Transformer Core Magnetic Balance Test

Inspection template for recording three-phase transformer magnetic balance readings to help detect core or winding faults and supplement ratio and resistance testing.

Test Record and Transformer Identification

• Asset identifier, location, and transformer nameplate details recorded
  Record the transformer asset ID, substation or facility location, manufacturer, kVA/MVA rating, voltage class, serial number, and winding configuration.
• Transformer phase count and winding arrangement confirmed
  Confirm the unit is a three-phase transformer and note the winding arrangement used for the test.
• Test date, time, and inspector recorded
  Document when the magnetic balance test was performed and who completed it.
• Related test references noted
  Record related ratio test, winding resistance test, insulation resistance test, or prior maintenance report references used for comparison.
• Test purpose documented
  Use this record to capture magnetic balance readings that supplement transformer ratio and resistance testing and help identify possible core or winding faults.

Safety Preconditions and Test Readiness

• Lockout-tagout applied and verified before test setup
  Verify the transformer and associated circuits are de-energized, isolated, and controlled under an approved lockout-tagout procedure per OSHA 1910.147.
• Absence of voltage verified at all required points
  Confirm absence of voltage using an approved meter before connecting test leads.
• PPE appropriate for electrical testing available and worn
  Verify required PPE is available and in use, including arc-rated clothing, insulating gloves, eye protection, and other site-required protection per the electrical hazard assessment and OSHA 1910 Subpart I / NFPA 70E practices.
• Work area controlled and test boundaries established
  Confirm barriers, signage, and access control are in place to keep unauthorized personnel clear of the test area.
• Test leads, meter, and connections visually inspected
  Check for damaged insulation, loose terminations, cracked housings, or other deficiencies before energizing the test circuit.

Test Equipment and Method Setup

• Test instrument identification and calibration status recorded
  Record the test set model, serial number, and current calibration due date or certificate reference.
• Test method and connection scheme documented
  Record the magnetic balance test procedure used, including lead placement, phases tested, and any manufacturer-specific steps.
• Ambient temperature and weather or site conditions recorded
  Record conditions that may affect interpretation of results or test setup.
• Transformer tap position recorded
  Record the tap changer position or fixed tap setting used during the test.
• Test setup verified against manufacturer or site procedure
  Confirm the connection arrangement and test sequence match the approved procedure or OEM guidance.

Magnetic Balance Readings

• Phase A magnetic balance reading recorded
  Enter the measured magnetic balance value for Phase A.
• Phase B magnetic balance reading recorded
  Enter the measured magnetic balance value for Phase B.
• Phase C magnetic balance reading recorded
  Enter the measured magnetic balance value for Phase C.

Results Review and Fault Indicators

• Phase readings are reasonably balanced across all phases
  Assess whether the readings are consistent enough to indicate no obvious core or winding imbalance.
• Any abnormal deviation or asymmetry documented
  Describe any phase-to-phase deviation, unusual trend, or suspected fault condition such as winding displacement, core issue, or connection problem.
• Comparison to prior test results completed
  Confirm whether the current readings were compared to previous magnetic balance, ratio, or resistance test results.

Deficiencies, Corrective Actions, and Sign-Off

• Deficiencies or non-conformances documented
  Record any deficiencies, suspected faults, or follow-up actions required.
• Corrective action assigned or escalated
  Document the corrective action, responsible party, and target completion date if a deficiency was found.
• Inspector signature captured
  Inspector sign-off confirming the test record is complete and accurate.