Turbine designs continue to grow in power size, while reducing the space provided for the transformer in the nacelle area. This presents several challenges in transformer bushing designs, one of which is the considerable increase in the ambient temperature.As a result, H-J has developed a new high-temperature epoxy used on transformer bushings to help transformer manufacturers match their high-temperature insulation systems.
This new high-temperature epoxy is suitable for continuous use at 155°C, thus allowing users to pack more power into smaller footprints by running the systems hotter. H-J currently produces bushings with proprietary epoxy blends for 105, 120, and 155°C maximum operating temperatures.
The following paper created by H-J’s Engineering team would provide details about this very important topic and we are pleased to share with you.
Abstract
Electrical insulating component design has become increasingly challenging due to rapidly changing requirements in power industry applications. Cost reduction and increased performance requirements present new challenges for traditional insulation solutions. Modern insulating component designs must push the limits of dielectric performance while maximizing mechanical strength characteristics in a host of environments. In particular, the recent advancements in the use, size and scale of renewable energies such as solar and wind power necessitate enhanced performance epoxy insulating materials capable of delivering high dielectric and mechanical strength in high temperature environments.
This paper summarizes a brief history and current state of epoxy component insulation with commentary on advancements made for applications requiring enhanced material performance for high temperature applications.
Index Terms: Epoxy, High Temperature,Insulator, Bushing, Power Transformer,Switchgear.
I. Introduction
Epoxy materials have been used in electrical insulation applications in North America since the 1960s. Advancements in materials leading to improved performance have led to steady growth of epoxy use in insulating.
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Component Type
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Typical Applications |
Material / Environment
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Switch & Bus (Standoff)
Insulator
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Switchgear
Bus Duct
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Bis-A Epoxy – Enclosed
Applications.
Cycloaliphatic Epoxy –
Outdoor Applications
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Roof Entrance or Cover
Mounted Bushings
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Switchgear, Distribution
Breakers
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Cycloaliphatic Epoxy –
Outdoor applications
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Transformer Bushings
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Distribution transformers
Power Transformers
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Bis-A Epoxy – Enclosed
applications.
Cycloaliphatic Epoxy –
Outdoor Applications
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Separable Connector
(Deadbreak Bushing)
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Distribution transformers
Switchgear
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Cycloaliphatic Epoxy
SF6 compatible Epoxy
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component design since that time. The design flexibility facilitated by the use of a cast resin system has provided many advantages over traditional insulating materials. Initial applications using Bisphenol-A (Bis-A) materials in basic enclosed applications evolved to outdoor, UV-exposed applications with the development of cycloaliphatic epoxy materials. Epoxy materials are now found in a wide range of electrical insulation applications in varied environments including outdoor, UV-exposed; high contamination environments; high ambient temperature environment; and, gas insulated systems such as SF6.
Typical epoxy materials and environments are:
- Bisphenol A: indoor applications or fully-enclosed, outdoor applications without UV exposure.
- Cycloaliphatic: outdoor applications with UV exposure.
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SF6 compatible: gas insulated systems.
Some examples of typical applications and materials used are:
II. Trends
Continued advancements in equipment design and the evolution of new applications have created a need for epoxy materials that exhibit enhanced properties with respect to electrical, thermal and mechanical performance. Most recently, a trend towards higher operating temperatures exceeding most common industry temperature classes of 105°C and 120°C has necessitated the development of epoxies capable of operating at significantly higher Tg (glass transition temperatures) and HDT (heat deflection temperatures). Tg and HDT properties are more clearly defined as follows:
A. Glass transition temperature (Tg)
Is the temperature range in which a material alters state, going from a glass-like rigid solid to a more flexible, rubbery compound.
B. Heat deflection temperatures (HDT)
Commonly referred to as heat deflection temperature or heat distortion temperature is the temperature at which a polymer deforms under a specified load.’ The HDT, is a useful indicator of the temperature limit above which the material cannot be used for structural applications…’ [1]
The primary drivers for this trend of higher operating temperatures are:
- Equipment design: cost reduction efforts and space limitations have led to smaller equipment footprints with reduced cooling capability; and, requirements for more efficient component designs with current carrying components operating at higher current densities. Hence, higher ambient temperatures and component operating temperatures are more commonplace.
