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Start by
Baljinder Bansal
08-17-2014 04:31 PM

Current Transformer applications interchange

Can the CT' s used for Differential protection can be used for metering purpose or vice-versa?
08-17-2014 06:58 PM
Top #2
08-17-2014 06:58 PM
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08-17-2014 09:50 PM
Top #3
suryanarayana raju indukuri
08-17-2014 09:50 PM
The short answer is no.
Metering and protection CTs are made to different specifications
08-18-2014 12:37 AM
Top #4
Antonio Baronas
08-18-2014 12:37 AM
To make it simple, protection CT has saturation factor (SF) 10, 20 or more, meaning that will reproduce current with accuracy at i.e 20 times rated value, measurement transformers has 5 as SF to protect measurement devices. Have to check specs of measurement device to know if it will withstand.
Check the following:
1.- Short circuit level for horizon year example: 5 KA
2..- If current transformer is 500/5 then 5,000/500 = 10
3.- Check if measurement device withstands 10 times rated current
08-18-2014 03:24 AM
Top #5
Gary Fox
08-18-2014 03:24 AM
Maybe yes, maybe not.
Many CTs rated per ANSI standards have accuracy ratings for both metering and protection purposes.
The burdens of modern digital relays and digital meters are low enough allow both burdens to be on a CT secondary without forcing the CT into saturation. Secondary wire resistance is another matter you have to look out for.
However, to make the CT for differentail protection work might require a higher ratio than one you would rather use for metering purposes. So it depends on specific circumstances, and how severe the through fault currents are going to be.
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