A lot more than 50% of the compression and pumping systems over 3 MW require a variable-speed drive. Frequently medium-voltage motors fed by frequency converters and parallel shaft gears are selected. Others are Variable Speed Gearbox employing epicyclic gears with a hydrodynamic superimposition drive.
Taking advantage of the state of the art in electric powered motors and frequency converters, the driving system for the superimposition of the earth carrier is founded on a Long term Magnet Synchronous Superimposition (SI) motor and a dynamic 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.
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 using epicyclic gears with a hydrodynamic superimposition drive.
It started with hydraulic liquid couplings generating slippage with results not much better than the throttle.
The look of hydraulic clutches then improved and included a torque converter and a superimposed epicyclic drive.
Adjustable Frequency Drives (VFD) were developed and, at the same time, the price of the shaft trains improved, and so did efficiency. The issue of THD (Total Harmonic grid Distortion) rose and kept VFD out of many applications.
Taking advantage of the state of the artwork in electric motors 
and frequency converters, the driving system for the superimposition of the planet carrier is based on a Long lasting Magnet Synchronous Superimposition (SI) electric motor and a dynamic Front-End Cycle Converter. Therefore – E stands for Electric.
That is a high-speed gear drive system incorporating parts 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 current to the motor. In a normal situation, the vibration will end up being monitored and kept on a periodic basis. If the 360 Hz signal is present in the vibration spectrum, it is not normally of any concern. If, however, various other unexplained frequencies come in the vibration spectra, then it would be advisable to take a look at both current waveform and the current spectrum. In the web pages that follow, a few examples of problems found out in DC drives and motors are presented.”
It started with hydraulic liquid couplings generating slippage with results not much 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 improved, therefore did efficiency. The problem of THD (Total Harmonic grid Distortion) rose and held VFD out of several applications.