Cantilever withstand test
- Evolving technologies and applications: the significant rise in solar and wind generation activity has brought about new equipment design challenges in both transformer and switchgear design. Transformer applications have challenged designs to become compact with operation at high currents, often in overload conditions. Extremely high ambient temperatures in excess of 40°C are common, and in some cases up to 75°C in continuous operation in enclosures where traditional cooling methods are not possible.
In all cases, these operating conditions are in stark contrast to typical component design criteria.
The H-J Family of Companies chemical engineers have developed and implemented epoxy formulation solutions to meet these more demanding requirements. The basic challenge was to design a formulation capable of withstanding high ambient and high continuous operating temperature for component designs. This led to the development of an epoxy system capable of operation in these extraordinary conditions, while maintaining the required electrical and mechanical performance. Developed as an enhanced Bisphenol-A epoxy system，the material provides Tg and HDT performance above 155°C class operating requirements. Achieving these higher material ratings allows component operation at or above 155°C with no detrimental effect on the structural performance of the material. Suitability for operating above the 155°C rating may be application and component geometry specific.
H-J high voltage test lab
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Standard
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Units
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Values
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Dielectric Properties
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|||
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Volume Resistivity
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ASTM D257
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Ω-cm@ 25 ° C
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5.7x1015
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Dielectric Strength
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ASTM D149-09
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V/ MIL 0.125” THICK
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680
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Dielectric Constant
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ASTM D150-11
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@ 23 ° C, 600 Hz
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> 4.0
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Dissipation Factor
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ASTM D150-11
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@ 23 ° C, 600 Hz
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0.01
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Incline Plane Tracking
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ASTM D2303
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MINUTES @ 2.5 KV
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>500
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Mechanical Properties
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|||
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Flexural Strength
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ASTM D790-10
proc A
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psi
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13000
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Compressive Strength
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ASTM D695-10
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psi
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>22,000
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Tensile Strength
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ASTM D638
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psi
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7,600
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IZOD Impact Resistance
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ASTM D256-10 method A
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ft-lb/in2
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0.32 |
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Continues operation temperature, Class
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° C
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>155
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|
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Flammability Test
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ASTM D3801, IEC
707, ISO 1210
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1/4” Thickness
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V0
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Water Absorption
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ASTM D570
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% wt.
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0.1%
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Ⅲ.Material data and test summary
A series of material tests were performed to verify suitability of the enhanced Bis-A epoxy system in these applications. The
tests summarized below verify the technical characteristics of the material and confirm its suitability for application in insulating component design in these operating environments. The results meet or exceed requirements for the environments outlined in this document. Tests performed include:
Ⅳ.Designs and applications to date: high operating and ambient temperatures
As previously outlined, a prime driver for the evolution of higher operating temperature requirements has been newer technologies including wind and solar generation. Component development specific to these sectors includes:
- Transformer bushings: typically high current carrying capability or high voltage application, coupled with high ambient temperature environments.
H-J examples of bushings
- High overload applications: customers require frequent overload capability with limited loss of life which conventional epoxies cannot meet.
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Separable connectors such as deadbreak bushings used in wind farm transformers and solar applications.
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Cable termination bushings used in solar inverter applications.
Ⅴ.Summary and conclusions
Trends toward more optimized equipment design and new technology applications continues to drive research activities to ensure that insulating materials used in component design meet these challenges. The design flexibility offered by epoxies,
coupled with the availability of material rated for high operating and ambient temperatures, continues to make epoxy insulating solutions a preferred choice for insulating component designs now and in the future.
REFERENCES
Webpage：Polymer Properties Database 2015,
Available：https://polymerdatabase.com/ polymer%20physics/HeatDistortion.html
IR test image