Transformer testing and diagnostics protects the most valuable single asset in a substation. A failed power transformer can mean months of lead time and seven-figure replacement cost; a data-driven condition program, per the IEEE C57 family and ANSI/NETA specifications, catches degradation years before failure and turns emergency replacement into planned management.
The core electrical test set
Turns ratio (TTR) confirms winding integrity and correct tap operation – a shifted ratio indicates shorted turns or tap changer damage. Winding resistance detects poor internal connections and tap changer contact wear. Insulation resistance with DAR and Polarization Index screens moisture and contamination of the insulation system. Power factor / Tan Delta and capacitance of windings and bushings is the premier aging diagnostic – rising power factor signals moisture and insulation deterioration; bushing capacitance change warns of partial breakdown between layers, one of the leading causes of catastrophic transformer failures. Excitation current reveals core and winding anomalies.
Interpretation – where the value is
Raw measurements only become protection when interpreted: comparison against nameplate and factory results, temperature correction of power factor values, phase-to-phase symmetry analysis, and above all trending across campaigns. A bushing whose power factor doubled since the last test may still be below an absolute alarm value – and still be the most urgent finding in the substation. Our reports rank findings by risk, not just by threshold.
When to test
Acceptance testing at commissioning per ANSI/NETA ATS establishes the fingerprint baseline; periodic maintenance testing per ANSI/NETA MTS (typically every 2 to 3 years for critical units) tracks aging; and event-driven testing after through-faults, differential trips or oil alarm events verifies integrity before re-energization. Combined with oil laboratory analysis (DGA), the electrical test set gives a complete picture of transformer health.
Equipment and standards
OMICRON CPC 100 platform for ratio, winding resistance and excitation tests; dedicated insulation and power factor test systems; procedures per IEEE C57.12.90, C57.152 and ANSI/NETA tables with temperature-corrected acceptance criteria.
What you receive
A transformer condition report per unit: complete measurement records with baseline and previous-campaign comparison, temperature-corrected values, condition classification per winding and per bushing, risk-ranked findings and clear recommendations – continue in service, increase monitoring, plan intervention or remove from service. Suitable for insurers, asset managers and reliability audits.
Why Tecnvolt
Since 2012 Tecnvolt has tested transformers from industrial distribution units to large power transformers in 500 kV substations, for oil and gas, steel, ports and utility clients. ISO 9001, ISO 14001 and ISO 45001 certified.
Frequently asked questions
Does testing require the transformer offline? Yes, the electrical test set is performed de-energized and isolated – typically completed within one day per unit including setup.
How does this relate to oil analysis? DGA detects active faults through dissolved gases; electrical tests characterize the insulation and mechanical integrity. They are complementary – a serious program uses both.
Can old results from other contractors be used as baseline? Yes – any documented previous campaign improves trending. We normalize temperatures and methods to make results comparable.
About our U.S. transition
Tecnvolt Engenharia is a Brazilian company founded in 2012, currently in the process of establishing a U.S. company in Houston, Texas. During this transition we are receiving inquiries and scheduling future work. Request a quote / register interest