### 1 Transformer Products 1900 East North Street Waukesha, WI 53188 Phone: (262) 524-4355 Fax: (262) 524-4513 October 31, 2011 Mr. Richard Parker jerry.corkran@cooperindustries.com richardparkerdc@gmail.com

Subject: Analysis of M3 Compared to Amorphous Core Designs

Dear Richard:

We have examined the 25 kVA single phase Design Line 2 Pole Type Transformer to understand fundamental relationships between M3 Core Material and that of Amorphous Core. We offer these comments for your consideration for the DOE Negotiations.

I. Observations:

a. Amorphous core transformers have lower core loss than M3 Silicon iron transformers but higher winding losses. At 50% load, they bo th have the same efficiency. At less than 50% load, amorphous core transformers have lower total losses than M3 silicon iron but that is always at night when electric power cost is at a minimum. During the day when the load peaks and exceeds 50% of nameplat e load, amorphous core transformers have higher total losses than M3 transformers de signed for the same efficiency at 50% load. During the day when peaking generators ar e running the electric power costs are the highest, sometimes hitting 3 times the night time rate and yet at that point the amorphous core transformers have higher total losses than the M3 transformers. b. Amorphous core transformers are generally more costly to build than M3 silicon iron transformers and sell for higher prices.

c. Amorphous core transformers may not result in energy savings and total cost savings to the end users and in fact may result in higher energy usage and costs.

II. Assumptions

a. Considerations are made at the present 2007 mandatory energy efficiency standards of transformers but the starting point does not r eally affect the conclusions in this memo. b. DOE Design line 2 is the 25 kVA and is most representative of single phase poles.

c. The present 25 kVA mandatory ef ficiency for Design Line 2 is 98.91% at 50% load. d. Two designs are considered, one amorphous and one M3 and both meet the mandatory 98.91% efficiency at 50% load, and with a total allowable loss of 137.8 watts.

e. The peak efficiency for each core material occu rs when the core loss = the total load loss. f. For the 25 kVA, with M3, the core loss is assumed to be 1⁄2 of 137.8 watts or about 68.9 watts. The load loss at 50% load is also 68.9 watts. Hence the load loss of the M3 design at full load is 4* 68.9 or 275.6 watts. Total loss for the M3 design at full load would be 68.9 + 275.6 or 344.5 watts.
g. We assumed that amorphous cores have ~1/3 the core loss of M3. Hence the amorphous transformer would have approximately 26 watts of core loss. Hence the amorphous transformer would have 68.9-26 or 42.9 more watts of load loss than the M3 design at 50% load. This means that the amorphous design would have 68.9+42.9 or 111.8 watts of load loss at 50% load or 447.2 watts of load loss at full load. Total loss for the amorphous design would be 26 + 447.2 or 473.2 watts. h. Hence the amorphous design has 68.9-26 or 42.9 watts less than the M3 transformer at no load but 473.2-344.5 or 128.7 watts higher loss than the M3 design at full load.

### 2 i. Night time load cycles may dip to 10% of rated load at night but rise to a normal 80% of rated load several times during the day. j. During cold load pickup after an outage, tota l load often reaches 120% or higher of rated load and persists for periods of up to an hour or more. k. The IEEE Loading guide C57.91allows for up to 200% of rated load for periods of up to 30 minutes. During such periods the amorphous core has 1814.8 watts of loss while the M3 silicon iron transformer has 1171.3 watt s, resulting on an added 643.5 watts or 55% greater strain to the system that requires extra generation when it is least available.

III. Graphical results of the analysis

a. Table I shows the efficiency of both transformers as a function of percent Load:


### Per Unit

Load M3 Amorphous
0.1 97.21 98.79
0.2 98.43 99.13
0.3 98.77 99.12
0.4 98.88 99.03
0.5 98.91 98.91
0.6 98.89 98.77
0.7 98.85 98.62
0.8 98.79 98.46
0.9 98.72 98.31

1 98.64 98.15
1.1 98.56 97.98
1.2 98.47 97.82 Efficiency

b. Graphical results of Table I

Night load = 10%

Day Load = 80%

RMS load = 50%

Cold Start = 120%

97.00 97.50 98.00 98.50 99.00 99.50

0 0.5 1 1.5 M3 Efficiency
Amorphous Efficiency

c. 

### Table II shows watts loss versus percent load

### 3 PU Load Amorphous M3
0.1 30.6 71.6
0.2 44.0 79.9
0.3 66.3 93.7
0.4 97.6 113.0
0.5 137.8 137.8
0.6 186.8 168.1
0.7 244.9 203.9
0.8 311.8 245.2
0.9 387.7 292.0

1 472.5 344.4
1.1 566.2 402.2
1.2 668.9 465.6 Total Watts Loss

d. 

### Graphical results of Watts loss versus load

Night load = 10%

Day Load = 80%

RMS load = 50%

Cold Start = 120%

0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 800.0

0 0.5 1 1.5 M3 Total Watts
Amorphous Total Watts

IV. Recommendations

Our recommendation continues to be to base the new mandatory efficiency standard on M3 silicon iron and not to base it on amorphous cores; for the many factors of transformer weight, size, reliability, load regulation, and even ferroresonant ov ervoltage problems with amorphous. Silicon iron core transformers continue to have better losses and efficiency and to tal economics for load growth, cold load pickup and peak demand conditions.

Very truly yours, Sincerely,


## Philip J Hopkinson **Jerry L Corkran**

Philip J Hopkinson, PE Jerry L. Corkran President & CEO HVolt Inc Staff Engineer-Cooper Industries