Syensqo’s 800V Ajedium? PEEK slot liners & KetaSpire? PEEK Magnet Wire Outperform enamels & NKN with up to 7( pp) Economic Savings & 10( pp)Slot Fill

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

Syensqo Materials

An increasing number of automotive and heavy duty vehicle OEMs are expanding their eMotor portfolio by introducing high voltage (> 800 Volts) permanent magnet eMotors in their vehicles. Driven by the consumer’s desire to get a battery electric vehicle (BEV) with improved range and with the ability to use direct current (DC) fast charging, numerous 800V eMotors will enter the market in the coming years.

Engineers are faced with a range of design and processing decisions as they work to create next-generation eMotors that offer a combination of higher efficiency, reduced weight and compactness, while also being made with sustainable materials and processes. This is where Syensqo’s Ajedium? PEEK slot liners and KetaSpire? PEEK magnet wire come into play.

The prevailing design options for 800V slot liners are typically based on the use of Ajedium? PEEK slot liners or laminates like NKN (Nomex-Kapton-Nomex). For 800V magnet wire insulation, the two options are typically KetaSpire? PEEK or thick enamels . Given these material options, engineers also factor into which materials are most compatible with their magnet wire winding process, such as hairpin or continuous wave winding as well as their slot liner insertion process.?

To evaluate the optimal design solution for slot liner and magnet wire material selection, Syensqo performed a virtual engineering (VE) study based on the Volkswagen ID4 rear eMotor topology. Figure 1 below shows the eMotor model used in the design VE study including the stator dimensions and slots.

Figure 1: VW ID4 rear eMotor topology used in VE Study

One of the main objectives of the study was to take advantage of the technical benefits of combining Ajedium? PEEK slot liners and KetaSpire? PEEK. One of the major limitations of NKN slot liners is the need to increase the thickness of the slot liner for 800 volt systems. As shown in Figures 2 and 3 below , Ajedium? PEEK slot liners have superior partial discharge inception voltage (PDIV), breakdown voltage (BDV), and also resistance to corona discharge. Taken together, Ajedium? PEEK slot liners provide engineers with the ability to maximize copper slot fill by using a thinner slot liner. Thinner slot liners and PEEK’s higher thermal conductivity also results in better heat dissipation from the system.

Figure 2: PEEK vs. NKN vs. Nomex Slot Liner PDIV & BDV Comparison

Figure 3: PEEK Voltage Endurance vs. NKN and Nomex

As previously mentioned, the typical choice of magnet wire insulation for 800V eMotors is between PEEK and thick enamels? There are several differences between PEEK and enamels and one of the main differences are in the process of applying the insulation to the magnet wire, extrusion for PEEK versus enameling. The extrusion process for PEEK offers two advantages. First, extrusion allows for better thickness uniformity. The other benefit is sustainability. The PEEK extrusion process is more sustainable because it uses less energy and avoids the use of volatile organic solvents in the process. One of the key advantages of PEEK over enamels is the compliance of the bending and insertion process. A holistic view is shown in Figure 4 below.

Figure 4: Magnet Wire Material Insulation Material Comparison

In the VE study, two different baselines were used, one system based on 560V and the other based on 800V. The two baselines were then compared using three different iterations and varying either the slot liner (NKN or PEEK), the thickness of the PEEK slot liner, while keeping the PEEK magnet wire insulation constant. Ajedium? PEEK at 50 um may be of interest to those designers who do not have a PDIV target for the slot liner and are using it primarily to protect the wire as it is inserted. Ajedium? PEEK also offers a unique value proposition for this design approach, as traditional slot liners cannot meet the tear resistance properties needed to be processed at this low thickness. The enameled and PEEK magnet wire thicknesses were selected based on achieving the same wire-to-wire PDIV for the entire eMotor operating life, hence taking into consideration the PDIV decay due to thermal aging. More detailed explanations of the assumptions made are given below.?

IEC 6000-34-18-21/41 specifies how to test insulated wires and explains how to ensure that the winding insulation remains PD-free throughout the entire operating life (Type I) with appropriate safety factors. These safety factors include the effect of thermal aging on PDIV and formulas are provided for estimating the PDIV decay.

