| Company | CESC Ltd |
| Location | Kolkata, India |
| Timeline | 2016 |
| Project Overview | CESC retrofilled distribution transformers with MIDEL 7131 to improve fire safety, reduce costs, and enhance reliability in densely populated areas of Kolkata. |
| Product | Midel 7131 Synthetic Ester Transformer Fluid |
Overview
CESC Limited has been powering Kolkata for over a century, serving around 3 million customers across residential, commercial, and industrial sectors. With more than 8,000 distribution transformers across its network, reliability and safety are critical—especially in a densely populated city environment.
To address fire risks, CESC had traditionally relied on dry-type transformers in urban areas since the 1990s. While effective, these units come at a significantly higher cost. As the network expanded and aged, CESC began exploring alternatives that could offer the same level of safety, but with improved cost efficiency and performance.
Challenge
Operating transformers in a city like Kolkata comes with unique pressures:
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High population density, increasing the importance of fire safety
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Close proximity to homes, schools, and factories
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High ambient temperatures and humidity, which can affect transformer performance
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Cost constraints, particularly when scaling dry-type transformer installations
Mineral oil-filled transformers posed fire risks, while dry-type transformers were expensive to install and maintain. CESC needed a solution that balanced safety, cost, and performance without compromising reliability.
Solution
CESC identified retrofilling with MIDEL 7131 as a smart alternative. By replacing traditional mineral oil with a synthetic ester fluid, existing transformers could be upgraded without the need for complete replacement.
Two pilot transformers were selected for on-site retrofilling:
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Transformer 1: Installed at a plastic factory in a densely populated area
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Transformer 2: Located at a manufacturing workshop close to a school
Both units were rated at 400kVA, 11/6kV and chosen for their challenging environments where safety and reliability were essential.
MIDEL 7131 was selected for three key reasons:
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Improved fire safety, reducing risk compared to mineral oil
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Environmental protection, due to its biodegradable properties
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High moisture tolerance, making it well suited to humid conditions
Benefits
The retrofilling approach delivered a range of practical advantages:
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Enhanced Fire Safety: Safer operation in high-risk, populated areas
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Cost Efficiency: Lower cost compared to installing new dry-type transformers
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Environmental Protection: Reduced impact in case of leaks, thanks to biodegradability
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Improved Reliability: Better performance in high temperature and humidity conditions
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Extended Asset Life: Existing transformers gained renewed operational capability
Results
After comprehensive testing and monitoring, both retrofilled transformers were successfully returned to full operation.
The outcome was clear:
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Reliable performance in demanding urban environments
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Improved safety standards without the high cost of dry-type units
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Confidence to consider wider adoption across the network
The project demonstrated that retrofilling with MIDEL 7131 could deliver practical, scalable benefits for CESC’s distribution system.