The Correct Answer is Option D: Correct Polarity

Explanation:

The satisfactory parallel operation of transformers requires several conditions to be fulfilled to ensure safe and efficient operation. Among these conditions, one of the most important is the correct polarity of the transformers.

Importance of Correct Polarity:

The polarity of a transformer refers to the direction of the induced voltage in the secondary winding relative to the primary winding. It is crucial to have the correct polarity for the parallel operation of transformers because:

1. Proper voltage regulation: Transformers with correct polarity will have their secondary voltages in phase with each other. This ensures that the combined voltage output from multiple transformers is stable and within the desired range, providing proper voltage regulation.

2. Balanced load sharing: Transformers with correct polarity will share the load equally in parallel operation. This is because the phasor sum of the secondary voltages is additive, resulting in the desired load sharing between transformers.

3. Preventing circulating currents: If transformers with incorrect polarity are connected in parallel, the phase relationship between their secondary voltages will be opposite. This can lead to circulating currents between the transformers, causing increased losses and overheating.

Procedure to Ensure Correct Polarity:

To ensure correct polarity during the parallel operation of transformers, the following steps should be followed:

1. Polarity marking: Each transformer should be clearly marked with a polarity indicator. This indicator is typically denoted as a dot or a polarity mark on the transformer's terminals.

2. Polarity verification: Before connecting transformers in parallel, their polarity should be verified by measuring the voltage phasor relationship between the primary and secondary windings. This can be done using a phase sequence meter or a voltmeter.

3. Corrective action: If any transformer is found to have incorrect polarity, it should be corrected before parallel operation. This can be done by reversing the primary or secondary connections as necessary to achieve the desired polarity.

4. Testing and commissioning: After correcting the polarity, the transformers should be thoroughly tested and commissioned to ensure proper operation in parallel.

Conclusion:

In conclusion, correct polarity is a crucial condition that must be fulfilled for the satisfactory parallel operation of transformers. It ensures proper voltage regulation, balanced load sharing, and prevents circulating currents. Following the proper procedure for verifying and correcting polarity is essential to ensure safe and efficient parallel operation of transformers.

In Parallel operation there is two important points for parallel connection of transformers

1. Terminal voltage of the transformer should be equal to reduce the circulating currents
2.Polarity should be identical,phase sequence should be equal in case of three phase
this two conditions are mandatory without which parallel operation not possible .