Oil Testing Analysis and Field Inspection

oil testing analysisOil Testing Analysis and Field Inspection on transformers are crucial maintenance practices that help assess the health of both the insulating oil and the internal components of the transformer (windings, insulation, core, etc.). These tests are preventive in nature and help avoid costly failures or outages.

Oil Testing Analysis, Gas Analysis and PCB Analysis samples from transformers can be taken and sent out for evaluation, which can provide valuable insight into transformer overall health.

Transformer Oil Testing Analysis

Transformer oil (usually mineral oil or ester) serves two main purposes:

  • Electrical insulation

  • Cooling

Over time, the oil deteriorates due to heat, oxygen, moisture, and contaminants. Routine oil testing detects problems before they lead to insulation failure or transformer damage.

Field Inspection on Transformers

These are on-site inspections performed either visually or with basic testing tools.T

Routine Field Checks

  • Oil level in conservator or gauge

  • Color of oil through sight glass or sample

  • Buchholz relay oil/gas presence

  • Breather silica gel color (blue = dry, pink = saturated)

  • Thermometer and pressure gauge readings

  • Cooling system function (fans, radiators)

  • Leaks or cracks on body, bushings, gaskets

  • Corrosion, paint damage, physical deformation

  • Grounding connections

  • Noise or vibration during operation

Offline Electrical Tests in Field

  • Insulation Resistance (IR) Test

  • Power Factor / Tan Delta Test

  • Turns Ratio Test (TTR)

  • Winding Resistance Test

  • Sweep Frequency Response Analysis (SFRA)

  • Magnetizing Current and Capacitance Tests

Recommended Frequency of Testing

Test/Inspection Frequency
Oil BDV & Moisture Every 6–12 months
DGA Annually or more if critical
Visual Inspection Monthly or quarterly
Full Oil Test Suite Every 2–3 years
Electrical Tests Every 3–5 years or after major event

Sample Transformer Maintenance Checklist

  • Check oil level and color

  •  Inspect for oil leaks

  •  Verify thermometer, pressure relief device

  •  Inspect conservator and silica gel

  •  Perform IR and Tan Delta tests

  •  Send oil sample for lab analysis (DGA, BDV, moisture)

  •  Check grounding and lightning arresters

  •  Record all readings and deviations

Contact Infra-red to find out more.