For protective relaying, can differential current protection be used for phase-to-phase faults?

Discussion in 'Homework Help' started by Mountain_cat, Aug 11, 2016.

  1. Mountain_cat

    Thread Starter New Member

    Jul 11, 2016
    If a phase to phase fault happens on a cable, then current differential, phase comparison and directional relays wont be helpful because the measured values at the start and end of the cable will be the same, correct?

    So this leaves only the over current relay protection scheme as a viable option for phase to phase faults?

    Am I correct in this thinking?
  2. MrAl

    Well-Known Member

    Jun 17, 2014

    If you draw a diagram of your circuit and what is being measured now and what you want to measure in the future to improve the design that would help understand what you are after.

    For example, if you measure current in a line and the phase of the source changes and there is no load then yes you cant detect a change in current. But if there is a load then you should be able to detect that change in line current. Just one example as i am not sure what you have there exactly and dont know what kind of load you have.
  3. YZee

    New Member

    Aug 11, 2016

    In protection design you would not use a differential protection scheme for a transmission line. The differential protection scheme is used for protecting equipment such as a transformers.

    To protect a transmission line you would use protection schemes designed for that purpose. This could include using overcurrent relays or zone/distance relay.