A standard low voltage (LV) drive offers a cost-effective alternative to its medium voltage (MV) counterpart when configured in a HI-LO-HI type power configuration. There are numerous advantages in using a VLT® drive in this configuration:
• The design represents a high degree of user friendliness by virtue of using standard components and proven low-voltage IGBT technology.
• It retains the existing ac motor, eliminates voltage reflections, common mode voltages and potentially harmful bearing currents, thereby prolonging the life of the motor. This is made possible by the use of a sine filter which delivers a sinusoidal voltage at the motor terminals. The solution is therefore motor friendly.
• Derating of the drive motor for inverter operation is not necessary, since the motor sees a sinusoidal voltage at its terminals and losses remain the same as for operation from a fixed frequency mains supply.
• The user has the advantage of stocking standard spares and thereby reduces inventory costs.
• Existing users of VLT® drives need not undergo retraining to assimilate new technology, which would be the case with a direct MV Drive. Hence the system saves on training costs.
The solution was put into practice at an application involving an electric submersible pump (ESP) for crude oil extraction from an underground oil well. Sinar Surya Graha Persada, a sub-contractor for Pertamina Corporation, a state owned Petroleum Company located in Jambi province of Sumatra, Indonesia, decided to use the Danfoss solution. This involved replacement of an existing MV Drive with a VLT ® Automation Drive which was engineered in a LO-HI configuration.
Some key reasons for choosing Danfoss, included:
• Its vast experience of supplying drives for critical applications.
• Positive feedback from other customers regarding the performance of VLT® Automation Drive
• Its ability to provide quality application know-how, and service at short notice.
