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ET series (italian standard)

An Italian designed Buchholz relay for oil-immersed power transformers


  • Inlet diameter up to 100 mm
  • Waterproof (IP65 protection degree)
  • Large inspection window
  • Suitable for replacing similar existing and old Italian models


Inlet diameter 25mm, 50mm, 75mm and 100mm
Standard references Italian standards
Waterproof (IP65 protection degree)
Body in aluminum alloy casting
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 to be used with Gas Collecting device RG3.3 type
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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 ET series Buchholz relay is waterproof and features an IP65 protection degree, enabling its usage even in very rainy and wet environments.
The ET series is even equipped with a large graduated window, allowing clear and easy inspection from the outside.
The ET series Buchholz relay has been designed in order to enable the replacement of both similar old (DIN 42566) and new models (EN50216/2).
The ET 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.



Relay type Inlet diameter Connection type Flange design Bolt circle execution Standard reference Catalogue
ET025 (old T1) 25 mm Flanged Round with 4 holes PN6   pdf
EU26 (old T0/DN25) PN6 + PN10 (special drilling) pdf
ET 50 50 mm PN6 pdf
T3 75 mm pdf
DN100 100 mm Round with 8 holes PN10 pdf
Wiring diagram pdf

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