Current Transformer

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leosks134 Member Join Date: Jan 2009 Posts: 9	Current Transformer 01/21/2009 2:25 AM
	what is the secondary of Cts are earthed in switchgear ? i have heard that it is for person safety working on ct ,is it so?
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sb Guru Join Date: Mar 2007 Posts: 2550 Good Answers: 103	#1 Re: current transformer 01/21/2009 8:10 AM
	The current transformers typically work on low voltage and high current (based on the ratio of course) mode. The insulation between the primary and secondary is based on the rating (like in VTs). However tha main difference is that the CTs secondary are virtual short circuits where as in case of Vt is almost open circuit. In case of a secondary fault - ie the secondary getting opened - a very high voltage is created in the secondry due to its large number of coils and its corersponding inductance. This voltage is usually sufficient to destry the transformer as well as breaking the insulation between primary and secondary. And you can imagine what will happen to the personnel nearby, or the person who has by error put the line switch off. To avoid this from taking place the secondary is earthed. __________________ Fantastic ideas for a Fantastic World, I make the illogical logical.They put me in cars,they put me in yer tv.They put me in stereos and those little radios you stick in your ears.They even put me in watches, they have teeny gremlins for your watches
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CJMcGill Guru Join Date: Jul 2008 Location: SoCal USA Posts: 556 Good Answers: 23	#2 Re: current transformer 01/21/2009 12:17 PM
	Ga for sb. The simple answer to leosks134 is YES. Earthing (grounding as it is called in some places) is always for the safety of the humans involved. It also enhances the protection for equipment, buildings, wiring, animals (especially dairies) etc., and applies to CT's as SB has explained. __________________ I do not 'know it all', but i will admit that I would like to. CJM
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