Viat Instrument

General Description of Viat Instrument

Viat Instrument is a family-founded, owned and run organization that manufactures instruments and accessories for transformers for the last 50 years. Today, we have manufacturing facilities in two Indian cities and dozens of global distributors and warehouses with whom we can ship to any country in the world. Viat supplies over 500 transformer OEMs in 70 countries and is widely approved by utilities and OEMs globally.

The Viat founders started transformer instrument manufacturing with a company called ‘Atvus’ in 1970, making Buchholz relays in the living room of an apartment. The operations of Atvus were eventually merged into Viat Instruments, which was formed in 1995.

Today, Viat has over 50,000 square feet of covered area in our manufacturing facilities, which are in two separate cities providing redundancy and organizational depth. We offer the widest range of models and are among the largest global manufacturers for several of the product categories we supply.

We have been one of the fastest-growing suppliers of instruments of components in the world of transformers.

  • Instruments in operation in over 10,000,000 transformers in 70 countries.
  • Presence in every continent. The customer list includes over 500 transformer manufacturers including most leading brands worldwide.
  • 50 years of experience in the transformer industry
  • Export house status granted by the Govt. of India.
  • Constant R&D helps us improve products. Launching better models regularly help us improve transformer protection, as needed by the industry.
  • We customize products to meet individual requirements.
  • Product design and quality standards are continuously upgraded
  • A very responsive team for both sales and after-sales services.

Line of Business Viat Instrument

Magnetic Oil Level Gauge

Viat Instrument
Magnetic Oil Level Gauge

Continuous oil level monitoring specially developed for use in transformers and compatible with all kinds of oil used in them. High contrast dial with a bright coloured indicator to show oil levels at different temperatures as well as minimum and maximum oil levels. Switches are factory calibrated and various setting options including high, low and very low are possible.

  • Magnetic Oil Level Gauge (MOLG) With/Without Contacts, Radial Movement Float To EN -IEC Standard
    • Available in sizes 3.5” and 6” for seperate flange design. (405-7 series)
    • Sizes 100 and 140mm dial size in standard signle piece design. (408 series)
    • Switch option from 1 to 4 switches.
    • Switching at low / very low / high
    • Plug in connections / terminal box.
    • Free breathing housing with IP55 / sealed type housing to IP65.
    • SS316L model for off shore application.
    • C5M option.
  • Magnetic Oil Level Gauge (MOLG) For Conventional/Aircel Type Conservators With 4”, 6” And 10” Dials. Optional SCADA 4-20mA Output
    • Aluminum bodies with magnetic coupling for leakproof performance
    • Vertical or inclined-mounted options
    • Multiple switch, and dial marking configurations are available
    • Variants for Aircel type or conventional conservators available. Customized applications possible
    • Solid Nitrophyl® floats provide a reliable long-term level indication
    • Models with 4-20mA SCADA connection output available

Liquid Level Indicators for Distribution Transformers

Viat Instrument
Liquid Level Indicators for distribution transformers

Our liquid level indicators provide visual indication to the level of oil inside a tank. These instruments are compact, flange mounted and have a radial moving float. They have large dials with high contrast marking for ease of use.

  • Liquid Level Indicators for distribution Transformers
    • Oil Level Indicators, Round dial Type, with magnetic coupling
      • Sizes 80 and 100mm size
      • Customized dial
      • Adjustable float arm
      • Suitable for the conservator and side wall mounting in sealed-type transformers.
    • Oil Level Indicator, Square Flanged Type, magnetic coupling
      •  Straight adjustable float arm / fixed bent arm options.
      • Customized dial
      •  Combo model with thread and flange mounting.
      • Suitable for the conservator and side wall mounting in sealed-type transformers.
      • Ideal for single and three-phase pad-mounted transformers.
  • Liquid level Indicators for Hermetically Sealed Transformers
    • Direct Indication Model
      • Sizes 1” and 2” BSP (G threads to ISO 228) for direct indication model
      • Variable vertical float arm length
    • Magnetic Indication with double window
      • Magnetic model with G 1.5” threads
      • High contrast Low level Indicator
  • Protection relay with Indicator and/or Contacts
    • Vertical Protection Relay monitors the oil level in Hermetically Sealed Transformers eventually protecting the transformer. Falling level of oil / gas accumulation  operates a switch contact.
    • Features:
      • Standard G 1.5” thread mounting
      • Model with and without indicator
      • 1CO or 2NO contacts
      • Gas collection valve optional
  • Oil sight gauge & Prismatic Oil Level Indicator
    • Oil Sight Gauge
      • Available in BSP / NPT threads.
      • Option of black and red indicating float.
      • Brass / Aluminum body
      • Toughened glass used instead of plastic
    • Prismatic Oil Level Indicator
      • Direct viewing of oil level
      • Suitable for mounting on conservator / side wall of transformer
      • O ring sealing.
      • Ideal for CT/PT high pressure application.
      • Viewing window can be marked for oil level.

Pressure Relief Valves And Devices

Viat Instrument
Large Pressure relief devices with without contacts

These Pressure Relief Devices are recommended to be used on all sizes of transformers ranging from distribution transformers to large power transformers. For very large power transformers, it is usual to use multiple devices. There is no general formula or standard to link the size of the device to the size of the tank. This parameter is decided by the transformer designer or as agreed upon with the end user. As a general practice, one device can be used for every 38,000 litres (10,000 US gallons) of cooling liquid.

