The problem of early fault detection in driven-variable frequency drive induction motor is a subject that is far to be completely solved. The investigation with real data sheets reveals difficulties in separating the faulty data sheets from the healthy ones, which reinforces the importance of constant on-line monitoring. The use of variable frequency drive adds the possibility of to embed the system directly in the equipment, which means more protection to the variable frequency drive besides all the discussed benefits of early fault detection to the machine and to industries. The great advantages of this non-invasive detection system make its improvement a task with great potential; one possibility involves the choice of relevant spectrums as parameters to training the classificator which is not an ended issue and is directly related with the classifier accuracy.

Variable flow water system has played an important role in the field of energy saving with the VFD widely used in practical projects. How to control the VFD to work properly is an essential issue which we must first emphatically solve. The control technology of VFD is closely related to characteristics of pumps. Based on the mathematical a model of pumps with or without variable frequency drives, the paper discusses some issues in detail, such as variable frequency drives configuration, flow rate regulation and overload. These are key issues of control technology of variable flow water system. For those multiple-pump water systems, the engineers may select synchronous frequency conversion control technology or Add-Sub pumps control technology to achieve the maximum energy saving benefits.

Pumps are the most common engineering facilities in the field of building, but we still need to figure out how to make them work correctly. Most importantly, variable frequency drives have come into wide use nowadays with the development of variable flow technology. Combined application of variable frequency drives and water pumps brings us not only good energy-saving benefits but some new problems, such as variable frequency drives configuration and overload etc. This paper has presented a theoretical study to solve the problems.