The Challenge

To backup CCS's century-long reputation for superior strength, Copperweld's engineering team received several requests from customers to perform lab tests that measure the flex-fatigue endurance of Copperweld CCS products compared to equivalent-ampacity copper conductors. So, they stepped up to the challenge.

Flex Fatigue Testing

In conductor manufacturing, breakload tests are popular for assessing conductor strength. Copperweld performs dozens of breakload batch tests every day to ensure that every foot of our CCS conductors is performing to specification. But while breakload tests are excellent for measuring tensile strength, they only measure mechanical strength across a single, linear event. Real-world abuse involves a wide range of motion and a high level of repetition.

Real-world abuse involves a wide range of motion and a high level of repetition.

Whether simulating the high-pressure contraction and expansion in buried applications or the repetitive stresses in overhead applications, an accurate way to measure real-world endurance is a flex fatigue test. Flex fatigue testing measures the number of stress cycles (180 degree bends) endured before conductor breakage is observed. A conductor’s breaking point is typically measured when continuity is interrupted. Unfortunately, stranded conductors expose an inherent limitation when simply testing for continuity.

Finding the True Breaking Point

Because a stranded conductor can maintain continuity after one or more strands have broken, a traditional flex-fatigue test that measures continuity disruption is more suited for single-end conductors. This method of testing endurance provides an unfair advantage to stranded conductors like our stranded CCS products. So, we devised a test method to more accurately and fairly measure the comparative flex-fatigue performance of both stranded and solid conductors.

We devised a test method to more accurately and fairly measure the comparative flex-fatigue performance of both stranded and solid conductors.

This new test setup utilizes the sound spike created when a single strand of a stranded conductor breaks to identify the cycle at which the conductor is compromised, despite maintaining some conductivity. With this setup, a sound meter and monitoring software are used to cross reference elapsed test time of the sound spike (breaking point) with the number of bend cycles in the flex fatigue test. This provides a reliable method of testing the flex endurance for both conductor construction types. View Figure 1 below.
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Our Test

To test the flex endurance of products that traditionally receive significant abuse in the field, we focused the study on our most popular transformer riser cables (Stingray 135 and Stingray 195) and their copper equivalents (6 AWG and 4 AWG). Pole-top transformer riser cables are subjected to a high level of shear force trauma in the form of flexing, bending, jerking, and vibration — making them ideal test subjects for this study.
 
In each test, five samples of each conductor — CCS and copper — were cut into two-foot sections with 1” of insulation removed from both ends to connect to the Flex Fatigue Tester. A Reed R8080 Sound Level Meter was then connected to monitoring software to capture single-end strand breakage. To mimic the extreme stressors that many conductors encounter in the field, we performed a standard 180-degree test consisting of a 90-degree bend to the left and a 90-degree bend to the right constituting a full cycle.

Stingray 135 vs 6 AWG Solid Copper Results

When comparing Copperweld CCS samples (Stingray 135) to solid-copper samples (6 AWG), CCS displayed greater flex endurance than copper. The average full-cycle count for the Stingray 135 samples was 224.8 cycles while the average full-cycle count for the 6 AWG copper samples was 36.2 cycles. This indicates that the CCS sample (Stingray 135) has 5.2 times more flex endurance than copper (6 AWG). See Graph 1 below for the visual representation of the findings.
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Stingray 195 vs 4 AWG Solid Copper Results

When comparing Copperweld CCS samples (Stingray 195) to solid-copper samples (4 AWG), CCS displayed greater flex endurance than copper. The average full-cycle count for the Stingray 195 samples was 87.6 cycles while the average full-cycle count for the 4 AWG copper samples was 30.6 cycles. This indicates that the CCS sample (Stingray 195) has 1.9 times more flex endurance than copper (4 AWG). See Graph 2 below for the visual representation of the findings.
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Conclusion:

Using flex fatigue testing and sonic breakage detection, Copperweld CCS conductors displayed up to 5 times greater flex endurance than the equivalent copper samples.

Copperweld CCS conductors displayed up to 5 times greater flex endurance than the equivalent copper samples.