neutral connection of CT 2

[144x]

usually only one point in the neutral connection of a CT is earthed .why is it so?
thanx

 

[RRaghunath]

It is true that the CT neutral point is earthed at only one end and preferrably at the Swgr / Swyd end.

Earthing the neutral at more than one point can lead to circulating currents in the neutral wire. These currents can affect the CT secondary circuit (through induced currents) and cause maloperation of the respective protective relays.

 

[jbartos]

Suggestion: Also, it depends on the system grounding method. The ungrounded system can be completely isolated from the ground.

 

[busbar]

thread238-18531

"...so that the station ground bus itself will never serve to complete any part of the instrument transformer secondary circuit."

 

[peterb]

Regardless of the system earthing method, IT IS AN URGENT SAFETY REQUIREMENT THAT INSTRUMENT TRANSFORMER (PT & CT) SECONDARY CIRCUITS BE EARTHED. This is necessary to prevent capacitive coupling between primary & secondary, which could result in the secondary wiring floating at up to the primary voltage to ground. Having said that, there are instrument transformers that are equipped with electrostatic shields between primary & secondary - the shield itself is earthed and the secondary need not be in this case.