Due to the remote location, poor grid quality, and large inrush current associated with the direct on-line (DOL) connection of electrical motors, INGEDRIVE™ Variable Frequency Drives (VFDs) are becoming more commonly used as motor starters. By nature, a VFD is able to limit the inrush current being supplied to the motor to a minimal percentage of the rated current of the motor, allowing it to have a small impact on the grid upon starting, while also being able to start the unloaded compressor with the time window specified by the operator. This is something that soft-starters cannot accomplish, since they are not able to fully control the inrush current supplied to motor. Additionally, the VFD has the capability to vary the rotational speed of the motor by delivering a variable frequency output. This allows the system operator to operate at reduced levels during times when full load production is not desired
Basis of Operation
As per a project developed for a privately held midstream company in the United States, the operator sends the Start Motor #X command in order to start one of the LNG compressors, and the VFD closes the appropriate Variable Speed Contactor, connecting the output of the VFD with the unloaded motor that is to be started. The VFD will start the motor by gradually increasing the output frequency until it is spinning at the rated speed. Once the rated speed is achieved, the VFD will synchronize the output phases of the VFD with the grid.
After the synchronization of the VFD Output and the Grid has been confirmed, the Full Speed Contactor will be closed. There is a momentary overlap when both the Variable Speed Contactor and the Full Speed Contactor are closed, making it a bump-less transfer involves negligible mechanical torque pulsations.
Unlike some other VFD systems, we offer the possibility of using no additional output reactors on the output of the INGEDRIVE™ VFD to have a Closed or bump-less transfer since the sinusoidal output filter can be added as a standard feature in the VFD. Once the Full Speed Contactor has been closed, the transfer can be completed by opening the Variable Speed Contactor, leaving the electrical motor connected to the grid for full speed operation. This process can be repeated for all four of the motors. When the motor is to be stopped, the Full Speed Contactor is opened, allowing the motors to freewheel down to zero speed, or the Variable Speed Contactor can be reconnected for a controlled stop.
Converter driven compressor soft-start diagram.
INGEDRIVE™ Frequency Converters
INGEDRIVE™ is available with powers up to 44 MVA, from 400 V to 690 V in low voltage and from 3 kV to 6.9 kV in medium voltage, offering a high level of performance and reliability together with a user-friendly interface.
About Ingeteam Group
Ingeteam is an International Technological Group specialized in electric power conversion. Ingeteam’s state of the art developments in power and control electronics (inverters, frequency converters, controllers and protections), rotating electric machines (Indar motors, generators and submersible motor & pumps sets), systems (electromechanical engineering and automation projects), and services (operation & maintenance services), enables the organization to provide the best solutions in a wide variety of sectors, namely: wind, solar PV, hydro and fossil fuel power generation, metal and mineral processing, mining, marine, rail traction, water, e-vehicle charging and power grid automation, always achieving sustainable and efficient energy generation, transmission, distribution and consumption.
The company operates throughout the world, and is permanently based in 24 countries, with a headcount of more than 4,100 employees. Continuous innovation, research and development are the backbone of Ingeteam’s business activity, as 5% of The Ingeteam Group turnover is annually invested in R&D.
Aitor Martinez | Sales Manager, Industry & Marine Drives, Ingeteam Power Technology.
David Benson | General Manager, Industry & Marine Drives, Ingeteam Inc.