A lot more than 50% of the compression and pumping systems above 3 MW require a variable-speed drive. Often medium-voltage motors fed by frequency converters and parallel shaft gears are selected. Others are employing epicyclic gears with a hydrodynamic superimposition drive.
Taking advantage of the state of the art in electric motors and frequency converters, the driving program for the superimposition of the planet carrier is based on a Permanent Magnet Synchronous Superimposition (SI) motor and an Active Front-End Cycle Converter. So – E means Electric.
That is a high-speed gear drive system incorporating Variable Speed Gearbox components that allow the usage of a low-cost constant-speed (electric) driver for a variable-speed application.
A lot more than 50% of the compression and pumping systems above 3 MW need a variable-speed drive. Frequently medium-voltage motors fed by frequency converters and parallel 
shaft gears are chosen. Others are using epicyclic gears with a hydrodynamic superimposition drive.
It started with hydraulic fluid couplings producing slippage with results not much better than the throttle.
The design of hydraulic clutches then improved and included a torque converter and a superimposed epicyclic drive.
Adjustable Frequency Drives (VFD) were developed and, simultaneously, the price of the shaft trains increased, therefore did efficiency. The issue of THD (Total Harmonic grid Distortion) rose and kept VFD out of several applications.
Taking advantage of the state of the art in electric powered motors and frequency converters, the driving program for the superimposition of the planet carrier is based on a Long lasting Magnet Synchronous Superimposition (SI) motor and an Active Front-End Cycle Converter. So – E stands for Electric.
That is a high-speed gear drive system incorporating components that allow the use of a low-cost constant-speed (electric) driver for a variable-speed application.
All of the above plots were taken by analyzing the existing to the electric motor. In a normal scenario, the vibration will be monitored and stored on a periodic basis. If the 360 Hz signal is present in the vibration spectrum, it is not normally of any concern. If, however, other unexplained frequencies come in the vibration spectra, then it would be advisable to check out both the current waveform and the existing spectrum. In the pages that follow, some examples of problems discovered in DC drives and motors are presented.”
It started with hydraulic fluid couplings producing slippage with results very little much better than the throttle.
The design of hydraulic clutches then improved and included a torque converter and a superimposed epicyclic drive.
Variable Frequency Drives (VFD) were developed and, at the same time, the cost of the shaft trains increased, and so did efficiency. The issue of THD (Total Harmonic grid Distortion) rose and kept VFD out of many applications.