Inside a Forensic Transformer Teardown
Updated: Oct 16
One of three related large power transformers at an Arizona solar generation facility experienced a significant internal failure. The failed unit had a documented dry weight of over 745,000 pounds. Removing equipment of that size was already a substantial field operation. The presence of two related transformers at the facility made the investigation more consequential.
The damaged transformer contained physical evidence that could contribute to a broader Root Cause Analysis, or RCA. Recovering that evidence required more than opening the tank and removing recyclable material. Internal components had to be exposed in a controlled sequence so technical representatives could inspect newly accessible areas, document conditions, and direct the next stage of dismantling.
Transformer Technologies performed the controlled teardown during an approximately 25-day field project. Its role was to expose, remove, stage, and separate the transformer’s internal components for inspection.
The distinction that is central to understand forensic transformer work: physical damage provides evidence, but the most visible damage is not automatically the cause of the failure.
What makes a transformer teardown forensic?
A conventional transformer dismantling project is generally planned around safe removal, environmental compliance, material recovery, and efficient processing. Once the insulating fluid and regulated materials are addressed, the equipment can be reduced into manageable sections and separated for recycling or disposal.
A forensic teardown has a different priority: preserve the investigative value of the equipment while dismantling it.
The work proceeds in stages so engineers and other technical representatives can examine conditions before the surrounding material is disturbed. Engineers may need to photograph a winding in its original position, inspect a connection before it is cut, or examine the relationship between damaged and undamaged areas.
On this project, technical representatives could stop the dismantling process, inspect newly exposed sections, and request particular removal tasks before work continued.
The ability to pause, document, and then proceed was the defining difference between controlled forensic dismantling and ordinary transformer processing. The sequence of the work became part of the investigation.
Why the other two transformers mattered
The failed transformer was one of three related units built by the same manufacturer.
The value of the investigation was more measured: evidence from the failed transformer could help the owner determine what questions should be asked about the remaining equipment.
Depending on the eventual engineering findings, an owner might consider additional testing, monitoring, inspection, maintenance, component review, operating changes, replacement planning or reimbursement.
A carefully developed failure investigation could help the owner understand whether the event was isolated or whether particular conditions should be evaluated elsewhere.
Preparing a 745,000-pound transformer for investigation
The transformer’s dry weight gives only a partial sense of the field challenge. Before its core and winding assembly could be examined, the project required a designated work area, heavy lifting capacity, access equipment, containment, and a material-handling plan
coordinated with the technical investigation.
Most of the insulating oil was to be removed before dismantling began although residual oil can remain in low points, insulation, windings, and internal assemblies after bulk fluid removal.
Steel plating and protective plastic sheeting were placed beneath and around the work area to manage that residual fluid. These controls also created designated surfaces where removed components could be staged.
Large mobile-crane services, aerial lifts, and extended-reach material-handling equipment supported the work. These were not simply tools for moving heavy scrap but to also lift components without unnecessarily altering areas that still required inspection.
At this scale, a cut in the wrong location can destroy evidence. The plan had to account for both physical disassembly and investigative access.
Opening the transformer in the field
Transformer Technologies used a non-flammable saw-cutting method to open the upper portion of the transformer tank. This avoided introducing a flame-based cutting process into an area where residual insulating oil was expected.
After the necessary cuts were completed, crane and rigging services were used to remove the core and lid and provide access to the active portion of the transformer. Lifted components were staged within the prepared containment area.
Removing the core-and-winding assembly provided an initial view, but it did not expose every area investigators might need to examine. A large power transformer is constructed in layers. Leads, bracing, clamping structures, windings, insulation, the upper yoke, and stacked core laminations can conceal the components and surfaces beneath them.
The teardown therefore had to progress beyond lid core removal without eliminating the
opportunity to inspect each newly exposed layer.
Dismantling the transformer in stages
The sequence includes:
Removing the lid and upper yoke
Removing upper core laminations
Exposing the winding assemblies
Lifting winding bundles by crane
Staging the assemblies within containment
Separating designated winding sections
Removing core columns
Removing lower laminations
Each stage created a new inspection point.
