Aug 2024

Helical Splice Shunt Testing at PLP New Zealand

A series of mechanical tests were performed in the PLP test lab on Helical Splice Shunt (HSS) fittings. The aim of these tests was to determine the repair capacity of these fittings.

PLP NZ’s laboratory is IANZ accredited for mechanical, heat cycle and short circuit testing to International Standards such as IEC, ANSI, AS and BS. Through the application of internationally recognized Standards, PLP NZ consumers can be confident in the test results, inspection reports and certifications provided.

What is a Helical Shunt?

A helical splice shunt is a repair fitting which can be applied over compression midspan splice fittings that are defective or have deteriorated. They are applied just like any other helical fitting and are composed of sets of rods which wrap onto the conductor and over the midspan splice. Electrically they are designed to restore 100% of the conductor’s ampacity. Mechanically they are designed to restore 100% strength of the aluminium strands and 10% strength of the steel strands.

Where are Helical Splice Shunts Used?
A helical splice shunt can be used to repair a compression splice fitting that is found to be in a deteriorated state. The deteriorated fitting will be running hot and is likely to degrade further, which will ultimately cause electrical or mechanical failure. The helical splice shunt will repair the electrical conductivity and mechanical integrity of a compression splice fitting to prevent further damage or failure.

Another use for helical splice shunts is to repair splices which have been incorrectly installed or poorly compressed. These incorrectly installed splices will degrade quickly and will have reduced mechanical strength and electrical integrity. A HSS can be applied to repair these incorrectly installed fittings until the defective joint can be replaced.

Tests Conducted at PLP’s Testing Lab

The mechanical tests conducted by PLP sought to discover how much of the mechanical strength could be restored by a helical splice shunt fitting.

The tests were performed on several common ACSR conductors used on transmission lines, ranging from Coyote ACSR (15.9mm OD) to Pheasant ACSR (35.1mm OD). Three scenarios were tested:

1. Helical Splice Shunt Only

Only a HSS was applied to join two conductor lengths. This test aims to ensure that the HSS meets the repair rating.

2. Helical Splice Shunt with Steel Midspan Only (Aluminium midspan uncompressed)

This scenario represents a situation where the aluminium tube of the splice is poorly compressed, incorrectly installed, or is not properly centered over the steel midspan. All of the mechanical loading is on the HSS and the steel strands.

3. Helical Splice Shunt with Aluminium Midspan Only (Steel midspan uncompressed)

This scenario represents a situation where the steel tube of the splice has been poorly compressed or is incorrectly installed. All of the mechanical loading is on the HSS and the aluminium strands.

Scenario 1: Repair Rating Test
Only a helical splice shunt was applied to join the two conductor ends. This assembly was pulled until failure (breaking point) in the mechanical test bed. The helical splice shunt was able to hold above the repair ratings (100% the strength of the aluminium strands + 10% the strength of the steel strands).

Scenario 2: Aluminium Tube Incorrectly Installed or Not Centered

The helical splice shunt was applied over the incorrectly installed compression splice (aluminium tube was left uncompressed) and was pulled until failure in the mechanical test bed. The helical splice shunt was able to repair the aluminium strands so that the conductor failed at above 90% of the nominal breaking load of the conductor. These results show that the HSS fitting can effectively restore the strength of the aluminium strands when the aluminium splice is incorrectly installed.

Scenario 3: Steel Tube Incorrectly Installed or Poorly Compressed
The helical splice shunt was applied over the incorrectly installed compression splice (steel tube was left uncompressed) and pulled until failure in the mechanical test bed. The helical splice shunt was able to repair the steel strands so that the conductor failed at above 90% of the nominal breaking load of the conductor. These results show that the HSS fitting is able to effectively restore the strength of the steel strands when the steel splice is incorrectly installed.
The results of testing show that the helical splice shunt fittings are able to repair a significant amount of the conductor’s mechanical strength and can be used to restore defective joints. In cases of damage or installation error, the HSS can be used to repair the mechanical strength of the joint until the joint can be replaced. Helical splice shunts are available for a large range of ACSR and AAC conductors.