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

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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