WO2018055004A1

WO2018055004A1 - Dielectric heating of motor insulation with rf energy stimulus to repair defects and degradation in the insulating material in-situ

Info

Publication number: WO2018055004A1
Application number: PCT/EP2017/073825
Authority: WO
Inventors: Adam BIERMANN
Original assignee: Aktiebolaget Skf
Priority date: 2016-09-23
Filing date: 2017-09-20
Publication date: 2018-03-29

Abstract

A system and method for repairing defects of an insulation material used to insulate stator motor winding coils in large electric motors includes providing an RF profile applied to the stator motor winding coils with a controlled RF power supply, controlling the RF profile while measuring the temperature rise and thermal release of the coils, storing the measured temperatures with a controller, distributing heat through the thermal release and intelligently controlling the temperature change rates with the controller, determining an overall volume of insulation material to be heated, identifying specific melting points of the volume of insulation material, driving the insulation material with the controlled RF supply to a semi-liquid state, controlling the changing state of the insulation material to fill in the voids or defects, allowing the insulation material to solidify when the RF power is removed, and testing the insulation material for breakdown to verify the repair.

Description

Dielectric heating of motor insulation with RF energy stimulus to repair defects and degradation in the insulating material In-Situ

CROSS-REFERENCE

This International Application claims the benefit of priority to U.S. provisional application no. 62/398,810, filed September 23, 2016, the contents of which are herein fully incorporated by reference.

TECHNOLOGICAL FIELD

The disclosure relates to the dielectric heating of motor insulation with RF energy stimulus to repair defects and degradation in the insulation material in-situ. The disclosure further relates to dielectric heating of motor insulation with a controlled RF energy stimulus to repair defects and degradation in the insulation material of large electric motors in-situ.

BACKGROUND

During the process of vacuum impregnation or dipping of motor stators to coat coils in insulation, voids or defects in the material from the process may give rise to locations susceptible to localized breakdowns, which in turn degrade and ultimately destroy motor windings due to conductor faults. The locations and defects are identifiable through offline surge and partial discharge testing. The only current solution being to re-dip or rewind the motor to locate and resolve the defective area. This can lead to discontinuities within the insulation and cost time and money to repair. The ability to resolve defects in motor windings that currently require the entire stator to be removed and re-dipped is currently a very expensive procedure. The motor typically has to be sent off site to a facility that has the capabilities to perform this process. According to the invention, a self-healing polymer that reacts to RF energy allows the repair to be done on site with the motor in place.

The instant application proposes this solution to the problem as will be further disclosed hereafter. SUMMARY

The basic inventive concept provides a method for repairing defects of an insulation material used to insulate stator motor winding coils in large electric motors, the method includes providing an RF profile applied to the stator motor winding coils with a controlled RF power supply, precisely controlling the RF profile with the RF power supply through the stator motor winding coils while measuring the temperature rise and thermal release of the coils with sensors attached to the winding coils, the measured temperature rise and thermal release of the coils being stored within a controller, the stored temperatures used by the controller as feedback, distributing heat through the thermal release of the stator coils and intelligently controlling the temperature change rates with the feedback, determining an overall volume of insulation material to be heated, identifying specific melting points of the volume of insulation material used in the stator to be repaired, driving the insulation material with the controlled RF supply to a semi- liquid state, controlling the changing state of the insulation material with the controller to fill in the voids or defects, allowing the insulation material to solidify under a controlled cool down period as controller removes the RF power, and testing the insulation material used in the motor stator windings for breakdown to verify the defects have been resolved.

In a first aspect of the method the insulation material is a polymer comprised of short chain polymers with minimal cross-linking.

In a second aspect of the invention an application of a high voltage, high RF signal of 600W to 1000W directly into the motor winding produces a heating effect in the insulating material. The RF frequency used is dependent on the material it is being applied to, and the frequency is in the range of lMHz to 10GHz.

In a further aspect of the invention the insulation material oscillates in response to fast changes in polarity of the alternating RF field and the high voltage produces strong electromagnetic field strength which pulls the material in alternating directions. In a further aspect of the invention the molecular movement of the chains in the polymers produces friction, which in turn generates heat.

In a further aspect of the invention the longer the RF alternating field is applied and the more power the field contains the more temperature rise will occur in the windings. In a further aspect of the invention, as the controlled temperature of the insulation material rises it will exceed the glass transition temperature of the material, the insulation material will become less solid and will behave more as a liquid than a solid.

