Washing machine 240, 50Hz - 240, 60 Hz?

The plug fuse is for protection of the appliance flex only, not the appliance. If an appliance requires fusing in order to remain safe, it must include appropriate provision within itself. It is not permitted to rely on the plug fuse. Plug fuses go down to 2A in value, and that's still almost

500W which is plenty enough to ignite a christmas tree.

On 12 Nov 2006 08:24:23 GMT Andrew Gabriel wrote: | In article , | snipped-for-privacy@ipal.net writes: |> It's that increasing current I was wondering about. |> |> But you guys have actual fuses in your plugs. Why not set that fuse to |> a bit above the proper current? Of course someone will end up replacing |> the fuse with one of the wrong value. | | The plug fuse is for protection of the appliance flex only, | not the appliance. If an appliance requires fusing in order | to remain safe, it must include appropriate provision within | itself. It is not permitted to rely on the plug fuse. | Plug fuses go down to 2A in value, and that's still almost | 500W which is plenty enough to ignite a christmas tree.

The string of Christmas tree lights isn't really an appliance. The ones we have over here are basically the same wires coming out of the plug and going all through the string. So there isn't any real boundary between the flex cord and the rest of the string, unless you want to define that as being the first bulb.

I remember some past light strings my family had. An older set of strings my father got from his father was parallel wired with C7 bulbs. The plug on these were strangely very flat and wide. You could easily plug several outlets spaced very close together. They were non-polarized. But the one interesting thing about these plugs is they were fused. You could twist the prongs with a bit of force and release them and the prong and fuse would come out. The prong actually connected directly to the fuse. There was a small spring behind the fuse. But once the prong was twisted in, it could not move either inward or outward. I do remember once my father managed to have one come out while in the socket. Both prongs were fused and neither were polarized (you could rotate the plug 180 degrees). I'm sure the non-polarized aspect would be prohibited today, and the fuse on the neutral might be as well (e.g. it's unsafe to have an apparently dead, but hot, wiring).

We also had a series string with blinker lights. They blinked by means of a thermal element that shorted the filament when it heated up. There was what was called a "ballast bulb" at the head of the string. It was a larger bulb with a different socket. It glowed a bit dimmer, but was always going up and down in brightness as more or fewer blinkers shorted out. There was no dead bulb bypass so if one bulb burned out the whole string went dead. There were typically about 6 burn outs per season.

Today we have some non-blinker series strings with some kind of burnout bypass. The bulbs have some very fine wire wrapped around the posts to hold the filament. I suppose this is the bypass. These bulbs indicate a 2.5 to 3.5 volt operating range.

OK, so let's assume 3 volts per bulb. You would have 80 bulbs for your

240 volts, and we would have 40 bulbs for out 120 volts. I think they are about 1 watt each. I'd have to go dig them out early to see that right now (should be doing that in about a month, anyway), as well as count exactly how many are on a string. That would mean a current of about 1/3 amp. So why not put a 1/2 amp fuse in the plug? It would be better than say a 5 amp fuse just because the cord can handle 5 amps. Then if too many bulbs burn out, and the current rises too high, the fuse will blow. Or do they just not make 1/2 amp fuses in the size to fit plugs? They should, at least for the light strings.

One thing I have found with these light strings is that about 30% of the burnouts do not result in the bypass. Then I have to find the dead bulb. The strings and lights are made in some small Asian Pacific Rim country.

The AC side needs a source of AC voltage at the desired frequency. It also needs to be able to supply reactive. If you are working with a low power setup, an oscillator (as you suggest) will do but an AC grid able to accept what is being transmitted works better when dealing with hVDC systems. Rather than try to deal with this textually (as diagrams do help) I suggest that you go to

a start. There are more detailed explanations (fraught with equations) of commutation in various EE texts (both for motor control and for power systems).

