construction of gas insulated bushing

hello every one..

while construction of a gas insulated bushing, i have read that the condensor core will be replaced by some concentric cylinder electrodes and intermediate electrodes.
correct me if i am wrong.
if i am right, how can calculate the capacitance in that bushing.
i calculated the capacitance but i am getting in micro farads but when i referred some standard values it is in picofarads.
the values
1000kv,15amps


URL: http://able2know.org/post/ask/