What’s in Your TRXLPE?
Tree retardant, cross linked polyethylene or TRXLPE is one of the most commonly used polymer compounds found in medium and high voltage underground distribution and transmission cables.
TRXLPE insulated cables have the lowest losses when compared to other insulating materials used in underground cable design, such as oil impregnated paper in paper insulated lead covered (PILC) or ethylene propylene rubber (EPR) cables.
Additionally, when compared to EPR, approximately 98% of the raw TRXLPE compound comes directly from the compound manufacturer in the form of pre-made pellets. The cable manufacturers only add 2% proprietary compounds to complete the insulation composition. Whereas when dealing with insulations such as EPR, 40%-60% of the base resin comes from the supplier and the manufacturers then add the remaining proprietary compounds to complete the insulation composition.
All cables used in a utility setting (transmission or distribution) need to be tested to requisite industry standards. When you compare test reports from any manufacturer of a TRXLPE cable, you can rest assured that 98% of the insulating material of the cable is consistent among all cable manufacturers. However, when comparing test reports from various manufacturers for EPR cable, there is a 40%-60% difference in proprietary compounds, therefore, how can you measure the overall quality of EPR cable manufactured by one cable manufacturer compared to another? This becomes a challenging task.
Even though 98% of the raw material for TRXLPE is supplied directly by the compound manufacturer, within that 98% there maybe slight variances. That’s why it’s nice to know who supplies your cable manufacturer with their raw material.
There are currently two TRXLPE manufactures on the market; 1- DOW Chemical and 2- Borealis.
Borealis manufactures their flagship TRXLPE product known as LE4212. DOW chemical manufactures three different types of TRXLPE: 1- HFDA 4202, commercialized in 1983. 2- HFDB 4202, commercialized in 1998 and 3- HFDC 4202 commercialized in 2011-12.
It should be noted that the Borealis LE4212 is commercially similar to DOW HFDA 4202 and HFDB 4202, indicating that there hasn’t been much in the area of research and development on the TRXLPE compound side for the past 24 years. Whereas DOW appears to periodically collaborate with utilities to understand business needs and determine how they can further improve their product.
That being said, both LE4212 as well as HFDA, HFDB and HFDC pass all benchmark ICEA and AEIC qualification tests.
DOW’s HFDC 4202 outperforms its predecessors, HFDA 4202 and HFDB 4202; therefore, given the commercial similarity between LE4212 and 4202 HFDA and HFDB, it would be reasonable to conclude that within the current TRXLPE market, DOW’s HFDC 4202 would also out perform Borealis LE4212 and has been one of the most robust insulating compounds on the market since 2016.
Compound Improvement: Reduction of Water Tree Size and Shape (HFDC 4202) 
ASTM D6097 is a laboratory test designed to simulate the growth of vented water-trees in a solid dielectric insulating material. The water trees are initiated by inserting a sharp pointy object into the insulation under a wet environment in a high electrical field.
At the conductive, insulating interface, vented water-trees (as seen) are formed. The test method provides comparative data. The standard test conditions are designed to grow a sufficient water-tree length before breakdown occurs.
Tests are performed for a total of 30 days, though insulations with a higher resistance to trees can last up to 180 days.
360 Day ICEA Qualification Test 
ICEA qualifications tests are a combination of eight tests including but not limited to:
- Dry-electrical test for Class III insulation (MV-105)
- Dissipation factor characterization test
- Thermomechanical qualification test at 140 degrees
- Good original and retention of physical properties
- Long term wet aging performance demonstrated by ACLT and AWTT testing
Comparison of TRXLPE Accelerated Aging Performance 
ACLT or Accelerated Cable Life Test is where the cable is aged in the laboratory as per IEEE 1407.
Prior to performing the ACLT, the cable must be in continuous operation in air at 90 degrees, for 21 days (500 hours).
After this period, four times the nominal voltage rating of the cable is applied cyclically loading the cable as follows, 8 hours on and 16 hours off. The intent being to age all samples to failure.
- Test data generated by DOW in DOW laboratories on plaques of material as a part of the product development process.
- Graph obtained from tests performed at Southwire Retention of AC breakdown stretch after accelerated water trees testing (AWTT)
- Data for HFDB 4202 and HFDC4202 generated at the Marshall Test Center in Marshall TX, under contract with DOW. Data for Borealis LE4202 material taken from Borealis website
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