Why ct earthed

Does it matter which connection is earthed? This is to keep the voltage level on the secondary from floating. You ask about removing the ground while in-service If both leads are run back to the connected equipement and then one leg is also grounded, then removing the ground should not cause an immediate problem. However, during transients, you could see relative voltage on the secondary of the CT get very high.

Generally, the non-polarity terminal is the one that is grounded. To be honest, I can't think of a good reason why it would matter I've never really thought about it. If the CT secondary is grounded at the CT, then removing the ground would be very dangerous, as you would essentially open-circuit the CT secondary. If the CT has a relay accuracy rating, the open-circuit voltage could be in excess of 50 kV or more. Aside from scottf's mention of open-circuiting CTs, omitting or lifting a CT-secondary ground can cause electrostatically induced high voltage from winding to ground.

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The single grounding of current transformers eliminates the problems of the voltage generated at different ground points of the current transformer. If the current transformers are grounded at multiple ground points, the normal current does not create any problem.

However, during a fault condition, the magnitude of potential rise at the different ground points of the current transformer will be different. The rise in ground potential may not be an exact representation of the primary current and the relay may trip even there is no fault in the protection zone. Tripping a differential relay due to a fault external to the zone of protection is one of the more popular nuisance trips. If each current transformer is grounded separately, during fault conditions the potential rise for CT1 and CT2 secondary may be different and the relay may get tripped with this even there is no fault in the protection zone.

To avoid this problem, the recommended method of grounding is to install a single ground point at the one point either at the switchboard or at the relay panel. Learn more. Why is a Current Transformer always connected to ground? Ask Question. Asked 2 years, 5 months ago. Active 2 years, 5 months ago. Viewed 2k times. Ph3ng Ph3ng 1 1 gold badge 4 4 silver badges 18 18 bronze badges. While you're drawing your schematic show where you think the current would flow to through the earth connection.

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