Stators are the stationary part of an electric motor and provide a rotating magnetic field that drives the rotating armature. The core of the stator is built up of high-grade alloy steel laminations, which is wound with round or flat wire conductors into slots. Once the winding of a stator has been completed, the final stage of manufacture will be to bond the winding by using an impregnating or encapsulating process. 
 
Other benefits that can be derived from the Impregnation or Encapsulation process would be void filling in the slot or improved thermal flow as well as increases chemical resistance, environmental protection and mechanical wear and damage. In general, the process ensures:

• Electrical insulation
• Chemical protection
• Mechanical protection

Processing Methods
The application method to apply the impregnation or the encapsulation resins are quite different.  However, the process should ensure the wound coils in the slots are fully saturated and void free. 
 
Impregnation ProcessThere are several processes by which the impregnation resins can be applied, the determination as to which method to use depends on the dimensions of the stator and the daily product quantity. A summary of various impregnation processes is listed in the table below:

_{* Vacuum Pressure Impregnation}

Encapsulation Process
Many variations on a standard encapsulation process are available. In principle the stator is placed into a mold, then resin is poured over the winding head. After the resin has entered the wound coils in the slots following a gelation and curing process. The cure may be performed at ambient temperature or at elevated temperature in an oven. Applying vacuum during the process will result in an excellent, void free encapsulation.

Advantage/disadvantage of encapsulating vs. impregnation

Requirements for eMobility application
Electrical insulation materials for eMobility motors face conflicting requirements. The eMobility motor is required to deliver high torque for brief periods and low torque for long periods. It will be subjected to a variety of environmental conditions from both high and low ambient temperature conditions, be resistant to oils, water, and salt from winter streets. Long-term reliability is an absolute, the electrical insulation must be tough enough to withstand high temperatures and chemicals, but also possess some degree of flexibility to manage temperature shocks and mechanical stress applied to the motor windings due the torque the motor develops.

 ELANTAS offers an extensive portfolio of high-performance materials for stator impregnating or encapsulating which meets the main requirements as:

• Very good chemical resistance
• Temperature Shock Resistance
• VOC-free product range
• Product portfolio for all processing methods
• High thermal conductive materials
• Partial discharge resistance

ELANTAS's globally available product range, ELAN-drive widely used in eMobility application: 

Today, rotors used for e-motors in electric cars are designed as Wound Rotors or Permanent Magnet Rotor (PM) in particular when higher power density is required. Depending on the rotor type and selected processing technology different materials are essential.

ELANTAS offers for all type of rotors and processing technologies the best material to stabilize the rotor against extreme centrifugal forces. 

ELANTAS products has proven superior properties in EV motors as:

• Bonding at high rotation speed
• Thermal shock stability
• Support thermal management
• Chemical resistance to aggressive oils and cooling fluids

The below table gives an overview on most common applied processing technologies, products and main characteristics in the manufacturing of wound rotors for e-motors:

Permanent Magnet Motors

Instead of coils, permanent magnet motors use strong magnets for the rotor element to generate the magnetic field. Collectively, these magnets need to be tightly fixed to the rotor steel package or the rotor housing. Motor developers have come up with various designs of magnet arrangements. Some magnets are pushed into pockets in the steel package of the rotor and are fixed with low viscous adhesive that fills the pocket; other magnets are fixed to the outside of the rotor which obviously is different as to the required adhesive strength and viscosity during application. Mostly, the maximum operation temperature of Magnets shall not exceed 80°C. For special high-end use in automotive the rotors are tested until 150°C.

ELANTAS products offered for magnet fixation

Electric motors for eMobility applications require higher power and torque at limited constructed space and weight in a car. This can be achieved by increasing the copper fill factor in the slots of the stator. Hence, flat wires are applied in the latest development of motors, especially for premium cars. 

Hair-Pin Technology
While conventional round wires are wound into the slots; flat wires must be inserted into the stator by the i-Pin or Hair Pin technique and thereof require welding on one or both sides of the copper pins connections following by insulation of the welded pins. Various technologies can be applied for this purpose: 

• Epoxy Powder coating,
• Potting
• Impregnation

ELANTAS hair-pin protection solutions save time and budget.

While Epoxy powder coating requires an additional process step, ELANTAS offers insulation materials which can be applied in one process step and with similar process equipment used today. Applying ELANTAS solutions further process benefits as reduced investment and faster process time can generated. 

ELANTAS has screened various electrical insulating materials for Hair Pin Protection and developed materials. During the extensive study (LINK) of materials in combination with the application technique ELANTAS developed materials with:

• excellent edge coverage
• excellent thermal shock resistance
• oil compatibility
• application by a conventional processing technique

As further requirement based on the motor design and operation condition needs to be considered, ELTANTAS offers our technical knowledge for individual technical consulting during the design, test and production phase.

