Repairs of Old Transformers

Repairing aged transformers is an important issue due to the fact that most of such units still operated are either close to or past their expected service life end. The high cost of new transformers makes a total replacement of all old transformers impractical; therefore, extending the lifetime of aging transformers is important from the economic point of view.

Transformer can be repaired with or without winding disassembly.

Windings are removed only in special repair facilities or at transformer manufacturer. Such repairs are problematic because the its cost is comparable to the cost of a new transformer. Removing the windings is only viable for new transformers after failures to restore them.

Repairing a transformer without removing its windings is a simpler process and can generally be performed on in the facility’s repair shop. In the worst case scenario, a transformer even can be repaired on site. Solid insulation can be repaired in one of three ways:

  1. without dehydration of the core.
  2. thermal diffusion dehydration of the core.
  3. washing and dehydration by spraying with oil at maximum allowable vacuum.

There are several stages, if the transformer must be repaired without removing the windings:

  1. Diagnosing the transformer. The diagnostics allow to determine the condition of all components and identify specific repair objectives and the scope of work.
  2. Developing a repair program and a work schedule. Procurement of components and consumables.
  3. Delivery and installation of the equipment required for oil and sorbent processing, as well as transformer core drying.
  4. Pre-repair trials and transformer oil analysis.
  5. Rigging, which must include core extraction.
  6. Core inspection, checking the grounding, measuring insulation impedance etc.
  7. Repairing identified core defects and other originally planned works.
  8. Reconstruction of transformer parts where needed.
  9. Preparation of transformer oil and sorbents. This item requires more attention: it takes a significant amount of time. If necessary, the oil is dried, purified, degassed and regenerated with subsequent introduction of an inhibitor. GlobeCore transformer oil processing units are designed to perform all of the above. GlobeCore equipment is mobile and can be easily transported from one transformer to another. The GobeCore process requires little power and doesn’t involve harmful emissions into the environment.
  1. Drying of core insulation is the final stage of repairs. It is recommended to apply the vacuum oil spraying method for old transformers.