Converting to electric motors and adjustable speed drives: A case study of a 20,000HP gas turbine driven compressor

Compressors of all forms, types and sizes are the workhorses of the oil & gas industry. Historically, the petrochemical industry has been dominated by mechanical prime movers like gas turbines, steam turbines, and diesel engines for multi-megawatt rotating machinery. Some installations date back almost 40-50 years. In recent times, the prime movers have become difficult and expensive to service and maintain. They often have lower efficiencies than new equipment and availability of spare parts can be difficult. As Environmental Protection Agency (EPA) permits expire and strict emission compliance is mandatory, many end users face the challenging task of decommissioning their entire compressor train and procuring a new one. However, a workable and cost-effective solution is to retrofit existing prime movers while retaining the functioning gas compressor. This paper will present a large pipeline company's experience in replacing an existing gas turbine driven axial compressor with an engineered electric motor driver and adjustable speed drive system (ASD). Issues such as power delivery, application, motor and drive voltage selection, harmonic distortion mitigation, ASD and motor cooling selection, and its effects on Motor & ASD design, and overall strategy for selection and procurement of the equipment will be discussed. The paper outlines a general guideline of how existing mechanical prime movers can be replaced with electric solutions, hence lowering operating cost and increasing efficiency, safety, environmental compliance and overall reliability of the entire compressor train from the utility down to the compressor shaft.