Transformer Transportation Damage, A Case Presentation of a Low ...

ABSTRACT 

TRANSFORMER TRANSPORTATION DAMAGE, 

A CASE PRESENTATION OF A LOW IMPACT EVENT 

Richard K. Ladroga 

Domenico E. Corsi 

William F. Griesacker 

Doble Global Power Services 

Transportation of large power transformers is typically costly and can sometimes become a substantial portion of the 

overall lead time of procuring a transformer. It is usually a positive milestone for both the manufacturer and the 

purchaser of a transformer when it reaches its final destination since both parties are one significant step closer to 

their respective objectives. When a transformer is damaged during shipment, both parties stand to loose. A recent 

low impact shipping event that resulted in the teardown and rebuilding of a large power generator step-up (GSU) 

transformer will be discussed to explain the shipping incident, damage to the transformer, the repairs and the lessons 

learned. Even though the impacts to the transformer were recorded at a low level, significant movement of the 

active parts gave reason for concern regarding the long term operation of the transformer. 

INTRODUCTION 

A new 450 MVA, large power GSU transformer was manufactured and shipped by rail to the purchasing utility’s 

site. During shipment the railcar that the transformer was transported on derailed at a relatively low speed, allowing 

the railcar to ride over the railroad ties. Despite the fact that the impact recorder registered relatively low impacts, 

the customer wisely took a cautious approach to ensure that their concerns of possible damage to the internal 

components of the transformer were fully investigated. They did not want to rely on electrical testing alone. Due to 

their insistence on conducting an internal inspection of the transformer, damage to the core and coil assembly was 

revealed that would eventually require returning the transformer to the factory for untanking, further inspection and 

repairs. 

BACKGROUND INFORMATION 

A utility began the process of evaluating one of their main GSU transformers. This transformer was in service at the 

power plant for almost 30 years. The operating and maintenance history of this transformer included several known 

conditions that could degrade over time and possibly lead to a failure event. This transformer was the sole GSU 

responsible for transmitting 100 % of the power from the station to the grid, making it a critical piece of equipment. 

Given the importance of the main GSU transformer and other transformers at the power plant of similar age, the 

utility sought an experienced third party to evaluate the condition of this and other key transformers at the power 

plant. The results of the in-depth condition assessment of the power plant transformers led the utility to decide to 

replace the main GSU. 

The utility went through a vendor selection process and awarded the main GSU transformer contract. During 

contract negotiations the responsibility of shipping the transformer was discussed; the vendor requested the utility to 

accept FOB Factory, which would have placed ownership of the transformer with the utility during shipment [1]. 

The utility’s decision to decline this responsibility would later prove to be critical based on the significant financial 

impact they would have been burdened with [2]. 

© 2010 Doble Engineering Company -77 th Annual International Doble Client Conference 

All Rights Reserved

DERAILMENT EVENT 

Transportation of the 450 MVA transformer from the factory to the utility’s site required rail shipment given that the 

shipping weight was on the order of 500,000 lbs. While the transformer was being transferred in a railroad 

switching yard, the railcar became derailed. The railcar was traveling at a relatively low speed at the time of the 

derailment; the derailment event did not turn over the transformer or railcar. The impact recorder on the derailed 

railcar recorded the relatively low impacts of X: 0.5g, Y: 3.0g and Z: 0.5g. One rail twisted over on its side due to 

the weight of the transformer and railcar. It was reported that the transformer and railcar traveled the length of about 

one railcar on the rail ties, see Figure 1. It was believed that riding over the rail ties subjected the transformer to a 

short but significant vibration event due to the multiple low level impacts that it experienced [3]. 

Derailment of Transformer Railcar during Shipment 

Figure 1 

There were some external signs of possible damage to the transformer but they were not significant. The paint on 

some tank end gusset welds had small hairline cracks indicating that the weld joint was overstressed. The paint at 

the bottom base plate braces was chipped off indicating contact between the tank base and bracing members. 

Neither of these was proven to be due to the derailment event and they did not appear to be significant or to indicate 

other possible damage. The electrical acceptance testing performed on the transformer upon arrival at the utility’s 

site did not indicate any problems with the transformer. SFRA testing was performed and there were no major 

problems detected but the results were inconclusive since there was no reference test performed before shipment that 

could be used for comparison purposes. 

