WHY SECONDARY OF CT SHOULD NEVER BE KEPT OPEN CIRCUITED?
Answer Posted / shashi
If secondary is opened while primary wdg carrying current, then secondary MMF reduce to zero while primary MMF is same.Consequently, the resultant MMF which is equal to primary MMF(as secondary MMF is zero)is very high and it will induce very large flux in the core till core saturates and when this flux links with secondary winding a very high voltage will be induced in secondary wdg .So,
1) This high voltage can breakdown the insulation of secondary wdg.
2) High voltage may even cause fatality to operator who opened the secondary wdg.
3) High resultant flux in core will cause high eddy current loss and hystersis loss .Thus, transformer will get overheated and damage permanently.
4)The high flux will make core permanently magnetised .So, residual flux will introduce error in measuring device.
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