8-E-i

APPENDIX 8-E. LIFE-CYCLE COST AND PAYPACK PERIOD RESULTS FOR 

SYMMETRIC CORE TRANSFORMERS

TABLE OF CONTENTS

8-E.1 Symmetric Core Transformers ............................................................................... 8-E-1

8-E.1.1 Liquid-Immersed Life-Cycle Cost and Payback Period Results ......... 8-E-1

8-E.1.2 Dry-Type Life-Cycle Cost and Payback Period Results ...................... 8-E-2

LIST OF TABLES

Table 8-E.1.1 Life-Cycle Cost Savings for Liquid-Immersed Symmetric Core 

Transformers (2010$) ................................................................................ 8-E-2

Table 8-E.1.2 Payback Period for Liquid-Immersed Symmetric Core Transformers 

(Years)........................................................................................................ 8-E-2

Table 8-E.1.3 Installed Cost for Liquid-Immersed Symmetric Core Transformers 

(2010$) ....................................................................................................... 8-E-2

Table 8-E.1.4 Life-Cycle Cost Savings for Dry-Type Symmetric Core Transformers 

(2010$) ....................................................................................................... 8-E-2

Table 8-E.1.5 Payback Period for Dry-Type Symmetric Core Transformers (Years) ..... 8-E-3

Table 8-E.1.6 Installed Cost for Dry-Type Symmetric Core Transformers (2010$) ....... 8-E-4
8-E-1

APPENDIX 8-E. LIFE-CYCLE COST AND PAYBACK PERIOD RESULTS FOR 

SYMMETIC CORE TRANSFORMERS

In this appendix DOE presents the life-cycle cost (LCC) and payback period (PBP) 

results for distribution transformer employing symmetric core . 

8-E.1 Symmetric Core Transformers

Symmetric core transformers are configured so that each leg of a three-phase transformer 

core is identically connected to the other two. This produces a continuously wound core with 

120 ̊ radial symmetry, resulting in a triangularly shaped core when viewed from above. In a 

traditional core, the center leg is magnetically distinguishable from the other two because it has a 

shorter average flux path to each. In a symmetric core, however, no leg is magnetically 

distinguishable from the other two. Symmetric core technology is only applicable to three-phase 

transformers: design lines (DLs) 4, 5 and 7 through 13.

Symmetric core transformer designs are best suited for installations that use delta-delta or 

delta-wye connections. Utility practice is to install liquid-immersed transformers using a wyewye connection. Symmetric core transformers can, in theory, be modified and installed using a 

wye-wye connection, the increase in cost, weight and installation complexity make it 

impractical. Commercial and industrial (C&I) practice is to install dry-type transformers with a 

delta connection; similarly, most liquid-immersed transformers serving C&I are sectors installed 

with a delta connection. 

The physical characteristics and installation limitations of symmetric core transformer 

designs are describe in greater detail in Chapter 5. 

8-E.1.1 Liquid-Immersed Life-Cycle Cost and Payback Period Results 

 DOE simulated the LCC and PBP for liquid-immersed symmetric core transformers 

using loading and economic parameters similar to dry-type transformers. DOE assumed that due 

to the connection limitations, outlined in section 8-E.1, that most liquid-immersed symmetric 

core transformer owners would belong to the C&I sector and be used in place of a similarly sized 

dry-type transformer. 

 To provide a reasonable comparison of symmetric core designs to tradition core designs 

DOE simulated traditional core designs using the same economic and loading parameters as it 

did for the symmetric core designs. 
8-E-2

Table 8-E.1.1 Life-Cycle Cost Savings for Liquid-Immersed Symmetric Core 

Transformers (2010$)

DL Core 

Technology

Rated 

Capacity 

(kVA)

Candidate Standard Level

1 2 3 4 5 6 7 

4 

Traditional 

150 2,310 2,592 2,974 3,203 2,777 1,309 NA

Symmetric 211 1,185 833 239 -798 -2,050 NA

5 

Traditional 

1500 7,828 19,260 19,625 20,092 18,798 -10,105 NA

Symmetric -679 1,872 2,559 2,163 -1,003 -16,721 NA

Table 8-E.1.2 Payback Period for Liquid-Immersed Symmetric Core Transformers 

(Years)

DL Core 

Technology

Rated 

Capacity 

(kVA)

Candidate Standard Level

1 2 3 4 5 6 7 

4 

Traditional 

150 

5.8 4.8 9.4 11.8 23.7 33.5 NA

Symmetric 28.1 8.4 12.0 16.9 24.3 32.9 NA

5 

Traditional 

1500 

16.5 6.5 7.5 8.3 17.8 39.9 NA

Symmetric 30.2 17.2 14.8 15.6 20.0 37.6 NA

Table 8-E.1.3 Installed Cost for Liquid-Immersed Symmetric Core Transformers 

(2010$) 

DL Core 

Technology

Rated 

Capacity 

(kVA)