In a further aspect of the invention the insulation material will be able to reflow and fill in the voids or defects.

In a further aspect of the invention, once the material reflows and fills in the voids or defects, the electric energy is removed and the system is allowed to cool to ambient temperature.

In a further aspect of the invention the polymer is a thermoplastic and a thermoplastic retains its capability to melt after an initial application and drying. In a further aspect of the invention the short chains in the material allow it to flow more easily, which enables the resolution of smaller defects.

The basic inventive concept further provides a system for repairing defects of an insulation material used to insulate stator motor winding coils having a motor having stator motor winding coils, the stator motor winding coils including the insulation material that encases the coils, an RF power supply having an RF profile that is applied to the stator motor winding coils, and a controller for controlling the RF profile that is applied to the stator winding coils.

In a further aspect of the invention, the RF profile is precisely controlled with the controller.

In a further aspect of the invention, the controller further measures the temperature rise and thermal release of the coils, and the measured temperature rise and thermal release of the coils is stored within the controller. In a further aspect of the invention, the temperature rise rates and thermal release rates from the stator motor winding coils are intelligently controlled with the controller. In a further aspect of the invention, specific melting points of a volume of insulation material used in the stator motor windings coils to be repaired are identified, and the insulation material is driven to a semi-liquid state with the controlled RF supply. In a further aspect of the invention, the changing state of the insulation material is controlled with the controller in order to fill in the voids or defects.

In a final aspect of the invention, the insulation material is solidifies when the RF power is removed, and the insulation material used in the motor stator windings is tested for breakdown to verify the voids or defects have been resolved.

BRIEF DECSRIPTION OF THE DRAWINGS

The invention will be better understood from the following detailed description of embodiments, representing non- limiting examples and illustrated by the accompanying drawings, wherein:

Figure 1 is a perspective view of a system for repairing defects and degradation in the insulation material of large electric motors according to a first embodiment of the invention,

Figure 2 is a block diagram of the steps required to carry out a method according to the system shown in the first embodiment of the present invention, and

like reference numerals refer to like parts throughout the various views of the drawings.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. As used herein, the word "exemplary" or "illustrative" means "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" or "illustrative" is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to make or use the embodiments of the disclosure and are not intended to limit the scope of the disclosure, which is defined by the claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.

For purposes of description herein, the terms "upper," "lower," "left," "rear," "right," "front," "vertical," "horizontal," and derivatives thereof shall relate to the invention as oriented in FIG. 1. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. It is also to be understood that the specific devices and methods illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims.

Description of the System

A system 10 for repairing defects 16 of an insulation material 12 used to insulate motor winding coils 14 of a stator 18 in large electric motors 20 is illustrated in Figure 1. The system 10 includes a RF frequency and voltage generator or power supply 22 and a controller 24 for controlling the output of the RF power supply 22.

Examples of a controller 24 include, but are not limited to, a processing circuit, a control circuit, a processor, a microprocessor, a multicore processor, and a central processing unit (CPU). Examples of the controller can also include electronic circuitry and or computer code including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), and programmable logic arrays (PLA) that execute computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the one or more embodiments herein.

This is an invention which utilizes key characteristics in the dielectric material found in thermoplastic motor insulation to repair degradation (including voids, cracks, and gaps) which occurs in the manufacture of motors and during their service lifetime.

The controller 24 intelligently and precisely controls the RF profile from the RF power supply that is applied to the winding coils. The controller further measures the temperature rise and thermal release of the coils. The measured temperature rise and thermal release of the coils is stored within the controller. The temperature rise and thermal release of the coils is obtained by connecting thermocouples from the controller to various locations on the winding coils. The thermocouples may include but are not limited an RTD type. An RTD type of thermocouple can be more easily connected to the insulation material without affecting its shape or characteristics. The temperature rise rates and thermal release rates from the stator motor winding coils are intelligently controlled with the controller via feedback from the thermocouples. Here, the temperature rise does not exceed the melt temperature of the material, as that would cause it potentially drip or run off of the motor conductors, which is not desirable. It also does need exceed the decomposition temperature, which would result in chemically altering the material and degrading it further.

