Transformer Paralleling

This post describes the advantages, disadvantages and conditions required for paralleling Transformers with ETAP simulation results.

TRANSFORMER PARALLELING:

Advantages:

Load sharing
Efficiency
Redundancy
Cost minimization
Reliable power supply

Disadvantages:

Increase the short circuit current that increases breaker capacity.
Bus rating could be too high.
Paralleling of transformers reduces the transformer impedance significantly.

Conditions for Transformer Paralleling:

Transformer rating should be the same.
Polarities of the transformer should be the same.
Percentage impedance should be the same.
Ratios of (X/R) should be the same.
Phase angle should be the same.
Phase sequence of the transformer should be the same.
Frequency should be the same.
Tap positions should be the same.
Transformers vector group should be identical.
The above conditions are validated with ETAP simulation results.

Case (1): Transformer with Same Rating

Figure 1. Transformers with the same rating

In case 1, Both the transformer ratings are the same for parallel operation, By the results, the 40 MVA load is equally shared by Both transformers.

Case (2): Transformers with different MVA rating

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