To assess the condition of switchgear bar supports through insulation resistance testing, a high-voltage megohmmeter is primarily used to apply a DC voltage and measure the insulation resistance. As switchgear bar supports age, due to accumulation of surface contamination, internal through-hole cracks, or moisture, both their volume and surface resistances decrease significantly. Test results below specified historical benchmarks or standard thresholds (e.g., below 100 MΩ, typically considered a warning threshold) indicate deterioration in the support insulation performance, with the potential for carbonization channels to form, posing a risk of creepage or through-hole breakdown. The test environment temperature and humidity must be calibrated, and horizontal comparisons with similar bar supports are more helpful in assessing the extent of aging.
Dielectric loss analysis focuses on evaluating the dielectric loss characteristics of switchgear bar supports under high-voltage AC fields. Measuring the dielectric loss tangent (tanδ) using a precision bridge circuit can sensitively reflect the overall deterioration of the insulation material and any internal defects. When a switchgear bar support ages (e.g., due to moisture delamination, air gap discharge, or resin matrix cracking within the insulation material), its dielectric polarization and conductivity losses increase, leading to an abnormally high tanδ value. The loss curve with increasing test voltage also changes (e.g., a distinct inflection point appears). This non-destructive method is particularly adept at detecting localized, but actively developing, deterioration within the bar support.
Combining these two methods provides a more comprehensive diagnosis of switchgear bar support degradation. Insulation resistance testing is highly sensitive to penetrating defects and severe moisture, while dielectric loss analysis is more sensitive to early, diffuse material degradation and interfacial polarization effects. A significant decrease in the insulation resistance of a switchgear bar support, accompanied by an excessive increase in dielectric loss, or an abnormal spectral pattern, particularly at high voltages, strongly indicates that the insulation structure has entered an accelerated aging phase or faces serious potential hazards, requiring timely maintenance or replacement. These two methods form a key collaborative diagnostic mechanism for the insulation condition of the bar support.
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