What Is a Transformer Bund Filter?

Published 25 Nov 2025

Transformer Bund Filter

A Complete Guide for Asset Managers

Environmental protection around LV, MV and HV transformers is a growing priority for utilities, renewable energy developers, industrial sites and BESS operators. With increasing regulatory pressure around oil containment, many sites are upgrading to modern Transformer Bund Filters—a passive, low-maintenance system that allows clean rainwater to drain while preventing oil from escaping a transformer bund.

What Is a Transformer Bund Filter?

A Transformer Bund Filter is a passive drainage system installed on oil-filled transformer bunds to let clean rainwater escape while automatically sealing if oil is detected. These systems contain hydrocarbon-absorbing media and a self-activating shut-off valve that prevents any contaminated water from leaving the bund.

Transformer Bund Filters | Draineezy Oil Removal Filters for LV MV HV Transformers (11kV, 33kV, 66kV)

Why Transformer Bund Filters Are Becoming Industry Standard

DrainEezy Bund Filters are now widely used across:

Onshore Wind Farm Substations
Solar Farms & Inverter Stations
Battery Energy Storage Systems (BESS)
DNO / IDNO Primary & Secondary Substations
Industrial Transformer Installations

Key Advantages

Zero power requirement – fully passive filter system
Automatic oil shut-off – the bund filter seals instantly on detection
Low installation costs – quick, easy, field-ready and retro-fittable
Minimal maintenance – no moving parts
Ideal for remote sites – extensively installed to steel bunded transformers in the Renewable Energy sectors

How the Draineezy Transformer Bund Filter Works

The Draineezy system uses hydrophobic media ensuring:

Allows clean rainwater to pass freely
Captures hydrocarbons instantly from oil transformer leaks
Triggers an automatic shut-off valve
The filter prevents any oil discharge from the transformer bund

Transformer Bund Filter

Draineezy vs Traditional Oil-Water Separators

Features	Draineezy Bund Filter	Oil-Water Separator
Power Required	No	Yes
Maintenance	Low	High
Installation Cost	Low	High
Environmental Risk	Very Low	Medium
Response to Oil Spill	Instant Automatic Shut-off	Manual Intervention

Applications Across Energy & Utilities

Wind turbine transformer bunds
Solar farm transformer/inverter bunds
BESS sites
DNO/IDNO substations
Industrial HV transformer bunds
OEM bund installations

Transformer Bund Filter

Need a Transformer Bund Filter?

Thorne & Derrick supply the full range of Draineezy Transformer Bund Filters, fitting kits, pre-filters and technical support.

Enquire Now


DrainEezy Bund Filter	DrainEezy New Design	Oil Filled Transformers

LV MV HV Transformers, Cables & Electrical Equipment

Thorne & Derrick distribute the most extensive range of 11kV 33kV Cables, Cable Jointing, Terminating, Pulling & Installation Equipment – we service UK and international clients working on underground cables, overhead lines, substations and electrical construction at 11kV 33kV and up to and EHV transmission and distribution voltages; approved stockists and suppliers of 3M Electrical (ColdShrink), Nexans (Euromold), Pfisterer (CONNEX) and Lovink cable accessory and connection products.