IS 1180 Standard for Distribution Transformers: Efficiency Levels, Loss Figures, and Compliance Guide (2025)

 

IS 1180: Standard for Energy Efficient Distribution Transformers

🔹 Introduction to IS 1180

IS 1180:2014 (Part 1) specifies requirements for Outdoor Type, Oil-Immersed Distribution Transformers up to 2500 kVA, 33 kV class. The main focus is on energy efficiency, minimum losses, safety, and environmental compliance.

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🔹 Scope of IS 1180

• Rated Capacity: Up to 2500 kVA

• Voltage Class: 11 kV / 22 kV / 33 kV

• Phases: Three-phase transformers

• Frequency: 50 Hz

• Efficiency Classification: Level 1, Level 2, Level 3 (corresponds with BEE star ratings)

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🔹 Key Requirements under IS 1180

1. Energy Efficiency Levels with Loss Figures

The standard specifies maximum allowable No-Load Losses (NLL) and Load Losses (LL) at 50% load.

📊 Typical Loss Values for 100 kVA, 11 kV Distribution Transformer (IS 1180:2014)

Rating (kVA)	Voltage Class	No-Load Loss (W)	Load Loss at 50% Load (W)	Load Loss at 100% Load (W)
100 kVA	11 kV	320	1,050	2,100
200 kVA	11 kV	480	1,650	3,300
500 kVA	11 kV	850	3,000	6,000
1000 kVA	11 kV	1,400	5,400	10,800
2500 kVA	33 kV	2,900	14,000	28,000

(Figures are indicative and may vary slightly for Level 1, 2, and 3 efficiency levels)

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2. Design & Construction Norms

• Core Material: CRGO steel (loss ~0.9 W/kg) or Amorphous alloy (loss ~0.2 W/kg).

• Winding Material: Copper or Aluminium, temperature rise limited to 50°C (oil) and 55°C (winding).

• Tapping Range: ±5% in 2.5% steps.

• Impedance: Typically 4% to 6% (depends on kVA rating).

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3. Voltage Classifications (Examples)

• 11 kV / 433 V → Common for urban & rural distribution.

• 22 kV / 433 V → Used in high-demand areas.

• 33 kV / 433 V → Used for bulk supply to industries & large townships.

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4. Testing Requirements with Values

• Impulse Voltage Test:

  • For 11 kV class → 75 kVp

  • For 22 kV class → 125 kVp

  • For 33 kV class → 170 kVp

• Temperature Rise Test:

  • Max rise in oil: 50°C

  • Max rise in winding: 55°C

• Short Circuit Test: Must withstand thermal & dynamic forces for 2 seconds.

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🔹 Safety & Reliability Provisions

• IP Rating: Minimum IP55 for outdoor enclosures.

• Noise Level: < 50 dB(A) for 100 kVA, < 65 dB(A) for 2500 kVA (measured at 1m distance).

• Dielectric Strength of Oil: ≥ 30 kV (BDV test at 2.5 mm gap).

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🔹 Environmental & Maintenance Aspects

• Insulating Oil: IS 335 mineral oil or IEC 60296 standard oil.

• PCBs: Not permitted (< 2 ppm).

• Moisture Content: < 30 ppm in oil.

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🔹 Importance of IS 1180 Compliance

• Loss reduction → Saves ~300–500 kWh/year per 100 kVA transformer.

• Higher efficiency → Direct reduction in AT&C losses for DISCOMs.

• Long-term savings → Payback within 2–3 years due to reduced electricity losses.

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🔹 Conclusion

IS 1180 ensures uniform quality, safety, and energy efficiency for distribution transformers across India. For DISCOMs, compliance means lower system losses, and for manufacturers, it is the gateway to BIS certification.

⚡ Engineer’s Tip: Always demand the loss figures (NLL & LL) as per IS 1180 in the purchase order. Even a 100 W reduction in losses can save ₹5,000–6,000 annually per transformer.