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Doctors Medicines MCQs Q&A

  1. Pilot wire differential protection
  2. Carrier current protection
  3. phase comparison carrier protection
  4. Current graded over current protection
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Option 4 : Current graded over current protection

​Unit protection scheme:

  • Unit type schemes protect a specific area of the system i.e. a transformer, transmission line, generator, or bus bar.
  • The unit protection schemes are based on Kirchhoff’s Current Law – the sum of the currents entering an area of the system must be zero.
  • Any deviation from this must indicate an abnormal current path.
  • Certain types of unit protection are known by specific names, e.g. Restricted Earth Fault and Differential Protection.
     

Non-Unit protection scheme:

  • The non-unit schemes, while also intended to protect specific areas, have no fixed boundaries.
  • As well as protecting their own designated areas, the protective zones can overlap with other areas.
  • While this can be very beneficial for backup purposes.
  • The non-unit type protection system includes the following schemes:
  1. Time graded over-current protection
  2. Current graded over-current protection
  3. Distance or Impedance Protection
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