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 chosen. Others are using epicyclic gears with a hydrodynamic superimposition drive.
Taking advantage of the condition of the art in electrical motors and frequency converters, the driving system for the superimposition of the earth carrier is founded on a Long lasting Magnet Synchronous Superimposition (SI) motor and a dynamic Front-End Cycle Converter. So – E means Electric.
This is a high-speed gear drive system incorporating components that allow the usage of a low-cost constant-speed (electric) driver for a variable-speed application.
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 using epicyclic gears with a hydrodynamic superimposition drive.
It started with hydraulic liquid couplings making slippage with results very little 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 issue of THD (Total Harmonic grid Distortion) rose and held VFD out of many applications.
Taking advantage of the state of the artwork in electrical motors and frequency converters, the driving system for the superimposition of the earth carrier is based on a Long term Magnet Synchronous Superimposition (SI) electric motor and a dynamic Front-End Cycle Converter. So – E means Electric.
This is a high-speed gear drive system incorporating components that allow the utilization 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 engine. In a normal circumstance, the Variable Speed Gearbox vibration will become monitored and stored on a periodic basis. If the 360 Hz signal exists in the vibration spectrum, it is not normally of any concern. If, however, other unexplained frequencies come in the vibration spectra, then it might be advisable to take a look at both current waveform and the current spectrum. In the webpages that follow, a few examples of problems uncovered in DC 
drives and motors are presented.”
It started with hydraulic liquid couplings producing slippage with results very little 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 expense of the shaft trains improved, and so did efficiency. The problem of THD (Total Harmonic grid Distortion) rose and kept VFD out of several applications.