# Two single-phase 150 kVA, 7200 / 600 volt transformers are connected in open-delta. The maximum three-phase load that they can carry is:

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Two single-phase 150 kVA, 7200 / 600 volt transformers are connected in open-delta. The maximum three-phase load that they can carry is:
1. 300 kVA
2. 75 kVA
3. 259 kVA
4. 249 kVA

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Correct Answer - Option 3 : 259 kVA

Open-Delta Connection:

• An open delta connection transformer uses two single-phase transformers to provide a 3-phase supply to the load.
• An open-delta connection system is also called a V-V system.
• The Open-delta connection system is usually only used in emergency conditions, as its efficiency is low when compared to the delta-delta (Closed delta) system.
• The total load carried by an open delta system is 57.7% of the closed delta system.

The capacity of open-delta system = √3 × Rating of one transformer

= 0.577 × Rating of the closed delta system

Calculation:

Given,

Rating of one transformer = 150 kVA

The capacity of open delta system = √3 × Rating of one transformer

= √3 × 150 = 259.8 kVA

Therefore, the maximum three-phase load that they can carry is 259.8 kVA