### September 22, 2011

Richard Parker,
Facilitator

Attached are two spread sheets with calculations and graphs showing the loss and efficiency evalua tions for a 50 kVA transformer. I compared three of DOE's designs of a 50 kVA transformer (DOE square tank) against a design selected from Memphis Light Ga s and Water's (MLGW) 2010 bid quotation. The transformer is a loss evaluated single

- phase pad

- mounted, liquid

- immersed, 22860 GrdY/13200 volt to 240/120 volt, 125 kV BIL, without H

- V taps design. The "A" and "B" factors used to select the design for MLGW have a value of

"A"

- $4.00 $/watt

"B"

- $1.27 $/watt As a side note, MLGW has been using “A” and “B” factors to evaluate transformer designs since 1980.

See attached DOE Design Lines.xls and DOE Design Lines w

- amorphous.xls file s

.

For discussion I have label ed these designs; T1 from MLGW's 2010 transformer bid, T2 DOE's D01_C03_F3_A11.00_B3.33 design using M3_CuAl_dgw_sh (silicon steel ),

T 3 DOE's D01_C05_G3_A16.00_B3.50 design using M2_CuAl_dgw_sh (silicon steel ), T4 DOE's D01_C07_G3_A16.00_B4.50 design using ZDMH_CuCu_dgw_sh (high

- B scribed steel)

, T5 DOE’s D01_C08_G3_A16.00_B7.50 design using SA1_AlAl_dgw_sh

, and

DOE’s D01_C09_F3_A16.00_B4.84 design using SA1_CuCu_dgw_sh

.

The T1 and T2 appear to be similar designs except T2 has a higher price and lower load losses. I am puzzled as to the large difference in the initial cost between the quoted price from MLGW's 2010 bid price and the DOE price.

The higher efficiency of the T3 and T4 designs do not have sufficient savings to offset the higher initial cost listed in the Department of Energy, Distribution Transformers Rulemaking, Liquid

- immersed Engineering Analysis Results; August 2011

. This is shown by the pay back years on line 49 and 50 in the Calculations tab in

the attachment.

Using DOE's 50% loading and the designs from the Aug. 2011 engineering analysis gave the following efficiencies:

Design: T1 (MLGW) T2 ( DOE) T3 ( DOE) T4 ( DOE)

============ ======================== = === == == Efficiency: 99.08% 99.15% 99.21% 99.23%

These designs do however incorporate readily available silicon steel from multiple suppliers.

### - 2

- To achieve a higher efficiency and a pay back period of less than 28 years would

req uire an amorphous metal core be used in the design. This design was investigated in the attached file labeled DOE Design Lines w_amorphous.xls . Again using DOE's 50% loading and the designs from the Aug. 2011 engineering analysis gave the following effic iencies:

Design: T1 (MLGW) T2 ( DOE) T5 ( amorphous) T6 (amorphous)

============================================== ==== = Efficiency: 99.08% 99.15% 99.35% 99.52%
See attached DOE Design Lines w_ amorphous.xls

. The designs require the use of a single source amorphous metal core.

In 1993 MLGW purchased three amorphous core 3

- phase pad

- mounted transformers. The transformers had to be removed from service and sent to a repair shop for inspection a nd repair due to gassing. The three amorphous core transformers are listed as follows:

MLGW Company Date Received Class Date Location

Number kVA New Item Removed Address

Z00410 750 Feb. 1993 47

- 6130 Oct. 1998 Rivermont

CR0105 2000 Sept. 1993 47

- 6205 June 2000 Methodist N.

CR0106 2000 Sept. 1993 47

- 6205 July 2000 Methodist N.

The inspection and tear down of the three transformers listed above revealed a failure in the core insulation. This failure allowed circulating curren t in the cores, frame and core ground.

The 750 kVA transformer was repaired with press board by an outside repair shop and

returned to MLGW’s transformer stock.

The tear down of the two 2000 kVA transformers revealed arcing had occurred between

the core laminations. This was due to core insulation failure that allowed circulating currents between the core frame and core. The 2000 kVA transformers were not repairable as the damage was too extensive to the core laminations.

See attached Scaling Factor.xl s file. In regard to the scaling factor used, I compared the scaling factor derived by DOE against trend lines with data points taken from Memphis Light Gas and Water's (MLGW) 2010 bid quotation. The s caled
total losses (TL) from a 25 kVA 1

- ph pole type (base) and a 50 kVA single

- phase pad

- mounted (base), both within a 125 kV BIL design line , were compared against the

DOE 0.75 Scaling Rule: TL1 = TL0 x (S1 / S0)^0.75. The pole type transformer designs as shown in the attached spre ad sheet graph scale to a

4 th order polynomial for losses

and a

3 rd order polynomial for price (I.C.). The 50 kVA pad

- mounted (square tank) transformer design shown in the attached graph

scaled to a factor of

0 .757 for load losses,

0 .7538 total losses,
linear for no

- load losses
and a

3 rd order polynomial for price (I.C.).

### - 3

- **RECOMMENDATION**

My recommendation would be to keep the current efficiency levels as published for a
minimum. In addition to this minimum efficiency requirement I would prefer to see a loss evaluation “A” and “B” factor added to the minimum efficiency requirement.

These factors could initially be in the range of

"A"

- $4.00 $/watt no

- load (core)
and

"B"

- $1.00 $/watt load loss (winding) to select the designs w ith the best evaluated total ownership cost. I would also recommend that the efficiency be based on the p.u. load of base rating that gives the highest efficiency. In the loss evaluated 50 kVA pad

- mounted transformer selected by MLGW the maximum efficien cy is 99.09% at a p.u. load of 0.43 of the 50 kVA base rating. The highest efficiency is that of the T6 referenced design at 99.54% at a load of 0.35 p.u. of base.

Best regards

,

John Rossetti, P.E. Systems Engineer Reliability and Power Quality Memphis Light Gas and Water Division City of Memphis Office: ( 901 ) 528.4743 ( 7:00 a.m.

- 3:30 p.m. c.s.t.)

cc: plim@mlgw.org droberts@mlgw.org brian.coffey@navigant.com

srosenstock @eei.org

Referenced spread sheet files: DOE Design Lines.xls DOE Design Lines w

- amorphous.xls Scaling Factor.xls