The table below shows the most global applied ELAN-drive materials for Hair Pin Protection:

To create an electromagnetic field in an electric motor, a conductive coil where each conductor of the coils has an electrical insulation wire is required. For low and medium voltage machines, the electrical insulation otherwise known as primary insulation is created by laying down, in multiple passes, and enamel. The wire manufactured by this process is known as magnet wire.  It is a unique product as the magnet wire, which comes in round or rectangular (flat) shaped wire and offers the following features:

• High dielectric properties
• High temperature durability
• Chemical resistance
• Excellent mechanical properties

Processing Methods
Motor coils are generally produced by high-speed winding or insertion machines. It is a requirements of motor manufacturers to produce electric motors as quickly and efficiently as possible to minimize costs. Magnet wire must withstand the forces applied to it to ensure the coils are tightly wound and compact, the magnet wire is pulled or threaded into the slots which exerts extreme force on the magnet wire and the primary coating. Finally, there may be a forming process to the wound coils which applies mechanical force so the magnet wire to form the required shape.

Requirements for eMobility application
For the eMobility motor application, the magnet wires must exhibit excellent thermal, electrical and mechanical properties. The shape of the magnet wire will be either round or rectangular, this will depend on the motor design. With increasing demands on high-voltage, high-output and large capacity motors, rectangle or flat wires with a higher space factor are more and more used for eMobility application to increase motor performance. 

Round wire will need to be withstand high speed winding. The motors winding could also be subject to partial discharge. ELANTAS provides corona resistant protection such and special partial discharge resistant coatings. As the winding could be subject to high temperatures, coatings such as Polyamideimde and Polyimide are also available. ELANTAS offers both and even in combination with corona resistance properties.

For rectangular or flat wire ELANTAS has developed unique products covering variety of properties such as:

• High conformity of coating (edge covering)
• Layer thickness up to 150 µm
• Corona resistance
• High flexibility
• Good adhesion to conductor and secondary insulation

ELANTAS offers an extensive portfolio of high-performance enamels for magnet wire to meet the conflicting requirements. With ELANTAS excellent primers and self-lubricated enamels, wire structures can be extended further, and the performance can be improved to even higher level.

ELANTAS’s globally available product range ELAN-drive widely used in eMobility application: 

 ^{*To achieve the best properties of a final magnet wire a combination of wire enamels is applied. Covering polyester or polyamide enamels with polyamide-imide leads to outstanding adhesion, dielectric and thermal properties. The resulting thermal index of such a combination will exceed 220°C (EIC and ASTM).} 

Recently, partial discharge has become a concern in lower voltage motors, especially for eMobility applications. These motors operate by variable speed drives (VSD). These drives control the motor speed using high frequency square waves as opposed to conventional sinusoidal waves. The frequencies incorporated are often up to 20 kHz, as compared to the conventional 50 or 60 Hz. VSD’s sometimes called ‘inverters’ offer great advantages such as high efficiency and fast accurate speed control.

Inverters are associated with problems such as voltage overshoots and reflected waves:

• Voltage overshoots vary in intensity but are often characterized by fast rise times.  
• Reflected waves are a result of mismatched impedance.  

The reflected wave becomes additive with another incoming wave resulting in a waveform that is twice the intended voltage.  Since these waves are fast rise time, there is insufficient time for the energy to be dispersed among the windings of the motor. This creates high turn to turn potential between adjacent strands of magnet wire. These increased voltages are high enough to create partial discharge in the windings within the motor.

Partial discharge (PD) is defined as an ‘electrical discharge that does not completely bridge the space between two conducting electrodes.’ Areas with voids, cracks or imperfections is location where the partial discharge occurs.
 
Partial discharge occurs in void spaces in insulation and results in the damaging of the insulation system.

Protection by Encapsulation
ELANTAS offers a full package of insulation materials to improve lifetime and endurance under the influence of high voltage surges or partial discharge.

One solution to partial discharge is to remove the air where it occurs. Full encapsulation or potting of a motor with ELAN-tron® MC 62/W363 or ELAN-tron® MC 622/W363 is a great way to implements this solution.

Protection with Co-Shield^® System
However, when full encapsulation is not being used, the best performance, is to utilize the Co-SHIELD® system. It provides superior resistance to partial discharge through the combination of wire enamels such as those described above impregnation resin such as the CORONA-Protect resins and ELAN-Film as flexible insulation material.

ELANTAS has developed magnet wire enamels which have demonstrated under pulse endurance testing longer life. The enamels provided by ELANTAS are the Corona Clear product and Allotherm CR along with the Tongmid CR products.

For an impregnation resin, the Corona Protect® 82-80A3 has shown that this has provided the longer life for EV motors particularly commercial electric vehicle applications.