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As per IS 4029:2010-Guide for Testing Three Phase Induction Motors. High Voltage test in special case performed at the site. The test voltage shall be__________ percent of the standard test voltage.
120
100
80
115
80
Quick Summary: According to IS 4029:2010, the high voltage test is typically performed at the factory with a standard test voltage. However, when the test must be performed at the installation site on a used or repaired motor, the test voltage is reduced to 80% of the factory-rated standard test voltage to avoid damage to the insulation.
According to IS 4029:2010, the high voltage test is typically performed at the factory with a standard test voltage. However, when the test must be performed at the installation site on a used or repaired motor, the test voltage is reduced to 80% of the factory-rated standard test voltage to avoid damage to the insulation.
Vsite=0.8×Vfactory — Site test voltage calculation
Vstd=2Un+1000 — Standard factory test voltage formula for rated voltage Un
The reduction in test voltage (to 80%) is a safety measure. Insulation systems degrade over time due to thermal, mechanical, and environmental stress. Applying the full factory-level voltage (which is meant for new insulation) on aged or site-exposed windings poses a risk of dielectric breakdown, potentially causing unnecessary failure of healthy equipment.
IS 4029:2010 is the Indian Standard for testing three-phase induction motors.
High Voltage (HV) tests verify the integrity of the ground wall insulation.
Site conditions (dust, humidity, vibration) influence the insulation resistance levels.
Reducing test voltage prevents 'testing to destruction' on aged insulation.
Prevents catastrophic breakdown of aged insulation during testing.
Allows verification of dielectric integrity after site repairs or overhauls.
Less stringent than factory testing, potentially missing minor insulation weaknesses.
Site-specific environmental factors can lead to inconsistent readings.
Post-repair testing at project sites.
Preventive maintenance schedules for large induction motors.
Commissioning of refurbished motors in industrial plants.
The standard test voltage for new machines is usually 2Un+1000V, applied for one minute.
Option 100% (B) would be applicable only for new equipment tested at the factory.
The 80% rule is specific to site conditions as per Indian Standard guidelines.
C is correct — The high voltage test for three-phase induction motors when conducted at the site must be performed at 80% of the standard factory test voltage.
Always distinguish between 'Factory Testing' (full stress) and 'Site/Maintenance Testing' (reduced stress) in electrical machine standards as this is a common theme in JE/AE exams.