The test is administered by taking an oil sample from

The test is administered by taking an oil sample from the tank and
determining the levels of different dissolved gases, which include acetylene, methane, hydrogen,
carbon dioxide, and ethylene [3]. This test indicates the presence of PDs as well as provides
additional diagnostic information because different levels of each of the gases can be correlated
to a specific type of fault within the HVT using extensively developed tables. Although this test
is widely used, there is some debate as to whether or not the levels of dissolved gas really
correlate to a specific type of fault. Some experts argue that the rate of increase of these gases is
more important than the absolute measure of their concentration [5].
Another test, HPLC, measures the byproducts of transformer wall insulation breakdown.
Because the insulation on the wall of the transformer is made of paper, the breakdown products
are glucose and degraded forms of glucose. The test is administered by evaluating oil samples
from the transformer in an offsite lab. However, there are problems with this test as well. The
glucose levels in the oil are very small because glucose is not highly soluble in mineral oil and
the degraded forms of glucose are not very stable. In addition, this test suffers the same
uncertainty as DGA because there are no standard values for glucose concentration and their
correlation to HVT faults [3].
Chemical testing has some limitations that prevent it from being the only method used for
PD detection. First, chemical testing does not provide any information about the position of the
PD or the extent of the insulation damage. However, further research is being conducted to add
chemical “tags” to transformer insulation that would be released and dissolved into the oil in the
event of a PD. If these tags could be manufactured and implemented into new transformer
insulations, then HPLC could provide valuable information about the type of PD fault that has
occurred within the transformer. However, this does not satisfy the need to elicit position
information from chemical PD detection. The second problem is that chemical testing cannot be
performed online. In most cases, the transformers must be taken out of operation to obtain the

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oil sample. In the case of HPLC, the oil sample must be sent outside of the HVT site in order to
be analyzed and results can take a long time to obtain. These problems limit the usefulness of
chemical detection and rule it out as a singular solution to PD detection and positioning.
Section 2.2.2: Electrical Detection
Electrical detection focuses on capturing the electrical pulse created by the current
streamer in the void. These pulses last on the order of single nanoseconds and have measurable
frequency components in excess of 1 MHz [1]. The pulse shape, its relative phase location
within the AC cycle of the HVT, and the signal intensity all lead to information about the type of
PD fault and the severity of the insulation damage. Electrical measurements are grouped into