----------------- Sure they are cheap- there is a downside to that. There may be a fixed resistor or a fuse built into the plug- I don't know? Since these are cheap and other causes for string failure exist "which bulbs have loose or poor contacts or are kaput" you are faced with the choice: a)waste a lot of time trying to find the problem which usually arises after you have tested and then put them up to find a dead string when it is cold enough to make you a eunuch. b)buy a device which helps you do this (in theory-I have one-better than hunt and peck and cost more than a new string of the little incandescent bulbs) and possibly not waste as much time. c) simply throw the string into the trash and spend the time with a hot toddy.

Your preference- I know mine.

I have a LED string which has a couple of dead lamps -can't replace them but It appears that the design is robust enough to allow for this so that after continuous use for a few months, no further failures have occurred.

Thanks for the "as usual" which is not warranted. Thanks for the history and thanks again for the details of the bypass devices which I either never knew or had forgotten (where did I put my wine glass?? I know that it was full and really want it.).

| The AC side needs a source of AC voltage at the desired frequency. It also | needs to be able to supply reactive. If you are working with a low power | setup, an oscillator (as you suggest) will do but an AC grid able to accept | what is being transmitted works better when dealing with hVDC systems. | Rather than try to deal with this textually (as diagrams do help) I suggest | that you go to |

| as a start. There are more detailed explanations (fraught with equations) of | commutation in various EE texts (both for motor control and for power | systems).

That didn't go into detail in the area I am interested in, which is how you get a good sine wave approximation (to minimize the subsquent L/C filtering) out of solid state switching if you can only do the switch steps during zero crossing. If you do something like pulse width, then you end up switching at other than zero crossing.

The receiving system has generation- which is a good sine wave source. Please note that switching is not necessarily at current zeros as in a single phase system. Switching will occur when an incoming phase takes over -i.e. current transfers from one set of SCr's to the next- natural commutation. Note that in such a case , in the rectification region, the active SCR's will cycle naturally as the voltage of the parallel SCR rises. In inversion, the same thing is true but the voltage is actually reversed with respect to the current -reversed power flow. (This is a damned crude and possibly incorrect way to state it but the key point is that there is natural commutation from phase to phase. Of course there will be harmonics and the current in a given AC phase will be roughly a stepped approximation of a sinusoid- just as in rectification with a 3 phase bridge. I really suggest a good text as, on this forum, a good explanation (no handwaving) is more than I wan't to attempt (and I would have to eradicate some rust (hey- I am long retired -phase retarded?))before trying in any case. Follow up leads on HVDC and/ or polyphase (typically 3 to 6 phases or more) inverters. The only names that I can come up with are old sources, Kimbark , El Hawari are two authors of power system texts who do touch on this.

It is quite possible that sometime in the future, devices will be developed that can switch high currents at high voltages opening up the use of pulse width modulation. Some avenues are being exploited but with how much success, I don't know. This would solve the DC circuit breaker problem as well.

-- Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer

----------------------------

|> That didn't go into detail in the area I am interested in, which is how |> you get a good sine wave approximation (to minimize the subsquent L/C |> filtering) out of solid state switching if you can only do the switch |> steps during zero crossing. If you do something like pulse width, then |> you end up switching at other than zero crossing. | | The receiving system has generation- which is a good sine wave source.

When converting DC (HVDC) to AC (HVAC) which end is the "receiving system". Sorry, I don't know that term.

| Please note that switching is not necessarily at current zeros as in a | single phase system. Switching will occur when an incoming phase takes | over -i.e. current transfers from one set of SCr's to the next- natural | commutation. Note that in such a case , in the rectification region, the | active SCR's will cycle naturally as the voltage of the parallel SCR rises. | In inversion, the same thing is true but the voltage is actually reversed | with respect to the current -reversed power flow. (This is a damned crude | and possibly incorrect way to state it but the key point is that there is | natural commutation from phase to phase. Of course there will be harmonics | and the current in a given AC phase will be roughly a stepped approximation | of a sinusoid- just as in rectification with a 3 phase bridge.

