Transformer diagnostics
Transformer Power Factor Testing
Comprehensive electrical testing for power and distribution transformers — evaluating insulation condition, turns ratio accuracy, winding integrity, and overall transformer health.
Transformers Are Your Most Valuable Electrical Assets
Power transformers represent some of the highest-value, longest-lead-time equipment in any electrical system. A failed large power transformer can mean months of lead time for replacement and millions of dollars in lost production or service interruption. Comprehensive transformer testing — performed at acceptance and at regular maintenance intervals — is the most effective way to detect developing problems before they cause a failure.
J. Wesley Services Group performs a full suite of transformer electrical tests in accordance with NETA ATS and MTS standards, IEEE C57 guidelines, and manufacturer specifications. Our testing programs cover everything from basic insulation resistance to sensitive power factor measurements that detect subtle insulation degradation years before it causes a failure.
Tests We Perform
Power Factor / Dissipation Factor Testing
Measures the dielectric loss of transformer insulation systems including winding insulation, bushing insulation, and core-to-ground insulation. Power factor testing is the most sensitive electrical test for detecting moisture, contamination, and insulation aging in transformers. Results are compared against NETA acceptance criteria and IEEE C57.12.90 guidelines.
Turns Ratio Testing (TTR)
Verifies that the transformer's actual turns ratio matches the nameplate specification at all tap positions. Incorrect turns ratio indicates shorted turns, open windings, or tap changer problems that affect voltage regulation and can cause circulating currents in parallel operation.
Winding Resistance Testing
Measures the DC resistance of each winding at all tap positions using a precision micro-ohmmeter. Unbalanced winding resistance between phases indicates connection problems, shorted turns, or tap changer contact degradation.
Insulation Resistance Testing
Megger testing of transformer winding insulation including polarization index (PI) and dielectric absorption ratio (DAR). Provides a baseline assessment of insulation condition and identifies gross insulation problems.
Excitation Current Testing
Measures the no-load excitation current of each winding phase. Unbalanced excitation current between phases is a sensitive indicator of shorted turns in the winding, which may not be detectable by other test methods.
Bushing Power Factor Testing
Individual power factor testing of transformer bushings using the bushing tap method. Bushing insulation is a common failure point in aging transformers — power factor testing detects moisture and contamination before bushing failure occurs.
Dissolved Gas Analysis (DGA)
Oil sampling and dissolved gas analysis to detect thermal and electrical faults developing inside the transformer tank. DGA is the most sensitive diagnostic tool for oil-filled transformers. See our Oil Services page for full details.
Core Ground Testing
Verification that the transformer core is properly grounded at one point only. Multiple core grounds create circulating currents that cause overheating and accelerated insulation aging.