Date: October 11, 2011

TO: Richard Parker, DOE, Navigant, LBL and Negotiated Rulemaking Committee Members and NEMA

Transformer Section Members

SUBJECT: Comments regarding limitations of design software, problems with core materials , difficulties

with mixed low volume production of LVDT by small manufacturers

1) General: Typical Small Transformer manufacturer

Although the comments made here based on specific experiences of ONYX Power, Inc (ONYX), the other

small transformer manufacturers, I talked to confirmed that their experiences are very similar.

ONYX has mixed transformer business. The rough distribution is 35% UPS related exempt transformers, 25%

special purpose industrial application & 50 Hz export transformers exempt from efficiency requirements and rest

40% transformers required to meet the DOE efficiency requirements. The mix is somewhat different for different

small manufacturers but all make other than LVDT products.  

The 40% Transformers that have to meet the efficiency requirements consists of about 70% for Data Centers 25%

for Solar Energy and rest are LVDT.

ONYX has manufacturing area of 60,000 sq. ft. and employs approximately 250 employees. ONYX on

average makes slightly over 2 transformers per design. The small transformer manufacturers I talked to, have

similar ratio of design to production units. The delivery time from order receipt to shipping is about 5 weeks. This is

very crucial for any small manufacturers to reduce in process inventory.

2) The limitations of design software: The widely used OPS software for transformer design is good

software but it is not perfect. It gives starting point for the ultimate production design. The final test results of a

production design may or may not agree closely to the performance predicted by OPS software. Below is the case

in point.

We designed 300 kVA. 208 Delta – 480Y/277, 60 Hz, 115C Rise LVDT.  The design used 3 Phase wound

(Evans) core with amorphous core material SA1. Ten units were manufactured and the performance details are as

follows.

                    Calculated by OPS software     Test Results     ERROR

Core Loss W     107    222 (Average of 7 units)    + 207%

249 maximum     +233%

        198 Minimum

Winding Loss W     2600       2988     +115%

Audible Sound Level    No Calculation     66.41 dB Average

         70.13 Maximum 15.13 db above

Acceptable by industry

standards

(Note: Core Loss Predicted by Core Manufacturer 173 Maximum, 144 Typical).

It is evident that OPS program does not calculate core area, flux density and watts/Lb correctly.  OPS uses stacking

factor of 0.86 Vs 0.84 specified by manufacturer and further OPS fails to account for the phase shifts in the flux
between two halves of the core legs. This happens only in 3 Phase Evans core and not in 1 phase wound cores. The

actual flux density in Evans core is 15.5% (1/ Cos30) higher than simple calculation suggests.

Similarly there are some other problems with the OPS, but I hope the comments above will throw some

light on the problems users of OPS are faced with. Small manufacturers who build one or two transformers per

order cannot afford to experiment and eat the cost of failures and lost customers.

None of the transformer design software can be perfect but OPS needs some major corrections. Even if

perfect software to exist and used , the test results of the  production transformer will deviate from calculations

because of raw material tolerances, the unavoidable variations in production processes and the measurement

errors  of test equipment which meet the DOE calibration requirements.

    

We, therefore, have to keep in mind all these software limitations in mind before we arrive at the

mandated efficiency standards.   

3) CRGO Core Material availability and quality: The problem we encountered with amorphous core as

detailed above is also experienced with other core materials manufactured and sold to small manufacturers. We

routinely find that when we use indigenously manufactured M5 or higher grade core material the tested losses

vary more than 30% within the identical transformers.  We never experienced this problem when grain oriented

steel of imported origin was used. When we contacted suppliers and steel manufacturers we always got run

around and we ended up eating our losses. There is another new problem is raising its ugly head. Case in point:   

Few weeks ago we built 1000 kVA, 3 Phase, 130C, 480 Delta – 400Y LVDT using with mitered core

construction using M5 material made in U.S.A. When the transformer was tested at room temperature the core

losses were 2482 W as against calculated loss of 2559 W. Tested sound level was 58 dB. When the transformer was

left energized with 480 Volt on primary and no load on winding for 12 hours the core loss increased to 3140 W and

sound level was 76 dB. We had similar case few years ago with 1750 kVA transformer with M5 and we could not

find the cause nor did any industry expert have any answers. With the same transformer when M5 core material

was replaced by M5 material imported from Europe, all problems disappeared. We do not have any clues for our

experience except to say we cannot always trust the quality of grain oriented core steel we can buy locally.  

