Cooling systems of large capacity adjustable speed drive systems

Over the years, there has been a significant evolution in power semiconductor devices from small, low power devices to very high capacity semiconductor devices. As a result, multi-megawatt range adjustable speed drive systems are gaining acceptance in the global onshore and offshore oil and gas industry. Adjustable speed drives are used on liquefied natural gas compressor trains, gas pipeline compressors and other critical rotating machinery. As power levels increase, cooling of a drive system becomes a key application consideration of the overall system safety, reliability, operation, maintainability and design. This paper highlights, contrasts, and compares drive cooling methods, and their operation, materials, fluids and technologies. Advantages and disadvantages of air and liquid cooling are discussed along with a decision making flowchart on which cooling method to use at certain power levels and applications. A comparative study of air versus liquid-cooling and how misapplication of cooling systems can lead to reduced reliability and high operating and maintenance costs. The paper concludes with general guidelines on specifying and evaluating cooling systems for adjustable speed drives.