Formulas provided in the above mentioned standard indicate that an enamel coated wire operated at its thermal class temperature will lose thickness and consequently PDIV up to a factor of 20%. If the same wire is operated at lower than the thermal class temperature, the property loss still occurs but is less prominent.?

The above mentioned phenomenon finds confirmation in several experimental technical papers as [1] and [2] and can be explained by the expulsion of volatile substances trapped in the enamel thickness.

On the contrary, PEEK extruded wires show excellent properties and PDIV retention when aged up to 240°C or above, with negligible decay, providing a potential to reduce coating thickness for given PDIV after aging target.

The exact thickness difference between KetaSpire? PEEK and an enamel coating depends on a variety of factors and has to be determined case by case.?

Targeted operating and validation test temperatures, material thermal classes, ATF exposure, bend geometry, assembly process, etc. are all factors that play a relevant role. In this case study we will assume that, thanks to the excellent thermal stability of KetaSpire? PEEK and its compliance to tight bending, the thickness difference needed to obtain the same PDIV, over the life of the eMotor, is 15% and we will quantify the benefits that results.??

Figure 5 reveals the potential gross fill factor that can be achieved by optimizing the PEEK slot liner and PEEK magnet wire thicknesses with the highest factor among the 800V solutions. In each design iteration, copper content is adjusted according to the different insulation thicknesses, keeping into account both slot liner and wire coating, as shown in the figure below.

Figure 5: VE eMotor Design Iterations

A complete drive cycle is taken into account rather than a single operating point that was repeated until steady state temperature in the winding was achieved. The drive cycle was designed to take into account all typical BEV driving conditions such as urban traffic, highways, and regenerative braking, among others.

In each iteration, the efficiency and thermal benefits were converted into a more compact eMotor design, delivering exactly the same performance at the same operating temperature. E-Motor level benefits are summarized at Figures 6, 7 and 8.

Figure 6: Stack length reduction while keeping the same peak temperature over the targeted drive cycle?

Figure 7: Weight reduction while keeping the same peak temperature over the targeted drive cycle

Figure 8: Efficiency (average on the drive cycle) increase while keeping the same peak temperature over the targeted drive cycle

Figure 9: Approximate BOM reduction

Figure 10: Overview of weight and raw material cost savings thanks to KetaSpire? PEEK and Ajedium? PEEK in 800V eMotor

In summary, using KetaSpire? PEEK and Ajedium? PEEK to insulate your 800 V eMotor brings potential to:

• Reduce eMotor active length by 12% (Figure 6), that corresponds to 21 mm for the simulated model
• Reduce eMotor weight by 7.6% (Figure 7), equivalent to 5.5 kg
• Increase eMotor average efficiency by 0.5 pp (Figure 8), providing a valuable benefit at system-level for range extension or battery downsizing, with associated weight, cost and sustainability improvements
• Reduce the eMotor BOM by 7.4%, which in this case is worth 30.2 $?

In conclusion, Syensqo’s extensive Ajedium? PEEK slot liners and KetaSpire? PEEK magnet wire provide engineers with the ability to maximize fill factor resulting in efficiency gains. The improved efficiency can be further leveraged to downsize the eMotor saving both space and weight and reducing overall system cost.

If you are interested in learning about our eMotor portfolio of solutions, please contact us.

[1] A. Rumi, L. Lusuardi, A. Cavallini, M. Pastura, D. Barater and S. Nuzzo, "Partial Discharges in Electrical Machines for the More Electrical Aircraft. Part III: Preventing Partial Discharges," in IEEE Access, vol. 9, pp. 30113-30123, 2021, doi: 10.1109/ACCESS.2021.3058090.

keywords: {Insulation;Partial discharges;Aging;Qualifications;Surges;Inverters;Stress;Partial discharges;More Electrical Aircraft;wide bandgap devices;SiC inverter;qualification;aging},

[2] M. Szczepanski et al., "How does PDIV change during isothermal aging of magnet wire," 2022 IEEE Electrical Insulation Conference (EIC), Knoxville, TN, USA, 2022, pp. 266-271, doi: 10.1109/EIC51169.2022.9833193. keywords: {Partial discharges;Temperature measurement;Insulation;Microscopy;Wires;Electric variables measurement;Aging;Electrical Insulation System;EIS;Partial Discharge Inception Voltage;PDIV;aging marker;type I insulation;thermal aging;enamel thickness},