5 MVA Transformer Urgent Inspection and Repair

Ampcontrol provided a review of oil analysis reports, onsite inspection and urgent workshop repair, of a production critical 5MVA transformer to get it back into service as soon as possible.


The customer, a mine in Southern Queensland has been supplying coal to local power stations in the area for over thirty years. The mine approached Ampcontrol due to concerns about the condition of a production critical 5MVA transformer on their plant.


Our review of their latest oil analysis results indicated the occurrence of a serious T3 Thermal Fault – high temperature heating (>700ºC). The presence of acetylene & elevated levels of heating gases in the sample pointed to the severity of the fault and possible involvement of electrical contacts. Transformer specialists from Ampcontrol in Mackay went onsite and conducted an internal inspection. Oil was drained to the top of the core and the inspection lid removed. The team identified what could have contributed to the elevated gassing in the DGA results. The paper on 1-off LV lead connection had significantly carbonised, and as such we recommended immediate action to further investigate the problem. The Transformer was immediately transported to Ampcontrol’s transformer facility in Newcastle, NSW to carry out further inspections and the necessary repairs.The internal inspection identified a partly unsecured and dislodged coil clamp block under the top core frame. A small amount of arcing discharge between some of the core steel sheets in the outermost step of the top yoke, located in the A-phase LV side of the transformer was also found. Four hot joints in the LV leads were found, and these were the most likely cause of high-temperature fault gasses in the oil. The hot joint observed on C-phase was quite severe as the heat had travelled down close to where the LV leads exit the winding. We believed the hot joints were caused by inadequate preparation when crimping the copper lug to the aluminium winding conductor. Ampcontrol provided both onsite and workshop specialist transformer services at short notice.Our detailed workshop repair program included replacement of damaged and incompatible materials that contributed to the heating problem, and a partial rebuild of the clamping structure. The core and coil assembly were processed in a vacuum oven, followed by vacuum filling and hot oil circulation to further ‘filter’ the liquid insulation of water, gasses and particles/ debris. Electrical testing was conducted in our Newcastle workshop before being transported back to site.


  • Reviewed oil analysis results and provided remote technical support to help manage a serious problem with a production critical transformer.
  • Provided onsite emergency support at short notice including an internal inspection that identified possible causes of the problem.
  • Conducted a workshop internal inspection and detanking of core at short notice to further investigate the causes of the problem.
  • Undertook a repair program that put the transformer back into safe operation quickly.

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Tuas Water Reclamation Plant Temporary Electrics

Ampcontrol’s Singapore team recently carried out installation, testing and commissioning of temporary electrics for Singapore’s Tuas Water Reclamation Plant.

Contracted to deliver services for the Public Utilities Board on behalf of McConnell Dowell South-East Asia, the Singapore team supplied a range of equipment and services to support the project.

This work included installation, testing and commissioning of all temporary electrics including substations, switchrooms, transformers and high and low voltage cables within the Tuas Water Reclamation Plant.

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Ampcontrol Manufactures 50MVA Power Transformer

The Project

To take their current production from 6.4Mta to 7.5Mta, a central New South Wales mine engaged Ampcontrol to design, manufacture and install high voltage infrastructure. The 132/11kV project included a 40/50MVA transformer, c/w 11kV substation, 3000A 11kV switchboard and associated protection system.

As part of the project Ampcontrol designed, manufactured and tested a 40/50MVA 132/11kV transformer, with a final fully assembled weight of 85 Tonnes.

The transformer was fully tested in house in Ampcontrol’s transformer facility, before being filled with oil above the core and coil assembly for transport, to the mine, where site erection work was undertaken by Ampcontrol’s High Voltage Service team.

The transformer will be energised at a later date during major site shutdown works.


  • Rating: 40/50MVA
  • Voltage ratio: 132/11kV
  • Vector group: Dyn11
  • Cooling: ONAN/ONAF
  • Tap changer: on load tap changer – Vacuum type on load tap changer supplied by Mischinenfabrik Reinhausen GmbJ (MR), Regensburg, Germany.
  • Oil: filled with inhibited transformer oil as per IEC60296
  • Transformer tested as per AS/NZS 600076

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Replacement Transformers On The Road To Western Australia

During the latter part of 2018, Ampcontrol was approached to supply a range of drop-in replacement transformers as part of a major upgrade of an iron ore mine in Western Australia.

This mine was looking to source reliable and robust equipment that was proven under onerous site conditions, including various levels of harmonics, ensuring continuity of supply and maximum product lifespan. Ampcontrol’s proven transformer designs and manufacturing credentials made us the ideal supplier.

In 2019 Ampcontrol delivered 20 transformers to the project ranging from 1000kVA 33kV to 10,000kVA 33kV all designed to suit existing mounting positions and cable connections within 5mm tolerances.

Production has been staggered to minimise site shutdown requirements and will be ongoing into 2020 when another 31 transformers will be manufactured, as well as routine and type testing to AS/NZS 60076, in our Tomago NSW transformer facility.