CR4® - The Engineer's Place for News and Discussion®

 Previous in Forum: Energy Savings Next in Forum: Number of Cores of CT
Participant

Join Date: Apr 2015
Posts: 2

# CT Ratio of Zero Sequence CT

11/25/2017 7:50 AM

How can we theoretically find CT Ratio of a Zero Sequence CT?

Pathfinder Tags: ct
Interested in this topic? By joining CR4 you can "subscribe" to

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 19436
#1

### Re: CT Ratio of Zero Sequence CT

11/25/2017 11:43 AM

..."50:5 and 50:0.025 are the only two CTs that are commonly used for zero sequence applications. CTs are available in many other ratios, but the other ratios are generally not used for zero sequence applications.

The ground fault short circuit current has to be calculated for the particular application just like the 3 phase fault current is calculated for each application. There is not a simple way to determine ground fault current if we know the 3 phase fault current. In general the ground fault current can range from 30% of the 3 phase fault current up to 110% - a wide enough range that selecting and setting ground fault protection requires a calculated ground fault short circuit value.
With resistance grounded systems, where a resistor is inserted between the transformer X0 terminal and ground, the ground fault current will be determined based on the system line to neutral voltage, the resistance value of the resistor, and ohms law. Generally a 50:5 CT is used with solidly grounded systems and any resistance grounded systems that have a high enough fault current for the relay to sense the ground fault current. The 50:0.025 CT is applied when the 50:5 does not have sufficient sensitivity to detect the available ground current."...

..."For more information on available CTs, this is a good reference from one manufacturer:

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Guru

Join Date: Dec 2008
Location: Long Island NY
Posts: 12253
#2

### Re: CT Ratio of Zero Sequence CT

11/26/2017 1:00 AM

The Critical Thinking (CT) on Continuous Transmission (CT) of power in Connecticut (CT) for Computer and Communication Technology (CT) happens when all three phases of the grid vector current sum to zero. In some cases a Contact Trip (CT) can then curtail a Cardiac Trauma (CT) from happening in a Connecticut (CT) China Town (CT).

{That was fun. }

__________________
"Don't disturb my circles." translation of Archimedes last words
Guru

Join Date: Dec 2006
Posts: 3317
#3

### Re: CT Ratio of Zero Sequence CT

11/26/2017 6:04 PM

Anonymous Poster #1
#4

### Re: CT Ratio of Zero Sequence CT

11/27/2017 3:18 AM
Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26779
#5

### Re: CT Ratio of Zero Sequence CT

11/27/2017 3:19 AM

How is the forum supposed to know what <...we...> is and its abilities (rhetorical question - NNTR)?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Interested in this topic? By joining CR4 you can "subscribe" to