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Harmonics in pole power transformers?

Started by Joerg April 17, 2016
The hookup wires are not electrically connected in the common sense. They 
serve only as a capacitor. One electrode is one of the hookup wires and 
the other electrode is one of the power leads, with the cable insulation 
and the hookup wire insulation between them. No "electrical" connection.
   And, I'd bet ($2) a lm358 would serve for an opamp. I checked a 
bunch of them recently and found the input current notably less than spec 
would suggest.

Hul

Joerg <news@analogconsultants.com> wrote:
> On 2016-04-19 15:27, Hul Tytus wrote: > > Assuming the transformer is on the top of the pole and power is brought > > down via a two wire cable; and that the cable leads to the pumps switch > > which is a few feet at least from the transformer. Put a foot or two or > > three of hookup wire on each side of the power cable & connect them to a > > length of coax, which, with adjusted length, will serve as a good voltage > > divider and provide an opam with fet inputs a 60 cycle signal to monitor. > >
> Unfortunately that requires an electrician which we'd like to avoid, > mostly on account of the remoteness of the installations.
> [...]
> -- > Regards, Joerg
> http://www.analogconsultants.com/
On Sun, 17 Apr 2016 13:55:05 -0700, Joerg <news@analogconsultants.com>
wrote:

>A system needs to be able to detect whether a pole transformer has >failed and stopped feeding power to a pump. The transformer will be >100ft or more away. The detection has to work even without any power >flow meaning we can only detect the presence of a 60Hz electric field >that leaks from the various boxs such as a breaker box.
You have not stated why a direct connection to the input side of the pump switch is not possible. What is wrong with a small power transformer ? If you need better insulation, get a certified voltage transformer, some of which are intended for outdoor installation.
> You have not stated why a direct connection to the input side of the > pump switch is not possible. What is wrong with a small power > transformer ? > > If you need better insulation, get a certified voltage transformer, > some of which are intended for outdoor installation.
Yes he did. No connection to any of the supply or load circuit allowed. One requirement is that no electrician be required for installation. Apparently they need a Central Psychic (tm) or one per district that will inform management when service is required and whom to send.
On 2016-04-19, David Eather <eather@tpg.com.au> wrote:
> On Tue, 19 Apr 2016 10:15:42 +1000, Joerg <news@analogconsultants.com> > wrote: > >> On 2016-04-18 17:09, David Eather wrote: >>> On Tue, 19 Apr 2016 01:43:25 +1000, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>> On 2016-04-18 08:32, John Larkin wrote: >>>>> On Mon, 18 Apr 2016 07:41:45 -0700, Joerg <news@analogconsultants.com> >>>>> wrote: >>>>> >>>>>> On 2016-04-17 15:02, John Larkin wrote: >>>>>>> On Sun, 17 Apr 2016 14:14:36 -0700, Joerg >>>>>>> <news@analogconsultants.com> >>>>>>> wrote: >>>>>>> >>>>>>>> On 2016-04-17 14:00, John Larkin wrote: >>>>>>>>> On Sun, 17 Apr 2016 13:55:05 -0700, Joerg >>>>>>>>> <news@analogconsultants.com> >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> Folks, >>>>>>>>>> >>>>>>>>>> A system needs to be able to detect whether a pole transformer >>>>>>>>>> has >>>>>>>>>> failed and stopped feeding power to a pump. The transformer will >>>>>>>>>> be >>>>>>>>>> 100ft or more away. The detection has to work even without any >>>>>>>>>> power >>>>>>>>>> flow meaning we can only detect the presence of a 60Hz electric >>>>>>>>>> field >>>>>>>>>> that leaks from the various boxs such as a breaker box. >>>>>>>>> >>>>>>>>> If the transformer fails, won't that stop power to the pump? >>>>>>>>> >>>>>>>> >>>>>>>> Yup. The system is a mote network that then needs to send out an >>>>>>>> alarm. >>>>>>>> The pumps aren't always running and the alert should not go out >>>>>>>> when no >>>>>>>> power is drawn but