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.

Background

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.

Problem

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.

Achievements

  • 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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Join us in June for our ‘Safety In Mining’ Webinar Series

As an industry leader offering integrated electrical protection, integrated power distribution systems, monitoring and control solutions and communication systems for coal and hard rock mining, we’ve launched the Ampcontrol Group ‘Safety in Mining’ webinar series. Running throughout June, we are offering a range of free, technical presentations designed for industry.

Kicking off on June 9, we’ll be welcoming ResTech Principal Engineer, Dr Peter Stepien, who will share insights from his ACARP research project around the ‘Control of Touch Potential Transients During Switching’. During a number of investigations into electric shock incidences in the past, machine frames measured touch potential transients when switchgear closed or opened. There were no faults present in the equipment or the earth fault limited supply, yet touch potentials occurred. This webinar will step participants through Peter’s current research that aims to understand the method by which these touch potentials occur and determine a method to eliminate them to improve mine safety.

On June 16, Philip Reilly, Ampcontrol’s Oil Service Manager, will deliver his webinar titled ‘Oil Analysis: Testing OLTC & Managing Corrosive Sulphur in Transformers’. Managing a large fleet of ageing transformers is a technical challenge faced by many Australian mines and reliability surveys show that the On Load Tap Changer (OLTC) can account for up to 30% of all transformer failures. This webinar will address failure modes & available condition monitoring techniques and will also outline the role of oil analysis.  The webinar will also provide insights into the mechanism of copper sulphide formation in transformers, failure modes, details of service experiences, and what assessment and mitigation techniques are available. 

Finally, Ampcontrol Group Engineering Manager, Dr Ian Webster, will deliver his webinar titled ‘Arc Faults (and Flashes) and the Hierarchy of Controls’ on June 23. This webinar will look at the application of the hierarchy of controls to the hazards associated with arcing faults in high powered electrical equipment in general, and in confined spaces such as mines and tunnels. 

We’re committed to connecting industry contacts across Australia with practical insights into real world issues being faced onsite. Attendance is free, secure your space today at one or all of the webinars in the series.

Remote Transformer Health Check Enables Fast Repair at Sugar Mill

Our transformer maintenance services team were contacted by an Asset Manager at a large Queensland sugarcane refinery after they reviewed their most recent transformer insulating oil analysis report. Results indicated occurrence of a serious T3 Thermal Fault – high temperature heating (> 700°C). Typically, these faults include large circulating currents in the tank and core, loose connections in the HV winding circuit, and misalignment of contacts in de-energised tap changers.

The request was to further review the test data provided by the Asset Manager, to offer an independent engineering opinion and to help pinpoint the cause of the problem. Recommendations for further investigation and management of the asset were also sought.

Resulting recommendations included regular DGA testing to monitor the fault and electrical testing to investigate the cause of the DGA gassing problem. Further recommendations also included an internal inspection / videoscope to identify burnt / misaligned contacts in the DETC (off load tap changer). Acetylene generation in the transformer pointed to either the severity of the fault or the involvement of electrical contacts.

On receipt of Ampcontrol’s recommendations, the Asset Manager conducted an internal investigation on the transformer. The source of the fault was identified as a contact in the DETC.

Read the full case study here.

Now offering remote transformer condition auditing and diagnostic support, our team can review third party oil analysis reports and provide technical expertise to diagnose issues while providing repair plans to ensure continuity of services when access to site can be challenging. Contact us for more information on how to access these services at your site.

Hire Stock and Fast Action Ensures Minimal Downtime

During routine high voltage maintenance at a surface mine in western NSW, conducted by Ampcontrol’s High Voltage Service team, a transformer failed testing and required inspection and overhaul. To ensure the mine experienced minimal downtime, the on-site team placed a call to our Tomago base to see if a suitable hire replacement was available.

The hire team received the call at 3:30pm and a suitable hire transformer arrived at the mine site at 8am the following day. Prior to leaving for site the following was undertaken:

  • An oil sample was taken from the transformer and delivered to Ampcontrol member company Verico to conduct fast turnaround oil testing
  • A sketch of the transformer was sent to the customer and a number of small alterations were undertaken
  • Delivery trucks and cranes were ordered

The replacement hire transformer was loaded to the truck at 6:30pm that same day for transport and an overnight stay in Mudgee. The following day a new gland plate was made in Ampcontrol’s fabrication workshop and driven to site by an Ampcontrol High Voltage Service team member.

Onsite, the existing failed transformer was uninstalled and loaded on the truck; while the hire transformer was installed, tested and commissioned. The failed transformer was delivered to Ampcontrol’s transformer workshop in Tomago NSW for inspection and overhaul.

Operating within an extended 16 hour shift so as to minimise customer downtime, the on-site HV service team conducted significant planning to ensure site alterations were kept to a minimum. Undertaking this planning ensured the failed transformer could be easily re-installed following the conclusion of repair works.

Read the full case study here.

2020 Transformer Maintenance Webinar Series

As a leading provider of transformer lifecycle support services, we’ve launched the Ampcontrol Transformer Maintenance Series and our next webinar is scheduled on 16 June. Managing a large fleet of ageing transformers is a technical challenge faced by many Asset Managers onsite. Reliability surveys show that the On Load Tap Changer (OLTC) can account for up to 30% of all transformer failures. To manage the overall reliability of a transformer, a condition monitoring program should also include condition assessment of the OLTC

Delivered by our Oil Services Manager Philip Reilly and titled ‘Oil Analysis: Testing OLTC & Managing Corrosive Sulphur in Transformers‘ this webinar will address failure modes and available condition monitoring techniques and will also outline the role of oil analysis.

Backed by his extensive technical experience in transformer oil testing, oil analysis’ condition assessment and oil filtration, Philip will provide insights into the mechanism of copper sulphide formation in transformers, failure modes, details of service experiences, and what assessment and mitigation techniques are available.

We’re committed to connecting industry contacts across Australia with practical insights into the best way to manage their critical HV assets – register to attend this free event today.

If you missed the first two webinars in our series covering the Ageing, Assessment and Management of HV Oil Filled Transformers and Power Transformers: Oil Diagnostics, Failures and Life Extension, you can view them at any time on our YouTube Channel.