The manufacturer, at this point in time, did not believe that there was damage sustained to the transformer and did 

not recommend any further investigation of the incident; however, the purchaser arranged for an internal inspection 

of the transformer before accepting the unit. 

INTERNAL INSPECTION 

An internal inspection of the transformer was performed at the utility’s site before the transformer was removed 

from the railcar. The unit was opened up and a dry air supply connected to the tank to help reduce the exposure of 

the cellulose insulation to moisture. The core and coils assembly and mechanical members were inspected. As is 

common with many transformers designed in recent years, the internal clearances were tight and limited access at 

times during the inspection. 

The internal inspection identified signs of overall movement of the core and coil assembly with respect to the tank. 

Tear marks in the pressboard isolation sheets used between the bottom of the core clamps and the tank bottom 

indicated longitudinal movement of the core and coils assembly relative to the tank, see Figure 2. The pressboard 

sheets were held in place with a steel locating pin welded to the tank bottom and a “guide rail” was located at the 

edge of the sheets. The sheets showed tear marks from the locating pins and “guide rails”, evidence that the core 

and coils assembly moved about 2 in. from end-to-end with respect to the tank base plate during shipment. 


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Tear Marks in Pressboard Isolation Sheets 

Between Bottom Core Clamp Feet and Tank Base Plate 

Figure 2 

There was evidence of movement of the core relative to the clamping frame blocks. Blocking material had shifted 

indicating longitudinal movement between the core and the core blocking and clamping frame, based on the 

displacement of the material, the displacement of the blocking material indicated movement up to ½ in. 

It was observed that each winding phase package had blocks between the coils and the top clamping ring that were 

loose, shifted and in some cases completely displaced from the radial column. Figure 3 shows a shifted block, some 

blocks were observed with as little as 50% of the surface area remaining in contact to transmit the clamping forces 

to the coils. The left frame in Figure 4 shows an example of a block over the outside winding that was completely 

knocked off of the radial spacer column and the right frame shows a block over an inner winding that was also 

displaced off its column. There were a considerable number of blocks that were either shifted or displaced from 

their column. A large number of the remaining blocks over the windings were loose. Due to the condition of the 

blocking, it was apparent that the windings were loose and susceptible to damage or even failure if they were subject 

to a short circuit event(s). 

Example of Shifted Top Coil Block 

Figure 3 



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Examples of Coil Blocks (Between Coils and Top Clamping 

Ring) Displaced from their Radial Spacer Column 

Figure 4 

Wraps were used on the outside of the windings. On one winding a segment of the wrap had slipped down over the 

blocks and was resting on the bottom clamping ring, blocking oil flow to about 1/3 of the bottom ducts, see Figure 5. 

This was possible since the wrap was made of more than one piece of pressboard, one segment of the wrap had 

shifted down. 

Shifted 

Wrap 

Outside Winding Wrap Segment that Shifted Down, Blocking Bottom Oil Flow Ducts 

Figure 5 

The main blocking located between the core clamping frames and the clamping rings showed shifting and 

displacement, see Figures 6 and 7. Figure 6 shows blocks at the clamping frame end; the two blocks labeled “A” 

and “B” should be parallel. Block “A” is oriented correctly but block “B” had pivoted about 45 to the right as 

shown. The block on the far right has sections that have also shifted. In Figure 7 it can be seen that glued layers of 

the blocking separated, which allowed sections of the block to shift significantly. About 50% of the bearing surface 

of this large block was left in contact. 



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A 

B 

Shifted Top End Block Located between the 

Core Frame and Top Clamping Ring 

Figure 6 

Shifted Top Block Located between the 

Core Frame and the Top Clamping Ring 

Figure 7 

Cracks were identified in some lead support beams, see Figure 8. The lead support beams were made of laminated 

pressboard; the cracks were parallel to the lamination surfaces. It was not possible to determine if the cracks in the 

beams were a direct result of the derailment event but they were observed and noted. 

