DRAFT – 2011 12 21

To: MV Committee

Date: 21 December 2011

Topic: Medium‐voltage dry‐type scaling methodology

Background

On Friday, 16 December several members of the MV committee met to (1) extend the plenary group’s

agreement on Efficiency Level 2 (EL 2) for Design Line 12 (DL12) to the remaining MVDT DLs and (2)

derive a sensible methodology for mapping those ELs to efficiency values for all MVDT transformers that

DOE covers.

Discussion

The MVDT design lines are chosen such that there are high and low kVA units in each of three BIL

buckets, as shown the table.

45 kV BIL 95 kV BIL 125 kV BIL

300 kVA DL 9 DL 11 DL 13A

1500 kVA (2000 for 13B) DL 10 DL 12 DL 13B

Both because the majority of the market resides there and because it was the middle of the three BIL

bins, the committee had centered its discussion around DLs 11 and 12. Ultimately the committee agreed

that EL2 was the appropriate choice for DL 12 and left it to the scaling group to determine the rest.

The scaling group noted that current standards were far more stringent for lower kVAs because the .75

scaling factor does not reflect for the fact that achieving a given BIL rating requires certain fixed spacings

that do not scale with kVA and impose proportionally more losses  on smaller units as a result. Selecting

for DL 11 one EL less than EL DL 12 avoids a standard that is disproportionately stringent on the lower

(sub‐300) kVAs. As a result, the scaling group suggested that ELs 1 and 2 were appropriate for,

respectively, for DLs 11 and 12.

To derive efficiency values for the higher and lower BIL DLS, the scaling group proposed using loss

adjustments of 10% in both directions. For example, DL 9 would receive an efficiency standard that

implied 10% lower loss (and DL 13A one implying 10% higher loss) than did EL 1 in DL 11. It is worth

pointing out that new ELs would need to be created for the high and low BIL DLs to map well to the +/‐

10% adjustments. These adjustments are in line with what is implied by DOE’s own analysis.
DOE did not directly analyze any single‐phase MVDT units because they account for a small proportion

of the market, and in previous work had derived standards by requiring single‐phase MVDTs to reach

efficiencies of the three‐phase units of their BIL bin and of three times the kVA rating. For example, a

100 kVA single‐phase 95 kV BIL unit would need to meet the same efficiency as did a 300 kVA three‐

phase 95kV BIL unit.

The scaling committee felt noted that this approach produced standards that were disproportionately

stringent on single‐phase units, and instead proposed deriving standards for single‐phase units by

permitting 30% greater loss than the three‐phase unit of identical kVA and BIL. For example, a 150 kVA

single‐phase 45 kV BIL unit would be permitted 1300 W of loss if a 150 kVA three‐phase 45 kV BIL unit

was permitted 1000 W of loss. It is worth noting that adopting such scaling would not change current

single‐phase standards because they are currently higher than would be calculated by the 30% loss

addition and because DOE is not legally allowed to lower standards.

Results

The following table presents the standards that would be implied by methodology described above,

noting that the single‐phase standards exactly match today’s standards.

EC 5 EC 6 EC 7 EC 8 EC 9 EC 10

single‐phase three‐phase single‐phase three‐phase single‐phase three‐phase

<=45 kV BIL <=45 kV BIL 46‐95 kV BIL 46‐95 kV BIL >= 96 kV BIL >= 96 kV BIL

kVA % kVA % kVA % kVA % kVA % kVA %

15 98.10 15 97.50 15 97.86 15 97.18

25 98.33 30 97.90 25 98.12 30 97.63

37.5 98.49 45 98.10 37.5 98.30 45 97.86

50 98.60 75 98.33 50 98.42 75 98.13

75 98.73 112.5 98.52 75 98.57 112.5 98.36 75 98.53

100 98.82 150 98.65 100 98.67 150 98.51 100 98.63

167 98.96 225 98.82 167 98.83 225 98.69 167 98.80 225 98.57

250 99.07 300 98.93 250 98.95 300 98.81 250 98.91 300 98.69

333 99.14 500 99.09 333 99.03 500 98.99 333 98.99 500 98.89

500 99.22 750 99.21 500 99.12 750 99.12 500 99.09 750 99.02

667 99.27 1000 99.28 667 99.18 1000 99.20 667 99.15 1000 99.11

833 99.31 1500 99.37 833 99.23 1500 99.30 833 99.20 1500 99.21

2000 99.43 2000 99.36 2000 99.28

2500 99.47 2500 99.41 2500 99.33