So how do you get the stepped approximation when the incoming voltage is a steady DC? What is the switching rate?

| I really suggest a good text as, on this forum, a good explanation (no | handwaving) is more than I wan't to attempt (and I would have to eradicate | some rust (hey- I am long retired -phase retarded?))before trying in any | case. Follow up leads on HVDC and/ or polyphase (typically 3 to 6 phases or | more) inverters. The only names that I can come up with are old sources, | Kimbark , El Hawari are two authors of power system texts who do touch on | this.

I'm just focusing on a single question. A book or text would be excessive time to just answer a question and I wouldn't pursue it even if you gave me the book.

| It is quite possible that sometime in the future, devices will be developed | that can switch high currents at high voltages opening up the use of pulse | width modulation. Some avenues are being exploited but with how much | success, I don't know. This would solve the DC circuit breaker problem as | well.

Just how high can this switching go in terms of voltage and current now, assuming you can build an array of them in series and/or parallel with syncronized switch as big as desired to get the greatest power level?

Can we do this for say 120 volts at 15 amps?

I'm less interested in the theory of how things work, right now, and more interested in which technology is actually used in real cases, varying from HVDC conversion for power grids all the way down to the gadget that plugs into the cigarette lighter to give you a few watts of 120 volts AC.

I might have an interest in the theory later. I already do understand how things like pulse width modulation and pulse density modulation work. What I want to know is just how far these technologies can go in terms of power levels for real available devices, and how much real inverters might be using them.

------- Receiving end is the AC end in this case.

---------

-------- The DC current will be shared betwen the phases just as in a 3 phase rectifier, The AC phase current will be a series of flat topped alternating pulses with a fundamental frequency dictated by the grid. line currents may have steps if delta or a dual inverter is used. Switching occurs when one phase takes over from another so for a 3 phase there will be 'on" switching every 120 degrees of the fundamental. Look at a 3 phase bridge (single phase won't do) with SCR's. Ignore source inductance and look at the voltage and current waveform assuming a constant current on the DC side. Note that current will switch from one phase to the next when the incoming phase voltage is higher. Look at this for different SCR turn on angles including those beyond 90 degrees where the action changes from rectifier to inverter (current the same but average DC voltage is negative). The reason for referring to books is that they do have the waveforms shown for different conditions.

------------ In the future they may be very useful. I believe that there are gate turn on transistors which show promise at lower levels of current and voltage. However, knife switches work well at low voltages and currents but not at HV levels.

| The DC current will be shared betwen the phases just as in a 3 phase | rectifier, The AC phase current will be a series of flat topped alternating | pulses with a fundamental frequency dictated by the grid. line currents may | have steps if delta or a dual inverter is used. Switching occurs when one | phase takes over from another so for a 3 phase there will be 'on" switching | every 120 degrees of the fundamental. Look at a 3 phase bridge (single | phase won't do) with SCR's. Ignore source inductance and look at the voltage | and current waveform assuming a constant current on the DC side. Note that | current will switch from one phase to the next when the incoming phase | voltage is higher. Look at this for different SCR turn on angles including | those beyond 90 degrees where the action changes from rectifier to inverter | (current the same but average DC voltage is negative). | The reason for referring to books is that they do have the waveforms shown | for different conditions.

So basically it comes down to the switching speed is no more than the rate of zero crossings. And all of this is because it's such high voltage or current?

| In the future they may be very useful. I believe that there are gate turn on | transistors which show promise at lower levels of current and voltage. | However, knife switches work well at low voltages and currents but not at HV | levels.

If you stack the devices appropriately, and have them well insulated, then you can get some high voltages. Perhaps leakage to air will be the limiting factor. As for switching high current, it seems if the switch is always letting the current go in some direction, it might be doable.

So what is the magic voltage or current below which PWM or PDM is happy?

