Syensqo’s KetaSpire® PEEK Magnet Wire Retains Higher PDIV After Heat Aging compared to Polyimide

By: DeeDee Smith, Victoria Lee, Luigi Marino, Alex Wist, Benoit Devaux, Jin Lee, Brian Baleno

Syensqo Materials

The selection of magnet wire insulation for high voltage (> 800 volts) permanent magnet synchronous motors (PMSM) is critical to ensure long term partial discharge inception voltage (PDIV) over the life of the eMotor. Design engineers typically choose between either PEEK or polyimide for high voltage magnet wire insulation. Syensqo has developed a monolayer PEEK solution, KetaSpire® PEEK KT-857, for extruded magnet wire. Engineering factors to consider include PDIV, thermal endurance, manufacturing process (hairpin or continuous wave winding), and compatibility with the cooling media, among others.

KetaSpire® PEEK opens up the design envelope, allowing engineers to optimize the copper slot fill factor. PEEK offers greater uniformity in thickness, tolerances and productivity compared to the enamel process, which requires multiple passes through a solvent versus single layer PEEK extrusion. Another significant benefit of PEEK is quality. Again, the extrusion process avoids pinhole defects, unlike enameling. With these factors in mind, engineers can start to consider PDIV. 

Following on from the [Article published by Brian on March 19th 2024], Syensqo has conducted a specific aging test to assess the retention of key properties, like PDIV, after aging. This is a particularly important parameter to monitor as, for PDIV-free type of designs, it determines the ultimate thickness that must be applied to ensure adequate insulation, especially given the dramatic impact that thickness has on TCO, weight and sustainability at system level as explained in some of our previous articles [article published by Brian on Nov 12th 2024].

Figure 1 below shows the PDIV of KetaSpire® PEEK KT-857 after both heat aging and exposure to ATF (oil).

Figure 1:  PDIV of KetaSpire® PEEK KT-857 - after heat & ATF aging

Enamel insulations include polyamide imide (PAI) and PI, both of which tend to lose insulation thickness over the course of electric motor operating conditions. Thermal stress can cause up to a 20% reduction in PDIV of PI magnet wire insulation. Unlike PI, KetaSpire® PEEK is much better at retaining its original thickness thereby maintaining a higher level of PDIV performance even after aggressive heat aging. 

To simulate PDIV retention, a test was conducted comparing hairpin samples of extruded KetaSpire® PEEK KT-857 to enameled PI test samples as shown  in Figure 2 below. Three different scenarios were applied to the hairpin test samples as detailed in table 1 below.

Figure 2:  PDIV of KetaSpire® PEEK KT-857 versus Polyimide (PI)

Table 1: Hairpin PEEK versus PI PDIV retention test scenarios

The results of the side by side tests demonstrate that at the hairpin level PEEK significantly outperforms PI under thermal stress conditions. Figure 3 compares the three test scenarios above revealing the percentage drop in PDIV. KetaSpire® PEEK KT-857 retains 99 to 103 % of PDIV while PI retains between 81 to 94 % of PDIV.  In addition, the test resulted in 3 out of 10 PI breakdown failures when measuring PDIV, with voltages applied well below the expected BDV. 

Table 2: Hairpin PEEK versus PI PDIV data and test scenarios

Figure 3:  PDIV Retention of KetaSpire® PEEK KT-857 versus Polyimide (PI)

In summary, the combination of PDIV loss after thermal stress, reduced thickness control and pinhole quality demonstrates that for high voltage eMotors, KetaSpire® PEEK KT-857 provides better PDIV retention, chemical resistance, and quality than PI.

This results in greater design space, the potential to reduce coating thickness, and increase fill factor with important cost, weight and carbon footprint benefits at eMotor and system level.