Why Three phase Capacitor banks connected in Delta?

Why Capacitor Banks Are Connected in Delta Instead of Star

Capacitor banks are widely used in power systems for power factor (PF) improvement and reactive power compensation. Interestingly, you’ll notice that almost all capacitor banks are connected in Delta rather than Star.

This choice is not arbitrary—Delta connection provides distinct advantages in terms of efficiency, reliability, and maintenance. Let’s explore them one by one.

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1. Lower Maintenance Cost

• In a Delta-connected capacitor bank, if one capacitor unit (cell) out of three fails, the bank continues to operate in open-Delta mode.

• The reactive power (kVAR) output only reduces by around 27%, instead of a complete shutdown.

• Maintenance becomes simpler: the faulty unit can be isolated and replaced without disturbing the other two.

• This translates to lower replacement cost and improved uptime compared to a star-connected bank.

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2. Higher Efficiency

• In Delta configuration, line current is higher compared to Star connection.

• This allows capacitors to deliver more reactive power per unit bank rating.

• As a result, the overall system efficiency improves when reactive compensation is supplied through Delta banks.

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3. Higher Capacitance (and More Reactive Power Supply)

• The equivalent capacitance of a Delta connection is greater than that of a Star connection for the same capacitor units.

• Higher capacitance → Higher reactive power (kVAR).

• Since the main purpose of capacitor banks is to supply reactive power and improve PF, Delta configuration serves better.

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4. Better Voltage Balancing

• In Star-connected capacitor banks, unbalanced system voltages can cause unequal stress on individual units.

• Delta connection naturally provides voltage balancing, preventing over-voltage across any single capacitor.

• This enhances service life and reliability of the bank.

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5. Practical & Economic Benefits

• Shunt Capacitor Banks (SCBs) are relatively inexpensive, easy to install, and can be deployed anywhere in the network.

• Delta configuration makes them even more practical by minimizing downtime and ensuring stable performance.

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Relevant Standards for Capacitor Banks

When designing, installing, or maintaining capacitor banks, engineers should refer to:

• IS 13925 (Part 4): 2013 — Indian Standard, identical with IEC 60871-4:1996

• IEC 60871 series — International standards for capacitor banks

• For protective devices: MCCB Standards (see MCCB Standards Reference)

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Key Takeaway

Capacitor banks are connected in Delta instead of Star because Delta offers:
✅ Lower maintenance cost
✅ Higher efficiency
✅ Greater capacitance (more reactive power)
✅ Better voltage balancing

This makes Delta connection the most practical and economical choice for power factor correction in modern electrical networks.

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⚡ Disclaimer: This article is for educational purposes. Always refer to the latest IS/IEC standards and manufacturer’s datasheets before design or installation.

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