## 3 Results  
Some Resources Related to IAEPf, ESP and CAEPf in Motor Condition Monitoring Experimentally Revealed  
Figure 10 shows the variation of IAEPf over time during a no-load run test with the motor idling at the first speed (750 rpm theoretical synchronous speed).  
At start-up (by direct connection to the electrical network), zone A (shown in detail in the centre left of the figure) indicates a severe transient regime in which the absorbed IAEPf is very high (peaking at 9506 W) due to the acceleration of the rotor (start-up takes 71.5 ms). The energy absorbed during this transient process (ESP = 334.5 W\(\cdot\)s) is calculated as the area (here coloured in cyan) bounded above by the IAEPf curve and below by a line representing the CAEPf value (437 W) and is converted mainly into mechanical energy, stored as rotor kinetic energy. The starting time, the ESP and CAEPf values (eventually the start-up time) can be considered indicators of the quality of the rotor (motor) condition. The CAEPf value is calculated as the average IAEPf during a stationary operation regime. This CAEPf supplies electrical dissipative phenomena (e.g., heating in the stator winding and rotor cage) and mechanical dissipative phenomena (e.g., dry and viscous friction during rotor movement).  
Figure 9: A sequence of \(u_{SL}[s\cdot\Delta t]\) signal involved in the determination of the IAS value and the angular origin of the rotor.  
A magnified view of B area (when the motor is electrically disconnected) is shown in the centre right of Figure 10. This shows the variable part of the IAEPf (as VIAEPf). Here, area C describes a phenomenon due to the electrical cut-off device (it does not characterise the motor behaviour).  
By comparison with Figure 10, Figure 11 shows the same starting, stationary and stopping regime with the motor in no-load operation at 1500 rpm theoretical synchronous speed. Details A, B and C have meanings already discussed in Figure 10, detail D is represented and discussed in Figure 12. This time, as expected, the ESP value (888.48 W-s) and the starting time (93.6 ms) are higher. Unexpectedly, the CAEPf value (213.5 W) is lower than before despite the increase in mechanical energy dissipation. This means that the proportion of electrical dissipation in the CAEPf is much higher than that of mechanical dissipation.  
Each of these two IAEPf graphs (taken at the beginning of the motor's service life and used as a reference) can be compared later with graphs taken at regular (reasonably long) intervals. By highlighting any differences between them, changes in motor condition (rotor behaviour) can be identified.  
Figure 11: The variation of the IAEPf over time during a no-load test at 1500 rpm theoretical synchronous speed.  
Figure 10: The variation of the IAEPf over time during a no-load test at 750 rpm theoretical synchronous speed.  
There are many other experimental resources available in the IAEPf signal. For example, Figure 12 shows a zoomed-in detail in region D of Figure 11 at the end of the transient (start) regime.  
Here, the damped periodic viscous free response of the rotor dynamic system (with angular vibration) has been illustrated via IAEPf evolution. This system was excited when the transient regime suddenly ceased. This is also an element of motor condition monitoring (via frequency and damping ratio). This subject has already been studied before in [45].  
This result provides additional evidence as to why IEP (via IAEPf) is more suitable than IC for engine condition monitoring. The IC alone cannot correctly describe the free response from Figure 12, nor the two short periods when the absorbed IAEPf is temporarily negative.