On offshore installations space has always been at a premium. With current market conditions requiring cost savings across the board, reducing the footprint of the ESP surface electrical equipment skid would result in reduced costs when fabricating offshore platforms. This paper presents a redesigned Medium Voltage VSD that is significantly smaller and incorporates new technologies that present an added bonus in additional cost savings and characteristics that can increase the run life of the ESP.
A typical offshore installation has one 2,000KVA Step Down transformer that supplies four or five skids, each with their own Low Voltage VSD and Step Up Transformer. With a Medium Voltage Drive, supply line voltage up to 6.6KV does not need to be stepped down, furthermore is no requirement for a Multi Tap Step Up Transformer as the VSD can provide the required medium voltage required for the ESP motor. The removal of these transformers has reduced the space and weight of the surface electrical equipment that influences the size and load bearing capabilities, and fabrication costs, of new installations.
In addition to the space and weight savings, by incorporating new generation VSD technologies, efficiency and reliability can be increased which ultimately prolongs pump run life and reduces operating costs. Cascaded Pulse Width Modulation (PWM) rectification significantly reduces the input harmonic distortion reflected back onto the supply, which can incur penalties from energy providers. The multi-level inverter technology on the output provides a near sinusoidal waveform, which removes the need for the expensive, and heavy, space consuming Sine Wave Filter (SWF) typically required on ESP installations. The cleaner power being delivered to the motor reduces the motor operating temperature and stresses on the electrical system's insulation resulting in a longer run life.
Maintaining a cool operating environment for the drive pushed conventional compressed gas air conditioning methods to their limits. A solution was to employ a Thermo Electric Cooling System. Operating on the principle of the Peltier Effect, a stable operating temperature can be maintained and as there are no moving parts, the TEC system is inherently reliable and economical in comparison to traditional A/C units. Furthermore, the TEC modules are very compact and can be operated in any orientation, in line with the requirement for a reduced footprint.
This new generation VSD technology has resulted in significant cost savings for Operators in terms of Capital and Operating Expenditure. Additionally, the power quality delivered to the motors can result in an extended run life, the ultimate goal for offshore applications.