Jul 2013
Electricity Transmission
400kV Synthetic Ester Filled Transformer Pilot Project
Jul 2013
Jul 2014
National Grid Electricity Transmission
Ruth Hooton, Paul Jarman, & Gordon Wilson
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Network Innovation Allowance
ET - Network improvements and system operability
The risk of transformers filled with mineral oil catching fire as a result of failure is mitigated in line with TS 3.1.3, incurring extra costs in the civil engineering design and construction phases.

Synthetic esters such as Midel 7131 pose fewer issues regarding environmental and fire consequences, whilst offering similar insulating performance. Midel 7131 is biodegradable to IEC 61039 and offers a reduced fire hazard compared to mineral oil (Midel has a flash point of 260°C and a fire point of 316°C compared with a flash point of around 150°C and a fire point below 300°C for mineral oil). It has an IEC fire class K3 rating and a well documented fire safety record over 30 years. Therefore the use of Midel may result in reduced civil design and construction costs along with reduced maintenance costs (i.e. fire protection scheme).

The objective is for this project to give proof of concept on the use of synthetic ester, rather than mineral oil, 
in a 400kV application. It will deliver a transformer test rig consisting of a representative sample of a full size 
winding and filled with synthetic ester which will be subject to HV testing in line with National Grid and IEC 
specifications (specifically Lightning Impulse Test but other tests may be carried out). The scope of the 
research scheme shall be sufficient to give Alstom whatever confidence it needs to supply National Grid with a 
standard size 400/132kV 240MVA transformer to the usual specifications on a standard contractual 
arrangement, subject to the usual procurement exercise, with the normal guarantees and liabilities.

The project will give confidence that synthetic ester can be specified for application in National Grid 
transformers up to 400kV. In achieving this National Grid will then have an option to deploy a low flammable 
liquid transformer to sites where this would provide business benefit e.g. remove the requirement for 
extensive fire protection; enhanced low-fire risk to address planning issues.

Project benefits could include commissioning the design and build of a full size synthetic ester filled transformer.