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How to calculate fault current and relay co-ordination?

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Question added by sandip dobariya , substation engineer , Reliance jio infocomm ltd, Reliance corporate park
Date Posted: 2015/12/15
Syed Muhammad Shoaib
by Syed Muhammad Shoaib , Project Engineer , ZRK GROUP

Calculation Of fault Current

1-Find Full load current

2-Transformer Multiplier from Z on nameplate or calcuate from rated current and Isc

3-Calculate f (fault) factor

4-Calculate Multiplier M=1/(1+f)

5- Isc (rms)= Isc* M

 

Relay Coordination

1-Find maximum load current

2-Select CT ratio as per relay pick up.

3-Calculate Short circuit ratio

4- Calculate time settings & plug settings of relay

5-If used as secondary protection or out of zone than add primary zone time in calculation

 

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