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280V motor on 230V circuit
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"daestrom" wrote in message ... wrote in message ... In alt.engineering.electrical Michael Moroney wrote: | Are the load tap generators configured make-before-break? | Break-before-make would mean a (very short) power outage every activation | but make-before-break would mean a momentarily short-circuited winding and | the break would involve interrupting a large short circuit current. I wonder how much regulation could be managed through the use of variable leakage inductance in the transformer windings. I suppose you could, but increasing leakage inductance means you're increasing losses aren't you? Just a percent or two on a unit rated for 250 MVA can be too much to tolerate. daestrom ------------- I don't see changing leakage inductance having much effect on losses ( a great effect on voltage regulation -likely all to the bad) but the problem is one of changing leakage inductance. Does this mean changing a gap in the core? Does it mean moving one winding with respect to another? In any case it does mean some fiddling with the core or winding. This has been done for series lighting circuits where the load current was kept constant by using a transformer which balanced the forces between coils against a fixed weight. If the current changed the secondary coil moved so that there was more or less leakage. The units that I have seen were rather cumbersome. -- Don Kelly remove the X to answer |
280V motor on 230V circuit
"Michael A. Terrell" writes:
wrote: In sci.electronics.repair jakdedert wrote: I'm a little confused about a 230 volt circuit. In what part of the world does the utility supply 230v? Continental Europe used to have 220 volts (before that it was 127 volts in some places), the UK used to have 240 volts. Nowadays, the common voltage is 230 volts -10% +6%. In other words, nothing has changed. They just wrote sloppier specs. It has changed, the voltage is now close to 230V, at least in Sweden. I guess the sloppiness was specified to allow a gradual switch from 220/240 to 230 and still be within spec. Residential power in Norway is normally 230V three phase btw, instead of 400V three phase. Their 230V outlets are two phase and ground instead of one phase, neutral and ground. Their three phase outlets therefore are blue instead of red and have four prongs instead of five. |
280V motor on 230V circuit
Thomas Tornblom wrote: "Michael A. Terrell" writes: wrote: In sci.electronics.repair jakdedert wrote: I'm a little confused about a 230 volt circuit. In what part of the world does the utility supply 230v? Continental Europe used to have 220 volts (before that it was 127 volts in some places), the UK used to have 240 volts. Nowadays, the common voltage is 230 volts -10% +6%. In other words, nothing has changed. They just wrote sloppier specs. It has changed, the voltage is now close to 230V, at least in Sweden. I guess the sloppiness was specified to allow a gradual switch from 220/240 to 230 and still be within spec. Residential power in Norway is normally 230V three phase btw, instead of 400V three phase. Their 230V outlets are two phase and ground instead of one phase, neutral and ground. Their three phase outlets therefore are blue instead of red and have four prongs instead of five. Do the math. The specifications allow continued use of the old standard n each country. -- http://improve-usenet.org/index.html Use any search engine other than Google till they stop polluting USENET with porn and junk commercial SPAM If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm |
280V motor on 230V circuit
"Michael A. Terrell" writes:
Thomas Tornblom wrote: "Michael A. Terrell" writes: wrote: In sci.electronics.repair jakdedert wrote: I'm a little confused about a 230 volt circuit. In what part of the world does the utility supply 230v? Continental Europe used to have 220 volts (before that it was 127 volts in some places), the UK used to have 240 volts. Nowadays, the common voltage is 230 volts -10% +6%. In other words, nothing has changed. They just wrote sloppier specs. It has changed, the voltage is now close to 230V, at least in Sweden. I guess the sloppiness was specified to allow a gradual switch from 220/240 to 230 and still be within spec. Do the math. The specifications allow continued use of the old standard n each country. If you read my comment you will see that I agree that the new spec covers the old voltages. I do not agree with your statement that "nothing has changed". We had 220V before and we now have 230V, so the actual voltage has definitely changed. |
280V motor on 230V circuit
In message , Thomas Tornblom
writes "Michael A. Terrell" writes: Thomas Tornblom wrote: "Michael A. Terrell" writes: wrote: In sci.electronics.repair jakdedert wrote: I'm a little confused about a 230 volt circuit. In what part of the world does the utility supply 230v? Continental Europe used to have 220 volts (before that it was 127 volts in some places), the UK used to have 240 volts. Nowadays, the common voltage is 230 volts -10% +6%. In other words, nothing has changed. They just wrote sloppier specs. It has changed, the voltage is now close to 230V, at least in Sweden. I guess the sloppiness was specified to allow a gradual switch from 220/240 to 230 and still be within spec. Do the math. The specifications allow continued use of the old standard n each country. If you read my comment you will see that I agree that the new spec covers the old voltages. I do not agree with your statement that "nothing has changed". We had 220V before and we now have 230V, so the actual voltage has definitely changed. In the UK, we had 240V. We now have err..... 240V. There may be places where it really has been reduced to 230V, but I've never been anywhere where I had occasion to measure the mains voltage, and didn't get around 240V - certainly not sufficiently different for you to notice the difference. -- Ian |
280V motor on 230V circuit
? "daestrom" ?????? ??? ?????? ... "Michael Moroney" wrote in message ... "daestrom" writes: P.S. In the US, a 'tap-changer' may be built for either for unloaded or loaded operation. The 'unloaded' type can not be stepped to another tap while there is load on the unit (although it can still be energized). It's switch contacts cannot interrupt load though, so if you try to move it while loaded, you can burn up the tap-changer. The classic 'load-tap-changer' is actually several switches that are controlled in a precise sequence to shift the load from one tap of the transformer to another while not interrupting the load current. P.P.S. Load tap changers typically have a significant time-delay built into the controls so they do not 'hunt' or respond to short drops in voltage such as starting a large load. 15 seconds to several minutes is typical. So even with load-tap-changers, starting a single load that is a high percentage of the system capacity will *still* result in a voltage dip. Are the load tap generators configured make-before-break? Break-before-make would mean a (very short) power outage every activation but make-before-break would mean a momentarily short-circuited winding and the break would involve interrupting a large short circuit current. Certainly modern ones likely use thyristors and zero crossing detectors. I figured someone would 'bite' :-) Typical large power load-tap-changers have a primary winding and two secondaries. You mean a secondary and a tetriary? The transformer for the hotel load of a 300 MW unit is powered directly from the turbo alternator (21 kV) and has a secondary of 6.6 kV and a tetriary of again 6.6 kV. This is done because it has wye-wye-wye connection (IIRC). The hotel load of such a unit is 10%, also 30 MW, including 7 brown coal mills. Typical size of a 6.6 kV motor is 1 MW. One secondary produces about 100% of 'rated' secondary voltage. The second secondary produces about 15% to 20% of the rated voltage, but has numerous taps from end to end, about 2.5% 'steps'. (for a total of about eight taps). The cental tap of the boost/buck winding is tied to one end of the main secondary. The boost/buck can be used to step from 90% to 110% of the 'design' output. I suppose some can step over a wider range, but I haven't run across them. *TWO* rotary switches have each tap tied to one of the positions of each rotory switch, and each 'wiper' is tied to single heavier contacts that are opened in the operating sequence. The output side of these two interrupting contacts are tied to each end of a large center-tapped inductor. So, normally both rotary switches are aligned to the same transformer tap, both interrupting contacts are shut, and load current flows from the boost/buck winding tap, splits and flows through both rotary switches, both interrupting contacts, enters both ends of the inductor and out the inductor center tap. Because the current flows into both ends of the inductor and the mutual inductance of the two parts cancel, there is little voltage drop in the inductor. Begin step sequence: 1) Open one interrupting contactor. Now load current doubles through half the inductor and is zero in the other half, so the voltage drop across the inductor actually makes output voltage drop, even if trying to step 'up'. 2) Move associated rotary switch to next step of transformer bank. 3) Close interrupting contactor. Now, the two rotary switches are across different taps. The inductor prevents a excessive current, otherwise you have a direct short of the two winding taps. Some tap changers can stop at this point and are called 'half-step' units. Obviously, the inductor has to be rated for sustained operation across a step of the boost/buck winding plus load current in order to survive sustained 'half step' operation. 