VECO-Drive Offers Electromechanic Speed Control

97% peak efficiency; significant cost savings in pump and compressor applications

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A first for Voith: the new VECO-Drive variable-speed drive family features the principle of an electrical superimposing gear, combining a mechanical planetary gear with frequency-controlled servo motors.
This article was originally published in the Aug./Sept. 2017 issue of COMPRESSORtech2. We only publish a fraction of our magazine content online, so for more great content, get every issue in your inbox/mailbox and access to our digital archives with a free subscription.

Voith has launched its VECO-Drive, a new family of variable-speed drives that come in four frame sizes and cover compressors with rated shaft power ranges from 5400 to 20,000 hp (4 to 15 MW).

Dr. Martin Tilscher, product manager for the VECO-Drive within Voith Turbo Division Industry in Crailsheim, Germany, said that the new VECO-Drive said that the VECO-Drive combines a mechanical planetary gear with frequency-controlled servo motors. “This opens up completely new possibilities to an overall system optimization,” he said. “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%.

Voith demonstrated this value 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 US$59/MWh (€50/MWh), the annual cost reduction can amount to more than US$118,600 (€100,000).

“We have built a prototype train with a rated power of 5.5 MW for test purposes,” Tilscher said. “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. We carried out a comprehensive measurement campaign, including mechanical values such as torque, speed, and vibration; lube oil data such as temperature and pressure; and data from the electric system such as 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.”

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For its new VECO-Drive, Voith built a prototype train with 5.5 MW rated power and tested it on a special test bed where comprehensive measurements were done to take into consideration all possible power losses in Voith’s scope of supply.

Tilscher added that the test also considered 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%,” Tilscher said.

The VECO-Drive was inspired by the principle of the Voith Vorecon drive, which can be found in more than 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 nine months.

The component is available in a modular series design, with four frame sizes in the power range from 5400 to 20,000 hp (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 and gas and petrochemical industries and for boiler feed pumps and fans in power plants. Tilscher said that he sees very good market opportunities in the oil and gas industry, especially in downstream and midstream applications.

“The four frame sizes currently available for VECO-Drive cover from 500 to 650 mm (19.7 to 25.6 in.) shaft height. The modular approach we adopted allows us to offer this outstanding delivery time,” Tilscher said. “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 main drivers.

“For pump driving, we offer VECO-Drive with a speed range from 50 to 100%, while for compressor drives we offer it with 70 to 105% speed range. The machine operates at ambient temperatures from -20° to 40°C (-4° to 104°F), and the cabinets at 0° to 40°C (32° to 104°F).”

The variable-speed drive is available also in an explosion-protected design, and offers some advanced functions such as 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 synchronize 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 employing a system such as the VECO-Drive is that the small part of power that is 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,” he said.

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