Forums

Harmonics in pole power transformers?

Started by Joerg April 17, 2016
Joerg wrote:


> No idea. We'll first try the 60Hz field sniffer. It might be a dud but > we won't know without trying. >
This can't not work, unless the power feed is in a metal conduit. Fluke and others sell voltmeters with field sensors in them. You can even buy screwdrivers with sensors in them. Even if some of the feed is in conduit, a lot of installations have some portion that is not shielded. Jon
On 2016-04-19 10:42, Jon Elson wrote:
> Joerg wrote: > > >> No idea. We'll first try the 60Hz field sniffer. It might be a dud but >> we won't know without trying. >> > This can't not work, unless the power feed is in a metal conduit.
Unfortunately it usually is :-(
> ... Fluke and > others sell voltmeters with field sensors in them. You can even buy > screwdrivers with sensors in them. Even if some of the feed is in conduit, > a lot of installations have some portion that is not shielded. >
Not these because they are outdoors but I am sure hoping for some leakage around the breaker box plus maybe some E-field remnants due to non-ideal grounding of the conduit but that will be like trying to listen to grass grow. However, that wouldn't be the first time so it doesn't faze me too much. -- Regards, Joerg http://www.analogconsultants.com/
On 2016-04-19 10:32, Jon Elson wrote:
> Joerg 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? >> > I'd guess, VERY linear. The non-linearity is due to saturation of the core. > Since the power company pays for all losses before the electric meter, I'd > guess they are happy to pay for a little more copper and iron, so they don't > have to pay for those losses over the next 50 years. >
After seeing how they handled phase angle issues around here I am not so sure about that. 15 years ago we had voltage surge issues that cause light bulbs to blow and it took so persistence on my part to have someone come out. Turns out they just connected a capacitor bank slam-bam style via timer, regardless of any measured values. -- Regards, Joerg http://www.analogconsultants.com/
On 2016-04-19 10:37, Jon Elson wrote:
> Joerg wrote: > > >> No, it is not. The fact that transformer or HV line failure is by far >> the highest concern in this application is based on clear statistical >> evidence. > Why not put capacitive plates next to the power feed (likely a Romex-style > cable) near the breakers. You can probably get a really good signal if you > wrapped two pieces of aluminum foil around the cable for 6" or so. Then, > you could connect these to a low-impedance amplifier, and test the signal > for the right frequency and voltage. It should have no trouble detecting > the difference between good mains power and some small induction when the > mains power fails. >
We'll see. One problem is that all the cabling is in metal conduit. -- Regards, Joerg http://www.analogconsultants.com/
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
On 2016-04-19 11:52, David Eather 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
Oh yes, we can take minutes or even tens of minutes. Though our times of running the electronics is limited because the whole thing is more or less battery-operated. So we can't have an ARM-Cortex crunch numbers for 10 minutes. -- Regards, Joerg http://www.analogconsultants.com/
On Tuesday, April 19, 2016 at 10:40:36 AM UTC-7, Jon Elson wrote:
> Joerg wrote:
> > No idea. We'll first try the 60Hz field sniffer. It might be a dud but > > we won't know without trying.
> This can't not work, unless the power feed is in a metal conduit.
Of course it CAN fail, a 220VAC drop, with center tap to ground, will indicate one phase if your probe is placed on one side, the opposite phase if it is placed on the other side, and SOMEWHERE in the middle, your probe won't detect anything. Also, if your transformer fails with an open phase, the center tap and one leg will still have voltage; it'll have the 60 Hz field, but won't drive your 220V motor. The obvious, correct, way to detect line power, is to plug into the line. The 'convenience outlet' is a common adjunct to many electrical installations, one oughtn't do anything exotic until you know it isn't available here.
On Tue, 19 Apr 2016 12:00:00 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Tuesday, April 19, 2016 at 10:40:36 AM UTC-7, Jon Elson wrote: >> Joerg wrote: > >> > No idea. We'll first try the 60Hz field sniffer. It might be a dud but >> > we won't know without trying. > >> This can't not work, unless the power feed is in a metal conduit. > >Of course it CAN fail, a 220VAC drop, with center tap to ground, will indicate >one phase if your probe is placed on one side, the opposite phase if it >is placed on the other side, and SOMEWHERE in the middle, your probe won't >detect anything. Also, if your transformer fails with an open phase, the >center tap and one leg will still have voltage; it'll have the 60 Hz >field, but won't drive your 220V motor.
Build clamp with three sensors. Select the best signal or sum (absolute value) of the three. This doesn't solve the conduit problem, though.
> >The obvious, correct, way to detect line power, is to plug into the line. >The 'convenience outlet' is a common adjunct to many electrical installations, >one oughtn't do anything exotic until you know it isn't available here.
I think the problem is that he's trying to solve a problem for all installations. Not all will have a convenience outlet. The solution may be to include multiple sensors (perhaps options) and select the one that works best. Perhaps use them redundantly and vote, or some such. I don't think one solution is going to work for all possible installations, give Joerg's long list of restrictions.
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.

Hul

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.
> -- > Regards, Joerg
> http://www.analogconsultants.com/
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/