Transformer Repair

3L2R Inc. can repair oil filled transformers that have failed, are ailing or have come to end of life. In most cases, the primary failed/aged components are the windings and insulation. The internal laminated steel core, the steel tank housing, often the oil and most of the components and accessories can be re-used. Should these components be damaged or require upgrading, we can replace them with modern OEM grade materials. Our focus is on transformers up to 30 MVA (30000 kVA) with voltage classes up to 138 kV. We have the in-house transformer design and coil winding capability to repair any manufacturers equipment.

Repair

Transformers are considered candidates for repair if they have “failed”, which usually means they are no longer functioning in an electrical system due to a fault internal to the transformer tank or bushings that has been detected by a protection trip or other more dramatic indication. Providing that the damage is not too severe, repairing damaged transformers is often a viable alternative to replacing with new equipment. Sometimes a transformer is still in service but is exhibiting concerning signs such as “elevated dissolved gas in oil analysis” (DGA) results. There is only so much that can be done in a field setting and moving the transformer off site to a repair facility offers the opportunity to “un-tank” the core and coil assembly to locate the root cause of the gassing, and then effect a repair.

Transformers that are nearing end of life may also be considered for repair. In most cases, the primary component that has aged is the insulation around the windings. As it is not practical to remove the winding insulation and reuse the winding conductor, rewinding the coils and re-using the core and other components is an option to rejuvenate the transformer and return the equipment as a trusted member of your energy supply fleet. In the above scenarios, should the investigation after un-tanking reveal a design or manufacturing related root cause problem, we have the in-house design engineering expertise and experience to identify and rectify the issue. The advantages of repair over buy new are as follows:

  • Repairing a transformer is often less expensive than buying new
  • By replacing only what is damaged and reusing components
  • Repairing may provide a faster turnaround time
  • Proximity to a repair shop and focused resources can respond in a timely manner to a customer’s needs
  • The need for exact mechanical interchangeability for the transformer foot print, location of bushings, and orientation of accessories sometimes makes repair the best choice

Refurbish

Another area of service to consider is refurbishment. This would include minor repairs including re-gasketing to stop oil leaks, replacing/repacking valves, replacing damaged bushings and other components including radiators, upgrading components to modern electronic/remote monitoring options, and re-painting, to name a few. Much of this work can be done in the field, but utilizing a repair shop allows the expertise of a group of people to participate in a controlled environment.

Redesign and reconfigure

We can change an existing design to overcome an inherent problem or squeeze out some more MVA. We can change the voltage and/or winding configuration to convert an outdated transformer into a usable asset again. We have the in-house engineering and manufacturing expertise and experience to make the required modifications.

Reuse and/or recycle

As discussed above, reusing components is central to a cost-effective repair process. Transformers can last for 30 + years and many of its components can certainly outlast the primary internal insulation. We practically believe in the “if it isn’t broke, don’t fix it” philosophy but will be guided by the customer’s needs and wants. Should components no longer be viable for re-use, we are committed to responsible disposal and have partnered with companies that specialize in this field. We have a stock of used transformer components for sale including bushings, bushing connectors, pressure relief devices (PRD), PRD shrouds, temperature gauges, sudden pressure relays and pressure/vacuum gauges. Please contact us for any of your transformer related needs.

Transformer condition assessment

In today’s power generation, transmission, distribution and industrial electricity systems, there is a growing need to determine the real-world condition of the critical apparatus. Some reasons for this growing emphasis on transformer condition assessment are the general aging of the equipment, increased loading and decreasing resources to monitor and maintain the assets. There have been a number of emerging technologies targeting transformers that are at varying stages of effectiveness. The cost and relative experience of these evaluation processes are factors when considering application, whether for a single transformer or an entire fleet. There are well-established, mature testing/evaluation methods available that when evaluated together, can provide an effective determination of transformer health. Our evaluation parameters include:

  • Dissolved gas in oil analysis (DGA)
  • Chronological age
  • Standard oil chemical analysis
  • Loading factors
  • Power factor/dissipation factor
  • Visual inspection, leaking, damage
  • Furan analysis
  • Cooling type, radiators, fans, pumps

There are of course other factors that can be used based on an organization’s monitoring standards. The more data the better, providing you have a process to organize and evaluate this data.

Establishing thresholds – what is normal?

We wouldn’t expect a transmission transformer that has been at half load for most of its life to have the same characteristics as a generator transformer operating at full load, or an industrial transformer application operating well above full load capability. In general, you can establish a set of criteria for these broad groups of transformer applications and then be prepared to adjust the norms for families of transformers within these groups. There are a number of Industry established thresholds. For DGA, IEEE has defined some levels. Oil testing labs will also offer some general guidelines. Threshold values are based on the population of transformers evaluated and the risk level an organization chooses to accept.

It is important to adjust threshold values for age where applicable, and for voltage class, as we expect more stringent guidelines as the voltage level of the transformer increases. Don’t ignore your own history. As an example, the “rule of thumb” for the power/dissipation norm of 0.5 % does not apply to many older transformers. The best analytical comparisons come from transformers of similar size and voltage class, exposed to similar loading and stress conditions. The keys that effect transformer condition assessment are:

  • Having sufficient data
  • Organizing the data in a way that it can be evaluated effectively
  • Actually evaluating the data, and comparing results against valid threshold levels
  • Having a well established set of “next step” scenarios
  • Getting expert advice for unusual situations
  • Acting on the results of your analysis

In the end, there is no magic box or formula that will predict end of equipment life, but with a structured process, some practical guidelines and common sense, many uncontrolled outages can be avoided and your transformer assets can be effectively managed. Turning data into usable information brings real value to your organization. Please contact 3L2R Inc. for any of your transformer related needs.

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