Electro-Mechanic Speed Control With New Veco-Drive

BY ROBERTA PRANDI

Voith recently launched its Veco-Drive, a new family of variable speed drives that covers from 4 to 15 MW of a compressor’s rated shaft power with four frame sizes.

Dr. Martin Tilscher, product manager for the Veco-Drive within Voith Turbo Division Industry in Crailsheim, Germany, said that the new Veco-Drive is an innovative solution combining a mechanical planetary gear with frequency-controlled servo motors. “This opens up completely new possibilities to an overall system optimization,” he added. “The electrical superimposing gear—or power-split concept—is the most efficient way to make speed variable, as most power is transmitted directly using the highest possible efficiency of a planetary gear.”

Servo motors are used to generate the superimposing speed and, since they need only a small part of rated power, the overall component efficiency reaches more than 97%.

This value was demonstrated by Voith during tests at its Crailsheim headquarters. The company was able to measure that, compared to a typical medium-voltage variable frequency drive train with step-up gearbox, the Veco-Drive is about 2% more efficient over the entire speed range. Voith calculated that potential annual savings can exceed 2000 MWh and, with a typical energy cost of €50/MWh, the annual cost reduction can amount to more than €100 000.

“We have built a prototype train with a rated power of 5.5 MW for test purposes. It increases the input speed of a four-pole motor running at constant speed and generates an output speed of up to 12 200 rpm; output speed can be turned down to 7320 rpm, which is a speed regulating range of 40%,” Tilscher said. “We carried out a comprehensive measurement campaign, including mechanical values such as torque, speed, and vibration; lube oil data as temperature and pressure; and data from the electric system as for example voltage, current and temperature.

“Input speed and torque gave us the mechanical input power; output speed and torque gave the output power transmitted by Veco-Drive; and voltage and current in the line to the frequency converter gave the amount of electric control power.”

Tilscher added that the test considered also transformer losses between the grid and the low-voltage variable frequency drive. So the efficiency measurements carried out by Voith considered all power losses in its scope of supply (variable speed drive, transformer, and low-voltage frequency converter) including those from the transformer, the power cabling, and those from the servo motors with their forced cooling system. On the mechanical side, the test considered machine gears, bearings, lube oil pump, oil splashing, and ventilation.

“All these measurements confirmed that Veco-Drive reaches a total component system efficiency of over 97% with maximum efficiency at rated point of 96.4%,” emphasized Tilscher.

The Veco-Drive has been inspired by the principle of the Voith Vorecon drive which has collected so far over 600 installations. The electric superimposed gear was a first for the company and was launched in Shanghai in May 2017. It is now commercially available worldwide with a delivery time of just nine months.

According to Tilscher, the component is available in a modular series design, with four frame sizes in the power range from 4 to 15 MW for output speeds between 5000 and 15 000 rpm.

The Veco-Drive is suitable for compressors and pumps in the oil & gas and petrochemical industry, and for boiler feed pumps and fans in power plants. Tilscher said that he sees very good market opportunities in the oil & gas industry, especially in downstream and midstream applications.

“The four frame sizes currently available for Veco-Drive cover from 500 to 650 mm shaft height. The modular approach we adopted allows up to offer this outstanding delivery time,” said Tilscher. “The machine can be used for 50 and 60 Hz grids, and four-pole constant-speed motors of 1500 or 1800 rpm can be used as the main driver.

“For pump driving, we offer Veco-Drive with a speed range from 50 to 100%, while for compressor drive we offer it with 70 to 105% speed range. The machine operates at ambient temperatures from -20 to 40°C, and the cabinets at 0 to 40°C.”

The variable speed drive is available also in an explosion-protected design, and offers some advanced functions as for example integrated PLC-based output controller, user interfaces, and condition monitoring.

“A mechanically-driven oil pump is also offered as an option, which provides lube oil as long as the train is turning so the customer does not need to install an overhead tank or a battery-buffered electric pump.

“Another valuable option is an integrated motor starter, whereby the servo motors are used to accelerate the main motor and synchronizing it before it is connected to the grid. This avoids large inrush currents and protects the electric grid at the site.”

One other important cost advantage of Veco-Drive is that the small amount of power needed for control allows additional power to be supplied to the drivetrain, with the potential for adopting a smaller main motor.

Veco-Drive is the start of a new Voith product family and Tilscher stated that it is very likely this family will be extended in the future in terms of power, speed and functionality. “We have had a very positive resonance after our recent launch in Shanghai; Voith is very proud for such a great start and is sure that this innovative product will soon be absorbed by the market.”