Information regarding the specific melting points of a volume of insulation material used in the stator motor windings coils to be repaired are calculated by the controller based on characteristics. As such, the material type and insulation thickness are inputted into the controller. The controller uses this information to controllably drive the insulation material to a semi-liquid state with the controlled RF supply based on the characteristics of the insulation material and its total volume for a given motor.

The polymer is comprised of short chain polymers with minimal cross- linking. The polymer is a thermoplastic, meaning it retains its capability to melt after initial application and drying. This is unlike a thermoset material which loses its ability to flow after curing due to chemical reactions occurring within it. The short chains in the material allow it to flow more easily and to resolve smaller defects. The polymer is at least slightly polar so that it will respond to the alternating electric field more strongly than would a non-polar material. Polymeric materials will oscillate in response to the fast changes in polarity of the alternating field and the high voltage produces strong electromagnetic field strength which pulls the material in alternating directions. This molecular movement of the chains in the polymers produces friction which in turn generates heat. The longer this field is applied and the more power this field contains the more temperature rise will occur. After a certain point the temperature will exceed the glass transition temperature of the material and it will become less solid and will behave more as a liquid than a solid.

The RF frequency used is dependent on the material it is being applied to and is in the range of 1MHz to 10GHz. It is desirable that the frequency used corresponds to the peak value of the dissipation factor of the material, which determines how much of the applied energy is absorbed and is highly frequency dependent. This is due to resonance characteristics of the materials being different as a result of differing molecular structures. Example frequencies that are preferable due to their broader acceptability by the FCC would be a 13.56MHz, 915MHz, or 2.45GHz signal. The frequencies used must span a broad enough bandwidth that currently commercially available thermoplastics, which are used in motor windings can utilize a frequency that is close to their peak dissipation factor.

Due to this transition the material will be able to reflow and fill in the above mentioned defects. Once this is achieved, the electric energy is removed and the system is allowed to cool to ambient temperature, with the defects in the material removed. The motor is then re-tested to verify these potentially vulnerable locations have been resolved. As such, the changing state of the insulation material is controlled with the controller in order to fill in the voids or defects. The insulation material is solidifies when the RF power is removed. The insulation material used in the motor stator windings is then tested for breakdown to verify the voids or defects have been resolved. Description of the Method

A method 200 for repairing defects of an insulation material 12 used to insulate stator motor winding coils 14 in large electric motors 20 is illustrated in Figure 2. A first step 210 includes providing an RF profile applied to the stator motor winding coils with a controlled RF power supply.

A second step 220 provides precisely controlling the RF profile with the RF power supply through the stator motor winding coils. This step includes measuring the temperature rise and thermal release of the coils and storing the measured temperature rise and thermal release of the coils being stored within a controller. The stored temperatures are then used by the controller as feedback.

The third step 230 further includes distributing heat through the thermal release of the stator coils and intelligently controlling the temperature change rates with the controller based on the aforementioned feedback.

A fourth step 240 provides determining an overall volume of insulation material to be heated. The material type and insulation thickness are inputted into the controller. The controller uses this information to controllably drive the insulation material to a semi-liquid state with the controlled RF supply based on the characteristics of the insulation material and its total volume for a given motor.

A fifth step 250 requires identifying specific melting points of the volume of insulation material used in the stator to be repaired.

A six step 260 includes driving the insulation material with the controlled RF supply to a semi- liquid state and controlling the changing state of the insulation material in a seventh step 270 with the controller to fill in the voids or defects.

In an eighth step 280 the insulation material is allowed to solidify under a controlled cool down period as controller removes the RF power.

Finally, the electric motor is retested in step 290 to verify that the defects or voids in the insulation material used in the motor stator windings have been resolved.

Additionally, the RF power level required is dependent on the application that it is being used for. The key factors determining this are:

- Material thickness (or overall volume of material to be heated)

- The phase transition profile, or how quickly the material goes from a solid to liquid, which is in turn determined by the degree of crystallinity of the polymer

- The temperature at which this phase transition begins (higher transition temperature will require more power applied for longer periods of time)

- The type of stator core that is being used, as different materials will absorb more of the energy than others instead of the insulation absorbing it

- The value of the loss factor at the applied frequency as some materials have much higher loss factors than others and thus will generate more heat.

