• 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.
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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