More than 50% of the Variable Speed Gearbox 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 chosen. Others are using epicyclic gears with a hydrodynamic superimposition drive.
Taking benefit of the condition of the artwork in electric motors and frequency converters, the driving system for the superimposition of the earth carrier is based on a Permanent Magnet Synchronous Superimposition (SI) electric motor and an Active Front-End Cycle Converter. Therefore – 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. Frequently medium-voltage motors fed by frequency converters and parallel shaft gears are chosen. Others are employing epicyclic gears with a hydrodynamic superimposition drive.
It started with hydraulic fluid couplings generating slippage with results very little better than the throttle.
The look of hydraulic clutches then improved and included a torque converter and a superimposed epicyclic drive.
Variable Frequency Drives (VFD) were developed and, simultaneously, the cost of the shaft trains increased, therefore did efficiency. The issue of THD (Total Harmonic grid Distortion) rose and held VFD out of many applications.
Taking advantage of the condition of the art in electric motors and frequency converters, the driving system for the superimposition of the planet carrier is founded on a Long term Magnet Synchronous Superimposition (SI) electric motor and an Active Front-End Cycle Converter. Therefore – E means Electric.
This 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 circumstance, the vibration will become monitored and kept on a periodic basis. If the 360 Hz signal is present in the vibration spectrum, it isn’t normally of any concern. If, however, various other unexplained frequencies come in the vibration spectra, after that it might be advisable to have a look at both the current waveform and the current spectrum. In the web pages that follow, some examples of problems discovered in DC drives and motors are provided.”
It started with hydraulic fluid couplings making 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.
Adjustable Frequency Drives (VFD) were developed and, simultaneously, the expense of the shaft trains increased, therefore did efficiency. The problem of THD (Total Harmonic grid Distortion) rose and held VFD out of many applications.