Product & Services

Transformer Accessories


    1 & 2” size PRD is used on either medium distribution or small power transformers.

    When transformer pressure rises beyond its predetermined limit, you need a pressure relief device you can count on to protect your valuable equipment.

    When internal tank pressure rises, the valve within the PRD begins to lift off the top seal. Once pressure is relieved the valve returns quickly to its sealed position.

    The NBR sealing ring and the particular design of the Stainless Steel spring and the center rings ensure a safe and steady service and long life.

    The NBR sealing ring and the particular design of the steel spring and the center rings ensure a safe and steady service and a long life. The sort tail allow an easy location in any portion of the cover, as it doesn’t interfere with the clearance between alive inside the transformer.

    Routine test : All of our PRD are tested with transformer oil and sealed before dispatch.


    Description and General Specifications

    Yamamoto maximum thermometer is designed for smaller distribution transformers without cooling or alarm functions. All have a reset able maximum pointer.

    In standard form they are available for front or top mounting, and can be fitted with different connection threads to suit different installation requirements.

    Type : Straight type ( S type )

    Casing : Stainless Steel ( SUS304 )

    Cover/locking ring : Stainless Steel ( SUS304 )

    Size : 75 Ø mm

    Temperature Range : 0 ~ 120 deg C, c/w Max pointer

    Ambient temp : -30 / + 70oC

    Protection degree : IP 54

    Class / Accuracy : ± 2% FS

    Window : Glass

    Length of sensor : Standard 90 mm ( max. length 300 mm )

    Dimension of sensor : Standard 8Ø x 90 mm

    Material of sensor : Copper with Ni Plated

    Connecting thread : R ½, R ¾

    Option : Thermo well

    Operating Instruction and Maintenance

    Operating Instructions :

    Mounting :

    Fixe the connection on the thermometer connection ( pocket ) by means of a spanner. Attention do not try to tighten the connection by twist the thermometer dial ( head ) as you may damage it ! Once the connection is fixed you mae need to position the dial to get the best readability, The positoning can be mad by means of the swivel nut of the thermometer.

    Maintenance :

    No particular maintenance is riquired. Only, on regular basis, schedule inspections to verify correct function and calibration. Typically a check of the precision must be done after 24 months and the check for contact functionality must be done at least once a year.

    In case the acrilic is dirthy, thus reducing the readability of the dial, you can clean it with a soft cloth, water and soap.

    Finnised goods quality control tests.

    Instrument Calibration : carried out through thermostatic bath

    The procedure varies according to instruments scale.

    The calibration procedure, being the thermometer scale = 0/+120oC is made by using 4 different bath set at the following temperatures :

    Bath 1 = 10oC

    Bath 2 = 20oC

    Bath 3 = 40oC

    Bath 4 = 120oC

    Performance Test

    Reading Test

    The reading test of the thermometers shall be made in accordance with the following:

    1). Test conditions

    a) The ambient condition shall be an arbitrary condition within the standard temperature condition of grade 4 ( 20 ± 15oC ) and standard humidity condition of grade 3 ( 65% ± 20% ). Given JIS Z 8703.

    b) The temperature sensor shall be immersed into the liquid at least minimum to the limmit of lenght of bimetallic spiral.

    c) The reading test of the thermometer shall generally be carried out by comparing with the reference thermometer.

    d) The inside of the hot bath used for the test shall be stirred well to keep the temperature distribution within the range of ± 0.1oC

    2). Tests

    a). Take readings after the readings of the thermometer have stabilized at scale values near the minimum and maximum scale values at the measuring range and at arbitrary two scale values between the minimum and maximum scale value. At the same time, take the readings of the reference thermometer. The differences shall be defined as the errors.

    The test shall be carried out in both processing of increasing and decreasing temperature.

    b). The thermometer may be tested after the pointer is adjusted within the tolerance at a temperature by means of the reference thermometer.


    This tool is designed to control the temperature in the oil-filled Transformers.
    All parts are made from non-corrosive materials.
    In the Matter of the control function. This tool is equipped with an electric Contact (magnetic snap-contact type).

    Type: Straight type (type S)

    Casing: Stainless Steel (SUS 304)

    Washer / lock: Stainless Steel (SUS 304)

    Size: 75 mm Ø

    Temperature Range: 0 ~ 120 ° C, c / w Max


    Ambient temp: -30 / 70 ° C

    Contact: Contact Magnetic snap-action


    Insulation Test: 3 90 kV

    Protection degree: IP 54

    Class (Accuracy): ± 2% FS

    Sensor length: Standard 90 mm (length max. 300 mm)

    Sensor dimensions: Standard 8o x 90 mm

    Sensor material: Copper Plated with Ni

    Cover: Anti-UV Acrilic with 5%

    Linking: R ½, R ¾ (union types)

    Option: Thermo good