The transportation of natural gas requires more compressors than any other sector of the oil and gas market due to the long distances the gas has to travel between gathering, processing, and distribution sites. Currently, the pipeline system has more than 1,400 compressor stations, with over 40 million horsepower of compression capacity that maintain pressure on the pipeline network and assure continuous movement of supplies. The average existing compressor is an 8,000HP gas turbine, and most of the existing horsepower is over 40-years and is highly inefficient. For environmental reasons, the use of electricity driven compressors for new pipelines and compressor replacements has been growing.

Advantages of Electrically Driven Compressors

Using electric motors to drive compressors offers distinct advantages over gas turbines:

• Lack of Emissions: Electric motors do not create any onsite emissions. In fact, emissions from power plants are far lower on a per KW basis compared to onsite gas turbines. The lack of emissions from electric motors also creates profit opportunities for gas pipeline owners to sell their emission rights to others. In addition, electric motors have lower noise emissions.
  
  

• Faster Permitting: No emissions (and lower noise output) allows a faster environmental permitting process for new sites. This process, which can prevent or delay gas turbine installations, is approved in a much shorter time for electrically driven compressors. Although new technologies, such as catalysts and filters, are being developed to reduce emissions from gas turbines, the cost of this additional equipment is as expensive as the gas turbine itself and requires very high levels of maintenance.
  
  

• Predictable Electricity Costs: Electricity costs are more stable compared to natural gas prices due to over 50% of electricity being generated from coal in North America and nuclear in Europe. Also, industrial buyers can negotiate predictable long-term electric costs with distributors. In addition, natural gas pipeline operators can take advantage of ‘packing,’ where gas is compressed in pipelines and storage locations at night when the electric prices are lower.

Advantages of DDS Permanent Magnet (PM) Motors

A DDS high-speed, PM solution offers multiple advantages over both gas turbines and conventional electric motors:

• Initial Cost: The initial cost of a DDS PM motor is lower than a gas turbine drive or a conventional motor/gear box.
  
  

• Maintenance Cost: The life of an electric motor is well over 15 years before a major overhaul (rewinding of stator). However, in a conventional motor, the bearings and oil lubrication system require maintenance. The necessary speed-increasing gearbox also requires regular maintenance and oil changes. A DDS PM motor that runs on magnetic bearings and requires no gearbox avoids these costs.
  
  

• Higher Efficiency: Electric motors provide much higher efficiencies at full or partial loads compared to any gas turbine on the market. In a gas turbine, gas is burned and turned into mechanical shaft power at maximum operating efficiencies of approximately 31%.  When a typical 60% load is added, efficiency is reduced to approximately 15%. DDS PM motors provide higher efficiencies than the conventional electric machines available today.
  
  

• No Gearbox: In order for a conventional electrical motor to drive a compressor, a mechanical gearbox must increase its speed to higher compressor shaft speeds. However, the gearbox is the least reliable component in a conventional electrical compressor system. Not only is it unreliable and subject to high levels of maintenance, but it also possesses dynamic imbalances, which cause vibrations and noise. In contrast, a DDS high-speed, PM motor runs at compressor speeds and does not require a gearbox.
  
  

• Lower Life Cycle Cost: Due to high operating efficiencies at full and partial loads, DDS PM motors provide owners with the shortest payback period and lowest life cycle cost without sacrificing reliability.