mains power is available. >>>>>>>> >>>>>>>> >>>>>>>>>> >>>>>>>>>> In order not to get fooled by 60Hz from other overhead lines I >>>>>>>>>> was >>>>>>>>>> wondering if classic pole transformers generate enough 3rd and >>>>>>>>>> 5th >>>>>>>>>> harmonics to distinguish the field emanating from secondary >>>>>>>>>> wires from >>>>>>>>>> that coming from overhead HV lines. Does anyone know where to >>>>>>>>>> find info >>>>>>>>>> about that? >>>>>>>>> >>>>>>>>> The way people often pick up an AC trigger for a scope or >>>>>>>>> something is >>>>>>>>> to wrap a couple of turns of insulated wire on top of the ac-high >>>>>>>>> insulated wire, and drive a high-impedance amp. Can you get >>>>>>>>> inside the >>>>>>>>> breaker box, or access a motor wire, free-air or inside a conduit? >>>>>>>>> >>>>>>>> >>>>>>>> That's exactly what we want to avoid. It's all outdoor stuff so >>>>>>>> even >>>>>>>> running a non-connected sniffer wire into the breaker box is >>>>>>>> frowned upon. >>>>>>> >>>>>>> Is the feed open-wire on a pole? >>>>>>> >>>>>> >>>>>> I don't quite understand that question. It's the usual, two 10-12kV >>>>>> wires string along on poles, a transformer, and a 240VAV two-phase >>>>>> drop >>>>>> of 100ft down to the pumps. They like to keep that last pole with the >>>>>> transformer away that far to minimise it being damaged by trucks, >>>>>> farm >>>>>> equipment and such. >>>>>> >>>>>> >>>>>>> Who's doing the frowning? >>>>>>> >>>>>> >>>>>> The customer. They want a solution they can crack out of a package >>>>>> and >>>>>> stick to the outside of the breaker box or somewhere around that. No >>>>>> wiring. Doing anything inside a breaker box legally requires an >>>>>> electrician to come out and that's not desired because of the high >>>>>> cost. >>>>> >>>>> Outside of a metal breaker box, there's no h-field with no current, >>>>> and no e-field leaking out. The ambient e-field will be dominated by >>>>> other stuff, like other circuits and light bulbs in the room. >>>>> >>>> >>>> There is no room. Just that last pole, the transformer, a meter and >>>> breaker box and the pumps. Other than that maybe some cattle. >>>> >>>> We'd be counting on the ever so small leaking E-field because with the >>>> pumps turned off that's all there is going to be. Hence my question >>>> whether we could use harmonics to see a change versus the E-field >>>> coming from the distant HV line. The engineer taking care of the >>>> software side is very good at extracting signature signals to hear >>>> "the grass grow". >>>> >>>> >>>>> Maybe it can't be done. >>>>> >>>> >>>> Possible. That's why we are engineers, to try out until we are 110% >>>> sure it truly can't be done. If it turns out it can be done the >>>> company has a leg up on the competition, big time :-) >>>> >>>> >>>>> Suppose you had a small, coin-sized magnetized thing. Would you need >>>>> an electrician to open the breaker box, stick it to the cover or the >>>>> side inside, and close it? You don't need an electrician to open the >>>>> box and flip breakers. >>>>> >>>> >>>> No, but many outdoor boxes have a gasket seal which you technically >>>> are not allowed to compromise. What we were mulling is a 2nd >>>> transmitter inside the box. But that would probably become a >>>> show-stopper. >>>> >>> >>> What about audio? The transformer and all the rest must produce some hum >>> and when the transformer dies I bet it sound different. >> >> >> It'll be very faint, the transformer is 100ft or more away (not an >> allowed site to install anything there) and there can be lots of other >> noise muffling such faint sounds. >> > > Yeah but I am thinking you don't need 'instant' notification of faults - > maybe a second or two is OK and the mains is a fairly fixed frequency you > can filter the hell out of the 60Hz to get your all OK signal
The frequency drifts during the day. eg: http://electronics.stackexchange.com/questions/57878/how-precise-is-the-frequency-of-the-ac-electricity-network -- \_(&atilde;&fnof;&bdquo;)_
On Sun, 17 Apr 2016 13:55:05 -0700, Joerg wrote:

> A system needs to be able to detect whether a pole transformer has > failed and stopped feeding power to a pump. The transformer will be > 100ft or more away. The detection has to work even without any power > flow meaning we can only detect the presence of a 60Hz electric field > that leaks from the various boxs such as a breaker box. > > In order not to get fooled by 60Hz from other overhead lines I was > wondering if classic pole transformers generate enough 3rd and 5th > harmonics to distinguish the field emanating from secondary wires from > that coming from overhead HV lines. Does anyone know where to find info > about that?
Can't you create your own power flow, by installing a low-current shunt and measuring current through that?
On 2016-04-20 14:43, Hul Tytus wrote:
> The hookup wires are not electrically connected in the common sense. They > serve only as a capacitor. One electrode is one of the hookup wires and > the other electrode is one of the power leads, with the cable insulation > and the hookup wire insulation between them. No "electrical" connection. > And, I'd bet ($2) a lm358 would serve for an opamp. I checked a > bunch of them recently and found the input current notably less than spec > would suggest. >
It would still require an electrician because customers would not allow their staff to open switch panels, switches, conduit or the like to lay a snippet of hook-up wire in parallel. Opening is the only way to get there. Unless we are able to sniff the 60/180Hz from the outside and that's what we'll try to do. A LM358 wouldn't quite suffice, it'll be at least partly discrete circuitry. Partly on account of a very low supply voltage but also because we'll need well in excess of 10M input resistance.
> Hul > > Joerg <news@analogconsultants.com> wrote: >> On 2016-04-19 15:27, Hul Tytus wrote: >>> Assuming the transformer is on the top of the pole and power is brought >>> down via a two wire cable; and that the cable leads to the pumps switch >>> which is a few feet at least from the transformer. Put a foot or two or >>> three of hookup wire on each side of the power cable & connect them to a >>> length of coax, which, with adjusted length, will serve as a good voltage >>> divider and provide an opam with fet inputs a 60 cycle signal to monitor. >>> > >> Unfortunately that requires an electrician which we'd like to avoid, >> mostly on account of the remoteness of the installations. > >> [...] > >> -- >> Regards, Joerg > >> http://www.analogconsultants.com/
-- Regards, Joerg http://www.analogconsultants.com/
On 2016-04-20 23:42, Jasen Betts wrote:
> On 2016-04-19, Joerg <news@analogconsultants.com> wrote: >> On 2016-04-19 03:07, Jasen Betts wrote: >>> On 2016-04-18, Joerg <news@analogconsultants.com> wrote: >>>> On 2016-04-18 09:41, Adrian Tuddenham wrote: >>>>> Joerg <news@analogconsultants.com> wrote: >>> >>>> That would require an electrician to come out and most would refuse this >>>> job because they, their employer or their union won't allow non-standard >>>> stuff. >>> >>> Yeah, and if they're paying a visit they could as easily install a >>> standard electical outlet for you to plug your alarm into. >>> >> >> The trick is to be able to install this without that truck roll. Because >> such a truck roll would increase the cost per install by several hundred >> Dollars, considering travel charges. > > yeah, but you save some that you'd otherwise have to spend on on cow-proof solar panels > and batteries... >
You need those anyhow. How else would you convery a mains power failure? Deducing that from a mote not transmitting isn't secure enough because then a damaged mote would trigger a utility truck roll. Which will come with a hefty bill if they found everything to be fine out there on the utlity's side. -- Regards, Joerg http://www.analogconsultants.com/
On 2016-04-20 21:49, upsidedown@downunder.com wrote:
> On Sun, 17 Apr 2016 13:55:05 -0700, Joerg <news@analogconsultants.com> > wrote: > >> A system needs to be able to detect whether a pole transformer has >> failed and stopped feeding power to a pump. The transformer will be >> 100ft or more away. The detection has to work even without any power >> flow meaning we can only detect the presence of a 60Hz electric field >> that leaks from the various boxs such as a breaker box. > > You have not stated why a direct connection to the input side of the > pump switch is not possible. What is wrong with a small power > transformer ? >
An electrician would need to come out for that. Too expensive in remote locations.
> If you need better insulation, get a certified voltage transformer, > some of which are intended for outdoor installation. >
-- Regards, Joerg http://www.analogconsultants.com/
On 2016-04-21 06:19, Przemek Klosowski wrote:
> On Sun, 17 Apr 2016 13:55:05 -0700, Joerg wrote: > >> A system needs to be able to detect whether a pole transformer has >> failed and stopped feeding power to a pump. The transformer will be >> 100ft or more away. The detection has to work even without any power >> flow meaning we can only detect the presence of a 60Hz electric field >> that leaks from the various boxs such as a breaker box. >> >> In order not to get fooled by 60Hz from other overhead lines I was >> wondering if classic pole transformers generate enough 3rd and 5th >> harmonics to distinguish the field emanating from secondary wires from >> that coming from overhead HV lines. Does anyone know where to find info >> about that? > > Can't you create your own power flow, by installing a low-current shunt > and measuring current through that? >
No physical tie-in allowed because that would require an electrician to drive out there. Sometimes way out there. -- Regards, Joerg http://www.analogconsultants.com/
Joerg <news@analogconsultants.com> wrote:
> On 2016-04-17 16:39, Jon Elson wrote: >> Joerg wrote: >> >> >>> In order not to get fooled by 60Hz from other overhead lines I was >>> wondering if classic pole transformers generate enough 3rd and 5th >>> harmonics to distinguish the field emanating from secondary wires from >>> that coming from overhead HV lines. Does anyone know where to find info >>> about that? >>> >> Geez, I would expect there to be VERY little 3rd or 5th harmonic from a >> transformer. These harmonics require a nonlinear response, and they >> shouldn't be nonlinear. >> > > All transformers are non-linear because there is an economical limit to > the amount of copper they put on there. My question is just, how > non-linear is the average pole transformer?
That's why they use aluminum windings (lower cost). Efficiency is still rather high with huge overload tolerance, which means they're not running saturated before or even at full load.