###### Abstract  
The industry has widely accepted Frequency Response Analysis (FRA) as a reliable method to detect power transformers mechanical deformations. While the FRA technique has been recommended in recent literature as a potential diagnostic method to detect internal faults within rotating machines, detailed feasibility studies have not been fully addressed yet. This paper investigates the feasibility of using the FRA technique to detect several short circuit faults in the stator winding of three-phase induction motors (TPIMs). In this regard, FRA testing is conducted on two sets of induction motors with various short circuit faults. Investigated faults include short circuits between two phases, short circuit turns within the same phase, phase-to-ground, and phase-to-neutral short circuit. The measured FRA signatures are divided into three frequency ranges: low, medium, and high. Several statistical indicators are employed to quantify the variation between faulty and healthy signatures in each frequency range. Experimental results attest the feasibility of the FRA technique as a diagnostic tool to detect internal faults in rotating machines, such as induction motors. type:phase induction motor; frequency response analysis; fault diagnosis; short-circuit faults; statistical indicators +
Footnote †: _Scienced Journal of Applied Sciences_
While another survey conducted by the Electric Power Research Institute (EPRI) on the reliability of motors less than 200 HP shows slight statistical differences from the IEEE survey, the likelihood of faults within the stator winding is still substantial [4]. Consequently, it is required to adopt a reliable tool to detect motor degradation at early stages to avoid any potential consequences. Short circuit faults within the stator windings of rotating machines may occur due to insulation breakdown as a result of overloading, insulation aging, and mechanical vibration [5]. Several online and offline diagnostic methods have been adopted by the industry to evaluate the condition of rotating machines, as summarized in Table 1. Partial discharge (PD) measurements are used to assess the stator winding insulation condition. PD test has shown good reliability to detect PD activities within winding insulations [6]. In addition, dissipation factor (tan \(\delta\)) testing is usually used to assess the motor insulation integrity [7]. Other techniques employ the motor current signature or measure the insulation resistance to investigate the insulation condition. Online vibration measurement was used to detect the mechanical integrity of the gearbox and drivetrain but encounters some drawbacks that limit its ability to detect short circuits and other internal mechanical faults within the machine [8]. Voltage withstands and insulation resistance testing methods can be used to investigate the stator winding condition, but they are limited to detecting poor connection and weak points [9; 10]. The test is carried out at low voltage levels for in-service machines. On the other hand, pole drop testing, dielectric response analysis, along with the FRA test, can be used to assess the stator winding condition and detect short circuit faults within the induction motors [11; 12]. Based on the application of FRA on power transformers, the FRA method can evaluate the mechanical integrity of the active winding within the machine [13; 14]. In addition, the FRA method can be used to investigate the condition of the winding insulation, which is considered a non-mechanical fault [15]. Therefore, the FRA method can be used as a comprehensive tool to assess rotating machines such as TPIMs. The FRA test is conducted by injecting a low voltage of a wide frequency range at one end of the winding terminals while measuring the response at the other terminal of the winding. FRA advantages include high dynamic range (>145 dB), high accuracy, low energized voltage, and high sensitivity and safety [10]. Figure 1: Percentage of failures by rotating machine components.