please elaborate your problem again. please write the voltage applied and method of current control if any applied. 

With heavy moisture, the resistance offered would be very less, hence control the rated current with minimum voltage applied. Heat developed would be, Heat= (I)(I)R Watts. Current would start dropping with time, as moisture reduces, go on adjusting current to rated permissible, by increasing voltage applied. Current would reduced to zero when  dryness is achieved. For measuring, insulation strength applied the voltage, for which insulator is designed for....

Thank you for your attention.

We are working on porcelain body. We want to dry a cylinder with 35cm diameter and 150cm length. The voltage is 350 V (DC) and the direction changes every minute.

The problem is that the cylinder does not dry homogenously.The two side of cylinder dry more quickly that the middle. And therefore current decrease.

According to your statement , you are injecting current from the end of the cylinders.

A) please try to inject current at middle and receive the same at the end side of the cylinders and vice versa. if even though it does not, then apply more current injections  points with receiving arrangements.

B) if cylinder is hollow then insert continuous strip (or rod which one suitable) within cylinder and apply external conducting plate or cylindrical sheet. now apply the supply across the central inserted strip and external sheet. this may solve your problem.

C) keep your complete cylinder within two conducting plates of sizes 40 x 150 cm. now apply the current.

please note that you are using dielectric type heating and there may be any more way to help you for this. 

also the material of the conductor terminals depends upon the humidity and temperature of your porcelain cylinder.

Your information is so helpful for me. thank you.

What is your suggestion about the time. I mean do you think one minute is ok to inverse voltage?

I read in documents about this method by appling AC current (low frequency). Which one do you suggest for me? (AC or DC)

You are so appreciated to give me document for more information about this method.

please give me your email Id or search on internet for Electrical utilization systems- heating applications- Dielectric heating.

AC current does not need inversion as it is already happening. AC may be more suitable , but take little longer period duration for drying.

This is my email address.

[email protected]

Dear Dr Desai,

With your comments, I found why this method is suitable for drying, homogeneously.

Would you please explain more about your last sentences? Do you mean I should apply high voltage to dryied body?

Dear Dr ambedkar,

Would you please let me to know more about the materials of conductor terminals?

Thank you

 Just something to note and I will also welcome your comments on it: it just occurred to me that, as the water dries off, it will start forming droplets on the surface of the material being dried. This will create an open circuit situation as the current will no longer be able to flow "freely" or continuously. The situation may even lead to "dry-band arcing": arcing in-between droplets and that could damage the material being dried or accelerate its age. 

This is just to point out what, in my view, could be the disadvantage of this method.

dear sir,

the voltage applied should be such that the 'dry band arcing' should be avoided.

if there is sandwich of charge (porcelain) between electrodes then the there may not be droplet formation  along the surface because only cylinder end sides are out of current flow.

please see attachment which may help you.

Dear Dr Huse,

Thanks for all information.

Why I could not find attachment?

Dear sir,

you got attachment.

just click on it to download. it is  pdf file.