Failure Mode Library: What VIE Catches and How Early
Every failure mode VIE monitors traces back to a physical process that is detectable before it becomes a failure. This article is a structured reference for engineers who want to know which metric detects which failure mode, what the physical mechanism is, and what the detection timeline looks like relative to observable damage.
Other Knowledge Center articles link here when discussing specific failure modes. This is the reference document behind those discussions.
Radial Winding Failures
Detected by: Radial Winding Health Metric (WHr)
Radial winding failures involve mechanical degradation of the winding conductors or their support structure in the direction perpendicular to the core axis — outward from the core toward the tank wall.
Forced buckling occurs when the winding conductor stack is subjected to radial compressive forces, typically from short-circuit events, that exceed the structural capacity of the winding. The conductor deforms outward in a localized region. VIE detects the change in winding mechanical stiffness that precedes visible deformation, as the relaxation of pre-stress in the winding structure alters the vibration response before buckling is complete.
Hoop buckling is a related failure mode in which the entire winding circumference deforms radially rather than a localized section. It is associated with loss of radial pre-stress uniformly around the winding. WHr rises as the pre-stress is lost, before the conductor geometry changes enough to produce a measurable SFRA response.
Broken conductor insulation produces changes in the winding's electromagnetic coupling and mechanical response. The localized loss of insulation between conductors changes the force distribution within the winding stack and is detectable as an anomaly in the WHr trend.
Winding bulge refers to radial displacement of a section of the winding, typically associated with a prior mechanical event. VIE detects the altered vibration response from the displaced section.
Spiraling is the progressive radial displacement of helical winding conductors under sustained electromagnetic force. It tends to develop slowly and is a leading indicator of further radial failure if not addressed. WHr rises gradually as spiraling progresses.
Detection timing for radial failures: VIE typically detects WHr changes at a stage of mechanical disturbance that precedes deformation visible to Sweep Frequency Response Analysis (SFRA). The exact timing depends on the rate of force accumulation and the initial pre-stress state of the winding.
Axial Winding Failures
Detected by: Axial Winding Health Metric (WHa)
Axial winding failures involve degradation along the vertical axis of the core-winding assembly.
Core lamination loss refers to the progressive loosening or delamination of the silicon steel laminations that form the transformer core. As laminations loosen, the magnetostrictive vibration path changes, and the axial vibration response at the tank surface reflects the altered coupling. WHa rises as lamination integrity degrades.
Microbending is localized elastic or plastic deformation of individual winding conductors along the axial direction, typically from sustained compressive force. It produces changes in winding axial stiffness detectable through WHa before it progresses to macroscopic displacement.
Tilting refers to axial displacement of the entire winding column relative to the core, typically from a through-fault event. VIE detects the change in axial vibration coupling produced by the displaced geometry.
Axial bending is a more severe form of tilting in which the winding column deforms along its axis rather than simply displacing. WHa and WHr may both be elevated when axial bending is present, reflecting the combined mechanical state.
Telescoping is the progressive axial displacement of inner windings relative to outer windings, reducing their electromagnetic coupling and mechanical alignment. WHa rises as the displacement accumulates.
Collapse of winding end support refers to failure of the insulating rings or end blocks that maintain the axial spacing and pre-stress of the winding stack. WHa rises as end support compression is lost, before the winding stack can shift or deform.
When both WHr and WHa are elevated simultaneously, the combination indicates high compressive force acting on the winding in both radial and axial directions, with meaningful risk of buckling.
Oil-Path Failures
Detected by: Oil Health Metrics (V2P and S2P), Thermal Metrics (Excess Heat Flux)
Oil-path failures involve degradation of the insulating fluid or the cellulose paper insulation that oil contacts. These failures propagate through the oil as the transmission medium and produce changes in VIE's oil and thermal metrics.
Cellulose paper degradation produces furan compounds in the oil and reduces insulation tensile strength. VIE's thermal metrics detect the increase in thermal losses from degraded paper insulation, and V2P and S2P track the associated oil quality changes.
Cooling obstruction from sludge deposits, fouled fins, or failed cooling equipment produces excess heat flux at lower sensor heights and a disturbed thermal gradient. VIE's multi-height sensor placement distinguishes this from upper-winding hotspots.
Overheating from any cause — excessive load, cooling failure, or insulation breakdown — accelerates oil degradation and paper aging simultaneously. V2P and S2P rise as oil condition worsens, and thermal metrics reflect the heat distribution change.
Paper aging produces progressively reduced tensile strength in the cellulose insulation and increased furan content in the oil. VIE's thermal model detects the increasing thermal losses associated with degraded insulation, providing a leading indicator for furan analysis.
Sparking and arcing produce rapid gas generation in the oil, accelerated attenuation of acoustic transmission, and thermal anomalies in the upper tank region. V2P and S2P reflect the rapid oil condition change, and thermal metrics show the associated heat pattern. Correlation with DGA confirms the fault type.
Thermal Failures
Detected by: Thermal Metrics (Excess Heat Flux)
Thermal hotspots are localized high-temperature regions in the winding or core, producing excess heat flux concentrated at the corresponding sensor height. VIE's thermal model isolates these by computing the residual between predicted and measured surface temperature at each sensor position.
Excess heat buildup from sustained overloading or degraded cooling produces rising residual heat flux across the upper tank region. VIE detects this before it reaches the threshold temperatures that accelerate insulation aging.
Cooling system degradation produces altered thermal gradient profiles detectable through VIE's multi-height sensor array. Progressive cooling degradation produces a slower-rising thermal residual than acute cooling failure.
Partial Discharge
Detected by: Partial Discharge indicators (structural vibration spikes, high-frequency non-harmonic content, thermal gradient shifts)
Void discharge is localized electrical breakdown in cavities within solid insulation. VIE detects the vibration transients void discharge produces, classified as red dot events in VIE's PD classification system.
Surface discharge along contamination tracks or degraded interfaces produces less phase-locked transient events, classified as black dot events.
Arcing and sparking are more severe electrical discharge events that produce rapid oil degradation, thermal anomalies, and acoustic signals. VIE detects the combination of PD transients, thermal gradient shifts, and oil metric changes that characterize active arcing.
Insulation breakdown precursors are the cumulative mechanical and electrical changes in the insulation system that precede full discharge. VIE's PD detection function identifies the statistical change in high-frequency non-harmonic vibration content that signals increasing discharge activity before it reaches the gas generation threshold detectable by standard Dissolved Gas Analysis (DGA).
For a detailed treatment of VIE's partial discharge detection physics, see [The Physics of Partial Discharge: How VIE Detects What You Cannot See].