What sort of transformers are you thinking of? They can vary between huge 50Hz things (as used in the public supply) to small 50Hz ones traditionally used in items of equipment or very small high frequency AF/RF or HF power conversion ones?

If its the large public-supply kind of thing, I would suspect the first parameter to measure would be temperature. (Although I'm not sure how kind such an environment would be for wireless comms...)

   - Andy.

What sort of transformers are you thinking of? They can vary between huge 50Hz things (as used in the public supply) to small 50Hz ones traditionally used in items of equipment or very small high frequency AF/RF or HF power conversion ones?

If its the large public-supply kind of thing, I would suspect the first parameter to measure would be temperature. (Although I'm not sure how kind such an environment would be for wireless comms...)

   - Andy.

I had the larger ones in mind, so thank you for your input regarding temperature sensors. 

I think you will be very lucky to build any sort of mechanical harvesting system that needs a power transformer, unless the energy harvester looks more like a generator !

But substation transformers, when monitored at all, usually look at oil temp as the main one, and then the  LV load balance (currents, and voltages) across the 3 phases.

An example of a commercial transformer monitor here, Note that since designing that range, Ash Wireless has since been taken over, and may not support that sort of product in the way they once did when they first developed it.

Mike.

I think you will be very lucky to build any sort of mechanical harvesting system that needs a power transformer, unless the energy harvester looks more like a generator !

I'm confused (easily done I know) - I'd imagined the OP was taking about powering a little sensor, plus it's wireless comms, from picking up stray magnetic fields from the transformer it's monitoring. Something along the lines of having only the secondary windings of a tiny transformer to power the sensor, it's being powered parasitically from the main transformer's primary. Apologies if I've got the wrong end of the stick.

   - Andy.

Aah. It is also possible that I have misunderstood - looking again, it could be read that way, But if you are connecting to TX monitor it why harvest power with great inefficiency from magnetostrictive vibrations,  when you already have a mains supply.,,,,

Mike.

But if you are connecting to TX monitor it why harvest power with great inefficiency from magnetostrictive vibrations,  when you already have a mains supply.,,,,

I can see it might be convenient - especially when retrofitting or if the monitoring is only wanted temporarily - just stick the device onto the side of the transformer - job done - no need for live working on maybe 1000A 400/230V connections and deal with 25kA+ fault currents.

   - Andy.

Maybe. But if you want to monitor output current and voltage you probably  need to get up close anyway.  I can see that clamp metering current on singles may be OK and if wire is unarmoured you could monitor voltage waveform capacitively through the insulation. An interesting idea, but I think the folk installing it would have the paperwork to go into the subastoin or up the pole anyway.

I must dig up a photo of an old style  open frame substation - bare bus-bars even when not open for maintainence...

Mike.