Project Subjects
Development of a Simple PCB Removal Method for ContaminatedTransformers and Rapid PCB Measurement Method
Background and Objective
In 2003 it was reported that PCBs might be still be present as a contaminant in insulating oil in a large
number of transformers. Cost effective procedures for PCB measurement and removal are therefore highly desirable. The ﬁrst object of this project is to develop a rapid, cheap screening method using a PCB biosensor alongwith an accurate, quantitative PCB measurement method using gas chromatography. Both methods are speciallydesigned for detecting for PCBs in insulating oil. The second object is to develop a simple process for removing
PCBs from the core and coil assembly of contaminated transformers using ﬂushing or energizing with circulationof heated PCB-free insulating oil after draining of original contaminated oil.

Main results
1. Improvement in PCB biosensor
PCB biosensor previously developed by us have been further improved [V08053]. Rapidness and measurement accuracy were improved by employing negative pressure concentration for separation of PCBs from oil
and a more sensitive detection cell to visualize reaction of antibody to PCBs as a red color (Fig. 1). The detection
limit and coefﬁcient of variation of the improved biosensor satisﬁed the requirements for a screening method
established by the Japanese Ministry of Environment.
2. Establishment of rapid measurement using gas chromatography instrument
The separation of PCBs from oil matrices on the basis of molecular size using gel permeation column
chromatography followed by a two-layer silica gel column was established. The puriﬁed PCBs were accurately
quantiﬁed by gas chromatography with electron capture detection. Excellent correlation between the new method
and the current ofﬁcial method for PCBs in oil has been established. In addition, the detection limit and coefﬁcientof variation of the new method satisfy requirements for use as a quantitative method established by the ministryof environment in the Japanese government (Fig. 2) [V09023].
3. Empirical experiment for PCB removal from contaminated transformer by ﬂushing or energizing
Circulative ﬂushing is a treatment process for used and stored transformer. Energizing is a treatment
process in service transformers. Contaminated transformers (50-200kVA, 88-250L, 37-73mg-PCB/kg-oil) wereused for PCB removal experiments after replacement of original contaminated oil by PCB-free insulating oil. In
the ﬂushing treatment, heated PCB-free oil was circulated by pumping to leach PCBs from the core assemblies
for 72-132 hours. In the energizing treatment, PCB-free oil placed in the transformer which was then energizedand loaded (simulating normal in service conditions) for less than 190 days. Energizing the transformers resulted
in heating and convective circulation of the oil. PCB analysis of the core assemblies of treated transformer after
ﬂushing or energizing showed less than regulatory criteria as PCB status. There results proved that low level PCB
contaminated transformers could be classiﬁed to non-PCB status, resulting PCB removal by circulative ﬂushingor energizing processes (Fig. 3).

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Stable Power Supply Technology
Relative response of biosensor(%)

PCB biosensor

Detection cell−PCB

Fig.1 Improvement of PCB biosensor
Density of red color of improved detection cell changed depending upon
PCB concentrations. The detection limit of the improved biosensor was
0.1mg-PCB/kg-oil with less than 30% coefﬁcient of variation.

GPC method(mg-PCB/kg-oil)+PCB

PCB conc.(mg-PCB/kg-oil)Fig.2 PCB separation from oil matrix
by gel permeation chromatography
PCBs were separated, depending uponmolecular size by gel permeation effect.
The detection limit of developed method
was 0.05mg-PCB/kg-oil with less than
3.7% coefﬁcient of variation. The measurement error against ofﬁcial method for PCBsin oil was within plus and minus 20%.

Official method(mg-PCB/kg-oil)

Circulative flushing with oil heating

HeatingUnitTransformer

Circulative flushingequipment

PPowerEnergizing

Energizing equipment

Oil is heated andcirculated in transformer
Transformer by energizing
Transformer

Fig. 3 Flushing or energizing procedure for transformer washing33