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EE series (ex BS series)

The newest Buchholz relay release for use in oil-immersed power transformers


  • Bottom petcock that allows for gas injection testing
  • Waterproof (IP65 protection degree)
  • Large inspection window
  • Suitable for replacing similar existing and old models (BS standards)


Inlet diameter 1", 2" and 3"
Standard references EN 50216, old British Standards
Waterproof (IP65 protection degree)
Body in aluminum alloy casting
Round flange execution 6 holes
Window material PMMA or tempered glass
Environmental conditions from -60°C up to +70°C
Oil flow rate from 0,65m/s up to 2m/s
Wiring diagrams availability from 1 up to 4 contacts
Finishing for exreme/high corrosive environments
Suitable for gas injection testing
Suitable to be used with Gas Collecting device RG3.3 type
Download PDF
Full catalogue pdf
Order form pdf



A Buchholz relay is a type of oil- and gas-actuated protection relay universally used on all oil-immersed transformers with a rating greater than 500 kVA – conservator type. Buchholz relays are used to protect transformers from faults occurring inside the transformer.
Short circuit faults such as inter-turn faults, incipient winding faults and core faults may occur due to overheating, bad connections and ageing. A Buchholz relay will sense such faults and close the alarm circuit. The Buchholz relay functions based on the fact that an electrical fault inside the transformer tank is accompanied by the generation of gas; if the fault is severe enough, it will be accompanied by an oil surge from the tank to the conservator.
The CEDASPE EE series is equipped with a bottom petcock that allows for gas injection testing. During transformer setup, commissioning or maintenance, proper Buchholz relay contacting can be checked by pumping or injecting compressed air from below.
The EE series Buchholz relay is waterproof and features an IP65 protection degree, enabling its usage even in very rainy and wet environments.
The EE series is even equipped with a large graduated window, allowing clear and easy inspection from the outside.
The EE Buchholz relay has been designed so that it can replace both similar old and new models according to British standards.
The EE series is also suitable for use with a RG3.3 gas collecting device that allows gases to be drained from the relay accumulation chamber operating at eye level; RG3.3 also enables gas injection testing.



Relay type* Inlet diameter Transformer Oil Oil flow rate [cm/s] Connection design Flange execution Standard reference Catalogue
EE1 1" up to 1000 kg 100±15 Flanged Square with 4 holes EN 50216 and Old BS pdf
EE2 2" from 1000 kg up to 10000 kg Round with 6 holes
EE3 3" from 10000 kg up to 50000 kg
Gas collecting device (suitable for EB 50 and EB 79/EB 80)
RG3.2 model pdf
Wiring diagram pdf
EE series - assembly sketch pdf
Gas analyzer for Buchholz Relay pdf
Pneumatic test pdf
* Special design on demand

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