4) But for tap changers that can't operate 'half-step', the sequence continues. And opens the other interrupting contactor. Now the other half of the inductor has full load current. 5) Move second rotary switch to next step (now both switches are on the new step) 6) Close the second interrupting contactor. You're back in the initial configuration, but with both rotary switches on a new transformer tap. Quite the same principle is done with diesel locomotives and is called diesel-electric transmission, and also in pure electric locomotives (E-Lok in german, for Elektrische Lokomotive). The diesel engine, 2-stroke and usually 600 to 900 rpm at full throttle, is coupled to a generator. The generator has small windings, connected in series for the last notch, higher voltage and relatively smaller current, and in parallel for start, higher amperage and smaller voltage. The traction motors are directly coupled on the wheel shaft, and are air cooled. An E-Lok has a trasformer, with the primary directly supplied by the cetenary, 15 kV 16 2/3 Hz in Germany, and 25 kV 50 Hz in Greece, The secondary uses the same principle. The typical size of a traction motor is 1 MW, 4 (one each shaft) and maximum voltage 700 volts, and are series wound motors with special construction to operate at 16 2/3 Hz (or 50 Hz with today's technology). Typical power of a diesel locomotive is 2850 HP, while an electric is 6000 HP. with 1500 HP at each shaft, also ~1MW. There is a heavy duty 12,000 HP diesel engine in USA(with 6 shafts, also 2000 HP at each shaft). The high speed ICE train (InterCityExpress) in germany is 13,000 HP, has a normal travelling speed of 200 km/h, 2 locomotives, 3-phase induction motors, electronic drive. Older units do this whole thing with a fancy cam/gear arrangement circa 1940's. Just takes a single reversable motor to drive the unit and some limit switches to be sure it can only stop at full 'steps' (or 'half steps' for those capable of running 'half-step') The one we have here operates with a motor. Because the system intermittently inserts an additional voltage drop through the inductor, the control circuits typically have time-delays that prevent it trying to reverse direction or something while stepping. As far as zero-crossing and thyristors, I suppose it's certainly possible, but I haven't run across them for large substations. I have seen such a setup in power-conditioners for computer complexes and such, but that's only a few kVA (one unit I know of was rated for 25 kVA). The mechanical-switch tap changer is well-matured and has the nice advantage that when they 'fail', they 'fail' at the last 'step' and power continues to flow (albeit perhaps the wrong voltage). When I was a kid living in a rather rural area, there would be a pair of these on poles every few miles, connected open delta. (all transformer primaries were connected phase-phase then). Those are smaller than the units I'm thinking of. I'm talking about multiple MVA rated units. I had no idea how it really works, but I got the general idea. -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr NB:I killfile googlegroups. |
280V motor on 230V circuit
Ο έγραψε στο μήνυμα ... In alt.engineering.electrical Tzortzakakis Dimitrios wrote: | A shame that Tesla won the infamous "battle" and we don't have DC:-() But | then, we would be having a power plant at each neighborhood, instead of the | 300 MW ones. And the latter make easy terrorism targets, too. I cross my fingers that terrorists get no electrical engineering degree:0 | I know, I know, my answer was a bit provocative:-) And of course there are | DC regulators.... You're talking about DC generators;the one a 300 MW uses | for excitation is 220 V, 1000 A DC and probably shunt field. I have seen | here in some machine shops the old type welding generator, which is a 3 | phase induction motor coupled to (usually) a compound field DC generator, | which provides the welding current. The modern ones are, maybe, not larger | than a shoe box and powered by a higher wattage 230 V 16 A receptacle. | (Usual receptacles are 230 V 10 A;16 A for washing machines, dryers and the | like). You don't use 400 V for anything heavy duty like an oven? Yep. All ovens sold in EU are wired for 3 phase, 400 V with neutral (and earth, goes without saying). Just if you connect it on 1 phase (as usually) you use a bridge, and connect all L1-L2-L3 to the one and only hot. 230 V is powerful enough for almost everything in a house, only large airconditioners are 3 phase, and all industrial motors, even if they are 1HP:-) ( -- -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr NB:I killfile googlegroups. |
280V motor on 230V circuit
"Don Kelly" writes:
"Michael Moroney" wrote in message ... Are the load tap generators configured make-before-break? Break-before-make would mean a (very short) power outage every activation but make-before-break would mean a momentarily short-circuited winding and the break would involve interrupting a large short circuit current. -------- Yes -you are shorting a part of the winding but the switching is a bit more complex than that so that short circuit currents are limited to reasonable values. It is a multistep operation with reactor switching. ... Thanks for your (and esp. daestrom's) explanation on how they work. When I was a kid living in a rather rural area, there would be a pair of these on poles every few miles, connected open delta. (all transformer primaries were connected phase-phase then). "on load tap changers"? Not likely. These were applied to transformers only where it was worth the effort. Definitely transformers in rural areas- typical pole pigs- would have to be de-energized as the tap changer is a manually operated switch inside the tank. Some larger transformers did have off-load but live changers operated from ground level. What you saw could have been somethng else altogether. I'm not completely sure what these are other than being told that they were voltage regulators (tapped autotransformers) long ago. These are large cans with 3 bushings on top, taller and slimmer than most pole pigs, and they usually have a control box on the pole around eye level. I see the same style cans in substations between the stepdown transformer and the distribution system except they sit on the ground and come in sets of three. Delta primaries as you indicate were around when you were a kid, would, in most areas mean that you are now a pensioner. I remember cases of conversion from delta to star for distribution primaries in small towns being done about 60 years ago and use of delta for transmission died much before that. While I'm hardly a kid, I'm no pensioner yet. In fact my father's place still has delta-connected distribution primaries in the area, at 7200 volts (I have an old fuse/switch holder from there labelled 7200V ??A). Where I mentioned they had pairs of these "voltage regulators" (or whatever they were) every several miles was a long run along a state highway. At some point they upgraded it to a wye configuration, probably at a higher voltage. However, several side branches haven't been upgraded yet. On the side branch feeding my father's place there is a bank of 3 transformers connected wye-delta immediately followed by a pair of these "voltage regulator" cans connected open delta. From that point on the distribution system is visibly old. |
280V motor on 230V circuit
Yep. Seen those types of units and was about to mention them. One model had a core that had a space in it much like a D'Arsonval meter movement. The space was filled with a 'bobbin' that when cross-ways left two large air-gaps and when aligned would neatly bring the gap between the two sides of the core. A weight and lever would turn the 'bobbin' into/outof the core to control the current. Problem with those is, if you get a loose connection or arc, the unit will just keep pumping power to the system no matter what. daestrom The only place I've seen those used was for regulating current in 6.6A (usually) series loop streetlighting. Lots of this still left in the Los Angeles area and a few other pockets but most is gone by now. It was very common from the 20s up through the 60s though, incandescent at first, but 6.6A matching transformer "ballasts" are available for HID lamps as well. Most airfield illumination is still 6.6A series, I suspect the modern control gear is solid state. Westinghouse had a design where the secondary was on a linear mechanism with a counterweight and would float above the primary. Current was adjusted by moving the counterweight. |
280V motor on 230V circuit
In alt.engineering.electrical Tzortzakakis Dimitrios wrote:
| | ? ?????? ??? ?????? | ... | In alt.engineering.electrical Tzortzakakis Dimitrios | wrote: | | | A shame that Tesla won the infamous "battle" and we don't have DC:-() | But | | then, we would be having a power plant at each neighborhood, instead of | the | | 300 MW ones. | | And the latter make easy terrorism targets, too. | | I cross my fingers that terrorists get no electrical engineering degree:0 I suspect quite many already have them. Many have degrees in a lot of other things like chemistry and physics. Some even have doctoral level degrees. | | I know, I know, my answer was a bit provocative:-) And of course there | are | | DC regulators.... You're talking about DC generators;the one a 300 MW | uses | | for excitation is 220 V, 1000 A DC and probably shunt field. I have seen | | here in some machine shops the old type welding generator, which is a 3 | | phase induction motor coupled to (usually) a compound field DC | generator, | | which provides the welding current. The modern ones are, maybe, not | larger | | than a shoe box and powered by a higher wattage 230 V 16 A receptacle. | | (Usual receptacles are 230 V 10 A;16 A for washing machines, dryers and | the | | like). | | You don't use 400 V for anything heavy duty like an oven? | | Yep. All ovens sold in EU are wired for 3 phase, 400 V with neutral (and | earth, goes without saying). Just if you connect it on 1 phase (as usually) | you use a bridge, and connect all L1-L2-L3 to the one and only hot. 230 V is | powerful enough for almost everything in a house, only large airconditioners | are 3 phase, and all industrial motors, even if they are 1HP:-) ( That means each element individually runs on 230 V and they just divided them up in three approximately equal sections, or use triple elements for each type of use. How many things that have just ONE (large) element would have it available in both 230 V and 400 V versions? -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
