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CT Ratio of Zero Sequence CT

11/25/2017 7:50 AM

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

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#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:

http://www.gedigitalenergy.com/produ.../OEM_Guide.pdf "...

http://forums.mikeholt.com/showthread.php?t=165507&page=2

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#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. }

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#3
In reply to #2

Re: CT Ratio of Zero Sequence CT

11/26/2017 6:04 PM

Conversational Twaddling (CT)

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#4

Re: CT Ratio of Zero Sequence CT

11/27/2017 3:18 AM
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#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)?

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