    In 2007 ‐2008 time frame and prior to that we could not buy any CRGO material from American

manufacturers. All their capacity was utilized by major transformer manufacturers here and overseas. Now during

recession years American manufacturers are trying to sell CRGO to small transformer manufacturers. At this time

overseas producers of CRGO steel are refraining from importing the product in U.S.A. for fear possible anti

dumping regulations. The small manufacturers are left with no option but to buy whatever CRGO from indigenous

manufacturers and hope that it meets the losses guaranteed by the manufacturer. When the problem with core

steel surfaces it is too late to do anything to meet the committed delivery time to the customer. We had lot of

unhappy customers who had Data Center ready but no transformers to get in operation. It has seriously affected

our business.

   

4)  Transformers that should be exempted from DOE efficiency regulations

1) Transformers for Data Centers :

a) Low Inrush Current : These Transformers have special requirements of Low Inrush currents  

typically 300% to 400%. This precludes the use of wound cores as wound cores retain more of

residual flux in the core thus increasing the Inrush current in the order of 800% to 1200%. High

inrush currents invariably trip the circuit breakers dropping the critical load.  We therefore, opted

to use Non Oriented Steel with low flux density and sometimes gapped core construction for

Data Center Transformers. This approach makes it very difficult to meet current DOE efficiency
requirements. Any further improvements in the efficiency requirements most definitely will

jeopardize the reliability of operation of Data Centers.

b) High Kfactor non linear power electronics load. This requirement necessitates lower winding

leakage reactance (1) to reduce voltage distortion of the load and (2) to reduce the stray losses in

the winding to keep windings from overheating. This forces to use less turns in winding and

bigger core. End result is the high efficiency point is shifted from 35% load to around 50% load.

The cost is increased to meet DOE efficiency at 35% load. The Data Center Transformer are

continuously loaded at constant load and do not have daily cyclic loading similar to LVDT

installed in residential area.  Further, Data Center transformer are frequently required to have

lower temperature rise and lower total losses at operating load typically over 35% to reduce

demand for air conditioning. This again shifts the high efficiency point towards 50% mark.   

c) Reliability, Dimensions and commercial life: The reliability is very important factor for these

transformers.  These transformers are used for vital operations such as Communications,

Banking, Airline operations and reservations, stock exchanges, social security, IRS, Defense etc.  

These transformers have dimensions constrants because the high cost of floor space at

sites similar to Manhattan in New York or other similar locations.   

These transformers unlike standard LVDT have a shorter commercial life span. Typically

the Data Center are replaced in 10 years.  For this reason some of the new Data Centers are now

installed in shipping containers and not in a permanent building structure.  

In light of the above we strongly suggest that these transformers should be

exempted from current and future  DOE efficiency requirements.  

2) Transformers for Solar Power: These transformers are required to work at varying load levels based on

the daily cycle of solar radiation. During the night the transformers are disconnected from grid. Considering

this operational criterion, the governments have mandated efficiency requirements to maximize the efficiency

solar energy to electrical energy. These transformers are typically 99% efficient based on the efficiency

formula developed by the governments. If these transformers are strictly designed to meet DOE efficiency

they will be cost effective but will not meet State/Federal qualification requirements for solar energy

incentives and also will be inefficient in converting solar energy to electrical energy.  DOE requirements

conflict with already existing government mandates for efficiency for solar energy.

These transformers should be exempted from DOE efficiency requirements.

          With Kind Regards,

           V. B. Tendulkar

                    Chief Technology Officer,

                  ONYX Power, Inc.