Variable frequency drives can be cost effective on a very large range of applications

Variable frequency drives can be installed with manual or automatic bypasses. In the early days of the variable frequency drives, bypasses were more common since variable frequency drives were not as reliable as they are at the present time. The bypasses were installed in the event of a drive failure to ensure the system or process would remain on line. Bypasses are still available but not always installed. The criticality of the application must be considered in each case to determine whether the added cost and security of a bypass is warranted. Harmonic filtering may be necessary in some applications. Variable frequency drives can produce harmonics that can make their way back to the rest of the building and interfere with sensitive electronic equipment and machines. Line reactors can be used on smaller drives of 20 hp and less to dampen and mitigate harmonics. For larger applications, an isolation transformer may be warranted. The isolation transformer can be installed either on the drive or on the piece of equipment to be protected from the harmonics. Because the equipment being protected may be much lower in power, it may be most economical to isolate the piece of equipment from the building supply.