Lead Support Beams with Cracks along Lamination Surfaces 

Figure 8 

The internal inspection of the transformer revealed several conditions that would require repair work before the 

transformer could be commissioned for service. There were indications of movement of the internal assembly, 

which gave rise to concerns that there may be further damage to the core and coils that was not observed due to 

limited access and the limitations of inspecting an assembled transformer. There were a large number of main 

blocks between the clamping rings and the core frame that had shifted, some were loose. A large number of the top 

coil blocks located between the coils and the top clamping rings were loose. A large number of these coil blocks 

were shifted, leaving partial coverage of the block surface area to transmit the clamping forces to the coils. There 

were also a large number of coil blocks that had been knocked off their respective radial spacer columns and were 

lying in the cooling ducts at the top of the coils. It was understood that the coil blocks in the core window area 

would probably not be able to be repaired in the field due to access limitations. The winding package had a large 

radial build since there were four windings in the radial direction, this would also limit access to make the repairs 

needed on the inner coils. The inner coils had the most top blocks completely displaced from their radial spacer 


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columns. The outside wraps over the windings, limited room in the tank and the normal obstructions of a fully 

assembled transformer prevented a comprehensive inspection of the active parts. However, the blocking items that 

were inspected showed movement and in some cases it was significant. 

The utility decided that they should receive a transformer in a “new” condition and based on these findings they 

requested that the transformer be returned to the factory to make further inspections and perform the repairs with 

proper access and tooling. The manufacturer decided that the repairs at the customer’s site were possible and 

proceeded to make preparations for field repairs. 

FIELD REPAIRS 

The transformer utilized a fixed clamping frame design. A hydraulic jack was placed between the top core clamping 

frame and the top clamping ring to press the winding package down and remove the top main blocks (the blocks 

between the top frame and top clamping ring). Due to limited access only one hydraulic jack was used, so jacking 

was performed at one location at a time. With the main blocks removed, the pressure was relieved from the coils in 

that area allowing blocks that were shifted to be tapped back into place. Shifted coil blocks at the top of the outer 

windings were realigned by tapping them back in place while the pressure was released. Blocks knocked off the 

radial spacer columns on the outer coils were put back in place but this was not an easy task for the blocks over the 

inner coils because of the limited access. The space available to access the inner coil blocks in the top cooling duct 

was about 5 in. wide, 1.5 in. high and 15 in. deep. This proved to be very difficult to manipulate the displaced 

blocks back onto their radial spacer columns, in many cases the blocks could not be realigned back onto the radial 

spacer columns over the inner windings. 

As the work proceeded it became more apparent that the repairs would not be adequate to return the transformer to a 

new condition primarily due to the limited access in the tank. The blocks in the core window region on each phase 

winding package were not accessible. The blocks over the inside coils were all but inaccessible and it was not 

possible to place many of them back on their columns. Nearly 25 to 30 % of the inside winding blocks were off 

their radial columns. After the tightening procedure was performed, the windings were inspected again. It was 

recognized after several attempts to tighten the windings that some areas still remained loose. Loose blocks were 

identified in the blocking over each coil of each winding phase assembly. 

At the conclusion of the field repair work, the manufacturer agreed to return the transformer to the factory for 

further inspection and repairs. The major inspection and repair work to be addressed at the factory included the 

following: 

 

 

 

 

 

 

Remove core and coils assembly from tank to allow adequate access to perform repairs. 

Thorough inspection of core and coils and tank. 

Remove top yoke and top clamping rings to allow inspection of the coils. 

Removal of outer pressboard wraps to facilitate inspection of the main outside HV winding. 

Realignment of blocking. 

Retightening of coils. 

UNTANKING AND INSPECTION 

Due to the tight clearances between the top of the core and the cover, it was difficult to inspect the top core yoke. 

Once the cover was removed, some problems were quickly identified. Overall, the top core yoke had mild but 

noticeable waves throughout the laminations that became increasingly worse as they progressed to one end, where 

they appeared to build up to a single large ripple that crossed nearly all steps of the yoke, see Figure 9. The miter 

joints at each end of the top yoke did not show signs of opening up, except in one location involving about three 



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laminations. Although, it appeared that the top yoke steel had shifted toward one end and the large wave was a 

result of the lamination displacement being stopped by the miter joint and clamping frame at that end. 

Top Core Yoke Movement, LV Left and HV Right 

A Large Wave Present at One End of the Top Yoke 

Figure 9 

There were other indications of top core yoke movement. Outside laminations on one side of the yoke were buckled 

as shown in Figure 10. Apparently part of the laminations experienced movement in one area and did not move in 

another area, causing a buckling effect in several laminations to make up for the difference in relative movement. 