---------- Yes - or in the case of a 3 phase converter- switching or commutation takes place when the next phase takes over- current through the individual SCR goes to 0 at the same time that it rises in the next one. Chopping doesn't occur. Note that a typical light dimmer will use triacs which are essentially back to back SCR's. You control the turn on time but the turn off time is at the current zero. These are so cheap that there would appear to be little incentive to go to pulse width modulation.

There is a reference on the net possibly from ABB which shows the currents and voltages for rectifier/inverter operation. There is also a reference below which indicates that there have been developments with regard to PWM. in the VSC converters using Gate turn off devices or IGBT (bipolar) devices. These are becoming useful for supplying isolated loads or smaller loads- say less than 200MVA at +/-80KV. SCR bridges are still the sole means at EHV (say 3000MVA at +/- 500KV ) levels.

------------ Stacking is already done. A "single" bridge element may have a stack of

4000A SCR's each capable of handling a reverse voltage of 10KV. It is BIG- lots of insulation and high clearances.

| Yes - or in the case of a 3 phase converter- switching or commutation takes | place when the next phase takes over- current through the individual SCR | goes to 0 at the same time that it rises in the next one. Chopping doesn't | occur.

I can see that being reasonable. If phase A is rising in current to the same level and polarity that phase B is falling to, they can be flipped at that point by changing the state of 4 of the 6 gates?

| Note that a typical light dimmer will use triacs which are essentially back | to back SCR's. You control the turn on time but the turn off time is at the | current zero. These are so cheap that there would appear to be little | incentive to go to pulse width modulation. Based on some waveforms I've seen, some turn on shortly after the zero cross and turn off somewhere mid way through the half cycle. The zero cross seems to be uninvolved. Not all are like that, but many are.

| There is a reference on the net possibly from ABB which shows the currents | and voltages for rectifier/inverter operation. | There is also a reference below which indicates that there have been | developments with regard to PWM. in the VSC converters using Gate turn off | devices or IGBT (bipolar) devices. | These are becoming useful for supplying isolated loads or smaller loads- say | less than 200MVA at +/-80KV. SCR bridges are still the sole means at EHV | (say 3000MVA at +/- 500KV ) levels. |

On page 2 see "Force Commutation Converters" ... they _are_ using PWM at higher than power line (net) frequency. No mention of PDM anywhere.

So they do have to be switching things at times other than when the current is at zero or is the same as another phase.

Maybe they can try PDM.

|> | In the future they may be very useful. I believe that there are gate |> turn on |> | transistors which show promise at lower levels of current and voltage. |> | However, knife switches work well at low voltages and currents but not |> at HV |> | levels. |>

|> If you stack the devices appropriately, and have them well insulated, |> then you can get some high voltages. Perhaps leakage to air will be |> the limiting factor. As for switching high current, it seems if the |> switch is always letting the current go in some direction, it might |> be doable. | ------------ | Stacking is already done. A "single" bridge element may have a stack of | 4000A SCR's each capable of handling a reverse voltage of 10KV. It is BIG- | lots of insulation and high clearances.

And optical fiber to control?

|> So what is the magic voltage or current below which PWM or PDM is happy? | ---- | Outside of the reference above, I have little information. This may help a | bit- look at HVDC light |

which may be the wave of | the future.

I'm interested in the 600 volt and below range. Can something switch a few amps on and off at times the current (and voltage) is not at zero crossing? The idea is to build an inverter that uses high frequency PWM or PDM to chop up the voltage from DC into an LC circuit to filter the high frequency out and produce AC at 50 or 60 Hz (or whatever frequency in that range is programmed in the pulse pattern synthesizer). I also want to do similar as a DC to DC regulator for controlling charge from solar arrays and AC to DC to control and diverter power from wind generators.

|> Based on some waveforms I've seen, some turn on shortly after the zero |> cross |> and turn off somewhere mid way through the half cycle. The zero cross |> seems |> to be uninvolved. Not all are like that, but many are. | -- | If that is the case- I don't know what you are looking at. Which zero | crossing - voltage or current ? | SCR's or Triacs that I have known don't do that. Are you sure something is | not reversed or out of whack in the scope?\

For resistive lights, the zero-crossing is pretty much the same. But as I am referring to waveforms that rise up from the zero-crossing and are then just suddenly turned off, there is no ambiguity unless this involves radically low power factors.

