The partial unloadings are generated in the system of isolation of the stator of the rotating machines, there where the local electrical field strenght surpasses value of breakage. The measurement of partial unloadings of rotating machines can take place in line (that is to say, during on-speed operation with load or in emptiness) or out of line (that is to say, during the shutdown of the machine, energizando each winding one after another one). The insulating materials that are used in the rotating machines are resistant at a certain level of partial unloading. Therefore, in normal conditions of operation a great amount of pulses of partial unloading in each one of the phases could be hoped. However, certain partial unloadings can be indicative of defects of aging in the isolation or damages in the structure of the winding: the loose coils or the aggravated semiconducting coatings can give rise to partial unloadings in grooves; the oquedades in the isolation or the deslaminacin can create internal partial unloadings; the humidity or contamination of winding will create superficial partial unloadings.

The different sources from activated partial unloadings simultaneously in the isolation of the winding of the stator are several. Therefore, the key for the correct measurement of the partial unloadings in the windings of the stator is the separation of sources of partial unloadings that are in parallel and the distinction between detrimental partial unloadings active, cases of normal partial unloadings and the outer, present noise inevitably in the industrial surroundings. The engineers use system MPD 600 habitually at present, digital system of measurement of partial unloadings synchronous multi-channel. He works with three or more synchronous channels to separate sources of internal partial unloadings to each other and also to separate them of the noise signals, and individually evaluates each source of partial unloadings in the winding of the stator.