This article presents a case study that aims to record the observations made of both processing and materials during a motor rewind using Zeus PEEK Lay-Flat® tubing as an insulating material and Zeus crystalline PEEK-coated magnet wire.
The study was carried out to compare Zeus Industrial products with traditional magnet wire and Nomex®, Dacron®-Mylar®-Dacron® (DMD) type insulation, and Nomex® laminate materials.
A small 0.75 horsepower, 4-pole, 460 V, Class F AC motor (Figure 1) was chosen for the model rewind. This motor was selected as it is compact in size and has lightweight dimensions to allow easy transportation. The motor style is also readily available in the market.
Figure 1. Original motor and test equipment prior to rebuild.
Particularly for the motor, the short stator provided a suitable way to assess the ease in which the slot insulation and PEEK magnet wire can be created and integrated into the motor. The stator slots are narrow and would help to assess the ease of integrating the magnet wire bundles into the stator slots. Phase paper was also used in this test and design.
There were 36 slots in the motor’s design. Distributed winding was used by the motor, which resulted in a relatively complicated winding diagram. In each winding, the large and small coils had 120 and 64 turns, respectively. The rewound motor features a lead wire, which was also PEEK insulated using crystalline 18 American wire gauge with 10.6 mils insulation. The original motor EXAR® 18 AWG lead wire was substituted by the latest insulation.
Standard 24 AWG magnet wire (MW 35-C) was the original wire in the motor. Zeus crystalline PEEK magnet wire sized 24 AWG, heavy build (1.1 mils) was used to replace this wire.
It was observed that the new wire was stiffer compared to the normal magnet wire, but this increased stiffness did not affect the winding process in any way and spooling was performed in the usual way using an automated spooling machine. However, it was rather difficult to install the PEEK magnet wire winding into the slot, compared to installing the normal wire. This is because bend is not retained by the PEEK wire as quickly as the standard wire (Figure 2).
Figure 2. Installation of the PEEK windings (right) into the stator slot of the motor (left).
The property of the PEEK wire was explained to the operator. After making some additional slot insertions and basic changes to the assembly style, the operator successfully installed the PEEK magnet wire without any further difficulty.
Once the windings were tied and laced, the stiffness of the PEEK magnet wire was still noticeable as the wire exhibited spring-back. As mentioned above, the PEEK magnet wire failed to bend and did not retain its shape as easily as that of the standard wire in terms of lacing and tying of the windings into the motor.
While some familiarity is required from the operator’s end to understand these problems, no major issue was encountered when it came to the operation of the motor itself. The end windings were effortlessly secured through proper tie cord and lacing application. In addition, it was observed that the PEEK magnet wire did not kink easily, which is deemed to be a desired feature when handling wire for applications like those described here.
Slip, lubricity, manufacturability, formability, cut through resistance, and other aspects of the PEEK magnet wire were all equivalent to or better than a typical magnet wire. The PEEK magnet wire can be well adapted to manufacturing environments without any major complications.
Slot and Phase Insulation
Another aspect that was investigated was replacing the standard Nomex® laminate, Nomex®, and Dacron®- Mylar®-Dacron® (DMD) type insulation materials with the PEEK Lay- Flat® tubing material for slot and phase insulation (Figure 3).
Figure 3. Completed stator winding with PEEK magnet wire, PEEK Lay- Flat® slot insulation, PEEK Lay- Flat® phase insulation, and Nomex® wedges.
11 mil Lay-Flat tubing extrusion was employed as a phase separation material, and 9 mil Lay-Flat tubing was employed for the slot liner. These specifications corresponded with the actual material thicknesses of Nomex® laminate insulation, which included Nomex®-Mylar®-Nomex® (NMN) 3-3-3 and NMN 3-5-3 for the slot and phase material, respectively.
In both the rewound motor and the original motor, Nomex® wedge material was employed. For use as a slot liner, the PEEK Lay-Flat® material was installed in a similar way as the traditional Nomex®. Although the PEEK Lay-Flat® material required a familiarization period, the operator was quickly able to acquaint himself with the attributes of the new material and continued to install the slot and phase insulation continued without any major difficulty.
In any motor manufacturing, the installed magnet wire has to be protected from the pointed edges of the slot exit during the winding process. This is done by extending the slot liner material further than the slot end and bending it across the outer edges of the slot exit to create a cuff.
