POWER TRANSMISSION AND DISTRIBUTION LINES INSPECTION TECHNIQUES BASIC AND TUTORIALS

 • Visual inspections — Most often, crews find gross problems, especially with drive-bys: severely degraded poles, broken conductor strands, and broken insulators. Some utilities do regular visual inspections; but more commonly, utilities have crews inspect circuits during other activities or have targeted inspections based on circuit performance.

The most effective inspections are those geared towards finding fault sources — these may be subtle; crews need to be trained to identify them.

• Infrared thermography — Roughly 40% of utilities surveyed use infrared inspections for overhead and underground circuits. Normally, crews watch a 20°C rise and initiate repair for more than a 30°C rise.

Infrared scanning primarily identifies poor connectors. Some utilities surveyed rejected infrared monitoring and did not find it cost effective. Other utilities found significant benefit.

• Wood pole tests — Visual inspections are most common for identifying weak poles. A few utilities use more accurate measures to identify the mechanical strength left in poles.

A hammer test, whacking the pole with a sledge, is slightly more sophisticated; a rotted pole sounds different when compared to a solid pole. Sonic testing machines are available that determine density and detect voids.

• Operation counts — Most utilities periodically read recloser operation and regulator tap changer counters to identify when they need maintenance.

• Oil tests — A few utilities perform oil tests on distribution transformers, reclosers, and/or regulators. While these tests can detect deterioration through the presence of water or dissolved gasses, the expense is difficult to justify for most distribution equipment.

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