A Variable Frequency Drive (VFD) Provides the Solution to Large Motor Starting Currents and Voltage Drops while Simultaneously Saving Thousands
A large 2500HP Medium Voltage drive rated at 275 amps (4160V) controls the green energy reciprocating compressor at a Chicago area municipal landfill that converts landfill gas (LFG) into electric power.
In early December 2013, a large landfill energy developer faced a problem with the local electrical utility company at one of their Chicago area plants. Despite the use of a Reduced Voltage Soft Starter (RVSS), their 2250HP compressor motor would draw so much current that the voltage dropped in neighboring residential areas. The voltage drops would shut off televisions, reset computers, and cause dimming and flickering lights, as well as many other power disruptions. Calls of complaint from the neighboring community would flood into the utility company with each start of the compressor. Finally, with tension high between the utility company and the local community, the utility company issued a cease and desist letter to the generation facility informing them that until a solution was implemented resolving the voltage drop issues, the motor could not be started. The shutdown resulted in over $30,000 a day, or over $200,000 a week, in production losses. With such a high production loss, it was imperative that the generation facility not only find a suitable solution, but find one quickly.
(Picture) Two different views of the reciprocating compressor.
If the landfill energy developer found a way to stop their compressor from drawing so much current on start-up, the voltage drops in the surrounding community would stop. To do that, they needed to find a way to eliminate the high starting currents when they started their large motor. Variable Frequency Drives (VFDs) not only have the ability to eliminate the high currents associated with starting a large motor, but they also have a very high power factor, which helps to reduce voltage drops.
Now that the solution had been identified, the difficulties of finding a manufacturer that could deliver and install a VFD with a quick turnaround time became a challenge. Since many Medium Voltage VFDs are used on applications that involve very specific requirements, it was unlikely that a manufacturer would have an option fitting their needs in stock and ready for shipment immediately. Average lead times for manufacturing Medium Voltage VFDs can take anywhere from 16 to 20 weeks, which was time the landfill energy developer did not have with such high production losses.
In addition to the challenge of finding a manufacturer, the upcoming holiday season created additional concerns. Slow shipping over the holidays, a question about whether an experienced engineer would be available for start-up and programming, and if they would be free to fly to Chicago on such short notice over the holidays were all major concerns.
Fortunately, with VFDs.com, all of those concerns were addressed and met. The landfill energy developer placed their order on December 18th, 2013 and just two days later, the VFD shipped to the facility. Considering the complexities and difficulties associated with providing a Medium Voltage Drive so quickly, the turnaround and delivery were significant.
(Picture) Shown above is the 2500HP, 275 Amp Medium Voltage Drive after installation at the facility.
After the order was placed and shipped to the Chicago area, an engineer from VFDs.com traveled to the facility over the holiday weekend between Christmas and New Year’s to oversee start up and programming. Upon completion, a call to the utility company was made and the generation facility was given the green light to start their compressor again. The success of the VFD was evident when, after the compressor had been started, the electrical utility operator had to ask if it had been turned on, as the voltage remained steady on his testing equipment.
While the VFD was the solution to the motor’s high starting current and voltage drops, VFDs can also be a leading cause of power quality problems on electrical grids. In order to ensure that the VFD implemented at the facility did not create yet another utility problem, a 24-pulse “clean power” VFD was supplied. By using this 24-pulse system, negligible harmonic distortion is produced and any potential problems with harmonics and power quality are averted. If no plan had been in place to control the high frequency noise from the VFD, it is likely that additional power quality problems would have been created, eventually leading to the utility issuing another order of shut down.
Knowing this, it was crucial that the facility worked with qualified engineers and VFD specialists so they could avoid creating another potential problem, which would have cost them additional thousands in production loss if they were forced to shut down again.
A beneficial byproduct of the facility shutdown was the significant energy savings generated from using the VFD on the large compressor. After the VFD was implemented at the facility, less energy was used to operate the compressor, which meant more energy available for sale going back to the grid. The energy savings realized for this specific facility has produced a verified savings in excess of $100,000 per year. In addition, there have been no customer complaints concerning voltage drops caused by the compressor since the installation of the VFD at the landfill energy developer’s facility.
VFDs.com and EMC
Based out of Salt Lake City, Utah, VFDs.com is a division of Energy Management Corporation (EMC). For over 30 years, EMC has been a leading provider of high performance Medium Voltage and Low Voltage Motor and Drive Systems. Services offered include: a wide variety of VFDs, custom VFD panels, engineering services, and drive repairs.
Landfill Energy Developer
Landfill gas-to-energy projects have been designed around the world to generate renewable energy from discarded and harmful waste. Landfill gas-to-energy projects are not only a significant source of renewable energy, but they also use readily available resources present in local communities to offset the use of non-renewable resources.