Omicron CP TD1 Reference Manual

139
Appendix
* C2 value is normally checked in air. C1 value is normally checked with lower end immersed in oil.
** C1 and C2 values are normally checked with lower end immersed in oil.
As can be seen from the above table, the C1 and C2 capacitance values of Type
AB bushing have basically very little effect from the type or proximity of the
ground plane within the practical range of clearances. Similarly the C1
capacitance of Type T bushings has minimal effect from the type or proximity of
the ground plane. The C2 capacitance of Type T bushing on the other hand
increased by 55% (from 278 pF to 431) when the bushing was tested with a
cylindrical ground plane surrounding the lower porcelain with an air gap of about
1 inch. This is because of greater coupling effect between the C1 layer/foil and
the external ground plane. The above bushings were tested in a clean and dry
environment and therefore the power factor values exhibit very little change if
any. If the lower end of the bushing was immersed in oil, the increase in
capacitance would be higher as the oil has a higher dielectric constant.
Another observable fact is the small difference of C2 PF and CAP test values of
Type T bushing between nameplate (with lower end immersed in oil) and those
taken with the bushing in air and no external ground plane. The test values with
the lower end in air are lower by about 10%. This could be due to the fact that
air has zero power factor and a lower dielectric constant compared to oil. Since,
Type T bushings have a greater coupling effect between the C1 plate and the
medium surrounding the lower porcelain, the C2 values are somewhat lower
when the test is made in air.
TYPE / STYLE -> AB / B035200AA AB / B035200AA T / 025V1000VY T / 025V1000VY
C1 / C2 PF % C1 / C2 CAP pF C1 / C2 PF % C1 / C2 CAP pF
NP Values 0.29 / 0.11* 508 / 494* 0.28 / 0.64** 1112 / 306**
In air. No grd.
plane
0.27 / 0.10 514 / 492 0.29 / 0.58
1124 / 278
(1 PU)
In air. Flat
vertical grd.
plane 3 in away
from the lower
porcelain
0.27 / 0.10 511 / 492 0.29 / 0.56
1119 / 292
(1.05 PU)
In air. Cylindrical
grd. plane which
is:
xx xx xx xx
6 in away from
the lower
porcelain.
xx xx 0.27 / 0.55
1108 / 303
(1.09PU)
1 in away from
the lower
porcelain.
0.26 / 0.10 505 / 495 0.27 / 0.60
1101 / 431
(1.55PU)

Omicron CP TD1 Specifications

General

Brand	Omicron
Model	CP TD1
Category	Measuring Instruments
Language	English