In alt.engineering.electrical Don Kelly wrote:
| ---------------------------- | "daestrom" wrote in message | ... | | wrote in message | ... | In alt.engineering.electrical Michael Moroney | wrote: | | | Are the load tap generators configured make-before-break? | | Break-before-make would mean a (very short) power outage every | activation | | but make-before-break would mean a momentarily short-circuited winding | and | | the break would involve interrupting a large short circuit current. | | I wonder how much regulation could be managed through the use of variable | leakage inductance in the transformer windings. | | | I suppose you could, but increasing leakage inductance means you're | increasing losses aren't you? Just a percent or two on a unit rated for | 250 MVA can be too much to tolerate. | | daestrom | ------------- | I don't see changing leakage inductance having much effect on losses ( a | great effect on voltage regulation -likely all to the bad) but the problem | is one of changing leakage inductance. | Does this mean changing a gap in the core? Does it mean moving one winding | with respect to another? In any case it does mean some fiddling with the | core or winding. The thought is to change the core in some way. Maybe that can be done in a gradual way, as opposed to winding taps that have to be either BtM or MtB. | This has been done for series lighting circuits where the load current was | kept constant by using a transformer which balanced the forces between coils | against a fixed weight. If the current changed the secondary coil moved so | that there was more or less leakage. The units that I have seen were rather | cumbersome. I'm thinking more along the lines of a motor drive to move the coil, and that be controlled by the same authority that would have controlled the steppable taps. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
In alt.engineering.electrical Don Kelly wrote:
| Yes -you are shorting a part of the winding but the switching is a bit more | complex than that so that short circuit currents are limited to reasonable | values. It is a multistep operation with reactor switching. On-load tap | changers are expensive and are generally limited to applications where this | is absolutely needed (I have seen one where the tap changer was nearly as | large as the transformer). I was thinking of what I might do to get some fine voltage control within a very limited range around 120 volts. The obvious option was a 0-140 volt variable transformer. But I wanted to make sure I had a setup that could be better limited, for example, to not allow an accidental too low voltage. I also didn't want to run all the power through the variable. So what I was going to do was get a smaller variable transformer, and two buck-boost transformers. One transformer would be wired 120-16 in buck mode to drop the voltage down to 104. The other transformer would be wired 120-24 and supplied via the 0-140 variable transformer, giving me a 0-28 variable boost. The end result is 104-132 over the full range of variable transformer control (assuming the boost transformer has no issues with being overfed at 140V). So I might envision a transformer where the taps can be part of a boost transformer added to the main transformer. The first buck transformer in my above example would not be needed because the main transformer would be designed with a 1st secondary at the lowest voltage of the adjustable range. A 2nd secondary on the same main transformer would have the adjustable taps and it would feed a separate boost transformer which has a secondary wired in series with the 1st secondary of the main. So the taps would only be dealing directly with a fraction of the power (assuming there is no back feed issue involved) based on the needed adjustment range. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
In alt.engineering.electrical Thomas Tornblom wrote:
| Residential power in Norway is normally 230V three phase btw, instead | of 400V three phase. Their 230V outlets are two phase and ground | instead of one phase, neutral and ground. Their three phase outlets | therefore are blue instead of red and have four prongs instead of five. Is this the system where the voltage is 133 volts relative to ground and 230 volts between phases (and formerly 127 volts relative to ground and 220 volts between phases)? If they still use that system, then I'm interested in buying a UPS designed for that. But it is my understanding it is phased out in cities and hard to find anymore in rural locations. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
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280V motor on 230V circuit
In alt.engineering.electrical Don Kelly wrote:
| Yes -you are shorting a part of the winding but the switching is a bit more | complex than that so that short circuit currents are limited to reasonable | values. It is a multistep operation with reactor switching. On-load tap | changers are expensive and are generally limited to applications where this | is absolutely needed (I have seen one where the tap changer was nearly as | large as the transformer). What about multiple parallel transformers, or at least multiple parallel windings on the same core (on whichever side the tapping is to be done), where the taps are stepped incrementally on each winding? Instead of a shorted winding segment, you'd have windings of differing voltage in parallel as each of the windings change their taps one at a time. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
|
280V motor on 230V circuit
On May 13, 10:30 pm, wrote:
Is this the system where the voltage is 133 volts relative to ground and 230 volts between phases (and formerly 127 volts relative to ground and 220 volts between phases)? Since I'm posting from GoogleGroups I can't respond to Phil, but the rest of you can be enlightened. In 120/240 or similar systems there is not the freedom to choose this ratio. The wiring of the source transformer determines it. As others have noted, in the "Edison" U.S. system the source is a center tapped transformer with the center tap grounded. This makes a two phase system with each 120v "leg" 180 degrees out of phase with the other one. The ratio of the high voltage (240v) and the low voltage (120v) is always therefore 2:1. In a three phase system there will be three transformers with secondaries (one for each phase) wired in a "star" or "Y" configuration. This is necessary because you need the center point of the "star" or "Y" to be ground for each low voltage phase. If you wire with a "delta" configuration there is no central grounding point available for the individual phases. IN three phase circuits the relationship between that individual phases to ground (say 120v) and the voltage measured between phases is not arbitrary. It is always determined by the square root of 3. Hence the between phase voltages being sqrt 3 x 120 = 208V. Just like the two phase system these ratios are determined by physics and can't be arbitrarily set. Of course there is the issue that electric companies often will name a voltage one thing while actually supplying an other for small variations about the "standard" voltage. |
280V motor on 230V circuit
Ο έγραψε στο μήνυμα ... In alt.engineering.electrical Tzortzakakis Dimitrios wrote: | | ? ?????? ??? ?????? | ... | In alt.engineering.electrical Tzortzakakis Dimitrios | wrote: | | | A shame that Tesla won the infamous "battle" and we don't have DC:-() | But | | then, we would be having a power plant at each neighborhood, instead of | the | | 300 MW ones. | | And the latter make easy terrorism targets, too. | | I cross my fingers that terrorists get no electrical engineering degree:0 I suspect quite many already have them. Many have degrees in a lot of other things like chemistry and physics. Some even have doctoral level degrees. | | I know, I know, my answer was a bit provocative:-) And of course there | are | | DC regulators.... You're talking about DC generators;the one a 300 MW | uses | | for excitation is 220 V, 1000 A DC and probably shunt field. I have seen | | here in some machine shops the old type welding generator, which is a 3 | | phase induction motor coupled to (usually) a compound field DC | generator, | | which provides the welding current. The modern ones are, maybe, not | larger | | than a shoe box and powered by a higher wattage 230 V 16 A receptacle. | | (Usual receptacles are 230 V 10 A;16 A for washing machines, dryers and | the | | like). | | You don't use 400 V for anything heavy duty like an oven? | | Yep. All ovens sold in EU are wired for 3 phase, 400 V with neutral (and | earth, goes without saying). Just if you connect it on 1 phase (as usually) | you use a bridge, and connect all L1-L2-L3 to the one and only hot. 230 V is | powerful enough for almost everything in a house, only large airconditioners | are 3 phase, and all industrial motors, even if they are 1HP:-) ( That means each element individually runs on 230 V and they just divided them up in three approximately equal sections, or use triple elements for each type of use. How many things that have just ONE (large) element would have it available in both 230 V and 400 V versions? Professional washing machines. One of my very first days 'in the field' was to connect some of them. They have a large heating element, you can connect it single phase, or 3 phase, it just heats up faster (of course) when you connect it 3 phase. (they have a single phase motor, so it works also in pure 230 V). -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr NB:I killfile googlegroups. |
