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Examoogle • User • info@examoogle.com • EE-2024-8821
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Drying of winding should be done during____________
Periodic maintenance
Preventive maintenance
Breakdown maintenance
Routine maintenance
Preventive maintenance
Quick Summary: Drying of electrical machine windings is a standard preventive maintenance procedure performed to remove moisture absorbed by the insulation material. Moisture significantly lowers the insulation resistance (IR) and dielectric strength, which is corrected via drying to ensure the long-term reliability and safety of the equipment.
Drying of electrical machine windings is a standard preventive maintenance procedure performed to remove moisture absorbed by the insulation material. Moisture significantly lowers the insulation resistance (IR) and dielectric strength, which is corrected via drying to ensure the long-term reliability and safety of the equipment.
Rins∝M1 — Where M is the moisture content in the insulation
Q=mcΔT — Heat energy required for moisture removal
Moisture ingress over time reduces the insulation resistance Rins of windings. During preventive maintenance, external heat (via hot air blowers, induction heating, or circulating current) is applied to the winding to raise its temperature above the ambient dew point, causing water vapor to evaporate. The process is monitored by measuring the insulation resistance until it reaches a stable, safe threshold as per standards like IS 2026.
Drying is essential if insulation resistance (IR) values drop below the recommended limits.
Common methods include oven drying, short-circuit drying, and hot air circulation.
Always perform a 'Polarization Index' (PI) test before and after drying to assess the condition.
Preventive maintenance ensures drying is done before insulation failure occurs.
Increases the operational lifespan of the winding insulation
Prevents partial discharge and potential dielectric breakdown
Requires equipment downtime
Needs controlled temperature monitoring to prevent thermal degradation of insulation
Large power transformers
High voltage induction and synchronous motors
If the IR value is below 1 MΩ per kV, immediate drying is generally recommended.
Breakdown maintenance is corrective, not proactive; waiting for a fault to dry a winding is hazardous.
B is correct — Drying of windings is a planned, proactive task performed during preventive maintenance to ensure moisture is removed before it leads to insulation failure.
Always check the Polarization Index (PI) value: a PI ratio <1.25 indicates the insulation is likely damp and requires a drying process.