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Participant

Join Date: Jun 2014
Posts: 1

PS Class CT Knee Point Voltage Clarification

06/01/2014 5:26 AM

Dear Sir,

I am having doubt on PS class CT. My question is: "For a certain PS class CT of Vk >= 220V, Ie<= 30mA @ Vk/2. hence what will be the Ie at Vk, when we will conduct knee point test on the PS class CT by gradually increase in voltage from 0V to 242 Volt i.e upto 110% of rated Vk." Again what is acceptance criteria of the knee point test & excitation current as per standard practice.

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Pathfinder Tags: PS Class knee Point test
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Guru

Join Date: Oct 2008
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#1

Re: PS Class CT Knee Point Voltage Clarification

06/01/2014 8:49 PM

A simple search got About 224,000,000 results (0.58 seconds) is it so hard to type "PS class CT" into a search engine?
Knee Point Voltage of Current Transformer PS Class ...

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Associate

Join Date: Jun 2019
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#4
In reply to #1

Re: PS Class CT Knee Point Voltage Clarification

06/27/2019 9:33 AM

Easy Explanation with examples

Knee Point Voltage Calculation of PS class CT

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Power-User

Join Date: Jan 2010
Location: Hyderabad
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#2

Re: PS Class CT Knee Point Voltage Clarification

06/02/2014 10:21 AM

CT with Ie of 30mA at Vk/2 will have more than 60mA at Vk. This because as the CT voltage approaches the knee point, the exciting current increases rapidly. The Vk itself is defined as the point where 10% increase in voltage requires 50% increase in the Ie. This way, the Ie at Vk can be as high as 90mA (60+30).

Having said that Ie at Vk/2 is relevant in differential protection (based on high impedance principle) setting calculations and no such significance is attached to the Ie at Vk.

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Raghunath
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#3
In reply to #2

Re: PS Class CT Knee Point Voltage Clarification

06/27/2019 9:29 AM
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