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 employing epicyclic gears with a hydrodynamic superimposition drive.
Taking advantage of the state of the artwork in electric powered 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. Therefore – E means Electric.
That is a high-speed gear drive system incorporating parts 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 above 3 MW need 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 liquid couplings creating 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, simultaneously, the cost of the shaft trains improved, and so did efficiency. The problem of THD (Total Harmonic grid Distortion) rose and held VFD out of many applications.
Taking benefit of the state of the artwork in electrical motors and frequency converters, the driving system for the superimposition of the planet carrier is based on a Permanent Magnet Synchronous Superimposition (SI) engine and a dynamic Front-End Cycle Converter. So – E stands for 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 over plots were taken by analyzing the current to the motor. In a normal scenario, 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, additional unexplained frequencies come in the vibration Variable Speed Gearbox spectra, then it might be advisable to have a look at both the current waveform and the existing spectrum. In the webpages that follow, some examples of problems found out in DC drives and motors are offered.”
It started with hydraulic fluid couplings producing 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.
Variable Frequency Drives (VFD) were developed and, simultaneously, the cost of the shaft trains increased, and so did efficiency. The problem of THD (Total Harmonic grid Distortion) rose and held VFD out of many applications.