Transformer cooler design

[babyG]

I am looking at changing a xfmr from ODWF to OFAF/OFAN. If i change the heat exchangers, do I need to worry about the pressure from the pumps?

 

[amps21]

I have questions myselves.

Whe u say -"If i change the heat exchangers", are u incorporating radiators etc. If not i dont know why u should worry about the pressure. Pressure was critical only when water was on the other side. But your transformer was always under the pump pressure, isint it?

 

[mauner]

The pumps may not be able to deliver the same cooling flow through the xfmr if the pressure loss across the new heat exchanger is greater.

Here are some basic questions that should point you down the right path.

Does the xfmr use a centrifugal pump?
What is the rated cooling flow and pressure loss across the old and new heat exchangers?
What is the rated pump pressure and flow (at what fluid SG)?
Is there a significant diffence in the specific gravity of ODWF and OFAF/OFAN?
Will the new heat exchanger change the average fluid operating temperature?

 

[ScottyUK]

Is there a significant diffence in the specific gravity of ODWF and OFAF/OFAN?

Not quite sure where that was going:

ODWF = Oil Directed, Water Forced
OFAF = Oil Forced, Air Forced
OFAN = Oil Forced, Air Natural

Questions:

Why are you changing the OD** designation to OF**? There seems little point in interfering with the internal oil flow for the transformer. The oil directors are usually intended to provided additional cooling at likely hotspots within the design. Are you implying that you are going to remove them?

Using OFAN is a relatively unusual mode - ONAF is the more common intermediate step prior to OFAF as it accumulates wear on the easy-to-maintain external fans and minimises running hours on the pump. Fan maintenance on an ONAF design typically doesn't require the transformer to be out of service unlike pump maintenance on an OFAN design (unless you have redundant pumps and isolation valves for each pump - a rare luxury except on very large or system-critical transformers!)

You will almost certainly have a lower pressure drop across a finned air radiator bank than an oil/water heat exchanger. You should check that the pump is suitable for service at a lower pressure, higher flow situation. Changing the pump performance may have knock-on effects on the efficacy of the oil directors at cooling the hot areas of the transformer. You should study the oil flow path very carefully and try to ensure that the conditions do not change significantly from the original design.

The best people to discuss this with are the transformer's manufacturer. What have they said about this proposal?


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I don't suffer from insanity. I enjoy it...

 

[babyG]

Sorry I wasnt being very clear

I want to remove water coolers & put radiators on... (for reasons that arent very relevant here so I wont go into them). so there are currently pumps on there.
I'm trying to decide whether I wanna leave those pumps on or not, and whether or not they will destroy the radiators.
I'm thinking of running the pumps @ lower power...

 

[patrick7]

be careful not to reduce the temperature by a differential amount that is great enough to produce a static charge when the cooler oil is reintroduced into the transformer. We had a situation where we needed to cool a transformer and this was one recomendation from the manufacture.

 

[Griseo]

Hi
As a transformer manufacturer engineer I can call your attention to two points: first, that a pump to work in an ONAN mode must be radial type (centrifugal are often used with pure ODAF heat exchangers!) to have low pressure drop when stopped, and second, you must have a head-vs-flow working point that insures an oil speed that while being enough for the expected cooling will not generate static charges in the insulating material. This speed must be indicated by the manufacturer; only him has elements to calculate the internal pressure drop and the optimal oil speed (I use to limit to about 12 to 13 cm/s in txfs >100 mVA, >230 kV).