Transformer Insulation Resistance (Megger) Test

Inspection template for recording transformer winding-to-ground and winding-to-winding insulation resistance, polarization index, test voltage, and temperature-corrected results using a megohmmeter.

Inspection Details

• Asset identification recorded
  Record transformer ID, location, nameplate rating, and serial number.
• Inspection date and time recorded
  Document when the insulation resistance test was performed.
• Inspector name and qualification recorded
  Record the technician or electrician performing the test and their qualification or certification if applicable.
• Work order or test reference recorded
  Record the maintenance work order, commissioning package, or test report reference.
• Transformer type and configuration recorded
  Record transformer type, voltage class, winding configuration, and whether the unit is energized or isolated.

Safety and Test Preconditions

• Lockout-tagout applied and verified
  Confirm the transformer is isolated, de-energized, and controlled under lockout-tagout per OSHA 1910.147 before testing.
• Absence of voltage verified
  Verify absence of voltage on all applicable terminals before connecting the megohmmeter.
• Required PPE worn
  Select all PPE used for the task, such as arc-rated clothing, voltage-rated gloves, safety glasses, and face shield as applicable.
• Test area barricaded and controlled
  Confirm the test area is restricted to authorized personnel and warning signs are posted as needed.
• Discharge procedure completed after test
  Confirm the transformer windings were discharged to ground after each test and before handling conductors.
• Test instrument calibration current
  Confirm the megohmmeter calibration or verification status is current and traceable.

Environmental and Test Conditions

• Ambient temperature recorded
  Record the ambient air temperature at the time of test.
• Winding or oil temperature recorded
  Record the transformer winding temperature or oil temperature used for temperature correction.
• Relative humidity recorded
  Record relative humidity because moisture can affect insulation resistance readings.
• Surface condition and contamination noted
  Document visible moisture, dirt, oil, or contamination on bushings, terminals, and test points.
• Test voltage selected
  Record the DC test voltage applied by the megohmmeter.

Insulation Resistance Test Results

• Winding-to-ground insulation resistance recorded
  Record the one-minute insulation resistance reading between each winding and ground.
• Winding-to-winding insulation resistance recorded
  Record the insulation resistance between applicable windings, if tested.
• Ten-minute insulation resistance recorded
  Record the ten-minute reading used to calculate polarization index.
• Polarization index calculated
  Record the polarization index as the ratio of ten-minute resistance to one-minute resistance.
• Temperature-corrected insulation resistance recorded
  Record the insulation resistance corrected to the reference temperature used by the site procedure.

Acceptance, Deficiencies, and Closeout

• Results meet site acceptance criteria
  Confirm the measured and temperature-corrected results meet the applicable site or OEM acceptance criteria.
• Deficiencies or non-conformances documented
  Describe any low readings, unstable readings, contamination, moisture ingress, or suspected insulation defects.
• Corrective action recommended
  Document recommended actions such as drying, cleaning, retesting, further diagnostics, or removal from service.
• Photo evidence attached
  Attach photos of the test setup, meter readings, nameplate, or any observed deficiencies.
• Inspector signature
  Signature of the person completing the inspection and test record.