E becomes an alternative solution bringing benefits in efficiency, maintenance, and total harmonic grid distortion (THD).

Energy efficiency is for sure the main advantage of this system; for lower speeds, the superimposition recycles the power subtracted from the main driver. For higher speeds, with the power of superimposition added to the main motor, the main motor can be downsized with lower purchase costs and lower losses.

System losses with the RECOVAR-E are clearly lower than those in systems with hydrodynamic superimposition. According to calculations at Renk, RECOVAR-E has an efficiency performance of approximately 95% across the whole speed range (RECOVAR-E covers speeds between 70 and 105%, but a larger speed range can be achieved).

Another important advantage of the RECOVAR-E is ease of maintenance and of first horizontal assembly, thanks also to the number of elements in the entire system that is kept to a minimum.

The configuration of the power-splitting gear set is composed of three planets and features a full horizontal split line that allows to remove each planet with its bearings and the central pinions directly on site, without the need for removal of the gear from the foundation. The superimposition motor can be removed on site too without disrupting the casing alignment.

When considering harmonic distortion to the electrical grid, RECOVAR-E showed an entire distortion in operation of about 15% of that with conventional VFDs, and this is especially appreciated in applications with limited grids as FPSOs or offshore terminals.

Renk will demonstrate the new RECOVAR-E variable-speed drive with electric superimposition during an event to be held at the Augsburg headquarters on February 12, 2020. For more information visit

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