# A Cost-Efficient MCSA-Based Fault Diagnostic Framework for SCIM at Low-Load Conditions
## 5 Experimental Study  
This study proposes an MCSA-based diagnostic framework, which was employed on a physical testbed at the Defense Reliability Laboratory, Kumoh National Institute of Technology, Korea. The testbed consists of different four-pole, 0.25 hp, three-phase squirrel cage (delta connection) induction motors operating at different operating conditions, as summarized in Table 1.  
Three-phase induction motors are often exposed to different failure modes that emanate from sources ranging from environmental, thermal, electrical, and other factors. However, some failure modes are more critical than others, and they are prioritized in this study. Misalignment in a motor drive system is severe and the most frequently occurring condition in motor driven systems and may present itself in the form of angular, parallel/offset and/or a combination of parallel and angular misalignment [42]. In reality, it may be highly impossible to experience a single type of misalignment in absolute absence of the other. Often, even an acceptably aligned rotor has some level of a combination of angular and parallel misalignment (though insignificant). On the other hand, another frequently occurring (and critical) failure in induction motors is a broken rotor bar, which often occurs due to mechanical stresses emanating from variable operating conditions [43]. In addition, inter-turn short circuit winding is yet another critical and highly severe failure mode that often results in complete motor breakdown if undetected. This failure occurs as a result of aging and thermal stress to the insulator separating some turns in a particular phase of the motor [1; 13; 44]. Consequently, our study prioritizes these three critical failure modes, which were replicated on the testbed shown in Figure 2.  
\begin{table}
\begin{tabular}{l l l} \hline
**Label** & **Failure Mode** & **Description** \\ \hline ARM-1 & Rotor misalignment & A condition where the center lines of coupled shafts do not coincide. \\ BRB-2 & Broken rotor bar & A stress-induced condition whereby the rotor break and/or cracks \\ ISC-3 & Inter-turn short circuit winding & A condition whereby two coils in a phase connect with each other \\ NOM-4 & Normal operating condition & No fault condition \\ \hline \end{tabular}
\end{table}
Table 1: The different fault conditions of induction motors used in the experiment.  
The induction motors were loaded via a DC loading mechanism--a DC power supply was connected to the driven motor to induce a magnetic field between its rotor and stator, which causes resistance in the driver, resulting in a low-load condition. The motors were operated at a constant speed of approximately 1780 RPM (30 Hz), while data were collected via the driver's terminals using a NI 9246 module connected to a cDAQ-9178 connected to a desktop computer, as shown in Figure 2 above. The digital current signals were collected via a LabVIEW interface and stored in.csv format at a sampling rate of 50 Hz; the spectral resolution of the signals was 0.0003 Hz. Figure 3 shows the manually induced fault conditions to replicate rotor misalignment (ARM-1), a broken rotor bar (BRB-2), and inter-turn short circuit winding (ISC-3) failure modes for the experiment.  
ARM-1 was achieved by first aligning the motors (driver and driven) using a precision laser alignment kit, and then to misaligned them by 0.3 mm for both parallel and angular misalignment. BRB-2 was imitated by drilling two holes of diameter 5 mm to a depth of 5 mm. ISC-3 was imitated by bridging seven (7) coils in the same phase. For control, a motor with no fault/failure mode (NOM-4) was also employed.