Three-Phase Transformer or Transformer Bank

These guys will have all the info you require...

https://www.powertransformernews.com/2017/11/06/ge-completes-construction-on-500220-kv-substation-in-egypt/

http://new.abb.com/products/transformers

"...which one will be better..." depends upon what parameters are most important to you, somethings that only you or your management knows.

It would helpful to the forum if you showed the results of your efforts so far; once you do your due diligence the answer will be obvious to you.

NB- I have performed that analysis numerous times, and the answer always depends upon the ranking of the "must haves" vs. the "like to haves", so talk to your superiors.

thank you for your replay

the three phase transformer and transformer bank is introduced in the same offer main offer and alternative offer less in price and at general i put this point to compare between the two type .

THE reasons for choosing three phase transformer instead of transformer bank ( three single transformer ) ?

1- Low cost compared with three units of single phase transformers.

AT least 20 % less than in cost due to the core material required is very less compared to a bank of three single phase transformers.

2- It requires less space to install.

At least 40 % less than the area required for transformer bank

Disadvantage

1- if any one phase is defective To restore the service, spare unit cost is more compared with one single transformer spare unit.

2- depend on ambient temperature When the three phase transformer are self cooled, the capacity of the transformer is reduced.

3. it is hard to transport very high power three-phase transformers using conventional roads and railways. Therefore, for these cases, banks of three single phase transformers are used instead.

the main problem to me this offer introduced to us by chines manufacture and the data for transformer same as our transformer and both of three phase transformer and transformer bank achieve parallel operation and give us references for his previous work and he sold transformer with the same rating so i ask if there is a problem in three phase transformer like tempreture or not

If both transformer arrangements have exactly the same ratings, and you are indifferent about the relative advantages and disadvantages of each configuration, then go with the lower installed cost. Just make sure that the TLC (Total Lifetime Cost) is properly evaluated.

thanks very much for you

Transport constraints play a major role when deciding on such large rating transformers.

The weight and dimensions of a single unit of three phase transformer could be unacceptable when a route survey is made to confirm the transportability from the port / manufacturing location to the site of installation.

It is found that generation, transmission, and distribution of electrical power are more economical in three phase system than a single phase system. For a three-phase system, three single-phase transformers are required. Three phase transformation can be done in two ways, by using a single three-phase transformer or by using a bank of three single phase transformers. There are advantages and disadvantages to each option.

A single 3 phase transformer costs around 15 % less than a bank of three single phase transformers. Again former occupies less space than later. For a very big transformer, it is impossible to transport a large three-phase transformer to the site and is instead easier to transport three single-phase transformers, which are erected separately to form a three-phase unit.

Another advantage of using a bank of three single phase transformers is that, if one unit of the bank becomes out of order, then the bank can be run as an open delta transformer.

For more information Refer - Construction of Three Phase Transformer

Not all of your statements are entirely accurate.

In "Disadvantages," point #2 applies to both three-phase and 3 single-phase transformers. Cooling or lack of cooling impacts the thermal capacity rating of the transformers whether they are 3-phase or single phase. So you need to look at what external cooling is necessary in both cases.

Disadvantage #3 is only a significant factor if you are responsible for transporting the transformer(s) to your station site. If you include the requirement for the supplier to transport it in their tender, they have to figure out what is required and how it is to be done. It may impact their price, but you will know right away what is the cost difference and you will not have to worry about any permitting, routes, special transport equipment, etc.

You may also want to ask the sellers to quote all the required rigging/setting on the foundation, site assembly, oil filling, and testing so that when they turn it over to you it will be ready to connect to your system and energize. Then if there is a problem, it is on THEIR warranty, not something they can point at you and say that you caused the problem.

If you buy three single phase transformers and (some day) one fails you can disconnect it and run open delta (at just over half capacity) till it is repaired/replaced. If single 3 phase fails you have zero capacity till repaired/replaced.