Why Use Parallel Operation?

• Increase total power capacity
• Improve reliability (backup if one fails)
• Allow maintenance without shutdown
• Better load sharing

Basic Concept

When transformers are connected in parallel:

• Primary windings connected to same supply
• Secondary windings connected to same load
• Load current is shared between transformers

Conditions for Parallel Operation

For safe and proper operation, the following conditions must be satisfied:

1. Same Voltage Ratio

• Secondary voltages must be equal
• Prevents circulating currents

2. Same Polarity

• Incorrect polarity causes short circuit

3. Same Phase Sequence (for AC)

• Important in three-phase transformers

4. Same Frequency

• Must operate at the same supply frequency

5. Similar Impedance

• Ensures proper load sharing

Load Sharing

Load is shared based on transformer impedance:

• Lower impedance → carries more current
• Higher impedance → carries less current

What Happens if Conditions Are Not Met?

• Circulating currents between transformers
• Overheating
• Unequal load sharing
• Possible damage or failure

Advantages

• Flexible operation
• Scalable power system
• Improved efficiency at varying loads
• Redundancy

Disadvantages

• Requires precise matching
• More complex protection system
• Risk of circulating currents

Example

Two transformers rated:

• Transformer A = 5 kVA
• Transformer B = 5 kVA

Total capacity:

Total Power = 5 + 5 = 10 kVA

Important Notes

• Identical transformers work best
• Always check polarity before connection
• Impedance mismatch leads to poor load sharing