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High-Efficiency and Harmonic Mitigating Transformer Fitting

Starting on January 1st, 2000 a new law in Massachusetts went into effect requiring most transformers sold in the state to meet a NEMA efficiency standard.  Specifically, the NEMA Standard TP1-1996 affects transformers with secondary voltages of 600 volts or less with primary voltages of 34.5kV or less.  This is significant for several reasons.

The Negatives:

  1. It affects almost every transformer purchased by a non-utility.
  2. The cost of TP1 rated equipment is sometimes twice as much as a standard efficiency transformer.

  3. They are often not readily available.

  4. At this time there are a limited number of high-efficiency transformer manufacturers.

The Positives:

  1. They are less expensive to operate and save KWHs.
  2. They save energy and therefore reduce air pollution from generation.

  3. The local utility offers a rebate for the installation of TP1 rated transformers.

  4. It is possible to improve power quality and mitigate harmonics with these devices.

  5. Replacing older inefficient transformers improves reliability of service.

Most dry-type transformers have a Design Life of 20 years under normal operating conditions.  After that, the reliability of continued service is questionable.  Some of us feel it makes good sense to replace transformers that are operating close to or beyond their design life with high efficiency devices.  The result is a practical way of improving the electrical system's reliability while saving enough electrical cost to return the investment amount of the upgrade in less than three years, or with a potential rebate, less than 18 months.  It is possible to analyze the feasibility of such a project in a matter of a few hours to a few days depending on the complexity of the application by making a site analysis and utilizing currently available software.

Non-Harmonic Applications:

In non-tripling harmonic applications such as a typical 480-volt application, the utilization of an amorphous core transformer offers a greater savings opportunity.  These transformers provide an 80% reduction in core losses over typical steel core transformers.

Amorphous metal cores are far better at allowing the magnetizing and demagnetizing process to occur because of its molecular structure without a significant effect in impedance.

Some transformers available today with coils wound to meet the NEMA TP1 efficiency minimum with amorphous cores will have a half to a full percentage better efficiency over conventional core TP1 rated transformers.  When you consider that most transformers in service are operating 24 hours a day, 7 days a week, 52 weeks a year, one percent greater efficiency adds up to enough additional savings to easily justify the extra cost.

NRG, Inc. is experienced in providing the necessary savings and feasibility analysis and comprehensive retrofit design for small and large applications.  We have completed a retrofit of transformers at the John Hancock Building Complex in Boston, Massachusetts.  The John Hancock Tower is well know and stands out in the Boston skyline as the tallest building in New England.

Harmonic Environments:

In some cases, in an effort to calculate savings potential as accurately as possible, a harmonic analysis is required.  The reason for this is that transformer efficiency is negatively affected by the presence of third order harmonics.  By mitigation of these harmonics, transformer efficiency is further improved.  This would mostly affect transformers with a 120/208-volt secondary supplying non-linear loads.

There are transformers currently available that mitigate third order harmonics with core and coils that meet the NEMA TP1 Standard.  The other benefit of this type of transformer is the lack of a need to be K-Rated, saving significantly in the installation cost of a retrofit application.

The K-Rated transformer core and coils are larger than a non-K-Rated transformer of the same kVA rating.  This causes two problems that increase the cost in a retrofit application.

  1. The K-Rated transformers' footprint will be larger and therefore may not fit in the same space of the transformer it is replacing.  This often requires relocating the transformer to a different part of the electrical room, or may require moving it to a completely different location.
  2. The K-Rated transformer will typically require a higher primary side ampere capacity, which will likely exceed the existing hardware, and require an upgrade of the breaker protecting the transformer as well as the conduit and conductor.

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