How to dectect when a (hot) wire has been cut

[Paul_KD7HB]

MY limited experience with irrigation pumps using 3-phase power, in the US, is the power company opens the circuit breakers feeding the transformers during the off season. If this is true in your situation, there is no power at all coming into the irrigation pump controller.

Paul

[jackrae]

Here's a link to sketch of how the capacitor all-line detection works
If both detectors (meters) register then the line is intact
If either detector fails to register then the line is broken
Note that when the contactor has closed, both detectors will register full line voltage
https://postimg.cc/image/bs9vdaubx/

[ted]

Apply to one of the phase 380V through resistor ( calculate the value of resistor so curret is abouth 100mA ) and use AC Leakage Current Sensors.

The idea is to make a loop with a small current which can be detected by Leakage Current Sensors. When wire is cut the loop is broken and current is = 0
Capacitor is OK, theory is good but practice is better, put 1nF and measure the current and play with the value of capacitor.

[allanhurst]

Use a second 3-phase relay which can only be operated when the main power one is 'off'.

Then measure resistances between the 3 wires.

Allan.

[Southpark]

Or when the system is off, then switch out the sources, and put in a time-domain reflectometer (or something similar). And every once in a while, activate the device to see if the profile is much different from what is expected.

And during normal pump operation, monitor current. If current level is expected, then all ok.

[edugimeno]

MY limited experience with irrigation pumps using 3-phase power, in the US, is the power company opens the circuit breakers feeding the transformers during the off season. If this is true in your situation, there is no power at all coming into the irrigation pump controller.

Paul

That's not happening here, if you pay the power contract every month, you have power every month...I don 't see why they'd do that, you may still need power for other duties

[edugimeno]

Here's a link to sketch of how the capacitor all-line detection works
If both detectors (meters) register then the line is intact
If either detector fails to register then the line is broken
Note that when the contactor has closed, both detectors will register full line voltage
https://postimg.cc/image/bs9vdaubx/

Would these work after a frequency speed regulator instead of a switch? They don't use just regular switches, they need to control the pressure thru the speed

[edugimeno]

Use a second 3-phase relay which can only be operated when the main power one is 'off'.

Then measure resistances between the 3 wires.

Allan.

That's what I'm thinking about, limiting the sensing ability to then the motor is off only

[allanhurst]

True.

If you want to detect while running ( and if a phase is cut it won't run well if at all ) use a current transformer on each phase and monitor them. Southpark suggested this in post #19.

Allan

[Paul_KD7HB]

That's not happening here, if you pay the power contract every month, you have power every month...I don 't see why they'd do that, you may still need power for other duties

In the US, the electric rate for irrigation power use is MUCH less than for any other use. So, that power line and meters are not shared with other uses. It is also very seasonal in use. Farmers don't want to pay for nothing for quite a few months. Power companies turn power off for free and reconnect for a small charge.

Paul

[allanhurst]

Here in the East of England ( the Fens) most irrigation is done by large diesel engined pumps, often radio controlled.

Drainage ( we're BELOW sea level ) is by fixed electric pumps.

Sounds dodgy, but it works.

Allan

[edugimeno]

True.

If you want to detect while running ( and if a phase is cut it won't run well if at all ) use a current transformer on each phase and monitor them. Southpark suggested this in post #19.

Allan

Allan, I need it to be able to detect cable theft at any time. On and off seasson. While running and while stopped. I can't use a current monitor as this would only detect while running (tbh not probable they want to touch the wires while motor is runnind and it's usually when the farmer is around).
But during SEASON I do truly need to detect when it's not running, but I can't have the farmer be switchig stuff on and off case 1)He will complain it's a hassle 2)He will end up forgetting tu turn off the security device, frying it

During off season, the frequency driver will probably be off all the time, and the tools shed may still have power, at this time they still need to monitor the cables

[edugimeno]

In the US, the electric rate for irrigation power use is MUCH less than for any other use. So, that power line and meters are not shared with other uses. It is also very seasonal in use. Farmers don't want to pay for nothing for quite a few months. Power companies turn power off for free and reconnect for a small charge.

Paul

I may be wrong, (Im not a farmer) but here I believe they use a separate power line (usually 3 phase 380v) for these pumps but they keep the contract up all the time, as suspending it and reactivating it after winter cost a lot
But it's not too bad for them as they sometimes need some water during winter operations...to soften the surface of the soil when they form a crust, to avoid some freezing with some early crops, etc...

[edugimeno]

Here in the East of England ( the Fens) most irrigation is done by large diesel engined pumps, often radio controlled.

Drainage ( we're BELOW sea level ) is by fixed electric pumps.

Sounds dodgy, but it works.

Allan

Yes, many farmers here use diesel pumps and yes I know some of them who have a radio operated switch to turn them on/off from the distance.
Some others use electric pumps, and some others use a mix->Electric pumps with a diesel generator to power them
It all depende of what primary energy provider they want to throw their money at

[jackrae]

Would these work after a frequency speed regulator instead of a switch? They don't use just regular switches, they need to control the pressure thru the speed

Without knowing the circuit of the inverter unit the only way you are going to find out is by actually trying it.  For the trial all you need is one voltmeter and a suitable capacitor.