Dry Type versus Oil Filled Transformer 2

[mhuckaby]

We are working on selecting a new transformers and main switchboard for an industial facility. We plan on using two 2500 kVA transformers (13,200 to 480 volts) and a main-tie-main main switchboard.

We can locate the transformers either indoors or outdoors.

What are the advantages and disadvantages of the dry type (e.g. Square-D Powercast) and oil filled transformers?

Thanks!
Michael

 

[wbd]

One big plus for dry type transformers is a reduction in fire hazard and environmental issues. We have used them extensively in our industrial plants with no problems.

 

[cortes]

1. Oil filled transformers are more efficient than dry type.
2. Initial cost for oil filled is lower than power cast.
3. Oil filled are more flexible for outdoors usage.
4. Oil filled handles moderates overloads and has higer BIL than dry type.

I suggest you to read Square D bulletin No. 7300pd9203.

Joseph Cortes.

 

[dpc]

It is important to distinguish between conventional dry type transformers and cast coil transformers.

Cast coil transformers can be placed outdoors and actually have a higher fan cooled rating boost than oil-filled.

But they are more expensive.

Biggest disadvantage to oil-filled transformers is fire hazard and the oil itself. High-fire-point oils are available, including vegetable oil, but these cost more than standard mineral oil.

Dry-type allows you to close couple transformer to secondary switchgear - with outdoor units, you must run bus or cable.

 

[cuky2000]

One of the major objections on liquid fill transformer is the potential contamination in case of spill, fire hazardous and periodic testing of the oil.

There are few dielectric fluids options that could help to mitigate some of the negative aspect associated with conventional dielectric oil in transformers. Today there are available biodegradable fluids with flash point ~330 oC & fire point ~360 oC. Other fluids have an acceptable fire retardant characteristic and not contaminant such as Dow Corning 561 Silicon Fluid with flash point ~300 oC & fire point ~330 oC.

There are several technologies available to perform online diagnostic of the oil with acceptable level of accuracy that could help reduce the O&M cost.

Sample of those products are.

http://search.abb.com/library/ABBLi...anguageCode=en&DocumentPartIdD=&Action=Launch

http://www.cooperpower.com/library/pdf/92009.pdf

http://www.faradayhouse.co.uk/ConditionMonitoring.htm

 

[mhuckaby]

Thanks for your help!

Michael

 

[LBolt]

All of the comments stated are valid. We use both types depending on the application. One other item that has not been mentioned is the predective maintenance tests that can be performed on these transformers. The liquid transformer would allow online test (oil samples) and also additional offline tests (Power factor) that give a better indication of what is happening inside. This would come in handy as the transformer ages.
Also, we used a silicon oil in some applications to minmize fire hazards.

Good luck.

 

[davidbeach]

While liquid filled are more efficient than standard dry types (VPI), the cast coil dry is more efficient than liquid filled. With a good outdoor location available, the lower cost of a liquid filled is a strong attraction. If it has to go inside the cast coil is likely to be the best solution, particularly if 1) you have to mechanically cool the transformer room, and 2) you are installing in a double ended configuration and are comparing fan cooled rating to fan cooled rating. The fan cooled rating comes into it because you will likely be comparing a cast coil one size smaller against an alternative one size larger.

 

[RonShap]

Cast coil has less heat rejection in the room vs all others. Cast coil is the way to go with an indoor installation.
Outdoor installation I would go with oil.

 

[GerH]

I think the deciding factor that favours cast resin dry type is if you must install indoors. Even so you still have the option of less flammable oil like MIDEL 7131 or Silicone. Refer FM Guidelines on Transformers for fire risk advice.

Oil seems to be more robust and over say last 10 years plus has in my experience shown less failures.

Dry type transformers can be noisy ( audible and electrical). Audible noise emissions seems to be from the tin work. Electrical arises from local arcing on the covers. Not good if you have sensitive equipment nearby.