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  • Pilot Wire Breakage During Cable Installation Works
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Pilot Wire Breakage During Cable Installation Works

bkf 042015
Photo: Upper part of transmission tower with deformed left middle cross arm

A fatal accident occurred during the stringing process of cable conductors between two transmission towers. During stringing process, an engine puller which is positioned at a designated distance from the transmission tower is used to pull a head board carrying two units of cable conductor and one sankarsi wire. Two workers were stationed at the cross arm of the transmission tower to install the conductor gripper on the two cable conductors as soon as the head board crosses over the pulley while being pulled by the engine puller. On the day of the accident, stringing process was being carried out as usual between a series of transmission towers and when the process was approaching the final phase, the pilot wire which is used to pull the head board suddenly snapped and caused the head board to hit the cross arm. The impact caused the cross arm to bend forward and one of the workers lost his stability and fell to the ground.

Below are some suggested safety measures:-

  1. An effective inspection and maintenance system must be formulated and carried out on machinery parts that are critical in cable instruction work, such as the pilot wire, head board and engine puller;
  2. The engine puller must be equipped with load indicator and load limiter that will enable the engine to stop immediately when the pulling load exceeds the allowable maximum load;
  3. Head board used during the stringing process must be clearly labeled with an allowable safe working load and must be tested according to a recognized international standard;
  4. The cable pulling speed must always be monitored and recorded when the engine puller is in operation;
  5. Engine puller operator must possess strong technical knowledge and the right skills to ensure that the pulling capacity matches the total load being pulled by the engine;
  6. During cable pulling or stringing process, designated persons must be stationed at each transmission tower to monitor the sagging value of the cable conductor by using a dynamometer. This is to ensure that the stringing tension does not exceed the sag tension value during stringing works and also to avoid the pulling capacity from exceeding the conductor maximum breaking load, Tmax(conductor);
  7. Ensure that the calculated Tmax does not exceed 10 % of the conductor rated strength as stated in the IEEE 524, and stop practicing the sankarsi method as this will cause additional load and increase the engine puller’s pulling capacity;
  8. Training in the usage of walkie-talkies must be conducted as often as possible to ensure that the walkie-talkies are always in good condition, and the practice of a proper communication method can ensure a good coordination between conductor grippers and engine puller operator;
  9. Must always refer to the IEEE 524 or any approved international standards for cable installation works to ensure that all work practices are according to the right procedure; and
  10. Risk assessments must be discussed between all parties involved in the cable installation works, and every job activity has to be properly assessed and itemized before any work is carried out;

References:-

  1. IEEE Std 524TM 2003, Guide to the Installation of Overhead Transmission Line Conductors published by The Institute of Electrical and Electronics Engineers, Inc
  2. Transpower Overhead Conductor Installation Guide, Recommended Practices First Edition, 2014 General Cable Technologies Corporation

 

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