- The heat capacity of the material

With the above referenced constraints; a thermoplastic resin can be heated to its reflow temperature, allowed to flow, and cooled with the termination of the energy input.

In view of the above, embodiments described herein may include the system and/or method that provides a way to repair dielectric heating of motor insulation with an RF energy stimulus in order to repair defects and degradation in the insulating material in-situ. The technical effects and benefits of the system includes a system and/or method to precisely control the application of RF energy that inherently pulses and increases the insulation temperature of the stator motor windings until a semi-liquid state is obtained. Thus, embodiments described herein are necessarily rooted in the controller to perform proactive operations to overcome problems specifically arising in the realm of motor winding repair.

Claims

A method for repairing defects of an insulation material used to insulate stator motor winding coils in large electric motors, the method for repairing defects comprising:

providing an RF profile applied to the stator motor winding coils with a controlled RF power supply,

precisely controlling the RF profile with the RF power supply through the stator motor winding coils while measuring the temperature rise and thermal release of the coils with sensors attached to the winding coils, the measured temperature rise and thermal release of the coils being stored within a controller, the stored temperatures used by the controller as feedback,

distributing heat through the thermal release of the stator coils and intelligently controlling the temperature change rates with the feedback,

determining an overall volume of insulation material to be heated,

identifying specific melting points of the volume of insulation material used in the stator to be repaired,

driving the insulation material with the controlled RF supply to a semi- liquid state, controlling the changing state of the insulation material with the controller to fill in the voids or defects,

allowing the insulation material to solidify under a controlled cool down period as controller removes the RF power, and

testing the insulation material used in the motor stator windings for breakdown to verify the defects have been resolved.

The method for repairing defects of an insulation material according to claim 1, wherein the insulation material is a polymer comprised of short chain polymers with minimal cross- linking.

The method for repairing defects of an insulation material according to claim 1, wherein an application of a high voltage, high RF signal of 600W to 1000W directly into the motor winding produces a heating effect in the insulating material, wherein the RF frequency used is dependent on the material it is being applied to, and wherein the frequency is in the range of lMHz to 10GHz.

4. The method for repairing defects of an insulation material according to claim 3, wherein the insulation material oscillates in response to fast changes in polarity of the alternating RF field and the high voltage produces strong electromagnetic field strength which pulls the material in alternating directions.

5. The method for repairing defects of an insulation material according to claim 4, wherein the molecular movement of the chains in the polymers produces friction, which in turn generates heat.

6. The method for repairing defects of an insulation material according to claim 5, wherein the longer the RF alternating field is applied and the more power the field contains the more temperature rise will occur in the windings.

7. The method for repairing defects of an insulation material according to claim 6, wherein as the controlled temperature of the insulation material rises it will exceed the glass transition temperature of the material, the insulation material will become less solid and will behave more as a liquid than a solid.

8. The method for repairing defects of an insulation material according to 2, wherein the short chains in the material allow it to flow more easily, which enables the resolution of smaller defects.

9. A system for repairing defects of an insulation material used to insulate stator motor winding coils, the system comprising:

a motor having stator motor winding coils, the stator motor winding coils including the insulation material that encases the coils,

an RF power supply having an RF profile that is applied to the stator motor winding coils, and

a controller for controlling the RF profile that is applied to the stator winding coils.

10. The system for repairing defects of an insulation material according to claim 9, wherein the RF profile is precisely controlled with the controller.

11. The system for repairing defects of an insulation material according to claim 10, wherein the controller further measures the temperature rise and thermal release of the coils, and wherein the measured temperature rise and thermal release of the coils is stored within the controller.

12. The system for repairing defects of an insulation material according to claim 11, wherein the temperature rise rates and thermal release rates from the stator motor winding coils are intelligently controlled with the controller.

13. The system for repairing defects of an insulation material according to claim 12, wherein specific melting points of a volume of insulation material used in the stator motor windings coils to be repaired are identified, and wherein the insulation material is driven to a semi- liquid state with the controlled RF supply.

14. The system for repairing defects of an insulation material according to claim 13, wherein the changing state of the insulation material is controlled with the controller in order to fill in the voids or defects.

15. The system for repairing defects of an insulation material according to claim 14, wherein the insulation material is solidifies when the RF power is removed, and wherein insulation material used in the motor stator windings is tested for breakdown to verify the voids or defects have been resolved.