Overcurrent Protection

Time-Current Characteristics—Application—Limits of Error—Ratings—Directional Overcurrent Protection—a.c. Tripping—Schemes for Radial Feeders—Construction—Application—Problem
  • A. R. van C. Warrington


Fault current can be used as a basis for selectivity only where there is an abrupt difference between its magnitude for a fault within the protected section and a fault outside it, and these magnitudes are almost constant. Where this is so, a current magnitude device can be used, such as a fuse or an instantaneous relay or trip device and selectivity can be obtained by grading current. A typical case where current grading can be used is shown in fig. 4.1, where there is a high impedance unit such as a transformer which makes the fault much less for faults beyond the transformer.


Fault Current Protective Relay Ground Fault Zero Sequence Directional Unit 
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Copyright information

© Albert Russell van Cortlandt Warrington 1968

Authors and Affiliations

  • A. R. van C. Warrington
    • 1
  1. 1.The English Electric Company LimitedStaffordUK

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