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Topic: How to dectect when a (hot) wire has been cut (Read 3083 times) previous topic - next topic

Southpark

I can't use a current monitor as this would only detect while running
Allan was meaning that the current monitoring devices can be used when the motor is running. It just means that if the wires are cut during normal operation, then the current monitors can sense that the current in one or more phases drop to zero.

And, for the case when the pumps are not running, it is possible for the source side to be disconnected, so that some other system can be inserted...such as low current system....a system that injects some level current. If we know that there is to be return current, then a device will monitor return current. If that return current disappears, then it could mean that the line is cut.

As for being able to monitor a cut line without injecting current....... then perhaps you might have to resort in vibration measurements along the line. Mechanical vibrations. If the vibrations detected by sensors exceed a particular level when the pumps are not operating, then that could mean cable is cut.

Otherwise, if nothing is allowed to be connected to the cable (for doing anything), then that's as good as putting on a blindfold --- and the problem becomes one of 'if a tree falls down in the forest ......' (a long way away). No implementable feedback mechanism ...... no detection.

jackrae

And, for the case when the pumps are not running, it is possible for the source side to be disconnected, so that some other system can be inserted...such as low current system....a system that injects some level current. If we know that there is to be return current, then a device will monitor return current. If that return current disappears, then it could mean that the line is cut.

Such as a capacitor and voltmeter perhaps ?  And before someone says a voltmeter doesn't measure current, they actually work on the basis of low current measurement.

Southpark

Such as a capacitor and voltmeter perhaps ?  And before someone says a voltmeter doesn't measure current, they actually work on the basis of low current measurement.
Yes, of course. Such as that.

edugimeno

And, for the case when the pumps are not running, it is possible for the source side to be disconnected, so that some other system can be inserted...such as low current system....a system that injects some level current. If we know that there is to be return current, then a device will monitor return current. If that return current disappears, then it could mean that the line is cut.
Ok, I understand, the issue is that I can't rely on the farmer to pay attentiondisengagin the VFD from the system, and plugging in the security system when it's not going to be in use for a period of time. He probably doesn't know when he's going to need water again, if it is going to be raining for the last days of summer or not, etc. so he would probably never remember to plug it in until it is too late.

The original idea was to develop a system that can coexist with the VFD at the same time, be tolerant to the voltage of spikes generated in the system while running, and be able to detect a cut wire when not running, but without the need to engage/disengage devices from the line.

Yes, I also understand this may not be feasible at all. This was just an idea from a real farmer, that we wanted to develop and maybe turn into a comercial product if viable

Thanks

jackrae

#34
Jun 12, 2018, 09:02 pm Last Edit: Jun 12, 2018, 09:07 pm by jackrae
Yes, I also understand this may not be feasible at all. This was just an idea from a real farmer, that we wanted to develop and maybe turn into a comercial product if viable

Thanks
You've been given at least two reasonable suggestions, why the negative response ?

Southpark

#35
Jun 13, 2018, 04:38 am Last Edit: Jun 13, 2018, 04:50 am by Southpark
The original idea was to develop a system that can coexist with the VFD at the same time, be tolerant to the voltage of spikes generated in the system while running, and be able to detect a cut wire when not running, but without the need to engage/disengage devices from the line.
Maybe you could look into a power lines communications method ..... like use a coil to couple energy into the active wire on one end, and have a coil on the return line, and see whether it's possible to transmit some kind of spread spectrum signal on one line, and see if it can be received on the return line. If the line is cut, then the coded signal isn't going to make it back.

Otherwise, order N+2 core cable for the pumps ...... where the "N" cores are used for power, and the other two cores can be used with a separate monitoring system. If they cut the cable, then they'll cut all the conductors. The monitoring system can then be independent of the 'power' side of things.

For cases where the constraint is one where power cables are not allowed to be switched in or out (manually or automatically), then that obviously puts a limit on what can be done. It's possible that the constraints for your case can mean no solution. On the other hand, you could explore those methods provided some of the members here.

ted

#36
Jun 13, 2018, 05:38 am Last Edit: Jun 13, 2018, 05:47 am by ted
https://www.youtube.com/watch?v=RltY3SlH-o4
This method is used in apartment buildings to monitor fire alarm system = condition of the loop
read my posts again.

ted



If there is no 380V, use signal  generator or something like this.

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