Removing the upper yoke and laminations provided access to the tops of the winding assemblies. Lifting individual winding bundles exposed surfaces that had previously been concealed by adjacent windings or the core. Separating designated sections allowed closer examination than would have been possible while the active assembly remained intact.
The order of work also limited unnecessary disturbance. If the windings had been removed immediately, their original positions, physical relationships, lead arrangements, and deformation patterns could have been harder to document.
The crew dismantled to an inspection point, paused when requested, provided access, and then continued based on the investigation’s needs.
Technical representatives interpreted the evidence. Transformer Technologies performed the heavy physical work required to make that evidence accessible.
Containment supported more than oil control
Containment was necessary for managing residual insulating oil and protecting the work area. It also helped maintain order during the investigation.
Removed winding bundles and other oil-wet components could be staged on controlled surfaces instead of directly on the ground. Designated assemblies could be kept separate from general debris, allowing technical representatives to retain access to components that might require closer inspection.
Meanwhile, the field team had to manage core steel, winding material, structural components, residual oil, and other waste streams throughout the 25-day project.
Forensic work does not replace the environmental responsibilities of transformer dismantling. Fluid control, housekeeping, component staging, and material segregation must continue while the equipment is being examined.
What investigators can learn from physical evidence
A controlled teardown can document the location, direction, and extent of internal damage.
Investigators may examine:
Displaced or deformed winding sections
Damaged conductors and insulation
Lead and connection conditions
Movement between adjacent assemblies
Core and clamping structures
Deposits or discoloration
Localized thermal effects
Relationships between damaged and less-affected areas
These observations can help engineers reconstruct the sequence of a transformer event and may also be compared with protection records, electrical test results, operating history, oil and gas data, design information, maintenance records, and other evidence.
The strength of a teardown is direct access to internal conditions that external inspection cannot fully reveal after a major event. Its limitation is that physical evidence still requires technical interpretation.
Visible damage is not necessarily the root cause
Project photographs show substantial deformation within portions of the winding system. That observation is important, but it is not a root-cause conclusion.
A major transformer event can subject windings and their supporting structures to intense electrical, thermal, and mechanical forces. Damage visible after the event may show where those forces acted most severely. It does not necessarily show where the event began.
An existing condition or initiating event begins the sequence. The transformer then responds electrically and mechanically. That response can produce additional damage, sometimes in areas away from the point of initiation.
By the time the tank is opened, the component with the greatest visible destruction may represent a consequence rather than a cause.
What the failed transformer could teach the owner
Once the engineering investigation is complete, the owner can compare relevant findings with the design, condition, operating history, test data, and maintenance needs of the remaining equipment. The findings may support further action, or they may indicate that no additional measures are warranted.
Either outcome is more useful than an unexamined concern.
Without an investigation, the owner knows only that one transformer failed. A properly supported RCA may help explain the sequence of events, identify conditions relevant to future asset decisions, and narrow the questions that should be asked about other units.
That does not mean one transformer failure necessarily predicts another.
What a forensic teardown cannot determine by itself
Although a controlled teardown cannot independently reconstruct every electrical and operational condition that preceded the failure, the controlled teardown reveals the internal condition and preserves physical evidence.
A complete transformer failure analysis may also require protection records, electrical test results, operating data, loading history, oil analysis, dissolved-gas information, design documents, maintenance records, witness observations, and laboratory examination.
Evidence can also be altered by fault energy, oil movement, emergency response, transportation, tank opening, and the dismantling process itself. Investigators must consider those possibilities before treating a post-event condition as evidence of what existed before the failure.
The available project records document the teardown, visible damage, and specialist OLTC observations. They do not include the final RCA conclusion.
Preserving the opportunity to learn
The value of a controlled forensic teardown is not simply in dismantling the transformer. It is in preserving the condition, sequence, and accessibility of physical evidence as the work progresses.
By pausing at defined inspection points and exposing internal components in stages, the teardown supports the broader investigation without assigning conclusions that belong to the RCA process.
That is the role of forensic dismantling: preserve the opportunity for the evidence to be examined before it is permanently altered or removed.
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