ODWF vs ODAF Transformer

[HydroPaul]

Does anyone have a feel for the relative cost comparison for a forced air cooled transformer compared to a water cooled unit, say at 100 MVA?

Thanks in advance!

 

[prc]

The cost is almost same, or sometimes water cooled ones marginally cheaper.But generally oil to air heat exchangers are preferred to water to air heat exchangers from maintenance liability,need for cooling water etc,etc.But for two applications water cooling is the preferred or the only solution viz transformers for underground hydro power stations and for rectifier transformers for aluminum industry where pollution level makes oil to air heat exchangers less effective.

 

[davidbeach]

Hydro doesn't need to be underground. GSUs at hydro plants are often water cooled.

 

[prc]

It is true in hydro electric stations water cooling used to be preferred due to readily availabe tail race water and space restrictions as switch yard/transformer yard is usually formed by cutting rocks.Water cooling require only a smaller foot print than oil to air heat exchangers. Some utilities prefer water cooling even for thermal stations.In India one utility used to go for closed loop water cooling for their thermal 200 MW Generator transformers.
The problem with water cooling is tube corrosion from various reasons.If the water velocity is high, corrosion from various erosions is the result.If velocity is low,crevice corrosion from galvanic cell formation can cause pitting. In many countries strict laws prohibit oil leaking in to rivers.So a solution widely used is double tube construction so that leaked oil will not go to river water.Still due to maintenace liabilty issues, whereever space allows new projects go for oil to air heat exchangers, but for underground hydrostations there seems no other alternatives to take away heat.

 

[sakaran51]

Furnace Transformers for open arc furnaces and the electrode cables which carry thousands of amps are water cooled.