Impact of U.S. DOE 2016 Regulation on Dry-type Transformers
Brian Little, North America Marketing Manager, DuPont Energy Solutions
The U.S. Department of Energy (DOE) has revised the efficiency standards for distribution transformers, effective 2016, to reduce energy losses in the grid. The DOE 2016 regulation will require original equipment manufacturers (OEMs) to change their transformer designs to provide more energy efficient transformers than had been previously used widely in industry.
Energy Efficiency Regulation Timeline
Prior to 2007, energy efficiency was not regulated for distribution transformers. As a result, the cost of manufacturing was a higher priority than energy efficiency. When applicable, OEMs generally calculated efficiency at 100% load.
Things began to change with the enactment of the DOE 2007 regulation, which defined efficiency requirements for low-voltage, general-purpose (LVGP) transformers at 35% load. This was followed by the DOE 2010 regulation, which defined efficiency requirements for medium-voltage (MV) transformers at 50% load. This enables the evaluation to be done at the typical loading for these classes of transformers which provides the optimum energy efficiency based on actual operations.
The energy efficiency definitions established by DOE in the 2007 and 2010 regulations made core losses more important. In response, OEMs modified their transformer designs to include larger cores and/or improved core steel grade to reduce losses. The result of these design changes included transformers that were proportionally larger and generally more expensive to manufacture.
The National Electrical Manufacturers Association (NEMA) developed guidelines for increased efficiency units, generally referred to as “NEMA Premium 30.”
New DOE 2016 Regulation
The DOE 2016 regulation redefines efficiency requirements for 3-phase LVGP and MV transformers. Requirements for single-phase LVGP and MV transformers remain unchanged from current DOE regulations.
Under the new DOE 2016 regulation, the requirements for 3-phase LVGP transformers are set to be approximately equivalent to “NEMA Premium 30” efficiencies. For 3-phase MV units, there is a ranging scale of loss reductions required—from 2% to 24% change compared to current DOE regulations.
DOE 2016 Regulation Changes for LVGP Dry-type Transformers
DOE 2016 Regulation Changes for MV Dry-type Transformers
Core Loss Reduction Is Key to Energy Efficiency
Because efficiencies are calculated at less than 100% load, the load loss component is less important than the core loss, which is independent of load. Therefore, OEMs will focus on core losses to improve efficiencies.
To reduce the core losses, OEMS will likely design transformers with lower volts/turn. At a given voltage, designers will likely increase the number of turns to reduce the core losses. However, the increased number of turns leads to increased impedance with fixed coil heights.
Designers may choose to increase the coil height in order to meet impedance requirements as the number of turns have increased. However, it is important to remember that as the coil height increases, the core height will increase proportionally.
Exploring Commercial Impact of DOE 2016 Regulation
To explore the commercial impact of the DOE 2016 regulation on the North America market, members of the DuPont™ Nomex® Energy Solutions team worked closely with industry-leading OEMs.
The OEMs shared bill of material (BOM) summaries for typical designs under the current DOE regulations, as well as those in compliance with the DOE 2016 regulation.
The DuPont team analyzed the results, summarized the trends and discussed the findings with the OEMs. In some cases, OEMs revised their designs and the analysis was repeated.
For this study, the following transformer designs were analyzed:
- LVGP—300 kVA, 480 V
- MV—1500 kVA, 15 kV, 95 kV BIL
- MV—1500 kVA, 15 kV, 95 kV BIL (enamel wire)
- MV—2000 kVA, 5 kV, 30 kV BIL
- MV—2000 kVA, 15 kV, 95 kV BIL (enamel wire)
Results from LVGP Analysis
In this study, the 300 kVA, 480 V transformer design that meets the DOE 2016 regulation cost 60% more than the design that meets the current DOE regulations. This higher cost is primarily due to an 86% increase in conductor costs (increased turns) and a 58% increase in core costs (size increase).
The efficiency increased from 98.60% to 99.02%.
Results from MV Analysis
For the 1500 kVA, 15 kV, 95 kV BIL transformer, the total cost for the new design that meets the DOE 2016 regulation increased by 33% compared to the cost of the design that meets the current DOE regulations. This increase was mostly due to a 32% increase in conductor costs (increased turns) and a 40% increase in core costs (size increase).
The efficiency increased from 99.1% to 99.30%.
Looking at the results for the 1500 kVA, 15 kV, 95 BIL transformer with enamel wire, the trends are similar. Total cost increased 16%, primarily due to a 17% increase in conductor costs (increased turns) and a 28% increase in core costs. In this design, the increased core costs were due to height increase and core steel spec change from M6 to high-B steel.
The efficiency increased from 99.12% to 99.3%.
For the 2000 kVA, 5 kV, 20 kV BIL transformer, the total cost for the new design that meets the DOE 2016 regulation increased by 42% compared to the cost of the design that meets the current DOE regulations. The increased cost is due primarily to a 52% increase in conductor costs (increased turns) and a 48% increase in core costs (size increase).
The efficiency increased from 99.27% to 99.43%.
The results for the 2000 kVA, 15 kV, 95 kV BIL with enamel wire showed a similar trend. The total cost increased by 24%, primarily due to a 24% increase in conductor cost (increased turns) and a 26% increase in core costs. In this design, the increased core costs were due to height increase and core steel spec change from M6 to high-B steel.
The efficiency increased from 99.18% to 99.36%.
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Six Key Trends
Based on discussions with industry-leading OEMs and the results of this study, six key trends associated with achieving the increased energy efficiency levels of the new DOE 2016 regulation were identified:
- Dry-type transformers that are compliant with the DOE 2016 regulation will be larger and more expensive to manufacture compared to current units.
- As designers focus on core loss reduction, some will move to higher grades of steel. A move from M6 or M4 to high-B steel was observed in some cases.
- Better core construction—mitered cores and wound cores, for example—will help reduce the losses of the core by approximately 25%, although this will increase costs.
- Increased core cross section is another way to reduce the flux density, therefore lowering losses, while maintaining the same volts/turn.
- Conductor usage is likely to increase as designers look to reduce the volts/turn parameter.
- Coil heights may increase as a way to manage volts/turn with impedance requirements. This would result in taller cores for the units as well.
Payback Period for Transformer Customers
Based on the efficiency increases delivered by the new designs versus the expected electricity prices (per the U.S. Energy Information Association), combined with the projected higher cost of transformers that are compliant with the DOE 2016 regulation, the payback period for transformer customers is expected to be more than 20 years.
Transformer customers should specify DuPont™ Nomex® brand insulation, which has been proven to maintain useful properties for at least 10 years of continuous exposure at (220°C). Many dry type transformers made with Nomex® paper have been in use for up to 40 years. This long performance life enables a higher probability of return of investment for the increased energy efficiency created with transformers that meet this regulation.