Harmonics in pole power transformers?

If the transformer fails, won't that stop power to the pump?

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?

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.

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?

Who's doing the frowning?

If you could depend on a little electric 'hum', maybe a microphone would do. Acoustic output from any inductor usually has a bit of 120 Hz, For that matter, maybe you could bypass the switch on the pump, with a safety-rated capacitor ad/or resistor, so there's always a small (1 mA) current, and do your acoustic sensing near the pump motor?

The pole that supports the transformer probably vibrates at 60 or 120 Hz. And I bet there's a healthy magnetic field near the transformer.

The transformer will get a little warm when it's powered up, but that would be expensive to sense from a distance.

Laser interferometer? That's not TOO silly.

The pump doesn't know that the other side of the relay/switch has power ?>:-} ...Jim Thompson

Hmmm, I constructed a Tone probe using a LM386 as the receiver. It does a good job at pickingup 60 hz Hum. Maybe that loosly coupled with the AC input of the pump and a 555 as a missing pulse detector would work.

Cheers

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.

Jon

If the pump is turned on by a relay (NO), can you use the NC contacts on that relay to operate a humming object (like, another relay)? That'd give you an acoustic signature at the control box, far from the transformer.

Heck, operate the alarm from the NC contacts of an always-on relay.

Where DO you have access to the wiring and/or apparatus?

This is what the utilities use: I don't think it will help you much since it is connected directly to the transformer, but might help to know what they're looking for.

POWER SYSTEM HARMONICS. A Reference Guide to Causes, Effects and Corrective Measures.

Unfortunately, that's for conducted harmonic content, not radiated. Also, the load has to become seriously unbalanced and non-linear, which puts the transformer core partly into saturation due to increased currents, before it will start generating harmonics.

Suggestion: A failing transformer usually like to overheat before boiling the cooling oil and exploding. I would think an IR thermometer and telescope would work to detect overload type failures. However, it won't do anything if the line is simply cut and the power goes away.

Magneto-striction causes the transformer to vibrate at 120 Hz, I don't know if you could sense that.

George H.

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.

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.

No wiring desired and acoustic is too prone to false alarms. Has to be very robust.

The pump does but the operator being far away does not. If no power the pump simply won't come on and that's a problem (after a while).

Tone probe would be one of my ideas as well. I'd have top find some cheap and most of all small IC that fishes out 60Hz plus maybe 180Hz. We've got a uC and ADC but it might become overwhelmed with all the other noise if there isn't at least some filtering. Passive filtering is out because of the inductor sizes. Oh, and it has to literally sip power, micro amps.

I'd have to concur that a system like that might very well give a false sense of security. If you're not drawing any current, how do you tell whether you've got an open, e.g. from a burned relay contact, a blown transistor, or a cracked trace?

I'd be wanting to move the goal posts and cycle the pump every few hours just to make sure.

Cheers

Phil Hobbs

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?

Their cores all saturate a little. I only need to know how much that is with pole transformers.

That's too iffy in terms of reliability. Also, we need to catch HV line failures and primary fuse failure as well.

Transformers can fail and still buzz.

There are many reasons why a pump might fail. Expending effort at sensing just a single one of these is misdirected.

Concentrate on the pump, not the power source.

RL