Why Electrical Transformers are Connected in Parallel Instead of Series?

 Why Electrical Transformers are Connected in Parallel Instead of Series

Transformers are the backbone of power systems—stepping up voltage for transmission and stepping it down for safe distribution. In practical systems, it is very common to connect two or more transformers in parallel rather than in series. This practice is followed for both single-phase and three-phase transformers to achieve reliability, flexibility, and efficiency in power supply.

1. Concept of Parallel vs Series Connection

• Parallel Connection:
  Two or more transformers are connected such that their primary windings share the same supply voltage, and their secondary windings deliver power to a common load while maintaining the same output voltage.

• Series Connection:
  Transformers are connected end-to-end, so the output of one becomes linked in series with the other. While this increases the overall voltage, it is rarely used in power distribution systems because it causes operational problems.

---

2. Why Parallel Connection is Preferred

(a) Flexibility in Load Sharing

• Parallel transformers can share the total load.

• During light load periods, one transformer can be switched off to improve efficiency.

• During heavy load periods, multiple transformers operate together to prevent overloading.

(b) Reliability and Redundancy

• If one transformer fails, the others can continue supplying power, ensuring uninterrupted service.

• This is critical in industrial plants, hospitals, and power stations where downtime is unacceptable.

(c) Expansion Made Easy

• Future load growth can be accommodated by adding another transformer in parallel, rather than replacing the existing one with a higher-capacity transformer.

(d) Voltage Regulation and Loss Reduction

• Properly connected parallel transformers maintain uniform voltage levels at the bus bar.

• Power losses are minimized since load is distributed optimally according to the kVA ratings of each transformer.

---

3. Limitations of Series Connection

Connecting transformers in series is avoided because:

1. Unequal voltage drops occur due to slight differences in impedance, causing circulating currents.

2. If one transformer fails, the entire system shuts down.

3. Power distribution networks require constant voltage at the bus, which is not maintained in series connection.

4. Series operation does not allow easy load sharing.

---

4. Conditions for Parallel Operation

To ensure successful parallel operation:

1. Same Voltage Ratio: Secondary voltages must match.

2. Same Polarity: Avoids circulating currents.

3. Similar Impedance and Phase Angle: Ensures proper load sharing.

4. Phase Sequence (3-phase): Must be identical to prevent short-circuits.

5. Vector Group (3-phase): Transformers must belong to the same vector group to maintain proper phase displacement.

---

5. Application to Single-Phase and Three-Phase Transformers

• Single-Phase Transformers: Common in residential and small industrial loads. Parallel operation provides flexibility to handle variable demand.

• Three-Phase Transformers: Widely used in power grids and heavy industries. Parallel operation ensures stable supply, balanced load sharing, and scalability.

---

6. Diagram: Parallel vs Series Connection

Here’s a simplified diagram (for better visualization).

         Parallel Connection of Transformers
          ______________________________
         |                              |
   AC ---| T1 Primary     T2 Primary    |--- AC
         |                              |
         |______ Sec1 ______ Sec2 ______|---- Load

   (Both transformers feed the load at same voltage)

         Series Connection of Transformers
          _______________________________
         |                               |
   AC ---| T1 Primary     T2 Primary     |--- AC
         |                               |
         |______ Sec1 ---- Sec2 _________|---- Load

   (Secondary voltages add up – not suitable for distribution)

---

7. Advantages of Parallel Operation (Summary)

✅ Increased system reliability
✅ Efficient load sharing
✅ Easy expansion for future demand
✅ Reduced transmission losses
✅ Better voltage regulation

---