Similar to the Nomex® material, the operator employed the hand forming method (standard) with the PEEK Lay-Flat® material when forming the cuff. In the same way, the operator used the foot-operated mechanical shear to cut the PEEK width and length. Pre-forming the slot liner is recommended to form a slot liner, which conforms more closely to the slot. This will boost the overall speed of the PEEK Lay-Flat® installation and also ease the magnet wire winding insertion process.
Once the PEEK Lay-Flat® was deployed, the operator observed that the material’s cut edges did not have the same level of softness as the laminate due to PEEK’s plastic nature compared to the softer cloth-like laminate material and Nomex®.
Conversely, the surplus amount of the PEEK Lay-Flat® material was removed from the winding area end by cutting the phase insulation into the required curve shape for application. The end result was that no major difference was found between the PEEK Lay- Flat® for phase insulation and the traditional Nomex® and laminate material.
This procedure can be further enhanced for manufacturing purposes using materials that are pre-cut to the required shape and size, for phase insulation and improving production throughput.
A trickle varnish process involving a polyester resin with traditional processing methods was used to impregnate the completed stator using a polyester resin with traditional processing methods (Figure 4). A pre-catalyzed resin was used in the trickle process and was gradually poured onto the end winding part of a heated stator. The resin was allowed to enter into the stator slots via capillary and gravity processes.
Figure 4. Impregnation of the stator windings with trickle varnish resin.
As the stator was turned around, the resin was allowed to cure in situ and more resin was introduced. It takes about one hour to complete this process. During the impregnation process of resin at the production plant, no major difference was observed after the PEEK slot and phase insulation material as well as the PEEK magnet wire was installed. The trickle resin entered into the slots, covering the end windings as required for a rewind operation.
After resin impregnation and the corresponding testing, the motor was cross-sectioned and it was later observed that insufficient areas of resin retention are present in the end winding sections by way of large open voids. Such voids can be prevented either by improving the winding process, or by making some alterations to the trickle resin application process to enable resin retention.
Following resin impregnation, no partial discharge (PD) activity was observed in the follow-up electrical testing. However, when standard phase insulating material and magnet wire substantial PD activity was seen before rewind.
In addition, the motor employed for this rewind operation and assessment was an off the-shelf motor without any modifications. The impregnation results suggest that while large open voids were present in the motor end windings, they did not pose any future concern in regard to the performance of the motor.
Similarly, the presence of voids could also be attributed to the production process that was not streamlined to reduce such voids. Figure 5 shows a cut-away of test motor exhibiting cross-section of stator core and windings.
Figure 5. Cut-away of test motor showing cross-section of stator core and windings.
In this analysis, the PEEK magnet wire was found to be relatively stiffer compared to a standard enameled magnet wire. This property of the PEEK magnet wire improves the motor’s capacity to endure coil motion, especially during surge conditions and start up when the end windings may be subject to maximum movement.
In spite of the different properties of PEEK and after a short familiarization period, operators were easily able to implement their manufacturing methods and use the PEEK magnet wire without any other difficulties. The PEEK Lay-Flat® material showed improved tear resistance compared to traditional phase and slot materials, however the PEEK Lay-Flat® did not display the same level of softness like the Nomex® material.
The Lay-Flat® material was cut to shape and size, and at the end of the stator slot the cuff was readily formed, retaining its shape. Compared to traditional and established materials, the PEEK magnet wire and the PEEK Lay-Flat® material handled in a different way. However, after operator familiarity, it became easier to adjust to these different properties with respect to production floor practices.
At the end, the final motor had superior appearance and displayed a strong end winding along with excellent final electrical performance. At this point, some potential barriers to adapt this method would include the transition of operators from the standard materials to the somewhat different manufacturing handling aspects of the PEEK Lay-Flat® materials and the PEEK magnet wire. However, these barriers are to be expected when moving to the latest manufacturing materials.
Additionally, when implementing the PEEK Lay-Flat products and magnet wires into the production setting, new tooling is not required and only basic education of the new methods would be required.
This information has been sourced, reviewed and adapted from materials provided by Zeus Industrial Products, Inc.
For more information on this source, please visit Zeus Industrial Products, Inc.