Candidate Standard Level

Base 1 2 3 4 5 6 7 

4 

Traditional 

150 8,293 8,797 8,837 9,273 9,656 11,346 13,393 NA

Symmetric 7,876 8,755 8,796 9,340 10,156 11,357 12,684 NA

5 

Traditional 

1500 31,806 35,234 38,108 38,776 39,317 45,407 81,533 NA

Symmetric 29,884 32,936 38,560 39,429 40,636 46,103 63,979 NA

8-E.1.2 Dry-Type Life-Cycle Cost and Payback Period Results 

Table 8-E.1.4 Life-Cycle Cost Savings for Dry-Type Symmetric Core Transformers 

(2010$) 

DL Core 

Technology

Rated 

Capacity 

(kVA)

Candidate Standard Level

1 2 3 4 5 6 7 

7

Traditional 

75

243 533 626 658 817 914 -783

Symmetric 633 864 1,038 1,112 1,042 968 4 

8 

Traditional 

300 1,376 2,626 2,396 3,761 227 NA NA

Symmetric 1,033 2,710 2,029 3,073 1,287 NA NA
8-E-3

9

Traditional 

300 1,383 1,455 2,313 2,557 -1,572 NA NA

Symmetric 2,423 2,178 2,625 3,808 601 NA NA

10 

Traditional 

1500 2,417 7,604 12,276 12,988 -7,204 NA NA

Symmetric 2,399 6,702 12,769 13,756 5,108 NA NA

11 

Traditional 

300 

563 1,943 1,318 197 -7,054 NA NA

Symmetric 893 2,315 2,853 2,088 -2,143 NA NA

12 

Traditional 

1500 

-168 2,644 7,474 9,063 4,962 -18,429 NA

Symmetric 2,894 1,860 4,821 9,228 8,342 551 NA

13 

Traditional 

2000 3,050 4,076 10,600 11,919 -9,581 NA NA

Symmetric 5,908 7,134 9,859 13,514 3,757 NA NA

Table 8-E.1.5 Payback Period for Dry-Type Symmetric Core Transformers (Years)

DL Core 

Technology

Rated 

Capacity 

(kVA)

Candidate Standard Level

1 2 3 4 5 6 7 

7

Traditional 

75

0.3 7.8 9.8 11.2 12.3 12.7 24.0 

Symmetric 0.4 1.3 4.5 6.7 11.4 12.8 19.6

8 

Traditional 

300 

6.9 6.9 11.9 10.7 18.6 NA NA

Symmetric 9.9 5.0 12.8 11.9 16.7 NA NA

9

Traditional 

300 

13.6 13.6 13.0 14.1 21.7 NA NA

Symmetric 9.4 12.0 12.6 12.7 18.8 NA NA

10 

Traditional 

1500 

18.5 13.3 10.4 11.1 22.5 NA NA

Symmetric 17.5 13.3 10.0 10.5 16.4 NA NA

11 

Traditional 

300 

17.5 13.2 15.3 18.5 34.4 NA NA

Symmetric 13.5 11.7 11.4 14.2 23.5 NA NA

12 

Traditional 

1500 

23.1 15.6 13.8 13.0 16.0 27.6 NA

Symmetric 10.9 16.7 15.2 12.9 14.1 18.4 NA

13 

Traditional 

2000 

14.4 17.4 13.7 13.8 21.8 NA NA

Symmetric 8.7 12.4 13.4 12.8 17.3 NA NA
8-E-4

Table 8-E.1.6 Installed Cost for Dry-Type Symmetric Core Transformers (2010$)

DL Core 

Technology

Rated 

Capacity 

(kVA)

Candidate Standard Level

Base 1 2 3 4 5 6 7 

7

Traditional 

75 3,595 3,592 3,802 4,109 4,441 5,073 5,468 7,837

Symmetric 3,722 3,707 3,730 3,903 4,170 4,999 5,627 7,308

8 

Traditional 

300 7,636 8,275 9,146 11,686 12,741 18,005 NA NA

Symmetric 7,788 8,290 8,699 11,805 13,188 16,666 NA NA

9

Traditional 

300 12,415 13,793 15,939 17,855 20,048 26,436 NA NA

Symmetric 12,415 13,793 15,939 17,855 20,048 26,436 NA NA

10 

Traditional 

1500 44,086 52,259 54,712 59,218 63,178 89,394 NA NA

Symmetric 41,317 45,350 51,854 55,940 58,878 72,838 NA NA

11 

Traditional 

300 20,751 22,218 24,514 26,531 28,832 36,993 NA NA

Symmetric 20,720 21,731 23,671 25,177 27,149 32,495 NA NA

12 

Traditional 

1500 50,519 56,807 61,759 68,546 70,977 81,156 108,869 NA

Symmetric 45,392 48,774 55,942 62,792 66,223 72,078 86,111 NA

13 

Traditional 

2000 60,175 67,930 77,924 84,664 94,164 124,652 NA NA

Symmetric 54,870 58,858 67,292 78,714 85,099 104,654 NA NA