PhD student Thanatheepan Balachandran, Post-doc Yalin Wang,
and MS student Yovahn Hoole with advisor K. Haran

A NASA-funded inside-out permanent magnet synchronous motor (PMSM) is developed to demonstrate electric propulsion for commercial electric aircraft. Air-core machine windings are manufactured at UIUC. Insulation qualifications of these windings are evaluated for ground, high-altitude, and life-time tests. The ground test qualifies the motor’s insulation capability for a laboratory test run. The high-altitude test qualifies the stator winding’s insulation capability at its operating condition. Since the machine is designed to operate at high altitude, windings are tested with varying pressure to simulate the aircraft’s flying altitude. Windings are tested inside a vacuum chamber at partial vacuum of up to 0.2 atm. Life-time windings prediction is investigated through an accelerated aging test. Here, windings are placed inside an industrial oven and heated above the rated temperature to accelerate the aging process.
To facilitate the above tests, a partial discharge (PD) test bench setup is built as shown in Figure 1.

Partial discharge test bench setup-Balachandran_Theepan

Figure 1. Partial discharge test bench setup

A linear power supply is used to ramp up the applied voltage at the rate of 0.1V/s. A potential transformer with a 1:40 turn ratio is used to step up the voltage. PD signals are monitored using an oscilloscope and continuously recorded in the work station. These data are used to analyze and detect the PD inception voltage (PDIV) of the insulation. PDIV, intensity, amplitude and duration of the PD signal are used as parameters to evaluate the winding qualification. Preliminary results indicate that high altitudes increase PD activity in the windings, as shown in Figure 2.

Balachandran_theepan PD signal comparison

Figure 2. PD signals comparison of samples at 1 atm (left) and 0.2 atm (right)