## 4 Analysis of the Diagnostic Signals--Experimental Results  
### Short Description of the Experimental Setup  
Experimental tests were conducted on a specially designed setup with the induction motor of special construction, which allowed for physical modelling of inter-turn short-circuits in each of three phases of the motor and exchanging of rotors with different rotor bar failures. The squirrel cage induction motor of 1.5 kW was fed from an industrial frequency converter (with 10 kHz modulation frequency), in the frequency range \(f_{s}=20\div 50\) Hz, operating in an open-loop system under scalar control \(u_{s}\)/\(f_{s}=const\). The rated data of the motor are presented in Table 1.  
The load torque of the tested motor was changed from zero value to nominal load. The measurement data acquisition and analysis of phase currents as well as phase-to-phase stator voltages were conducted using an industrial computer NI PXI 8186 (National Instruments, Austin, TX, USA) equipped with DAQ NI PXI-4472 measurement card with very high resolution. Stator and rotor winding damage monitoring was carried out using a computer measurement and diagnostic system based on virtual tools developed in the LabVIEW environment. To reflect the real nature of the stator winding damage, the current in the shorted turn was not limited with additional resistance. A schematic diagram and the real drive system are presented in Figure 3, while in Figure 4 the details of the fault modelling in stator and rotor windings are shown.  
The tests were carried out for various types of stator or rotor winding damage as well as mixed defects. During the tests, special attention was focused on the changing operating conditions of the machine, in order to ensure high efficiency of fault detection regardless of the load torque and reference speed of the drive system.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name of the Parameter** & **Symbol** & & **Units** \\ \hline Power & \(P_{N}\) & 1500 & [W] \\ Torque & \(M_{N}\) & 10.16 & [Nm] \\ Speed & \(N_{N}\) & 1410 & [r/min] \\ Stator phase voltage & \(U_{\text{s}N}\) & 230 & [V] \\ Stator current & \(l_{\text{s}N}\) & 3.5 & [A] \\ Frequency & \(f_{\text{s}N}\) & 50 & [Hz] \\ Pole pairs number & \(p_{p}\) & 2 & [-] \\ Number of rotor bars & \(N_{r}\) & 26 & [-] \\ Number of stator turns in each phase & \(N_{s}\) & 312 & [-] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Rated parameters of the tested induction motor.  
Figure 3: Experimental setup: (**a**) block diagram; (**b**) real view. PWM: pulse width modulation.  
The conducted research was limited to examining the impact of the following electrical faults of the driving motor:  
* \(0\div 5\) shorted turns of one stator phase that constituted 1.6% of stator turns in phase A,
* \(0\div 2\) damaged rotor cage bars that constituted 7.7% of rotor bars.  
The stator winding has been specially prepared so that you can make a short circuit of the proper number of turns in each phase of the stator. A corresponding group of coils was led out to the terminal board, and the short-circuit was physically modelled through a metallic connection. The research presents the impact of a fault in a single phase of the motor winding (Figure 4a).  
Rotor damage, in the form of broken bars, was modelled by preparing rotors with pre-drilled windings. In addition, the resulting holes were sealed to reduce the impact of the rotor imbalance (Figure 4b).  
On the basis of the conducted tests, the symptoms of rotor and stator defects of the induction motor were selected in order to start the process of Kohonen networks' learning. The self-organizing maps were implemented in the LabVIEW environment of National Instruments using Matlab software [45].