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From:
"Nutting, Phil" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Nutting, Phil
Date:
Wed, 1 Aug 2018 17:08:19 +0000
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Dean,

It is captive at the bottom under all the guts of the HV supply guts connected via a tube to the top cover for "breathing".  Sadly the bag is far from a "hydraulic" strength style.  Chosen by electrical types, not mechanical types.

Phil

-----Original Message-----
From: Stadem, Richard D [mailto:[log in to unmask]] 
Sent: Wednesday, August 01, 2018 12:52 PM
To: TechNet E-Mail Forum; Nutting, Phil
Subject: RE: question of fluid dynamics or physics

I am totally ignorant of giant oil filled capacitors, but I do know that a partially deflated pneumatic air bag is incredibly strong; thermally activated pneumatics are used in all kinds of applications to drive hydraulics, often to thousands of pounds per square inch (KPSI). 350 lbs is nothing to a thermal diaphragm as small as 5 gallons. Think of a hydraulic bottle jack; they are the strongest jack configuration made. Many are driven by a pneumatic diaphragm.
Is the air bag diaphragm secured to the bottom of the tank? If not, how do you know just where it is inside the tank during operation? If it expands, will it not float to the top, or possibly float to the top anyway? Why not secure the bag so it floats in the middle of the tank, ensuring a more even voltage potential between the top and the bottom of the capacitive cylinder? The top and bottom insulated tethers can have some slack to allow for a difference in pressure/temperature between the top and the bottom "reservoirs" created by the slightly expanded bag.
For whatever its worth,
dean

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nutting, Phil
Sent: Wednesday, August 01, 2018 10:02 AM
To: [log in to unmask]
Subject: [TN] question of fluid dynamics or physics

To my learned colleagues,

We have a situation that some think will work and others (myself included) think it is all wrong.  Let me give the setting.

40 gallons of dielectric oil, assume 8 pounds per gallon that expands with heat.
A 4 foot high container used for high voltage, filled with the oil.
Highest voltage in the tank is at the top so no air is allowed at the top.
An air bag (diaphragm) is installed at the bottom of the tank... that is filled with the oil.
Once the tank has finished filling with oil the air bag is inflated to set a desired expansion space and the oil ports are sealed.
The air bag is now depressurized presumably creating a cavity that can expand and contract with the oil as it changes temperature.

Now remember that the bag is at the bottom of the tank under about 360 pounds of oil and is expected to breath as the oil volume changes with temperature.

I maintain that because the air bag is at the bottom under 360 bounds of oil the bag will never inflate during oil cooling.
Having the bag or a diaphragm at the top would work as there is no pressure caused by the weight of the oil.

Can someone clarify the physics of the assumed function of the air bag placed at the bottom of the tank?

Phil Nutting  |  HVP Senior Development Engineer   |  Excelitas Technologies Corp

Lab: +1 978.224.4332   |  Office: +1 978.224.4152
35 Congress St, Salem, MA  01970 USA
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www.excelitas.com<http://www.excelitas.com/>


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