Question

Which of the following is NOT one of the advantages of a single three-phase transformer bank over a three single-phase transformer bank?
1. The core is of larger size which makes it robust.
2. It weighs less.
3. The cost is less.
4. It occupies less space for same rating.

Answer 1

Correct Answer - Option 1 : The core is of larger size which makes it robust.

Comparison between Bank of 3 Single Phase Transformer vs Single Three Phase Transformer:

Bank of 3 Single Phase Transformer	Single Three Phase Transformer
It is more expensive due to requirement of 3 single phase transformer. 3 single phase transformer means requirement of more iron for core, oil and accessories.	It is quite economic due to the use of less iron core, less volume of tank and hence less volume of Transformer Oil.
In such case star or delta connection on HV side requires six different HV Bushings to bring out the HV terminals of 3 single phase transformers.	This only requires three / four HV Bushings as the delta / star connection is done inside the tank of transformer.
Space requirement is more for installation.	Less space requirement for installation.
It offers greater flexibility in erection and installation.	Due to single unit, it doesn’t have any flexibility in erection and installation.
The spare inventory cost is less. Only one single phase transformer is required as spare which is less costly. Suppose a generating station has 2 generating units. For both the generating units (2xbank of three single phase transformer), only one single phase transformer is required as spare.	The cost of single three phase transformer as spare is quite high when compared with a single unit of single phase transformer.
The maintenance becomes easier due to separate units. Replacement of single unit is also easy.	It is quite difficult to repair and replace.
This is less efficient due to losses in the three units. The losses are more due to use of more iron core.	It is more efficient and losses are less due to lesser requirement of iron core.