Transformer contingency planning

05/01/2009 - Volume V - Issue II

Yogi Berra once said, “It's tough to make predictions, especially about the future.” Budget planning for T&D equipment owners also involves the challenging task of predicting the future. Transformer replacement programs are driven by prioritizing transformers according to their condition and their contribution to network reliability. Transformers in the most critical locations that are in the worst condition are the first to get replaced.

 

Ideally, a transformer is replaced at the moment before it reaches its end-of-life. In reality, however, no matter how scientific a replacement methodology may be, forced outages still occur because some transformers will fail before their predicted end-of-life. Once a failure occurs, damage control becomes the top priority. How quickly power can be re-routed or the failed transformer can be replaced will determine the extent of lost revenues. For example, if the failed transformer is a power plant generator step-up transformer, lost revenues can be in excess of one million USD per day.

 

Having a detailed replacement plan “on-the-shelf” can save millions in downtime costs. Yet, a recent survey of over 50 power plants and T&D utilities revealed that nearly one-third have no formal, written contingency plans in place to address an unplanned outage on any of their critical transformers. Even when a spare transformer is available on-site, days may be wasted developing hauling plans, comparing critical dimensions of the spare transformer, performing civil analysis, etc. For a nominal investment, these activities can be planned in advance saving valuable downtime when the transformer needs to be replaced in an emergency situation.

 

In addition to reducing downtime, a TCP study provides a predictable budget that can be shared with your insurer. Suppliers can be identified in advance to ensure a rapid response should a failure occur. The final report includes a detailed scope, project schedule and key contact information.

 

An assessment of site condition includes:

  • Assessing site access for equipment and materials

  • Evaluating location/siting of spare transformer

  • Developing a rigging and haulage plan for change-out

  • Reviewing critical civil and structural site details and constraints

     

    Evaluating transformer layouts (spare unit vs. installed unit) for critical dimensions and structural limitations for the following equipment:

  • Footings for cooler/radiators

  • Transformer main tank vs. pad layout

  • Jacking pad locations

  • ISO-phase bus layout and connections

  • High-voltage bus connections

  • Control cabinet location and layout

  • Other external connections and interfaces

     

    Reviewing availability of current drawings and other technical information, including:

  • Civil and structural

  • Deluge design.

  • Control and protection
  • Wiring diagrams (transformer interfaces)

  • Transformer design drawings

  • Operation and maintenance manuals

  • Transformer bill-of-material.

The readiness review of the spare transformer includes:

 

    Reviewing periodic maintenance records:

  • Oil Sample Data

  • Electrical test records and frequencies

  • Other recommended testing for benchmarking (i.e. SFRA)

  • Determining key sub-component availability and storage (bushings, etc.)

  • Assessing blanking plates and covers used during rigging and transportation

  • Evaluating availability of spare parts and consumables for installation (seal/gasket kits, etc.)

  • Recommending actions pre-outage.

The final report includes:

  • A detailed scope of work to replace transformer(s) including anticipated replacement schedule (gant chart format)

  • Identification of key project contacts for outsourcing (guaranteed response time, if requested)

  • An ancillary bill-of-material (connectors, supports, etc).