PROJECT: Floating solar farm transformers | India

ESTER TYPE: MIDEL 7131 synthetic ester

PURPOSE: Ensure high availability and safeguard waterways


National Thermal Power Corporation (NTPC), India’s largest energy conglomerate, recently announced the unveiling of a 75MW capacity floating solar PV installation in Kayakullum, Kerala.

The floating solar PV project at Kerala uses 16 free-breathing transformers rated at 5MVA/33kV, manufactured in India by Toshiba. The electrical system was designed and installed by Tata Power.

Floating solar is a relatively new development in the renewable energy world. The immediate advantages are clear; floating solar uses less costly real estate, so the surrounding land can be used for agriculture or commercial purposes. In addition, the water acts as an effective cooling agent that can improve PV panel performance.


Floating solar arrays are subject to heightened external stresses. Specifically, exposing components such as transformers to air and water increases risk of corrosion and rust, leading to the transformer insulating fluid being exposed to air.

For the Kerala project, the area’s high humidity provided an added challenge for the transformers’ optimum operation. High ambient temperatures also accelerate the oxidation process adding further engineering risk. Damage to system components by wildlife is also a recognised challenge in floating solar plants. Such damage could cause a short circuit and start a blaze in other components.

MIDEL 7131 has proven advantages as a synthetic organic ester transformer dielectric fluid:
• Delivers the highest fire safety rating (K3) which is >300°C fire point and net calorific value of <32MJ/kg
• Fully/readily biodegradable
• High oxidation stability
• Superior moisture tolerance (protecting the transformer’s solid insulation and thereby extending its lifetime)
• Compliant with BIS 16081, 16099 and 13503


MIDEL 7131 synthetic organic ester was chosen over natural ester because of its proven performance in free-breathing transformers (with its high oxidation stability) and biodegradable status, so non-toxic to aquatic life if any leaks were to occur. MIDEL 7131 filled transformers can be installed as per IEC 61936 with less protection enabling end-users to resolve practical challenges and reduce costs of traditional protection systems at these critical locations.

“Floating solar PV projects present specific engineering challenges. Using MIDEL 7131 synthetic organic ester rather than a natural ester removes transformer risk and future-proofs the project’s power system, giving the operator peace of mind for proven performance.” – Amit Kumar, Business Development Manager, MIDEL India, SAARC, Myanmar and Thailand

The use of MIDEL ester fluids in these sectors supports the following UN Sustainable Development Goals:

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