CP TD1 Reference Manual V 1.44
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Due to design and construction, the C2 power factor of condenser bushings
rated 69 kV and below may therefore exceed the C1 power factor limit of 0.5 %
specified in the IEEE Standard. The IEEE Standard does not specify any limit
for C2 power factor. The C1 power factor on the other hand is well below the
0.5 % limit specified by the IEEE standard.
For bushings rated 69 kV and below, IEEE Standard only requires stamping of
C1 power factor and capacitance on the nameplate. As a result of frequent
requests from customers, ABB Inc. Alamo, TN started stamping the C2 power
factor and capacitance test values on bushing nameplates since December of
2002.
With this addition, the nameplates of all AB, O Plus C, and T condenser
bushings are now stamped with factory test values of C1 and C2 power factor
and capacitance. We complied with the industry's need so that users can better
assess the condition of the bushing insulation. Because of reasons mentioned
within this paper, users may see a greater variation in C2 power factor and
capacitance values in different bushings of the same design.
It is important to compare the initial test values before installation with the
nameplate values. To verify nameplate values (especially for Type T bushings),
the measurements should be made with the bushing mounted on a metallic test
tank/stand with the lower end porcelain immersed in dry good quality oil. There
should be sufficient clearance (at least 16 - 20 inch) from the bushing lower
porcelain/terminal to the grounded tank. For C2 measurement, the center
conductor should be guarded and test tap voltage not exceeding 1 kV. For
detailed test set up and other information, refer to test equipment manufacturer's
instructions.
Once the bushing has been installed in the apparatus, it should be retested to
establish a benchmark value. It is important to compare the subsequent field test
values with the initial benchmark value after installation. Any significant
deviation (10% change in capacitance or doubling of power factor) from the
benchmark value would be a cause for concern and should be investigated. Test
values with lower end in air may vary from those with lower end immersed in oil.
12.5.5 Conclusions
Because of the inherent design of C2 capacitance and design/constructional
differences in bushings rated 69 kV and below, the C2 power factor and
capacitance can be affected by external factors. These factors may include
external contamination, humidity, and stray effect and proximity of other objects.
As a result of this, the field installed C2 power factor and capacitance test values
can vary from the nameplate values. Test values with lower end in air may vary
from those with bushing mounted on the transformer with lower end immersed
in oil. Sometimes, variations may be noticed between bushings of the same
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