280V motor on 230V circuit
? "daestrom" ?????? ??? ?????? ... "Tzortzakakis Dimitrios" wrote in message ... ? "daestrom" ?????? ??? ?????? ... "Michael Moroney" wrote in message ... "daestrom" writes: P.S. In the US, a 'tap-changer' may be built for either for unloaded or loaded operation. The 'unloaded' type can not be stepped to another tap while there is load on the unit (although it can still be energized). It's switch contacts cannot interrupt load though, so if you try to move it while loaded, you can burn up the tap-changer. The classic 'load-tap-changer' is actually several switches that are controlled in a precise sequence to shift the load from one tap of the transformer to another while not interrupting the load current. P.P.S. Load tap changers typically have a significant time-delay built into the controls so they do not 'hunt' or respond to short drops in voltage such as starting a large load. 15 seconds to several minutes is typical. So even with load-tap-changers, starting a single load that is a high percentage of the system capacity will *still* result in a voltage dip. Are the load tap generators configured make-before-break? Break-before-make would mean a (very short) power outage every activation but make-before-break would mean a momentarily short-circuited winding and the break would involve interrupting a large short circuit current. Certainly modern ones likely use thyristors and zero crossing detectors. I figured someone would 'bite' :-) Typical large power load-tap-changers have a primary winding and two secondaries. You mean a secondary and a tetriary? The transformer for the hotel load of a 300 MW unit is powered directly from the turbo alternator (21 kV) and has a secondary of 6.6 kV and a tetriary of again 6.6 kV. This is done because it has wye-wye-wye connection (IIRC). The hotel load of such a unit is 10%, also 30 MW, including 7 brown coal mills. Typical size of a 6.6 kV motor is 1 MW. One secondary produces about 100% of 'rated' secondary voltage. The second secondary produces about 15% to 20% of the rated voltage, but has numerous taps from end to end, about 2.5% 'steps'. (for a total of about eight taps). The cental tap of the boost/buck winding is tied to one end of the main secondary. The boost/buck can be used to step from 90% to 110% of the 'design' output. I suppose some can step over a wider range, but I haven't run across them. *TWO* rotary switches have each tap tied to one of the positions of each rotory switch, and each 'wiper' is tied to single heavier contacts that are opened in the operating sequence. The output side of these two interrupting contacts are tied to each end of a large center-tapped inductor. So, normally both rotary switches are aligned to the same transformer tap, both interrupting contacts are shut, and load current flows from the boost/buck winding tap, splits and flows through both rotary switches, both interrupting contacts, enters both ends of the inductor and out the inductor center tap. Because the current flows into both ends of the inductor and the mutual inductance of the two parts cancel, there is little voltage drop in the inductor. Begin step sequence: 1) Open one interrupting contactor. Now load current doubles through half the inductor and is zero in the other half, so the voltage drop across the inductor actually makes output voltage drop, even if trying to step 'up'. 2) Move associated rotary switch to next step of transformer bank. 3) Close interrupting contactor. Now, the two rotary switches are across different taps. The inductor prevents a excessive current, otherwise you have a direct short of the two winding taps. Some tap changers can stop at this point and are called 'half-step' units. Obviously, the inductor has to be rated for sustained operation across a step of the boost/buck winding plus load current in order to survive sustained 'half step' operation. 4) But for tap changers that can't operate 'half-step', the sequence continues. And opens the other interrupting contactor. Now the other half of the inductor has full load current. 5) Move second rotary switch to next step (now both switches are on the new step) 6) Close the second interrupting contactor. You're back in the initial configuration, but with both rotary switches on a new transformer tap. Quite the same principle is done with diesel locomotives and is called diesel-electric transmission, and also in pure electric locomotives (E-Lok in german, for Elektrische Lokomotive). The diesel engine, 2-stroke and usually 600 to 900 rpm at full throttle, is coupled to a generator. The generator has small windings, connected in series for the last notch, higher voltage and relatively smaller current, and in parallel for start, higher amperage and smaller voltage. The traction motors are directly coupled on the wheel shaft, and are air cooled. An E-Lok has a trasformer, with the primary directly supplied by the cetenary, 15 kV 16 2/3 Hz in Germany, and 25 kV 50 Hz in Greece, The secondary uses the same principle. The typical size of a traction motor is 1 MW, 4 (one each shaft) and maximum voltage 700 volts, and are series wound motors with special construction to operate at 16 2/3 Hz (or 50 Hz with today's technology). Typical power of a diesel locomotive is 2850 HP, while an electric is 6000 HP. with 1500 HP at each shaft, also ~1MW. There is a heavy duty 12,000 HP diesel engine in USA(with 6 shafts, also 2000 HP at each shaft). The high speed ICE train (InterCityExpress) in germany is 13,000 HP, has a normal travelling speed of 200 km/h, 2 locomotives, 3-phase induction motors, electronic drive. In US, diesel-electric used to always be DC machines, but modern ones are now AC generators with thyristers to regulate the power flow to the traction motors. Traction motors are still DC however to allow for their use in dynamic braking. I suppose in Europe the better way to go would be regenerative braking, putting the braking power back into the overhead line, but that would need a static inverter. Probably the transformer secondary has a four-quadrant converter to allow reversal of power flow ?? This is for sure in ICE, where they get 15 kV 16 2/3 Hz AC from the cetenary, and they convert it to 3 -phase AC for traction motors (3 phase induction), and they also use regenerative breaking.There's also the french TGV (Tren de Grand Vitesse) and the just new by Alstom (www.alstom.com) AGV (Autometrisse de Grand Vitesse). Classic E-Loks have regular breaking, and AC motors with series excitation, designed to work at 16 2/3 Hz. (Just like the ones you'll find in a drill, but much larger, at 1 MW or more). They are called universal motors, in the small scale, because they can work both in AC and DC. I'm wondering, how large their brushes are... In the 300 MW turbo generator, the brushes that suplly the excitation current, are as large as bricks. Newer type of turbo generators are brushless. The speed record for a classic E-Lok is held by Siemens' Taurus, IIRC 180 km/h with 12,000 HP. Nice thing about the newer solid-state control systems (AC-Generator/ DC-Traction) is the ability to control wheel-slip. In the old days it took a skilled engineer (the train-driving kind) to get maximum power without slipping a lot (and wasting a lot of sand). Now modern units have speed sensors on each individual wheel set and control the power flow to individual traction motors. As soon as a wheel set starts to slip it can redirect power flow to other traction motors to prevent the slipping set from 'polishing the rail'. This prolongs life of the wheels and rail and actually improves the maximum tractive effort a locomotive can deliver. And when hauling 100+ cars of coal in a unit train up grade, tractive effort is what keeps you moving. I have no idea about train driving, but in Germany I got a local train from a small city to Mannheim, and the Lokfuehrer (train driver) was driving it like a race car... He accelerated fully to 130 km/h, and when he was close to the next stop, he braked fully, too. It had one E-Lok, and two cars. Also, the ICE starts like a race car. It's longer than 500 m, 12 cars, and I think it accelerates to 100 km/h in 10 seconds. You forgot to mention that traction motors often have separately powered blower motors for air-cooling. This is because the motor may spend hours operating at low speeds and shaft-mounted cooling fans are not enough. The motor blower is usually mounted up inside the engine house and connects to the traction motor via a large flexible duct. Yeah, right, and the transformer is cooled by active oil cooling (that means that the oil cools the trasformer, and there's a separate oil cooler. Like the intercooler used in the tanks where I served at army, but that's a differrent story). Some diesel-electric unitl have six axles and six traction motors. The trade-off is between how much power you can get to the traction motors and how much weight you can keep on the wheels to keep them from slipping. Sand is okay for starting and some special situations, but you can't carry enough to use it for an entire run. But of course too much weight and you need more axles to protect the rail from damage (depending on the size of the rail being used). But isn't a locomotive by itself heavy enough? Like 120 tons and above, with fuel and all? (Check at www.wartsila.com some large diesels). In our new power station, they have installed two 50 MW, 70,000 HP two-stroke diesels. To see how 2-stroke diesels work, look in www.howstuffworks.com.. The ships that travel from Iraklion to Piraeus (the harbour of Athens) the new ones, have 4 Wartsila 12 V 46 4-stroke diesels. 12 is number of cylinders, in V, and with a diameter of piston, 46 cm. When they travel normally at night, they fire up 2 engines. But, when they make a day trip, they fire up all 4 engines at full throttle, and the whole ship vibrates. A ship is the only place you can get free electricity. In my last trip, I saw young students plugging their laptops to the ship's receptacles. A free lunch, after all:-) daestrom P.S. As you can see, I've seen a few railroad locomotives as well. Mostly just the older EMD's though, not GE's newer 'green' units. I have no idea what they are doing in continental Greece, they *should* have electrified all routes. -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr NB:I killfile googlegroups. |
