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 selected. Others are employing Variable Speed Gearbox epicyclic gears with a hydrodynamic superimposition drive.
Taking advantage of the condition of the art in electrical motors and frequency converters, the driving program for the superimposition of the earth carrier is founded on a Permanent Magnet Synchronous Superimposition (SI) electric motor and an Active Front-End Cycle Converter. So – 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.
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 using epicyclic gears with a hydrodynamic superimposition drive.
It started with 
hydraulic fluid couplings making 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.
Adjustable 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 kept VFD out of several applications.
Taking advantage of the state of the artwork in electrical motors and frequency converters, the driving system for the superimposition of the planet carrier is founded on a Long term Magnet Synchronous Superimposition (SI) engine 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.
All of the over plots were taken by analyzing the current to the motor. In a normal circumstance, the vibration will be 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, additional unexplained frequencies appear in the vibration spectra, then it might be advisable to check out both current waveform and the existing spectrum. In the web pages that follow, a few examples of problems discovered in DC drives and motors are shown.”
It started with hydraulic fluid 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.
Adjustable Frequency Drives (VFD) were developed and, at the same time, the expense of the shaft trains increased, therefore did efficiency. The problem of THD (Total Harmonic grid Distortion) rose and kept VFD out of many applications.