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.
Component Type
|
Typical Applications |
Material / Environment
|
Switch & Bus (Standoff)
Insulator
|
Switchgear
Bus Duct
|
Bis-A Epoxy – Enclosed
Applications.
Cycloaliphatic Epoxy –
Outdoor Applications
|
Roof Entrance or Cover
Mounted Bushings
|
Switchgear, Distribution
Breakers
|
Cycloaliphatic Epoxy –
Outdoor applications
|
Transformer Bushings
|
Distribution transformers
Power Transformers
|
Bis-A Epoxy – Enclosed
applications.
Cycloaliphatic Epoxy –
Outdoor Applications
|
Separable Connector
(Deadbreak Bushing)
|
Distribution transformers
Switchgear
|
Cycloaliphatic Epoxy
SF6 compatible Epoxy
|
- Bisphenol A: indoor applications or fully-enclosed, outdoor applications without UV exposure.
- Cycloaliphatic: outdoor applications with UV exposure.
-
SF6 compatible: gas insulated systems.
- 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.

- 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.

Standard
|
Units
|
Values
|
|
Dielectric Properties
|
|||
Volume Resistivity
|
ASTM D257
|
Ω-cm@ 25 ° C
|
5.7x1015
|
Dielectric Strength
|
ASTM D149-09
|
V/ MIL 0.125” THICK
|
680
|
Dielectric Constant
|
ASTM D150-11
|
@ 23 ° C, 600 Hz
|
> 4.0
|
Dissipation Factor
|
ASTM D150-11
|
@ 23 ° C, 600 Hz
|
0.01
|
Incline Plane Tracking
|
ASTM D2303
|
MINUTES @ 2.5 KV
|
>500
|
Mechanical Properties
|
|||
Flexural Strength
|
ASTM D790-10
proc A
|
psi
|
13000
|
Compressive Strength
|
ASTM D695-10
|
psi
|
>22,000
|
Tensile Strength
|
ASTM D638
|
psi
|
7,600
|
IZOD Impact Resistance
|
ASTM D256-10 method A
|
ft-lb/in2
|
0.32 |
Continues operation temperature, Class
|
° C
|
>155
|
|
Flammability Test
|
ASTM D3801, IEC
707, ISO 1210
|
1/4” Thickness
|
V0
|
Water Absorption
|
ASTM D570
|
% wt.
|
0.1%
|
Ⅲ.Material data and test summary
- Transformer bushings: typically high current carrying capability or high voltage application, coupled with high ambient temperature environments.
- High overload applications: customers require frequent overload capability with limited loss of life which conventional epoxies cannot meet.
-
Separable connectors such as deadbreak bushings used in wind farm transformers and solar applications.
-
Cable termination bushings used in solar inverter applications.