280V motor on 230V circuit
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280V motor on 230V circuit
In alt.engineering.electrical Tzortzakakis Dimitrios wrote:
| Professional washing machines. One of my very first days 'in the field' was | to connect some of them. They have a large heating element, you can connect | it single phase, or 3 phase, it just heats up faster (of course) when you | connect it 3 phase. (they have a single phase motor, so it works also in | pure 230 V). If it has 3 elements rated for 230 volts, with 3 separate connections that would be to three separate phase for a three phase feed, and all connected to the one phase for a single phase feed, then it should heat up at the same speed, while drawing three times the current (not accounting for the motor). I don't know why it should heat up faster in three phase, or why you would say "of course" about it. I would think it would heat up faster if you took it over to London and hooked it up to a 240 volt supply. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
In alt.engineering.electrical Benj wrote:
| Since I'm posting from GoogleGroups I can't respond to Phil, but the | rest of you can be enlightened. Actually, I do see the ones the respond to my own posts. I think the reader does that to keep the threading intact. New posts I won't see. And that is what most of the spam is (I've seen some spammers that do followups to other posts). | In 120/240 or similar systems there is not the freedom to choose this | ratio. The wiring of the source transformer determines it. As others | have noted, in the "Edison" U.S. system the source is a center tapped | transformer with the center tap grounded. This makes a two phase | system with each 120v "leg" 180 degrees out of phase with the other | one. The ratio of the high voltage (240v) and the low voltage (120v) | is always therefore 2:1. | | In a three phase system there will be three transformers with | secondaries (one for each phase) wired in a "star" or "Y" | configuration. This is necessary because you need the center point of | the "star" or "Y" to be ground for each low voltage phase. If you wire | with a "delta" configuration there is no central grounding point | available for the individual phases. IN three phase circuits the | relationship between that individual phases to ground (say 120v) and | the voltage measured between phases is not arbitrary. It is always | determined by the square root of 3. Hence the between phase voltages | being sqrt 3 x 120 = 208V. Just like the two phase system these | ratios are determined by physics and can't be arbitrarily set. There is no more or less option to choose once you have either system. The choice you have is between the systems. If you have single phase, you only get 2.0 as a ratio. If you have three phase, you only get 1.7320508 as a ratio. | Of course there is the issue that electric companies often will name a | voltage one thing while actually supplying an other for small | variations about the "standard" voltage. They call it 208 volts, but it's closer to 207.8460969 :-) Precise voltage is not really practical. The voltage standard is a target to stay near. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
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280V motor on 230V circuit
"daestrom" writes:
wrote in message ... What about multiple parallel transformers, or at least multiple parallel windings on the same core (on whichever side the tapping is to be done), where the taps are stepped incrementally on each winding? Instead of a shorted winding segment, you'd have windings of differing voltage in parallel as each of the windings change their taps one at a time. That's still essentially a shorted turn (or set of turns). So when one is set for say 118V and the other is set for 120V, you have a 118V source connected in parallel with a 120V source and the only impedance is the transformer windings?? OUCH!!! I think the magic smoke will be spewing in no time Phil, did you see daestrom's excellent explanation how they use an inductor to prevent a dead short but in a way such that the inductor is virtually not there during normal operation (counterflowing currents)? If these tap changers are rather expensive, I'm wondering what those pole pig "voltage regulators" I mentioned are. I thought they were just tapped autotransformers. |
280V motor on 230V circuit
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wrote in message ... In alt.engineering.electrical Don Kelly wrote: | Yes -you are shorting a part of the winding but the switching is a bit more | complex than that so that short circuit currents are limited to reasonable | values. It is a multistep operation with reactor switching. On-load tap | changers are expensive and are generally limited to applications where this | is absolutely needed (I have seen one where the tap changer was nearly as | large as the transformer). I was thinking of what I might do to get some fine voltage control within a very limited range around 120 volts. The obvious option was a 0-140 volt variable transformer. But I wanted to make sure I had a setup that could be better limited, for example, to not allow an accidental too low voltage. I also didn't want to run all the power through the variable. So what I was going to do was get a smaller variable transformer, and two buck-boost transformers. One transformer would be wired 120-16 in buck mode to drop the voltage down to 104. The other transformer would be wired 120-24 and supplied via the 0-140 variable transformer, giving me a 0-28 variable boost. The end result is 104-132 over the full range of variable transformer control (assuming the boost transformer has no issues with being overfed at 140V). So I might envision a transformer where the taps can be part of a boost transformer added to the main transformer. The first buck transformer in my above example would not be needed because the main transformer would be designed with a 1st secondary at the lowest voltage of the adjustable range. A 2nd secondary on the same main transformer would have the adjustable taps and it would feed a separate boost transformer which has a secondary wired in series with the 1st secondary of the main. So the taps would only be dealing directly with a fraction of the power (assuming there is no back feed issue involved) based on the needed adjustment range. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | -------------- If I read you correctly, you want to use a second secondary (lower power rating) which is tapped and put in series with the main secondary. Now once you do this, you have in effect a single secondary with taps just as in a conventional tapped secondary. Sure the "tapped section" is lower power- because it is a lower voltage but it still has to handle the same current. Nothing is gained. The problem in tap changing is not "power" but the current being switched. In either case the voltage driving short circuit current on tap changing is that between taps Delta V =A(delta n) Delta Z =B(delta n)^2. where delta n is the change in turns between taps. The short circuit current on such a change will be proportional to 1/(delta n). If you want fine control, then you could go to sliding carbon brush as in a variac. The first idea of a separate transformer feeding a variac will not solve the "too low" voltage problem of the variac because you are still dealing with an autotransformer. Don Kelly remove the X to answer |
280V motor on 230V circuit
