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Thermoplastics for UL/IEC Electrical Insulation Systems: Transformers, Motors, Coils, Relays, and Encapsulated Components Product Information2000/2001 Edition
Thermoplastics for UL/IEC Electrical Insulation
Systems: Transformers, Motors, Coils, Relays,
and Encapsulated Components
DuPont Engineering Polymers
Copyright © 2000 E. I. du Pont de Nemours and Company. All rights reserved.
d 2
Introduction
Starting with the discovery over 50 years ago of
polyamide 66 (Nylon 66) and polytetrafluoro-
ethylene (Teflon
®
), DuPont has gone on to become
one of the worlds leading suppliers of electrical
insulation materials. Offering a wide range of films,
high performance thermoplastic resins, fibers, wire
enamels, varnishes, and aramid papers and press-
board products, DuPont is able to meet virtually all
the electrical insulation requirements of todays
transformers, motors, relays, switches, sensors, and
encapsulated coils and components.
In addition to its extensive product lines, DuPont
has together with its distributors, converters, and
molders established a network capable of supplying
world-class quality products and services virtually
anywhere. Our production plants are located in all
regions of the world and are either certified or are
in the process of being certified to comply with
ISO 9002 norms. Also, as a Global Leader in
electrical insulation, we work closely with the
worlds standards bodies and agencies to ensure
that our products are properly qualified for their
intended end use. In the case of electrical insula-
tion, this means gaining systems recognition for
our materials within the standards frameworks
established by the IEC and UL.
As we go in to the 21st century, electrical insulation
systems are playing an ever more important role in
the global manufacturing of transformers, motors,
relays, contractors, lighting ballasts, and a host of
other electrical applications. Basically, such
systems are groups of materials that through
extensive testing are recognized to be well suited
for electrical applications at a given temperature or
class and at specified material thicknesses.
Systems are recognized under Underwriter Labora-
tory (UL) and International Electrotechnical
Commission (IEC) standards UL 1446 and IEC 85,
respectively, with qualifying tests described in
IEEE (Institute of Electrical and Electronic Engi-
neers) documents. (See Figure 2 for an example.)
More recently, the IEC has moved to standardize
the testing and evaluation of electrical insulation
systems (EIS) and to provide a uniform means of
qualifying them. The result has been the recent
adoption of:
1. IEC 61857Procedure for Thermal Evaluation
of EIS
2. IEC 61858Qualification of Additional
Materials in EIS
Also under development by the IEC are standards
for encapsulated coils and a revision of IEC 85, the
Thermal Evaluation and Classification of Electrical
Insulation. The target date for these two new
standards is 2002. Taken as a group, these new IEC
Figure 1. Plastron (from left to right) Ian Graham,
Sales Manager; Tim Brogla (DuPont); Gary
Sobczac, Engineering Manager.
electrical insulation system standards will meet
broad industry consensus that in this application
area there should be one set of standards and test
procedures worldwide.
Electrical Insulation Systems
Testing
Qualification of an insulation system to either
UL 1446 or IEC standards requires testing of
complete, assembled insulation systems. Electrical
equipment manufacturers are faced, therefore, with
testing the actual equipment, substituting a
motorette or transformerette that represents their
system, or using a recognized EIS through a
material supplier like DuPont who has already done
the testing. Because final recognition of a system
by UL can take a year or two and cost $40,000
(USA) in testing and meeting required standards,
many manufacturers use pre-approved systems.
In doing EIS testing, DuPont relies primarily on
motorettes as the test specimen. This has the
advantage of qualifying recognized systems for
motor and transformer applications simultaneously.
By running as many systems as possible without
varnish, there is the option of adding qualified
varnishes to a recognized system as a minor com-
ponent using a simpler UL 1446 sealed tube
procedure. 3
Figure 2.
A Typical Electromechanical Relay
IEC Publication 85 refers to standards for insulation
systems, including UL Standard 1446 for the testing
and evaluation of electrical insulation systems. UL
Standard 1446, paragraph 3.4, defines an electrical
insulation system as: an intimate combination of
insulating materials used in electrical equipment. For
example, the combination of a coil form, separators,
magnet-wire coating, varnish, lead-wire insulations,
and outer wrapping of a relay coil.
