COMMON LINE DAMAGE IN A DISTRIBUTION SYSTEM FEEDER LINE

COMMON LINE DAMAGE IN A DISTRIBUTION SYSTEM FEEDER LINE

 What are the common of line damages that occur in transmission and distribution lines?

 The cause of damages to transmission and distribution lines can be attributed to many potential reasons. Conductors are one of the most exposed electric company asset to many unfortunate events. The cost of conductors is one of the major expenses in any overhead power line construction. It is the primary component in the flow of revenue for a utility and the component most exposed to hazards.

With the introduction of aluminum conductor, the vulnerability to damage increased due to its easily abraded surface. The four types of motion occurring on overhead power lines are (1) aeolian vibration, (2) galloping, (3) sway oscillation and (4) unbalanced loading. Each is independent in cause and effect.

Insulator and conductor damage can be classified into four main points; where lines are seldom inspected, the first indication of damage may not be detected until the conductor fails and falls to the ground, which may be too late to apply simple corrective measures. In order to avoid the consequences of broken conductors, a visual inspection of conductor and hardware should be made as often as the severity of the conditions suggests.

The following is a classification of the most common types of damage and the corresponding clues to watch for in making line inspections:

1. Abrasion - Abrasion to outside surfaces is highly visible and therefore easy to detect. Abrasion damage is a chafing and impact wear that accompanies relative movement between a loose tie and the conductor or armour rods. Even well-made hand ties can loosen if subjected to prolonged or severe motion. Abrasion is surface damage and can be identified by black deposits on the conductor or tie. It can also be identified by aluminum deposit build-up on the insulator and/or scoring of the insulator glaze.

2. Fretting - Fretting of aluminum wires is a deterioration process created by a rubbing action between two wires (or between a wire and another object). The action wipes away the oxide film normally on the surface of the wires so that the underlying metal is exposed to further oxidation. Since aluminum is a chemically active metal, oxidation occurs at a rapid rate. The back-and-forth motion re-exposes the metal to oxidation and repeatedly makes and breaks the microscopic welds. During this process oxide fragments accumulate and the fretted surfaces become rough. The fragments look like black dust, and the fretted surfaces are usually black. Fretting is often hidden, especially when it takes place on the inner strands of the conductor. On multi-layer conductor, breaks from fretting may sometimes be detected by spreading the outer strands in order to view the inner layers. WARNING! Do not use screwdriver or other sharp objects that could cause additional damage to the conductor. A nylon-covered tool or nylon fid is best for this purpose.

3. Fatigue Breaks - Fatigue breaks are the ultimate failures of the conductor strands or tie wire. They are caused by any one, or a combination of (1) aeolian vibration, (2) galloping, (3) sway oscillation, and (4) unbalanced loading.

4. Tensile Breaks - These breaks are the result of a load exceeding the strength of the material broken and can usually be identified by the cup-cone nature of the break.