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wrote in message ... In alt.engineering.electrical Benj wrote: | Since I'm posting from GoogleGroups I can't respond to Phil, but the | rest of you can be enlightened. Actually, I do see the ones the respond to my own posts. I think the reader does that to keep the threading intact. New posts I won't see. And that is what most of the spam is (I've seen some spammers that do followups to other posts). | In 120/240 or similar systems there is not the freedom to choose this | ratio. The wiring of the source transformer determines it. As others | have noted, in the "Edison" U.S. system the source is a center tapped | transformer with the center tap grounded. This makes a two phase | system with each 120v "leg" 180 degrees out of phase with the other | one. The ratio of the high voltage (240v) and the low voltage (120v) | is always therefore 2:1. | | In a three phase system there will be three transformers with | secondaries (one for each phase) wired in a "star" or "Y" | configuration. This is necessary because you need the center point of | the "star" or "Y" to be ground for each low voltage phase. If you wire | with a "delta" configuration there is no central grounding point | available for the individual phases. IN three phase circuits the | relationship between that individual phases to ground (say 120v) and | the voltage measured between phases is not arbitrary. It is always | determined by the square root of 3. Hence the between phase voltages | being sqrt 3 x 120 = 208V. Just like the two phase system these | ratios are determined by physics and can't be arbitrarily set. There is no more or less option to choose once you have either system. The choice you have is between the systems. If you have single phase, you only get 2.0 as a ratio. If you have three phase, you only get 1.7320508 as a ratio. | Of course there is the issue that electric companies often will name a | voltage one thing while actually supplying an other for small | variations about the "standard" voltage. They call it 208 volts, but it's closer to 207.8460969 :-) Precise voltage is not really practical. The voltage standard is a target to stay near. ------------- Just a bitch that we have dealt with befo Phil- please realize that 207.846096....... is meaningless except that it is "about 208". 208V is correct to 3 significant figures which is actually better than one can assume to be true in practice. If the voltage line to neutral is actually 120.V (note the decimal) then we have 3 significant digits implying something between 119.5 Vand 120.5.V Then all you can truly claim is 208.V If it is 120.0V then there is reason to assume 208.0 V but no more decimals than that. If you have a meter which gives you 120.000000V with less than 1 part in 120 million error then you can claim 207.846097V for line to line voltage Do you have such a meter? Engineering and physics students who ignore the principle of "significant digits" lose marks for this "decimal inflation". Sure- you can let the calculator carry the extra digits (as it will do internally) but accepting these as gospel truth to the limit of the calculator or computer display is simply not on as you can't get better accuracy from a calculation than the accuracy of the original data (actually you will lose a bit). All that you get rid of is round off errors in calculations. Since, as you say, precise voltage is not really practical, then multi-decimal point numbers are meaningless. If we say 120V +/-10% then we are talking about 108-132V which for line to line becomes 187-229V (average 208V) and any extra decimal points don't mean anything. Don Kelly remove the X to answer |
280V motor on 230V circuit
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wrote in message ... In alt.engineering.electrical Don Kelly wrote: | Yes -you are shorting a part of the winding but the switching is a bit more | complex than that so that short circuit currents are limited to reasonable | values. It is a multistep operation with reactor switching. On-load tap | changers are expensive and are generally limited to applications where this | is absolutely needed (I have seen one where the tap changer was nearly as | large as the transformer). What about multiple parallel transformers, or at least multiple parallel windings on the same core (on whichever side the tapping is to be done), where the taps are stepped incrementally on each winding? Instead of a shorted winding segment, you'd have windings of differing voltage in parallel as each of the windings change their taps one at a time. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | ------------ So you have a differential voltage producing a circulating current through both windings leading to losses and heating due to circulating currents. In addition, there would be shifts in the load sharing between the two secondaries- with the possibility of overloading one of them. Also, you still haven't solved the problem of switching the current from one tap to another Note also to shift 2% you would have to make two 2% shifts, one on each winding so that you are essentially doubling the work and tap changing equipment while introducing other problems as Daestrom has indicated. - -- Don Kelly remove the X to answer |
280V motor on 230V circuit
In alt.engineering.electrical Don Kelly wrote:
| If I read you correctly, you want to use a second secondary (lower power | rating) which is tapped and put in series with the main secondary. Now once | you do this, you have in effect a single secondary with taps just as in a | conventional tapped secondary. Sure the "tapped section" is lower power- | because it is a lower voltage but it still has to handle the same current. | Nothing is gained. | The problem in tap changing is not "power" but the current being switched. No, that is not what I tried to explain. I'll try again: The main transformer would have 2 secondaries. These 2 secondaries are NOT wired in series with each other. The smaller of these secondaries will have taps. The tapped smaller secondary feeds another smaller transformer. The larger secondary of the main transformer, and the only secondary of the smaller auxiliary transformer, would be wired in series. So the taps are only dealing with the current of the lower power "tapping section". The smaller secondary of the main transformer, and the primary of the auxiliary transformer, can be wired for whatever voltage/current works out best. | In either case the voltage driving short circuit current on tap changing is | that between taps | Delta V =A(delta n) Delta Z =B(delta n)^2. where delta n is the change in | turns between taps. The short circuit current on such a change will be | proportional to 1/(delta n). | | If you want fine control, then you could go to sliding carbon brush as in a | variac. The first idea of a separate transformer feeding a variac will not | solve the "too low" voltage problem of the variac because you are still | dealing with an autotransformer. In that first scheme, adjusting the variac to the lowest voltage would be reducing the voltage contributed by the boost transformer. There is still the original supply voltage going around the variac, "plus" (actually minus) the buck voltage (to select the range I want). Since the variac is an autotransformer itself, it merely feeds the primary of the boost transformer. Note that in this case the "boost" transformer is wired as an isolation transformer. I should have mentioned that. If needed, I guess I could draw some ASCII diagrams or try to get something made graphically (all the tools I have to do that suck, except for Visio which needs Windows to run and I don't have a spare machine to do that at the moment). -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
In alt.engineering.electrical daestrom wrote:
| | wrote in message | ... | In alt.engineering.electrical Don Kelly wrote: | | | Yes -you are shorting a part of the winding but the switching is a bit | more | | complex than that so that short circuit currents are limited to | reasonable | | values. It is a multistep operation with reactor switching. On-load tap | | changers are expensive and are generally limited to applications where | this | | is absolutely needed (I have seen one where the tap changer was nearly | as | | large as the transformer). | | What about multiple parallel transformers, or at least multiple parallel | windings on the same core (on whichever side the tapping is to be done), | where the taps are stepped incrementally on each winding? Instead of a | shorted winding segment, you'd have windings of differing voltage in | parallel as each of the windings change their taps one at a time. | | | So when one is set for say 118V and the other is set for 120V, you have a | 118V source connected in parallel with a 120V source and the only impedance | is the transformer windings?? | | OUCH!!! I think the magic smoke will be spewing in no time I was afraid of that. That also means if you are going to parallel 2 transformers, they better have exactly the same winding ratio. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
In alt.engineering.electrical Michael Moroney wrote:
| Phil, did you see daestrom's excellent explanation how they use an | inductor to prevent a dead short but in a way such that the inductor is | virtually not there during normal operation (counterflowing currents)? I believe I missed that. | If these tap changers are rather expensive, I'm wondering what those | pole pig "voltage regulators" I mentioned are. I thought they were just | tapped autotransformers. Sounds like they may be more of a voltage selector. One set of transformers I saw once had a voltage selector which also revealed the voltage to me. Even those these huge things were well guarded behind a chainlink fence with barbed wire on top, I could clearly read the instructions on the voltage taps. It listed 5 or 6 different voltages in the 4160 volt range (I believe that was a middle one). The secondaries were a thick bundle of insulated wires not on insulator standoffs, so obviously LV, possibly 480V or 208V. These were 3 single tank transformers in roughly the design style of a pole pig (round tank) with a control panel on them with the tap control and some gauge I guessed may be temperature (but I could not see it clear enough at the distance I was at to be sure). The instructions did indicate that the transformer must be de-energized (not just unloaded) when making the change. So I'm guessing they were just to compensate for variations in the delivered voltage. These transformers were about 1 meter wide and 2.5 meters high, each (3 of them). I did not see any reference to a kVA rating. They were also very old looking (pre-WWII). They were humming. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