  • Large Pressure relief devices with/without contacts
    • Available in 150 mm port size.
    • Options of without and with multiple switches
    • With or without a directional shroud. Multiple kinds of shrouds
    •  Side switch or top switch for Europe or Americas
    • C5M option available in some models
    • Operating pressure from 4 psi to 20 psi.
    • Digital 4-20mA output also possible.
    • Stainless steel model  for submersible transformers available
    • High flow models with 150 mm pipe drain also available
  • Medium size Pressure relief devices with/without contacts
    • Available in 50 /80 mm  port size.
    • Options of without and with multiple switches
    • With or without directional shroud. Multiple kinds of shrouds.
    • C5M option
    • Operating pressure from 4 psi to 20 psi.
    • Digital 4-20mA output also possible.
  • Small Pressure relief valves for Distribution transformers
    • Standard BSP and NPT threads
    • Sizes ¼” to 2”
    • Special high flow model
    • With and without indicating model
    • Special models for FR3 / vegetable oil
    • Full stainless steel model for submersible transformers.
    • Operating pressure from 5 psi to 25 psi
    • SS316L model for off shore application
  • Krytox Lubricated PRV For Transformers Using FR3 Oil
    • Every valve individually lubricated with Krytox grease for easy operation and resealing in FR3 oil.
    • Indicating and non-indicating model.
    • Approved and meets all specifications of manufacturer of FR3  oil.
  • Pressure relief valves for traction transformers
    • This 50mm outlet Stainless Steel PRV is used in traction transformers and is available in a range of operating pressures. Please contact us for any other PRDs required for traction transformers as these may be available as customizations of other PRDs

Gas Actuated (Buchholz) relay

Viat Instrument
Buchholz relays with magnetic reed switch

The magnetic switches consist of two thin reed contact blades hermetically sealed inside a glass capsule n an atmosphere of dry inert gas. the switches are operated by a permanent magnet. the operating principle of the magnetic switches is very simple: when a magnet approaches the switch, the reeds close the circuit and when the magnets moves away from the switch, the contact gets open.

  • Buchholz relays with magnetic reed switch as per EN 50216-2: BS/BF/BR series
    • Sizes 25, 50 and 80mm with mounting to EN-IEC standards
    • Magnetic reed switch with ability to withstand shocks and vibration
    • Optional C5M models
    • Switching option of normally open NO / changeover CO / multiple 2-4 switches.
    •  Available in variable surge velocity for small, medium and large power transformers
    • All Aluminum alloy body with SS hardware.
    •  Valves for either side of the Buchholz relay are also available
  • Buchholz relays and Oil surge relays as per IS standards (With magnetic reed switch): GOR M series
    • Sizes 25, 50 and 80mm
    • Magnetic reed switch to withstand vibration
    • Time-tested bucket float for Indian conditions
    • Mounting as per Indian practices
    •  Plug and socket variant available for PGCIL 420/765 KV class (approved)
    • Each relay tested for all parameters including gas volume, oil surge and loss of oil.
  • Conservator Protection (Gas) Relay / Aircel leakage detector
    • A Gas collection device (GCD) is an accesory of Bucholz relays that is often used in large power transformers. It is connected to the Buchholz relay gas collection petcock, and is used to collect samples of gas and oil from the Bucholz relay easily from ground level. The color of collected gas is also very clearly visible in the GCD.
    • SS pipes to connect the GCD to the Bucholz relays are also available.

Radiator Valves

Viat Instrument
Radiator valves, Bolt-On, Cast Iron

The valve mainly consists of machined flange, flap, spindle and locking cap. The flap is machined to fit the bore. The spindle is riveted to the flap and can be rotated in either direction to operate the valve. The cap on top of spindle locks the valve in the open or closed position, which is indicated on the exposed plate marked open/shut.

Rapid Pressure Rise Relay

Rapid pressure rise relays are designed to respond to rates of pressure change above predetermined safe limits set by the transformer manufacturer.

Viat Instrument
Rapid Pressure Rise Relay

The purpose of this device is to detect a fault in a transformer quickly, while the pressure is still increasing and before the destructive effects of overpressure triggers the pressure relief device. The RPRR switches a set of contacts to indicate that it has detected a fault.

The RPRR is designed not to respond to normal pressure variations caused by temperature variation, mechanical shock and vibration or pump surges.

Flow Indicator


  •  Vertical and horizontal mounting.
  • Range of threads including BSP, NPT and NPS
  •  80 / 100 mm dial size
  • Full stainless-steel body and stem
  • All models with resettable maximum pointer.

Oil Level Indicator & Thermometer Combo

  • Integration of oil level indicator & thermometer in one Instrument
  • Rugged design for prolonged service.
  • Available for vertical mounting on top cover / horizontal mounting on side wall
  • 100% mechanical mechanism.
  • Precise operation, high consistency.
  • Nitrophyl float suitable for transformer oil.

Pressure Gauges and Switches

Terminal Boxes

  • CT Terminal Box and Core grounding terminal box
  •  CT terminal box available upto 12 terminals
  •  Core Grounding terminal box available upto 3 terminals
  • Robust Aluminium construction with leak proof terminals
  • Any terminal can be replaced by user
  • Fool proof mechanism with rotation protection
  • Individually tested for leak, IR and HV.
  • IP67 enclosure protection

De-Energised Switch (Off Load Tap Changer)

Load Break Switch


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Rudy Wiratama

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