These are waveforms I have seen published. I don't know what is being tested. But the point is that _something_ actually _can_ shut off at least a few amps of current. Whether it is a Triac, SCR, Thyristor, or what, I either didn't see, didn't care, or didn't remember at the time. I was only concerned with the harmonics of the waveform, not in how to achieve the waveform, back then.

My concern today is finding devices to turn voltage and current on and off at points specifically controlled. I'm not dealing with the power levels of transmission grid AC/DC or 50/60 converstion. What I do want to look at is DC regulators and DC to AC inverters in power levels up to 10kw or 20kw. But that's NOT per individual component. A design could parallel many components if need be. Ideally, such a device would have fast switching that would allow using pulse density modulation and be easier to filter. But pulse width modulation is certainly usable.

|> And optical fiber to control? | ----- | Yes that is used.

I don't know if I will need an optical control for turn on/off operations. The DC voltage levels could be from 48 to 600 volts open-circuit.

|> I'm interested in the 600 volt and below range. Can something switch a |> few |> amps on and off at times the current (and voltage) is not at zero |> crossing? |> The idea is to build an inverter that uses high frequency PWM or PDM to |> chop up the voltage from DC into an LC circuit to filter the high |> frequency |> out and produce AC at 50 or 60 Hz (or whatever frequency in that range is |> programmed in the pulse pattern synthesizer). I also want to do similar |> as a DC to DC regulator for controlling charge from solar arrays and AC to |> DC to control and diverter power from wind generators. | ------ | OK- this is low power/voltage stuff and is doable. It appears from the | reference that I gave that there have been advances in such switching. It | very much depends on the circuit inductance. Chopping involves high Ldi/dt | voltages which can cause problems. Obviously inverters do exist at this | level and are available on the market.

I don't know what is obvious. A number of inverters do exist on the market but so far not a single one of them reveals what technological method they use to convert DC to AC. Given the efficiency figures of _most_ of them, I'll confidently speculate they are not using class A analog amplifiers. For a few, I could not rule out a class B or maybe even a class C. I don't know if they are doing digital or analog.

One idea I want to explore in an inverter design based on pulse density modulation is to use pulse scattering among the individual components doing the pulse gating. Instead of having every component all gate on or off at exactly the same time, it would be rotated. So if the density level is at say 12.5% and there are 8 components in parallel, each one could be on for 12.5% of the time and all at different times. When the density is at 75% (voltage peaks under load), there would be overlap of on time, but the off times would now be rotated with some overlap.

12.5% on 25% pdm 25% pwm 50% pdm 50% pwm 50% hybrid gate0 10000000 10001000 11000000 10101010 11110000 11001100 gate1 01000000 01000100 01100000 01010101 01111000 01100110 gate2 00100000 00100010 00110000 10101010 00111100 00110011 gate3 00010000 00010001 00011000 01010101 00011110 10011001 gate4 00001000 10001000 00001100 10101010 00001111 11001100 gate5 00000100 01000100 00000110 01010101 10000111 01100110 gate6 00000010 00100010 00000011 10101010 11000011 00110011 gate7 00000001 00010001 10000001 01010101 11100001 10011001

This is just multiple gates for an individual phase. Multiple phases would each be under a different density percentage according to that phase's current point in the cycle, and any load imbalance.

Most other percentages would be more complicated. There would be more pulse intervals per cycle, variable cycle times, and a lot more gates. Control circuitry would be designed to ensure a balance of on-times among all the gates, possibly influenced by sensed temperature. The input LC circuit would smooth out the incoming DC current, and the output LC circuit would be there to smooth the pulses to a relatively clean sine wave and supply at least some reactive current. The control circuit would adjust the desnity/width of pulses to maintain the appropriate voltage in the output tank based on the power demand. It might well be measuring both voltage and current and making adjustments accordingly.

