Electric motors, efficiencies listed

The start-point for electrical design is the electric motor and other consumers list. This list is typically drawn up by process and mechanical engineers involved in the selection of the driven equipment. The electrical engineer needs to probe this data and understand how it was drawn up, with special reference to the expected load factors (namely, ratio of actual kW or kVA to the value used as design basis). Rarely, drive sizes are underestimated. More usually, they are consistently overestimated as a result of the practice of putting factors on factors . There may be a factor of conservatism for increased process performance requirements, a factor for driven-machine performance tolerances and deterioration of efficiency, and then perhaps a factor to allow for uncertainty, and, then again, rounding up to the nearest standard motor size. 

The losses from pressurization listed in Table 3.14 are theoretical losses. In an electrolysis cell, it is very difficult to achieve a pressure higher than 100 bars due to engineering difficulties and the crossover of the gaseous products through the electrolyte. Typically, people use compressors driven by an electrical motor to pressurize the gases. If the combined efficiency of the electrical motor and the compressor is around 80% by pressurizing H2 from 1 bar to 700 bars, then the overall efficiency of an electrolyzer due to activation loss, ohmic resistance loss, and pressurization loss will be slightly more than 70% (90% x 70%). 

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