henry@hutto.UUCP (Henry Melton) (04/09/89)
Does anyone have any definitive numbers on the efficiency of transformers? in particular, the ones on the poles outside the house. I was having a discussion with a friend the other day and he was claiming that upcoming improvements in core material would increase the public power distribution system efficiency by large (10%,20%) amounts. I was under the impression that the gadgets were already so efficient that there wasn't that much headroom to play with. But I don't have any real numbers. Who does? -- This is a test signature file.
larry@kitty.UUCP (Larry Lippman) (04/10/89)
In article <731@hutto.UUCP>, henry@hutto.UUCP (Henry Melton) writes: > Does anyone have any definitive numbers on the efficiency of > transformers? in particular, the ones on the poles outside the house. > I was having a discussion with a friend the other day and he was > claiming that upcoming improvements in core material would increase the > public power distribution system efficiency by large (10%,20%) amounts. > I was under the impression that the gadgets were already so efficient > that there wasn't that much headroom to play with. High-voltage distribution transformers are more efficient than many would believe, and in general, the efficiency improves as the kva rating increases. A typical single-phase oil-filled pole-mounted transformer rated at 10 kva has an efficiency around 97%. As the kva rating increases, the efficiency generally peaks out around 98.8% at 200 kva and above. Can't get much better than that... <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231, 716/773-1700 {att|hplabs|utzoo}!/ <> FAX: 716/741-9635, 716/773-2488 "Have you hugged your cat today?"
john@stiatl.UUCP (John DeArmond) (04/11/89)
In article <731@hutto.UUCP> henry@hutto.UUCP (Henry Melton) writes: >Does anyone have any definitive numbers on the efficiency of >transformers? in particular, the ones on the poles outside the house. When I worked in the utility power industry (as a health-physicist), a typical efficiency quoted by those who are supposed to know, for generator-to-outlet is about 98%. Transformer efficiency varies roughly as the inverse of capacity. The 2000 megawatt main station transformers are 99.99+% efficient - even 0.1% loss of 2000 megawatts would be 2 megawatts of heat dissipation! Most of these transformers are convection-cooled except in the hottest weather. The least efficient transformers are the pole-pigs hanging outside your house. These 20 to 40 kva transformers are typically 99+% efficient and represent the single largest loss center in the distribution center (opinion/guestimate). Improvements in transformer design would generally affect efficiency in the 0.1% or so range. Even in this range, the effect on the bottom line of a utility would be remarkable. Tenths of a percent improvements are well worth the effort. Most research work that I read about involve experiments with amorphous Iron for core construction and better magnetic coupling. 73, john -- John De Armond, WD4OQC | Manual? ... What manual ?!? Sales Technologies, Inc. Atlanta, GA | This is Unix, My son, You ...!gatech!stiatl!john | just GOTTA Know!!!
dc@hpmtlx.HP.COM ($Dave Crook) (04/12/89)
/ hpmtlx:sci.electronics / larry@kitty.UUCP (Larry Lippman) / 10:31 pm Apr 9, 1989 / In article <731@hutto.UUCP>, henry@hutto.UUCP (Henry Melton) writes: > Does anyone have any definitive numbers on the efficiency of > transformers? in particular, the ones on the poles outside the house. > I was having a discussion with a friend the other day and he was > claiming that upcoming improvements in core material would increase the > public power distribution system efficiency by large (10%,20%) amounts. > I was under the impression that the gadgets were already so efficient > that there wasn't that much headroom to play with. >> High-voltage distribution transformers are more efficient than >>many would believe, and in general, the efficiency improves as the kva >>rating increases. >> A typical single-phase oil-filled pole-mounted transformer rated >>at 10 kva has an efficiency around 97%. As the kva rating increases, >>the efficiency generally peaks out around 98.8% at 200 kva and above. In many cases, especially in residential lines, the losses in the power lines themselves are far greater than the losses in the transformers. If the transformer does not have large heat radiating tubes or fins, the chances are that it is quite efficient. Since all losses are converted to heat, the heat dissipating sinks are a directly measure of the losses the transformer was designed to dissipate at maximum load. Many "transformers" are actually transformer regulators. Inside the "transformer" is an electronic voltage detection circuit which controls the voltage ratio. Under heavy loads the ratio increases which compensates for significant voltage and power loss in the power lines feeding the transformer. Dave Crook Manufacturing Test Division Hewlett-Packard Loveland, Colorado
larry@kitty.UUCP (Larry Lippman) (04/16/89)
In article <880004@hpmtlx.HP.COM>, dc@hpmtlx.HP.COM ($Dave Crook) writes: > In many cases, especially in residential lines, the losses in the power > lines themselves are far greater than the losses in the transformers. This is true. Efficient power distribution has many trade-offs. There is a significant trend toward higher distribution voltages to minimize the effects of I^2R losses. Many electric utilities have switched from 4160 volts to 13.2 kV for distribution in residential areas. For commercial distribution 34.5 kV has also become common. However, a negative effect with higher voltages is increased losses due to capacitance, corona and - especially - insulator leakage losses during wet weather. > If the transformer does not have large heat radiating tubes or fins, the > chances are that it is quite efficient. Since all losses are converted > to heat, the heat dissipating sinks are a directly measure of the losses > the transformer was designed to dissipate at maximum load. While you have a point, this is not necessarily true. With advances in high-voltage insulating materials, many "intermediate"-sized transformers contain no oil or gas (like SF6), but are air-cooled through convection, and consequently have no fins as part of their design. Air-cooled transformers still get hot, though. > Many "transformers" are actually transformer regulators. Inside the > "transformer" is an electronic voltage detection circuit which controls > the voltage ratio. Under heavy loads the ratio increases which compensates > for significant voltage and power loss in the power lines feeding the > transformer. There are high-voltage power line voltage regulators of two types: (1) buck-boost autotransformer; and (2) a true transformer with a tap changer. However, these regulating devices are used more infrequently than you suggest. Large transformers of the multi-MVA variety that distribute voltages of 34.5 kV and above usually have taps that are changed either manually (through a switch on the transformer), or through a remote telemetering circuit by a human operator. Large transformers that employ automatic tap changing to achieve automatic regulation are not very common. <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231, 716/773-1700 {att|hplabs|utzoo}!/ <> FAX: 716/741-9635, 716/773-2488 "Have you hugged your cat today?"