At one end of the rippled sheets, the miter joint was observed to have opened up, see the right frame in Figure 10. It 

was apparent that these gap openings were caused by the shipping derailment event. Generally all other miter joints 

on the core had small uniform gaps. The core laminations at the top miter joint were protected with thin insulating 

sheets as shown in the right frame of Figure 10. 

Core Movement 

Left Frame - Outside Laminations Buckled 

Right Frame - Miter Joint Opened due to Displacement of the Laminations 

Figure 10 

After the top yoke was removed, it was revealed that the buckled laminations, shown in the left frame of Figure 10, 

were deformed from top to bottom, i.e. across the entire width of the sheets, see Figure 11. 



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Example of Buckled Core Lamination 

Figure 11 

It appeared that the top yoke laminations shifted toward the end where the derailment impact occurred. When the 

laminations were removed from the top core yoke, some displayed deformation along the miter cut edge at one end, 

see Figure 12. The deformation consisted of groups of parallel ridges that appeared to be due to compression of the 

yoke steel at the miter joint during the derailment event. It appeared that the ridges were created by the offset edges 

of the step lapped joint. The insulation was breaking away from the core steel at some of the deformed ridges. 

Examples of Core Steel Deformation near the Miter Cut Edges 

Figure 12 

When the core yoke was removed additional damage to the core steel was revealed. In one location a core block 

came loose causing damage to the core steel on the edges, see Figure 13. The insulation had delaminated from the 

steel due to the mechanical deformation and the steel was cracked in some locations, as indicated in the right frame 

of Figure 13 with a red arrow. This damage was localized to the area shown in the figure. 

Top Core Yoke Steel Damage due to a Loose Block 

Figure 13 



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Other than the damage discussed, the top miter joints of the core were tight with small and relatively uniform gaps. 

The miter joints at the bottom of the core did not display any detectable signs of movement. 

There were a number of insulating spacers that were loose and out of place. There was a cooling duct spacer 

dislodged and falling out of the bottom core yoke, it was identified when the core and coils assembly was being 

removed from the tank, see Figure 14. A second core duct spacer was also partially dislodged and observed to have 

fallen down. The manufacturer explained that these spacers are black due to the adhesive that is used to attach them 

to the core steel. A pressboard spacer under an end yoke block had broken free and had fallen down, see Figure 15. 

Displaced Core Duct Spacers 

Figure 14 

Displaced Core End Block Spacer 

Figure 15 

Once the top core yoke and top rings were removed, the top of the windings, insulation and blocking were inspected. 

Some axial spacers adjacent to windings and between cylinders were loose and had shifted. Figure 16 shows an 

example of loose and displaced axial spacers. It was observed that there was probably some shifting of the windings 

evident by the non-uniform gaps that were identified between windings and barrier cylinders see Figure 17. Due to 

the signs of movement at the top of the windings, the manufacturer decided that further investigation was warranted 

and the windings were removed from the core and the main coils were separated. Some of the gaps between coils, 

axial sticks and barrier cylinder were on the order of ½ in. on one side, while no measurable gap was present on the 

other side. The gaps were not uniform and were more than what would be expected for a typical manufacturing 

tolerance. 

Loose and Displaced Axial Sticks in Main High-Low Barrier 

Figure 16 



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Gaps Observed at the Top of the Windings. 

Figure 17 

The core dimensions were measured after the windings were removed and it was reported that there was no 

detectable movement in the core limbs. 

REPAIRS 

The objective of the repairs from the perspective of the utility was to return the transformer to a new condition. The 

following list notes the major repairs made to the transformer: 

 

 

 

Replacement of top core yoke laminations that were damaged. There was damage due to shifting of the 

yoke steel that caused buckling and permanent deformation of some laminations. A loose or shifted block 

near the core came in contact with the steel and caused damage. Handling of the laminations also created 

some damage, especially at the miter joints. 

