Three-Phase Transformers - GATE EE Electrical Machines Free MCQ Test

A V-V connected transformer can be connected in parallel with a delta-delta connected transformer, but it cannot be connected to:

• Delta-star connected transformers
• Star-delta connected transformers
• Star-V connected transformers

Thus, the correct option is that it cannot be connected to all of the mentioned types of transformers.

Three single phase transformers and one single unit of three phase transformer will be same only. this is done to reduce the cost and spacing.

The most suitable transformer for use in distribution systems is the delta-star transformer. This design is advantageous because it helps in:

• Reducing voltage levels effectively for safe distribution.
• Providing phase shift which is essential in three-phase systems.
• Minimising losses associated with power transmission.
• Enhancing system stability by balancing loads.

Overall, the delta-star configuration is preferred due to its efficiency in managing voltage and improving power quality.

Delta connected winding handle line voltages so it needs more turns in the winding but thin wires.

 If one of the transformers is removed from the bank of only delta-delta, then it behaves with 58% power delivery.

 If the core is not ferromagnetic then the transformer will not operate at all so no humming sound.

When a ferromagnetic material (like the transformer core) is magnetized, the magnetic domains align. This alignment leads to magnetostriction — the core length changes slightly.

On magnetization, the length of the ferromagnetic core increases.
On demagnetization, the length decreases back to its original state. (but a tiny residual elongation may remain)
Therefore, option (a) is the correct answer.
 

 If the frequency is reduced, the core flux density increases, so the noise also will increase.

In a star connected transformer, closed path to generate 3rd harmonic is not there. So the emf shape will be peaky in nature.

 The phase current will be reduced by 1/1.73.