In alt.engineering.electrical Don Kelly wrote:
| Just a bitch that we have dealt with befo | | Phil- please realize that 207.846096....... is meaningless except that it is | "about 208". 208V is correct to 3 significant figures which is actually | better than one can assume to be true in practice. If the voltage line to | neutral is actually 120.V (note the decimal) then we have 3 significant | digits implying something between 119.5 Vand 120.5.V | Then all you can truly claim is 208.V | If it is 120.0V then there is reason to assume 208.0 V but no more decimals | than that. | If you have a meter which gives you 120.000000V with less than 1 part in 120 | million error then you can claim 207.846097V for line to line voltage Do | you have such a meter? | | Engineering and physics students who ignore the principle of "significant | digits" lose marks for this "decimal inflation". | | Sure- you can let the calculator carry the extra digits (as it will do | internally) but accepting these as gospel truth to the limit of the | calculator or computer display is simply not on as you can't get better | accuracy from a calculation than the accuracy of the original data (actually | you will lose a bit). All that you get rid of is round off errors in | calculations. | | Since, as you say, precise voltage is not really practical, then | multi-decimal point numbers are meaningless. If we say 120V +/-10% then we | are talking about 108-132V which for line to line becomes 187-229V (average | 208V) and any extra decimal points don't mean anything. You didn't notice the :-) I put on the number? We've been over this. I know the practice of significant digits, and how the voltages are designated (two different reasons you can get 208). I do follow the practice of carrying exactly the result of calculations into other calculations. I also use over significance in comparison of numbers. But I also know that rounding is a form of noise. So I avoid it until the time I end up with the final result. So if I multiply 120 by the square root of three I do get a number like 207.84609690826527522329356 which is either carried as-is into the next calculation, or rounded if it is the final answer. If some other strange calculation happens to give me the value 207.84609690826527522329356 then I know it is effectively equivalent to 120 times the square root of three in some way. But if what I get is 208.455732193971783228 then I know it has nothing to do with 120 times the square root of three, even though it, too, would end up as 208 if rounded to 3 significant digits. When it comes to _measured_ amounts, as opposed to synthetic ones, then the significance rules dictate how to round the results. With synthetic numbers (e.g. numbers I can just pick), I can also pick the rounding rules for the final results. But if I don't know that the calculations are done (e.g. I am not merely giving a designation for a voltage system), where someone else may take those numbers and do more calculations and round the results, then I do use more significance. But that is no different to me than just carrying that number from one calculation stage to another. -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
In alt.engineering.electrical Thomas Tornblom wrote:
| writes: | | In alt.engineering.electrical Thomas Tornblom wrote: | | writes: | | | | In alt.engineering.electrical Thomas Tornblom wrote: | | | | | Residential power in Norway is normally 230V three phase btw, instead | | | of 400V three phase. Their 230V outlets are two phase and ground | | | instead of one phase, neutral and ground. Their three phase outlets | | | therefore are blue instead of red and have four prongs instead of five. | | | | Is this the system where the voltage is 133 volts relative to ground and 230 | | volts between phases (and formerly 127 volts relative to ground and 220 volts | | between phases)? | | | | Yes. | | | | | | If they still use that system, then I'm interested in buying a UPS designed | | for that. But it is my understanding it is phased out in cities and hard to | | find anymore in rural locations. | | | | It seems they are moving to 400V as well, but I know many Norwegians | | are paying a hefty premium on their three phase equipment, like | | heatpumps. | | | | My heatpump use an internally star configured 3x400V compressor, and | | it would have been easy to wire it for 3x230V if they had brought out | | all the leads. | | If all 6 leads of the 3 windings are brought out separate, then it can be wired | in star for 400/230 volt systems, and in delta for 230/133 volt systems. But | for Europe in general there would be little reason to do that. There is also | no reason to do that in North America, as we don't have any 360/208 volt systems | at all. | | It would allow the Norwegians to buy less expensive heatpumps from Sweden :-) | | It seems like a very simple and cheap thing to do. My guess is that in the cities, they have already changed over to a 400/230 system, or at least a 380/220 system that hasn't been voltage adjusted, yet. What I've heard is the 220/127 system was a leftover in some rural areas of Norway, and also in Spain. Apparently Suadi Arabia has this system so they can make use of both European and American single phase appliances. Mexico also has 220/127 but primarily uses the 127 volt connection (and it's 60 Hz). The really strange thing is Brazil has 220 volts all around the country, with 60 Hz in some parts and 50 Hz in others, and used to use the American 120 volt 2-blade outlet/plug with 220 volts (you can be in for a surprise with that). -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
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280V motor on 230V circuit
daestrom wrote:
But the trouble with overall weight is the combination of weight, power and rail capacity. When you get to larger units, the rail used on a lot of roads can't handle more than about 50,000 lbm per wheel set. That means you're limited to about 100 tons for a unit with just 2 axles per truck (4 total). Go up to a 120 ton and you need 3 axles per truck. But a 100 ton, 4-axle unit has 12,500 lbm per axle, while a 120 ton, 6-axle unit has only 10,000 lbm per axle. If the wheel friction coefficients are the same, the 4-axle unit can develop 25% more tractive effort when starting before slipping wheels. lbm? I'm not sure on your units. In another life I used to calibrate railroad electronic weigh bridges. 4 axle locomotives were about 265,000 pounds (US). 6 axle locomotives were about 360,000 pounds. One 3 axle drive truck weighed 65,000 pounds. (In a second other life, hauled it on a flatbed truck.) |
280V motor on 230V circuit
? "daestrom" ?????? ??? ?????? ... "Tzortzakakis Dimitrios" wrote in message ... ? "daestrom" ?????? ??? ?????? ... snip Nice thing about the newer solid-state control systems (AC-Generator/ DC-Traction) is the ability to control wheel-slip. In the old days it took a skilled engineer (the train-driving kind) to get maximum power without slipping a lot (and wasting a lot of sand). Now modern units have speed sensors on each individual wheel set and control the power flow to individual traction motors. As soon as a wheel set starts to slip it can redirect power flow to other traction motors to prevent the slipping set from 'polishing the rail'. This prolongs life of the wheels and rail and actually improves the maximum tractive effort a locomotive can deliver. And when hauling 100+ cars of coal in a unit train up grade, tractive effort is what keeps you moving. I have no idea about train driving, but in Germany I got a local train from a small city to Mannheim, and the Lokfuehrer (train driver) was driving it like a race car... He accelerated fully to 130 km/h, and when he was close to the next stop, he braked fully, too. It had one E-Lok, and two cars. Also, the ICE starts like a race car. It's longer than 500 m, 12 cars, and I think it accelerates to 100 km/h in 10 seconds. There is little doubt that electric trains are faster than other types as far as acceleration and overall speed. :-) Yes, because as the germans say-"Sie nehmen Strom direct aus der Leitung"-They draw power directly from the wire. So it's a higher impulse current than any on board diesel can provide;_) snip Some diesel-electric unitl have six axles and six traction motors. The trade-off is between how much power you can get to the traction motors and how much weight you can keep on the wheels to keep them from slipping. Sand is okay for starting and some special situations, but you can't carry enough to use it for an entire run. But of course too much weight and you need more axles to protect the rail from damage (depending on the size of the rail being used). But isn't a locomotive by itself heavy enough? Like 120 tons and above, with fuel and all? (Check at www.wartsila.com some large diesels). In our new power station, they have installed two 50 MW, 70,000 HP two-stroke diesels. To see how 2-stroke diesels work, look in www.howstuffworks.com.. I'm quite aware of how a 2-stroke works, as the large EMD's (654 series, up to V-20 cylinder) that have been around for years are exactly that. Also how the turbo-charger works, the four different lube-oil pumps (scavenging, piston-cooling, main, and soak-back). Not to mention the fuel injectors, overspeed trip, high-crankcase pressure shutdown, and air-start systems to name a few of the various components. And Westinghouse air brakes with several variations, and the MU (multi-unit) interface used to connect several locomotives together and allow them all to be 'driven' from one cab. ' Of