The main blocks between the clamping rings and the core clamping frames were twisted and several 

showed separation at the glue lines between the pieces making up the blocks. Typically, high density 

laminated wood material used in transformers has a shiny platen surface which prevents adhesives from 

bonding properly to the surface. To help with adhesion, the blocks were separated and scuffed to remove 

the shiny surfaces to allow proper bonding. Two (2) wooden dowel pins were added to each block through 

all layers to prevent the pieces of the blocks from shifting and pivoting. The blocks were aligned properly 

as they were reassembled between the frames and clamping rings. 

The top coil blocks were realigned and glued in place. The blocks at the top of individual coils were placed 

back on their radial spacer columns, aligned properly and glued in place. 



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The main outer HV coil was separated from the other coils for inspection. When the coils were 

reassembled, the gaps between coils were filled with pressboard packing. 

 

 

Lead support members with damage were repaired or replaced. 

The bottom blocks supporting the outside winding wraps were moved to provide more margin so that the 

wraps would not slip over the blocks. 

The transformer received complete re-processing since the exposure period during the repair process was over an 

extended period of time. The original factory acceptance test plan was repeated due to the extensive teardown, 

repair and rebuilding of the transformer. 

CONCLUSION 

A recorded low impact event resulted in a major inspection and repair effort to bring a large power transformer back 

to a new condition. The important lessons learned from this experience include the following points: 

 

 

 

 

 

The magnitude of recorded events during transportation may not reveal the true nature of the internal 

condition of a transformer subsequent to an impact. Although the recorded impact magnitude was low, it is 

concluded from the damage found that the multiple low level impacts experienced from the rail car riding 

over the rail ties, imparted a quick succession of impacts to the transformer that was similar to a severe 

vibration event. 

Understand the implications of the contracts when they are negotiated and accepted. This is very basic 

advice but in this case the difference in one word, FOB Factory or FOB Destination, would have had a 

significant financial impact on the purchasing utility. The purchasing utility was requested during contract 

negotiations to accept FOB Factory, this would have put a large portion of the financial burden of repairing 

the transformer on the utility if they would have accepted this condition. 

The utility’s initiative to follow up on this seemingly small impact event has probably prevented a failure 

and subsequent unscheduled outage, considering the true condition of the transformer that was uncovered 

during internal inspections. The conservative approach and thoroughness in investigating the transformer 

condition while under pressure to meet project deadlines proved to be invaluable. 

In this case, if SFRA testing would have been conducted at the factory, the results may have been helpful in 

diagnosing the damage and expediting the inspection and repair process. 

A conventional strip chart recorder was used to monitor the shipment of this transformer. There are impact 

recorders available that offer more capabilities [4], some recorders have features that include tracking the 

time, geographic location and impact events by digital means. Some impact recorders can transmit this 

data as it is collected allowing continuous monitoring of shipping progress and recorded impact events. 

REFERENCES 

[1] Horning, M., “Site Installation”, The Life of a Transformer Seminar, 2007, Doble Engineering Company. 

[2] Betancourt, E., Hernandez, C. H., “Large Power Transformer Transportation, A Manufacturer’s Perspective”, 

The Life of a Transformer Seminar, 2009, Doble Engineering Company. 

[3] Hansen, N. W., “Power Transformer Rail Shipment: A Manufacturer’s Viewpoint”, Proceedings of the 1993 

International Conference of Doble Clients, 1993, Sec 6-7. 

[4] Baker, D., “Impact Recorders”, The Life of a Transformer Seminar, 2007, Doble Engineering Company. 



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BIOGRAPHY 

Bill Griesacker is a member of Doble Global Power Services, he is employed as a transformer engineer, working on 

projects that include forensic analysis, factory inspections, condition assessment, design reviews and general 

consulting. He previously worked for Pennsylvania Transformer Technology Inc., where he held various positions 

including Engineering Manager. His worked included high voltage insulation design, transient voltage modeling of 

power transformer windings and development of LTC and DETC switches. He also worked for Westinghouse in the 

Generator Engineering Department on synchronous generator projects. Bill started his career with Cooper Power 

Systems in large power transformers and later worked in the Kyle Switchgear, Vacuum Interrupter Department. He 

has earned a M.S. degree in electric power engineering from the Rensselaer Polytechnic Institute and a B.S. degree 

in electrical engineering from Gannon University. Bill is an active member of the IEEE, PES Transformers 

Committee where he holds positions in several working groups and subcommittees. 


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