+ Post New Thread
Results 1 to 9 of 9
  1. #1
    Member level 2
    Points: 1,072, Level: 7

    Join Date
    Sep 2015
    Posts
    50
    Helped
    0 / 0
    Points
    1,072
    Level
    7

    3-phase Δ-connected 11kV Open Circuit Fault Detection?

    Is there any cheap method to detect open circuit fault/broken conductor (high impedance) for a 3-phase Δ-connected 11kV lines without neutral?

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 2
    Points: 3,126, Level: 13

    Join Date
    Jan 2019
    Posts
    573
    Helped
    149 / 149
    Points
    3,126
    Level
    13

    Re: 3-phase Δ-connected 11kV Open Circuit Fault Detection?

    get some good resistors to measure the line to line voltages

    resistor divider to provide a sample
    resistor and simple zener or transistor regulator to provide power
    simple optical emitter and optical receiver about 4(?) 5(?) inches apart to provide optical isolation

    when sample is good, turn on optical emitter
    when sample is bad, remove signal

    any fault in circuit or 11kV line causes lack of "good" indicator



  3. #3
    Super Moderator
    Points: 54,121, Level: 56

    Join Date
    Apr 2011
    Location
    Minneapolis, Minnesota, USA
    Posts
    13,192
    Helped
    2628 / 2628
    Points
    54,121
    Level
    56

    Re: 3-phase Δ-connected 11kV Open Circuit Fault Detection?

    Somewhere in the current loop you should be able to measure a resistance sufficient to develop 2V or so. Enough to drive a red led (a cheap method).

    Such a resistance might be present across the ends of one long piece of wire, or across a connector or several connectors , or across two wires. The less your led's forward voltage, the better.

    Say you have 1A peak in the loop. Then 1.9 ohms is sufficient. Install two anti-parallel led's if you wish.

    Click image for larger version. 

Name:	led lights while sufficient current flows.png 
Views:	0 
Size:	30.5 KB 
ID:	157722



  4. #4
    Super Moderator
    Points: 54,121, Level: 56

    Join Date
    Apr 2011
    Location
    Minneapolis, Minnesota, USA
    Posts
    13,192
    Helped
    2628 / 2628
    Points
    54,121
    Level
    56

    Re: 3-phase Δ-connected 11kV Open Circuit Fault Detection?

    1 VAC peak is able to light an led, by sending it through a single Villard cell (or voltage multiplier). The diode should be low barrier type (0.3 V forward). The capacitor acquires DC charge less than 1V, thus it can be electrolytic type.

    Click image for larger version. 

Name:	led lights from 1VAC on resistor via Villard cell (low fwd thresh).png 
Views:	1 
Size:	28.9 KB 
ID:	157723

    - - - Updated - - -

    Notice 1V in a 1 ohm resistor makes 1W peaks. Then it should be feasible to install a 1 ohm 1W resistor in the current path.



    •   AltAdvertisement

        
       

  5. #5
    Super Moderator
    Points: 83,919, Level: 70
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,812
    Helped
    4582 / 4582
    Points
    83,919
    Level
    70

    Re: 3-phase Δ-connected 11kV Open Circuit Fault Detection?

    Assuming there is a load on the lines, I would use current monitoring rather than voltage monitoring. An open line will not conduct any current but there could still be voltage at both sides of a break. On the feed side because it is 'upstream' of the break and on the load side because of transformers or or other devices still sitting across the other phases.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


    1 members found this post helpful.

  6. #6
    Advanced Member level 5
    Points: 15,453, Level: 30
    schmitt trigger's Avatar
    Join Date
    Apr 2013
    Posts
    2,572
    Helped
    822 / 822
    Points
    15,453
    Level
    30

    Re: 3-phase Δ-connected 11kV Open Circuit Fault Detection?

    11 kV with no neutral and "cheap" don't belong together.

    My personal opinion is to follow the suggestion outlined by Brian.
    Use ONLY current transformers with the creep and insulation ratings suitable for the potentials they will be subjected to.
    My batteries are recharged by "Helpful Post" ratings.
    If you feel that I've helped you, please indicate it as a Helpful Post



  7. #7
    Member level 2
    Points: 1,072, Level: 7

    Join Date
    Sep 2015
    Posts
    50
    Helped
    0 / 0
    Points
    1,072
    Level
    7

    Re: 3-phase Δ-connected 11kV Open Circuit Fault Detection?

    All these methods are simple but impractical since the system has 11000V! and it can neither be disconnected to install these solutions nor can be altered.
    If it is possible to use line communication after the distribution transformer (220V) at either ends... I know distribution transformer itself behaves as low-pass filter but I have a feeling that it is still possible. Any suggestions on this method?



    •   AltAdvertisement

        
       

  8. #8
    Super Moderator
    Points: 83,919, Level: 70
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,812
    Helped
    4582 / 4582
    Points
    83,919
    Level
    70

    Re: 3-phase Δ-connected 11kV Open Circuit Fault Detection?

    The problem with sensing after the voltage is dropped is the transformer typically sits across two of the phases (delta-Y configuration) so it is still prone to picking up voltage from after the break. We often get single phase failures in my locality but the result is a drop from about 250V to about 150V so it results in a 'brown out' rather than complete failure.

    You might be able to sense a failure by carefully dropping each line with high voltage resistors then analyzing the waveform for distortion but it is tricky and not entirely reliable. You have to check relative to ground and at least check for 120 degrees shift between voltages. If one phase fails, it's peak probably won't measure as 120 difference from the remaining phases but something else depending on the nature of load and the phase shifts it produces. You probably wouldn't get a sine wave either so correlating it to the other phases might be difficult.

    The non-invasive solution to monitoring current is to use Hall sensors or clamp-on current transformers, they do not require the cables to be re-routed through the detection equipment. For simple 'open/broken' checking you only have to see if they produce any output, no measurement or analysis is needed.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



  9. #9
    Member level 2
    Points: 1,072, Level: 7

    Join Date
    Sep 2015
    Posts
    50
    Helped
    0 / 0
    Points
    1,072
    Level
    7

    Re: 3-phase Δ-connected 11kV Open Circuit Fault Detection?

    Non-invasive method using hall-effect sensor seems quite attractive.

    For 11kV lines without neutral, microstrip lines for electromagnetic coupling to power up the stand-alone circuit for fault detection is the most practical and economical solution... the circuit just need to be fixed to the line.

    I need some application note on this technique... perhaps a high voltage hall-effect sensor, microstrip lines design and a RF transmitter to signal the fault for the main circuit breaker with RF receiver.



--[[ ]]--