course you are, but I thought there might be other members of the group, that don't. I didn't know until I read the article. The large, 15,000 HP, 11 MW diesels we have here at our local power station, have a final steam stage, for better efficiency. The URL of our local college, where I got my degree, is www.teiher.gr , but I'm not sure if they got an english version. But the trouble with overall weight is the combination of weight, power and rail capacity. When you get to larger units, the rail used on a lot of roads can't handle more than about 50,000 lbm per wheel set. That means you're limited to about 100 tons for a unit with just 2 axles per truck (4 total). Go up to a 120 ton and you need 3 axles per truck. But a 100 ton, 4-axle unit has 12,500 lbm per axle, while a 120 ton, 6-axle unit has only 10,000 lbm per axle. If the wheel friction coefficients are the same, the 4-axle unit can develop 25% more tractive effort when starting before slipping wheels. Of course if the 120 ton, 6-axle unit has more overall horsepower, then even though it develops less tractive effort at low speeds, it can achieve a higher speed when loaded to it's rated tractive effort. Below a certain speed, the maximum you can pull is dictated by wheel slip. Then you're limited by tractive motor cooling up to a second point. Beyond that, the overall horsepower becomes the limit. Once you're 'horsepower limited', you can go faster, but only if you can reduce the amount of tractive effort needed (i.e. you want to go faster, you have to pull fewer cars or not climb as steep a grade). This 'hp limited speed' is in the range of just 15 to 20 mph for a lot of 4-axle units, somewhat faster for 6-axle units. With typical freight trains in the US, they look at the steepest grade on the road and figure out enough locomotive units and maximum cars to just be horsepower limited on that grade. So while the train may go faster on less steep sections or level grade, it'll be at notch 8 (full throttle) and struggling to make about 15 mph up the steepest part of the route. And stalled if one of the locomotive units dies. So more hp means you may be able to pull it faster, but you can't always pull as much. Kind of 'weird' until you work out a few problems, but that's how it works. In Germany, they have special locomotives for freight trains, and special for passenger ones. The former desingned for larger traction power, the latter for higher speed. I have more experience with ships, since there are no railroads in Crete, but there's a lot of sea, and islands in Greece:-) I'll never forget my trip to Rhodes, where my batallion was situated, by rail from Korinthos (the infamous boot camp) and with ship to Rhodes. She was full of soldiers and commuters:-) NB.:There are railroads in continental Greece. -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr NB:I killfile googlegroups. |
280V motor on 230V circuit
? "Bruce in Bangkok" ?????? ??? ?????? ... On 15 May 2008 05:20:27 GMT, wrote: In alt.engineering.electrical Michael Moroney wrote: | Phil, did you see daestrom's excellent explanation how they use an | inductor to prevent a dead short but in a way such that the inductor is | virtually not there during normal operation (counterflowing currents)? I believe I missed that. | If these tap changers are rather expensive, I'm wondering what those | pole pig "voltage regulators" I mentioned are. I thought they were just | tapped autotransformers. Sounds like they may be more of a voltage selector. One set of transformers I saw once had a voltage selector which also revealed the voltage to me. Even those these huge things were well guarded behind a chainlink fence with barbed wire on top, I could clearly read the instructions on the voltage taps. It listed 5 or 6 different voltages in the 4160 volt range (I believe that was a middle one). The secondaries were a thick bundle of insulated wires not on insulator standoffs, so obviously LV, possibly 480V or 208V. These were 3 single tank transformers in roughly the design style of a pole pig (round tank) with a control panel on them with the tap control and some gauge I guessed may be temperature (but I could not see it clear enough at the distance I was at to be sure). The instructions did indicate that the transformer must be de-energized (not just unloaded) when making the change. So I'm guessing they were just to compensate for variations in the delivered voltage. These transformers were about 1 meter wide and 2.5 meters high, each (3 of them). I did not see any reference to a kVA rating. They were also very old looking (pre-WWII). They were humming. All distribution transformers, sometimes called "pole pigs", that I have seen had some sort of voltage adjusting system, usually referred to as taps. Usually they are an actual bolted "tap" and you open the transformer and set the output voltage by making the proper tap connection when the transformer is installed and frankly it is usually ignored thereafter. The other "cans" you often see on poles are capacitors used to adjust the power factor on some secondaries. Or disconnect switches, plain or with high-voltage fuses. Bruce-in-Bangkok -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr NB:I killfile googlegroups. |
280V motor on 230V circuit
Ο έγραψε στο μήνυμα ... In alt.engineering.electrical Tzortzakakis Dimitrios wrote: | Professional washing machines. One of my very first days 'in the field' was | to connect some of them. They have a large heating element, you can connect | it single phase, or 3 phase, it just heats up faster (of course) when you | connect it 3 phase. (they have a single phase motor, so it works also in | pure 230 V). If it has 3 elements rated for 230 volts, with 3 separate connections that would be to three separate phase for a three phase feed, and all connected to the one phase for a single phase feed, then it should heat up at the same speed, while drawing three times the current (not accounting for the motor). I don't know why it should heat up faster in three phase, or why you would say "of course" about it. I would think it would heat up faster if you took it over to London and hooked it up to a 240 volt supply. Maybe you connected with single phase just one element? The rest two remained unconnected? (3 230 volts elements, connected wye). I'm sure it heated up faster, in 3 phase connection. -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr NB:I killfile googlegroups. |
280V motor on 230V circuit
|
280V motor on 230V circuit
Ο έγραψε στο μήνυμα ... In alt.engineering.electrical Thomas Tornblom wrote: | writes: | | In alt.engineering.electrical Thomas Tornblom wrote: | | writes: | | | | In alt.engineering.electrical Thomas Tornblom wrote: | | | | | Residential power in Norway is normally 230V three phase btw, instead | | | of 400V three phase. Their 230V outlets are two phase and ground | | | instead of one phase, neutral and ground. Their three phase outlets | | | therefore are blue instead of red and have four prongs instead of five. | | | | Is this the system where the voltage is 133 volts relative to ground and 230 | | volts between phases (and formerly 127 volts relative to ground and 220 volts | | between phases)? | | | | Yes. | | | | | | If they still use that system, then I'm interested in buying a UPS designed | | for that. But it is my understanding it is phased out in cities and hard to | | find anymore in rural locations. | | | | It seems they are moving to 400V as well, but I know many Norwegians | | are paying a hefty premium on their three phase equipment, like | | heatpumps. | | | | My heatpump use an internally star configured 3x400V compressor, and | | it would have been easy to wire it for 3x230V if they had brought out | | all the leads. | | If all 6 leads of the 3 windings are brought out separate, then it can be wired | in star for 400/230 volt systems, and in delta for 230/133 volt systems. But | for Europe in general there would be little reason to do that. There is also | no reason to do that in North America, as we don't have any 360/208 volt systems | at all. | | It would allow the Norwegians to buy less expensive heatpumps from Sweden :-) | | It seems like a very simple and cheap thing to do. My guess is that in the cities, they have already changed over to a 400/230 system, or at least a 380/220 system that hasn't been voltage adjusted, yet. What I've heard is the 220/127 system was a leftover in some rural areas of Norway, and also in Spain. Apparently Suadi Arabia has this system so they can make use of both European and American single phase appliances. Mexico also has 220/127 but primarily uses the 127 volt connection (and it's 60 Hz). The really strange thing is Brazil has 220 volts all around the country, with 60 Hz in some parts and 50 Hz in others, and used to use the American 120 volt 2-blade outlet/plug with 220 volts (you can be in for a surprise with that). -- There should be no problem with the frequency, the local US base (In Gournes-decomissioned after the end of the Cold War) used a regular 15 kV, 50 Hz feed, from the cretan grid, which was stepped down to 4150 volts and then to 120/240. All with US switchgear and tranformers! (NB for US guys.#10 wire gauge-10 mm2 main feed of residence, #12 -6 mm2 stove,#14-4 mm2 water heaters, #16-2.5 mm2 washing machines, dryers, #18-1.5 mm2 lighting.-approximately). I think that the personnel of the base used standard US fluorescent light fixtures and other equipment, sone of it was left as some of the buildings "inherited" by the greek state, were converted by us to 230/400 volts, with regular Schuko receptacles. -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr NB:I killfile googlegroups. |
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