Other projects that would use some of this would be charging regulators for charging batteries from photovoltaic sources, and diverters for wind generators to manage the alternator loading under varying usage loading and wind speeds. It might also manage the exciter power for alternators not using permanent magnets.

--------- With a conventional SCR or a Triac, I can see the waveforms that you describe- if the scope was across the dimmer. In that case one would expect the voltage to rise to full line voltage and follow that until the device is gated on(assuming SCR's or triacs which are cheap in the size involved) - after that the voltage across the device would be the normal forward drop of a diode. What would be of interest is the load voltage and current. A inductive pf near 1 (not low) would cause a slight delay in the current zero and this accounts for the "shortly after" that you mentioned.

I too doubt if there is a low power factor- most lamp dimmers can't cope with loads such as motors and a "dimmer" meant to handle a small motor is quite a bit more expensive than those intended for incandescent lamps.

There is also the possibility that the device is a gate turn off device.

I am not familiar with these devices ( retired about 12 years ago and wasn't involved with advances in power electronics ) but it seems that for PWM devices, they are the cat's meow. For simple lamp dimmers- probably not.

------------

Look to the GTO's -there are many manufacturers in this area and seem to cover well beyond your needs. >

-------- Looks interesting and doable if what I see is now available in GTO's etc.

| With a conventional SCR or a Triac, | I can see the waveforms that you describe- if the scope was across the | dimmer. In that case one would expect the voltage to rise to full line | voltage and follow that until the device is gated on(assuming SCR's or | triacs which are cheap in the size involved) - after that the voltage | across the device would be the normal forward drop of a diode. What would be | of interest is the load voltage and current. A inductive pf near 1 (not low) | would cause a slight delay in the current zero and this accounts for the | "shortly after" that you mentioned. | | I too doubt if there is a low power factor- most lamp dimmers can't cope | with loads such as motors and a "dimmer" meant to handle a small motor is | quite a bit more expensive than those intended for incandescent lamps. | | There is also the possibility that the device is a gate turn off device. |

| | I am not familiar with these devices ( retired about 12 years ago and | wasn't involved with advances in power electronics ) but it seems that for | PWM devices, they are the cat's meow. For simple lamp dimmers- probably not.

[...]

| --------- | Look to the GTO's -there are many manufacturers in this area and seem to | cover well beyond your needs. >

It sounds like a gate-turn-off device might be what I want.

[...] | Looks interesting and doable if what I see is now available in GTO's etc.

I'll need to find out what voltage between line and gate, and what current it can handle, principly for gating off. My bet is capacitors will likely need to be very close on both sides to minimize the voltage rise as the gate shuts off.

AC Transmission = One less conductor and its associated set of insulators, more efficiency, minimal reactance, no AC induced voltage to fences, telephone wires, other adjacent transmission circuits, no ac vibration stress on conductors.

Downsides - More complex and expensive substations - Circuit breakers are harder to break arcs under load.

My question - Do they do live line work on DC Transmission? (i.e. clamping an insulated lift truck platform or bonding a worker from a helicopter to an energized line). I know AC induction is a problem for linemen, but what about steady state DC electric fields?

The bonding or clamping of an insulated platform is not to done to deal with inductive effects but the electrostatic effects. The same conditions as for AC will be there for line workers. The same techniques will be used for protection, including bonding and mesh outerwear to make the body an equipotential. Line workers connected to the live line are not concerned about induction but about distortion of the electric field due to their presence. Whether actual line work is done live- I guess that depends on the utility, and the location and the economics of doing so.

In Finland I have owned several cristmas lights that have not had any fuse in the plug, but another type of protection: one of the bulbs on the christmas light is special "fuse bulb" that does not have that piece of wire wrapped around the lead-in wires. That bulb is clearly marked and instructions say that this bulb should be only replaced with the exactly same type bulb.