Power Transformers

Capacitance and power factor (tan δ) measurements evaluate the condition of insulation in windings and bushings. They quantify dielectric losses and help you assess insulation performance.

An increased dissipation factor indicates moisture ingress, aging, contamination, or partial breakdown between capacitive layers. Detecting these trends early can prevent bushing failure and reduce the risk of outages. The results also support condition-based maintenance and compliance with International Electrotechnical Commission (IEC) and Institute of Electrical and Electronics Engineers (IEEE) limits.

Insulation resistance tests detect moisture, contamination, and deterioration in transformer insulation before breakdown occurs. By trending the resistance values, polarization index (PI), and the dielectric absorption ratio (DAR), you can identify aging effects or leakage paths that increase the risk of failure.

Regular testing supports your maintenance planning and extends the service life of your assets. It also reduces unplanned downtime by revealing insulation weaknesses early.

Winding resistance measurements verify the integrity of conductors, helping you identify contact problems, open circuits, and high-resistance connections in windings and on-load tap changer (OLTC) paths.

Deviations between phases or tap positions indicate a risk of overheating or mechanical issues. The test helps you validate factory data and supports tap changer diagnostics, ensuring reliable current distribution under load.

Dynamic resistance measurements evaluate how an on-load tap changer (OLTC) switches during operation by capturing the transient current during its movement.

It reveals contact wear, timing deviations, and interruptions that static tests cannot detect. Identifying switching irregularities early enables predictive maintenance planning, preventing severe OLTC failures.

Vibro-acoustic measurements assess the mechanical condition of an on-load tap changer (OLTC). This method analyzes vibration signals that occur during switching.

Changes in the acoustic pattern indicate contact wear, mechanical misalignment, or drive issues. You can perform this test online without shutting down the transformer. Detecting mechanical degradation early helps you increase reliability and plan effective maintenance activities.

Transformer turns ratio tests verify the accuracy of the ratio and the phase displacement between windings by detecting shorted turns, open circuits, and incorrect tap positions. These issues can affect voltage regulation and protection coordination.

Comparing results with nameplate data ensures compliance with International Electrotechnical Commission (IEC) and Institute of Electrical and Electronics Engineers (IEEE) standards. This test also confirms that a transformer is operating correctly.

Exciting current measurements evaluate insulation between turns, the magnetic core's condition, and the tap changer's integrity during no-load conditions.

Phase deviations or abnormal patterns indicate shorted turns, core damage, or wiring issues. The test provides a quick insight into the condition of the magnetic circuit and complements transformer turns ratio (TTR) and winding resistance diagnostics.

Short-circuit impedance tests detect winding deformations that may have resulted from fault currents or transport stress.

Variations from nameplate impedance values indicate mechanical displacement and can reduce dielectric strength.

This measurement helps you safeguard transformer stability and verify the unit's structural integrity before returning it to service.

The frequency response from stray losses (FRSL) measurement helps you identify strand-to-strand short circuits and local overheating. This method analyzes the short-circuit impedance's resistive component across a range of frequencies.

An increase in stray losses at higher frequencies reveals faults in parallel conductors. This test provides advanced diagnostics, going beyond conventional impedance measurements.

Demagnetization removes residual magnetism from the transformer core after testing direct current (DC) or isolation. Residual flux can cause high inrush currents and distort diagnostic results later.

Controlled demagnetization helps protect personnel and equipment during energization, ensuring accurate exciting current and sweep frequency response analysis (SFRA) measurements.

Dielectric frequency response (DFR) analysis determines moisture content in cellulose insulation and evaluates oil conductivity. Moisture accelerates aging and reduces dielectric strength.

This method models the dissipation factor over a wide frequency range, providing a reliable, non-invasive assessment of insulation condition. The results can be used to support service life management decisions.

Sweep frequency response analysis (SFRA) detects mechanical movement, winding deformation, and core displacement. This method compares a transformer’s frequency response with reference data.

Even small shifts in resonance indicate structural changes after faults or transport, and this test provides a highly sensitive mechanical integrity assessment without applying high voltage.

Bushing current transformer (CT) analysis verifies the accuracy of the ratio, phase displacement, excitation behavior, and protection class.

Incorrect CT performance can cause protection maloperation and asset damage. Testing the bushing CT ensures compliance with the International Electrotechnical Commission (IEC) and Institute of Electrical and Electronics Engineers (IEEE) standards, ensuring reliable signal transmission for protection systems.

Partial discharge (PD) measurements detect insulation defects in windings and bushings before catastrophic failure occurs. PD activity indicates voids, contamination, or aging between voltage potentials.

Detecting PD early reduces the risk of outages. This test also supports acceptance and maintenance testing, improving a transformer's long-term reliability.

Partial discharge localization identifies the exact physical source of insulation defects, using acoustic or combined detection techniques.

Knowing the position of a defect allows you to plan targeted repairs and reduce risk, optimizing your maintenance schedule and preventing progressive insulation damage.

Online partial discharge (PD) measurements evaluate insulation condition during normal operation by trending PD activity over time.

Continuous or temporary monitoring helps identify an increase in defect severity. It supports condition-based maintenance without shutting down the transformer.