SGB-SMIT CALIDUS offers a range of transformer accessories which are generally used for indication, recording and protection purposes.

The range of transformer accessories includes breathers, Buchholz relays, oil temperature indicators, winding temperature indicators, explosion vents, oil level gauges and magnetic LOC’s.

A Buchholz Relay is a protection device for monitoring the gas and oil movements in oil immersed transformers. It is designed to detect the faults and minimise the propagation of any damage which might occur within oil circuit, induction coils; etc.

The examples of the faults which could cause gas accumulation or strong oil flows in the oil circuit are as follows:

  • short-circuited core laminations
  • broken-down core insulation
  • overheating of windings
  • bad contacts
  • short-circuit between phases
  • earth faults
  • puncture of bushing insulators inside tank
  • falling of oil level due to leaks
  • ingress of air as a result of defective oil circulation system

Form-A Oil Level Indicators are used in distribution transformers of less than 5000 kVA for the purpose of monitoring transformer oil levels. Indicator part has no contact with the oil.

Oil level indicators do not allow oil leakage at temperatures of 110°C, 0,5 bar effective pressure and vacuum.  The technical specification can be viewed below:

  • Case: Injected Aluminum, electrostatic powder painted (RAL 7033 or RAL 7001)
  • Indicator dial: Aluminum sheet, coated with black paint and yellow serigraphy
  • Pointer: Yellow painted brass
  • Indicator glass: Polycarbonate (UV resistant)
  • Joint Gasket: Nitrile Rubber, hardness: 70 Shore A
  • Float: Oil resistant, closed cellular type special plastic foam

Oil Temperature Indicators or OTI’s are used for temperature indication with integrated control and alarm functions. These indicators are designed for use where the point of measurement is not easily viewed by personnel requiring separate or remote indication.

These types of thermometer are designed for indication of oil temperature in both transformers with expansion conservators or hermetically sealed type transformers.

It is fitted with two electric switches and a maximum indicating pointer. The thermometer operates efficiently under very hot and very cold weather conditions.

Pressure Safety Valves are used to prevent the rapid build up of pressure within the transformer tank that might cause an explosion hazard. They are designed to operate and discharge any pressure greater than their set value to the atmosphere. 

Gas-actuated protective relays are designed to detect faults as well as to minimise the propagation of any damage, which might occur within oil-filled transformers.

These relays are therefore particularly effective in case of:

  • short-circuited core laminations
  • broken-down core bolt insulation
  • overheating of some part of the windings
  • bad contacts
  • short circuits between phases and turns
  • earth faults
  • puncture of bushing insulators inside tank

Furthermore these relays can prevent the development of conditions leading to faults in the transformer, such as the falling of the oil level due to leaks, or the penetration of air as a result of defects in the oil circulating system. The adoption of other forms of protection does not therefore exclude the use of a gas-actuated Buchholz relay, as this device is the only means of detecting incipient faults, which if unnoticed, can cause heavy failures.

Various sizes of transformer bushings are available from LV bushings 250A DIN 42530 up to 3150A DIN 42530 to HV bushings up to 36kV. Outdoor or indoor bushings should be specified.


The caster wheels are supplied either zinc plated, galvanised or wet or electrostatic power painted. The wheel housing is manufactured from mild steel and the wheels from cast iron.

The Viat range of transformer accessories include:

  • Pressure Relief Valves – these range from T50, 80 and 125 up to 150, with or without switch
  • Bimetal Thermometers and Pressure Vacuum Gauges – with or without contacts
  • Gas Actuated Buchholz Relays – 25, 50 and 80mm
  • Radiator Throttle Valves – 80mm to 125mm
  • Liquid Level Gauges and Indicators – 100mm, 140mm, 150mm and 250mm.

SGB-SMIT CALIDUS’s range of breathers have been designed to better suit customer specifications.  The sole function of Silica Gel Breathers is to dehydrate (remove moisture) the air and to remove dust particles of the air breathed in by the transformer.

Silica Gel (Air dehydrating) breathers are transparent hollow cylinder tubes which contain chemically pure silicium salt (Silica Gel) with cobalt indicator. This grade of Silica Gel is called as “indicating grade” of Silica Gel.

The range includes:

  • Increase in ranges supplied
  • The walls of the silica gel containers are 100% UV protected shatterproof polycarbonate. They are built up from cylinders of polycarbonate with specially designed tapered male/female ends that give a seal when under pressure. The joints are permanently fused using a special solvent.
  • The SA1 100 and SA200 breathers are built up using standard size container cylinders of 100 and 200mm diameters. Therefore the breathers can be built up to any reasonable length using the appropriate number of cylinders, meeting the transformer oil capacity.
  • The polycarbonate oil bowl system is more than twice the length of the original, eliminating the possibility of silica gel being contaminated by oil.The SA 200 range of breathers are also made up in multiple units, both in series and parallel.

SGB-SMIT CALIDUS provides transformer breathers filled with Envirogel, which is a self-indicating silica gel desiccant. This desiccant is orange/yellow in colour when active, but turns green when saturated.

Maintenance of the breather

  • Inspections should be carried out weekly where practical, otherwise monthly as a minimum.
  • The oil baths should be checked for stains or cracks and where applicable, replaced or cleaned and filled with clean oil.
  • Where silica gel has turned pink the percentage that has turned pink needs to be replaced.
  • The container should be checked for cracks, warping and external damage.
  • Viewing surface must be clean
  • Check gaskets and sealing washers for damage and ageing, replace where necessary
  • Breathers must be airtight.

It is strongly emphasised that correct and timeous inspections and servicing of transformer breathers prevents oil contamination and leads to cost savings due to less frequent maintenance of transformer oil (or even failure).