Failure analysis of retrofitted cooling towers' fans motors with variable frequency drives

For approximately one year a frequent failure of coupling parts was observed after the successful retrofitting and operation of the motors of the cooling towers (CTs) fans with variable frequency drives (VFDs) at the airport site. The technician detected a powder underneath the coupling, which contained particles of rubber sleeve. A thorough investigation showed that the VFDs' configurations were not in accordance with VFDs Company's schematic control layout. Moreover, the CTs' leaving water temperature sensor goes directly to the building management system (BMS) and then to VFDs controls panels. Subsequently, any fault in the BMS control has direct effect on the temperature sensor signal to the VFDs controller. Recommendations were given to the client to replace the existing VFDs with advanced VFDs, since the existing electrical components of VFDs panels, such as the capacitors, transistors, and electrical wiring, are considered outdated according to their limited lifespan. Moreover, it was suggested to install a temperature sensing probe in the CTs' leaving common water header to the VFDs panels directly to avoid any faults from the BMS.