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GSU Cooler out of service û for max cooling should cooler be isolated?

GSU Cooler out of service û for max cooling should cooler be isolated?

GSU Cooler out of service û for max cooling should cooler be isolated?

(OP)
This is a 1980's vintage McGraw Edison GSU transformer with 6 coolers in two banks. During winter months one bank shuts off on temprature.

We have one pump not working.   We don't trust the flapper valve isolation to allow fixing the pump. So we expect to operate this way through the summer.

QUESTION: Do we get better cooling if we close one or more flapper valves on the idle cooler or if we leave them open?

The normal direction through the cooler is top to bottom.
With the pump secured, there are two items working in opposite directions:
1 – Thermal driving head tends to keep flow going in normal direction (downward) which would help.
2 – Pumping head from remaining pumps tends to push flow in reverse direction (upward) which would hurt since it robs flow that would otherwise go through the transformer.
Which effect is stronger?
Or is there a check valve (I didn't see one... unless it sits inside the pipe where the Qualitrol flow indicator is?)

I do realize the flappers shouldn't be reopened while enenergized if we choose to close them.
 

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RE: GSU Cooler out of service û for max cooling should cooler be isolated?

Keep the flappers open.  It simply makes the cooler into a radiator.  Granted, the open valve will affect oil flow, however the more surface area you have radiating heat, the more cooling you are acheiving.  The temperature drop from the top of the cooler to the bottom is not that significant.  Probably less than 2 degrees.

Rarely is there a check valve.  You usually find a check valve in the case where there is an idle spare that should automatically turn on in the event of lost flow.

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If it is broken, fix it.  If it isn't broken, I'll soon fix that.

RE: GSU Cooler out of service û for max cooling should cooler be isolated?

(OP)
Thanks for those comments.

ASSUMING there is reverse flow (which I think you agreed?)

1 – The oil the goes into the idle cooler  (from bottom of transformer) just came out of a cooler and is already pretty cool, so won't transfer tremendous amount of heat.
2 – When the oil get to the top of the idle cooler, it will turn around and flow again through a running cooler.

I think there would be extreme diminishing returns in flowing oil through 3 coolers in a row.  Wouldn't you think that the benefit from cooling the same oil 3 times would be so miniscule that it will not overcome the direct reduction of cool oil flow into the transformer from the operating coolers?
 

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RE: GSU Cooler out of service û for max cooling should cooler be isolated?

Yes, I agree there would be backflow through the one cooler.  The flow will go down through two of the coolers and be split up between the transformer tank and the idle cooler.  The reason is that in most cases cooler banks are all connected to a single cooling pipe with jets that distribute oil into the transformer.  The pressure in the pipe will cause some (but admittedly not much) backflow. The oil backflowing through the idle cooler is still much hotter than the ambient temperature so it will be further cooled before it exits at the top of the cooler.  

In the idle cooler since the flow rate is reduced through the cooler, the exiting oil will likely be cooled much more than in your other cooler banks.  However it will not immediately be sucked into another cooler causing a loop.  it will mix with the hotter top oil of the unit and reach nearly the same temperature before being pulled into the neighboring pumps.

Of course, I'm basing this off of a core form transformer design.  A shell form may be slightly different since the oil must flow through the windings (via the oil ducts) before making it to the top of the coolers again.  So in the case of a shell form, you might be best closing your flappers.  I can't be sure on that design.  I seem to remember several instances of shell forms where we increased the oil flow rate by uprating the pumps (which actually caused premature failures due to damage to the insulation).  This methodology didn't seem to affect the core form units.

------------------------------------------------------------------------
If it is broken, fix it.  If it isn't broken, I'll soon fix that.

RE: GSU Cooler out of service û for max cooling should cooler be isolated?

(OP)
Thanks. These are shell form GSU's.  (700MVA 345KV/25KV)

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