Understanding primary & secondary distribution system in India

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Primary and Secondary Distribution System in India – Complete Guide with SLD. 

What is a Distribution System?

The distribution system is the final stage of the power system that delivers electricity from substations to end consumers such as homes, shops, and industries.

In India, distribution is mainly divided into:

  1. Primary Distribution System (High Voltage side)
  2. Secondary Distribution System (Low Voltage side)



This Single line diagram shows general layout of Distribution System.



Primary Distribution System (India)

Voltage Level- 11 kV / 22 kV / 33 kV
Purpose- The primary distribution system carries power from the distribution substation to the distribution transformers located near load centers. This system covers longer distances and does not supply power directly to consumers.

Equipment Used in Primary Distribution

1. Distribution Substation Transformer-Steps down transmission voltage (66 kV / 132 kV) to 11, 22, or 33 kV.

2. HT Feeders- Carry high-voltage power to different distribution areas.

3. Conductors (ACSR / AAAC)- Transmit electrical power efficiently over long distances.

4. Poles (PCC / Steel / H-Pole)- Support overhead HT distribution lines.

5-Insulators (Pin / Disc Type)- Prevent leakage of current from conductors to poles.

6. Circuit Breaker (VCB)-Automatically isolates faults such as short circuits or overloads.

7. Isolator-Provides visible isolation during maintenance work.

8. Lightning Arrester-Protects HT equipment from lightning and switching surges.

9. Drop-Out (DO) Fuse-Protects distribution transformers from overcurrent faults.

10. Recloser - Help restore supply automatically and isolate faulty sections, reducing outage time.

11. Earthing System- Safely dissipates fault current into the ground.

Secondary Distribution System (India)

Voltage Level-415 V (Three Phase) / 230 V (Single Phase)
Purpose-The secondary distribution system supplies electricity directly to consumers from the distribution transformer. The distribution transformer marks the end of the primary distribution system. It covers short distances and focuses mainly on consumer safety and metering.

Equipment Used in Secondary Distribution

1. Distribution Transformer (DT)-Steps down 11 kV to 415/230 V.

2. LT Feeders-Carry low-voltage power to streets, buildings, and consumers.

3. Conductors / Cables (AAC / ABC)-ABC cables are widely used to reduce theft and improve safety.

4. LT Poles-Support LT overhead lines.

5. Shackle Insulators-Used for LT line insulation.

6. LT Distribution Box (DB)-Distributes power to multiple service connections.

7. Protection Devices (MCB / MCCB / ACB)-Protect LT circuits from overload and short circuits.

8. Energy Meter-Measures electricity consumption for billing purposes.

9. Service Cable-Connects LT line to individual consumer premises.

10. Earthing System (Consumer & System)-Protects people and appliances from electric shock.

Conclusion

The primary distribution system ensures efficient and reliable power delivery up to distribution transformers, while the secondary distribution system ensures safe and accurate supply to consumers.
A well-designed distribution system reduces losses, improves reliability, and enhances safety — making it a critical part of India’s power infrastructure.