Figure 3.
Encapsulated Transformer using a Class B
130
°
C EIS (Valentine).
Figure 4. Motor spiders molded in Rynite
®
PET by
Polymar, a division of ASM Industries.
For encapsulated systems, encapsulated solenoids
that are bifilar wound are used as the test samples.
Test procedures and applications for encapsulated
systems are found in our brochure, Electrical/
Electronic Thermoplastic Encapsulation.
For the insulation systems used in transformers,
motors, etc., the EIS test procedures are found in:
UL Standard 1446
Test Procedures for Electrical
Insulation Systems
Construction of Test Rigs (Motorettes)
UL or a UL-approved test lab constructs the
candidate and control test rigs. Ten rigs are
constructed for each test temperature, for both the
control and candidate systems. Test cycles then
proceed as follows:
Heat Aging
Highest temperature: 3-day cycle
Next lower temperature: 7-day cycle
Next lower temperature: 14-day cycle
Lowest temperature: 28-day cycle
Test at end of each cycle
Cold Shock
Hold until stabilized at 20
°
C
Mechanical Stress
Vibration at 60 Hz for 1hr
Moisture Exposure
Hold for 48 hr at 92 to 100% relative humidity at
room temperature.
End of Life Test
Test rigs are dielectric stressed by 600 V applied
phase-to-phase and phase-to ground and 120 V
turn-to-turn, each for 10 min. It is required that
the lowest test temperature shall result in a
geometric mean time to end-of-life of at least
5000 hr. 4
Figure 5.
EIS Test Motorette
Figure 6. Fasco Coil Forms molded in Rynite
®
FR 530 to meet UL EIS requirements.
Figure 7. Plasti-coil (from left to right) Craig
Ferguson, President; A.K. Shah (visitor
from India); Bob Cordoba, Operations
Director; Tim Brogla (DuPont); Birgit Staub
(DuPont).
Figure 8. Laurent Chapellier of Moulinex and
Frederic Segretinat of DuPont France
examining microwave oven transformers
using Rynite
®
PET coil forms.
Figure 9. Garage door opener transformer coil forms
in Zytel
®
HTN (Thermotech, Division of
Menasha).
This test procedure qualifies the major components
of the insulation system. Major components include
ground insulation, magnet wire, interwinding
insulation, and varnishes. However, the dip varnish
can also be considered a minor component if the
motorette or transformerette did not use a varnish.
The varnish, like other minor components, can be
added to insulation systems by sealed-tube testing.
An ISO 9002 certified laboratory well equipped to
do this testing is:
ELTEK International Laboratories
248 Hughes Lane
St. Charles, MO 63301, USA
(636) 441-6200
Fax (636) 447-6289
Web site: www.elteklabs.com
Manufacturers can test their actual equipment or
they can substitute a motorette or transformette
that represents their system. The motorette pictured
can be used to simulate the actual component
(ELTEK International Laboratories). 5
Sealed Tube Testing
Sealed tube testing was devised so that additional
materials could be added to the original EIS with-
out going through the full, very laborious motorette
or transformerette testing discussed above. Tapes,
lead wires, sleeving materials, and dip varnished
can be added to various insulation systems using
the sealed tube procedure described below.
UL Standard 1446
Sealed Tube Procedure/
ASTM D 5642
Sample Preparation
Twisted Pairs of Magnet Wire. Twisted pairs of
magnet wire used in the original insulation
system are prepared, a minimum of five
samples for each tube.
Reference Tube. This tube contains only
materials employed in the original insulation
system.
Minor Component Tube. This tube contains all
new or substitute materials plus all materials
and alternates currently used in the approved
insulation system.
Preparation of Tubes
Cleaning. Tubes are cleaned and dried as
needed.
Loading. Component materials are placed in
tubes, followed by the twisted wire pairs
avoiding contact of the materials with the
magnet wire if possible.
Sealing. Filled glass tubes and the sealing
materials are dried 1 hr at 105
°
C. Tubes are
then sealed immediately and cooled to room
temperature (see photo).
Sample Condit