SAT Bushing tan delta on transformer

[Mlmlzx]

Dear sirs,

Per tests performed on single phase autotransformers for 53.3 MVA, 132/220 kV :factory values and site test value for 220 kV bushings is 0.353% and 0.188%.

1.Is it possible to have lower than factory values at site? These tests were done after three years on newly brought unused ones.

2. Site acceptance test shows 0.5% value. Seems okay. But difference is 0.17. in my knowledge: this should be less than 0.1 to be acceptable.

Can somebody please guide

Regards

 

[Mlmlzx]

If not acceptable, is it good to ask for replacement if within warranty period?

 

[prc]

Site values are usually higher than factory values. Please check the measuring method.

 

[Kiribanda]

I believe that Mimizx is referring to bushing capacitances C1 & C2.
C1 is totally depends on the design and therefore cannot change after installation.
But C2 can have variations because C2 depends on the grounding method used, contamination etc. etc. at the installation.
All in all per IEEE the acceptable capacitance variation based on bushing name plate values
should be +/-1% corrected to 20deg C for all bushing types (Oil impregnated, resin impregnated, solid etc.)

 

[Kiribanda]

Sorry I missed the subject line.
You are referring to TAN DELTA of 220kV bushings.
Per IEEE the acceptable variation depends on the bushing type.
I believe that these are oil impregnated bushings since the operating voltage is 220kV.
For oil impregnated bushings the acceptable variation is +/-0.02 corrected to 20deg C.