Introduction to Current Transformers Part 2: CT Polarity

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In this series, we will introduce the current transformer and will give an example where we would want to use a CT. We'll also look at polarity marks for CTs and talk about the current transformer ratio and how to relate primary current to secondary current. Then we will take three CTs and connect them to the WYE and delta connection. In the last, we will draw the current transformer model and show the voltage currents and impedance's that are associated with the CT model.
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Read our blog on "Current Transformer". The current transformer is an essential part of the power system. The basics of the current transformer including construction, applications, working principles are going to be discussed in this article. Click here: gpac.link/3kozYom
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𝐆𝐞𝐧𝐞𝐫𝐚𝐥𝐏𝐀𝐂 𝐛𝐲 𝐀𝐥𝐥𝐮𝐦𝐢𝐚𝐗 - 𝐌𝐚𝐤𝐢𝐧𝐠 𝐏𝐨𝐰𝐞𝐫 𝐒𝐲𝐬𝐭𝐞𝐦𝐬 𝐈𝐧𝐭𝐮𝐢𝐭𝐢𝐯𝐞, 𝐎𝐩𝐞𝐧 𝐚𝐧𝐝 𝐅𝐫𝐞𝐞 𝐭𝐨 𝐄𝐯𝐞𝐫𝐲𝐨𝐧𝐞, 𝐄𝐯𝐞𝐫𝐲𝐰𝐡𝐞𝐫𝐞!

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[@fioricoziuc1792]

I knew it that in the primary the current should " goes in" where the primary dot is. But I was not aware that the secondary current has to " goes out" in the secondary dot... Thank you again!

[@Generalpac]

Glad you like them! You might also be interested in our Power System Fundamental courses. Get started with FREE courses here: gpac.link/2GO6m4X. You can support us by becoming our Patron on patreon.com/generalpac. Make a difference and be a contributor to the GeneralPAC community. Thanks GeneralPAC Team.

[@Generalpac]

Hey you guys, thanks for the feedback. For all our upcoming videos we won't add any music. Unfortunately, KZbin doesn't allow us to remove the music from previously uploaded videos. Thank you for your understanding. -GeneralPAC team

[@raja-righteousrhetorics4516]

Plz continue ur work... much handy and informative for people... thanks

[@acoustic4037]

Does anyone know why it is an issue since alternating current goes both ways?

[@milesrowe2263]

thank you for making these videos

[@Generalpac]

Glad you like them! You might also be interested in our Power System Fundamental courses. Get started with FREE courses here: gpac.link/2GO6m4X.

[@amyxie2011]

Thanks for the explanation it’s really good! What software are you using to write?

[@ganeshk2404]

Is any possibility to physically check type of Dot used in CT ? And the grounding of secondary terminal make any change on polarity?

[@marcusrose9189]

So in your 4th drawing, 5:22, wouldn't this cause a malfunction of your relay? Due to your polarity being incorrect as current should flow into it? This also relates to faults within the transformer, wouldn't this cause an issue as the direction of current travelling to switch due to the fault?

[@Generalpac]

Hey Marcus, You are right. This video is just for the understanding purpose that how current flows through CTs primary and secondary for different scenarios.

[@UnbornAssassin7]

These are very helpful, thank you

[@fransjack1234]

hi sir ...can i use three CT in wye to connect them to my automatic meter reading..? thanks

[@mohamednasr6529]

isn't the connection of the c.t s at star side should be collected as delta connection to remove the phase shift in the main transformer between delta and star windings or what??????!!!!!

[@norhafizie1883]

Hi. I found during installation that CT's are marked P1-P2 and S1-S2. Could you explain according to this symbol, as I am always confused which one should be grounded/connect to relay whether S1 or S2.

[@Generalpac]

Hi Nor Hafizie, Thank you for reaching out and sharing your concern with us. GPAC team will try its best to address it. The CT's primary winding connection are denoted as "P1" and "P2" (in some cases "K" and "L") and secondary windings as "S1" and "S2" (or "k" and "l"). For primary, the connections are made in such a way that P2 is the load facing side and the energy flows from P1 to P2. For secondary remember to use the same rule for the directional flow of energy from S1 to S2. Also, you can either connect S1 and S2 to the ground terminal. However, for protective relays, ground that terminal which is nearest to the protected equipment. Hope so this answer is helpful to you. You can support us by becoming our Patron on patreon.com/generalpac. Make a difference and be a contributor to the GeneralPAC community. Thanks GPAC Team

[@nadakhater23]

@@Generalpac Thank u 4 all the effort And please I wanna ask If the ct was installed reversed as p2 is towards the source and p1 towards the load then i reversed s1 and s2 into the measuring device is that correct????

[@emnuc30]

@@nadakhater23 It depends on the drawing and specs and application of the CTs. To keep polarity the same, then yes.

[@basyoni95]

I have a problem with the dot convention. "out of the dot" could be in any direction right ?

[@basyoni95]

okay I kinda get it now. the dot is like a portal, the current keeps it's direction but in a different place. is that right ?

[@basyoni95]

god damn it :(

[@jackyhan4622]

"out" from the winding, to the load

[@JSunday45]

I came to understand why is there a polarity in an AC system. Still can't. If anyone can help me understand will be grateful.

[@Generalpac]

Hi Yordan, the polarity here basically refers to the flow of current not the direction of the current. You can say that a current starts flowing from generation to transmission and then to load (distribution). Hope you find it useful. Regards, GeneralPAC by AllumiaX

[@JSunday45]

@@Generalpac I got that. Also found that the meter finds the direction due to a current/voltage offset of 180-degrees. Gues s I still find it hard to comprehend how dose a 180-degree current offset actually feeds in the grid. I thought that to feed the grid all vectors must be the same.

[@jimshenry6656]

I need help. I am confused with the dot convention. Out of the dot could be in either direction isn't it? please help me out.

[@Generalpac]

+Jims Henry not sure what you mean... Can you elaborate? Thanks,

[@rickhamel8578]

It is with respect to the CT. Flowing into the dot would mean the current moves from the dot through the winding. Out of the dot means current flows from the dot away (or out) from the winding.

[@ahtishampervez5021]

This background music is very disturbing

[@Generalpac]

Thanks for the feedback. We have received a lot of feedback on the background music. Now, we have totally removed it from our New videos. You can check our new series - "Brief Introduction to CT and Its Applications" yt.vu/p/PLqJ0Y2s60r-5twLWQpqUX6jA8V9AQBryv

[@Generalpac]

In Current Transformer course we will start from very basics: This course combines brief introduction to Current Transformer with its main characteristic and applications. You will emerge with the knowledge in principles, working, applications, sizing of CT that empowers you to have strong grip on the fundamentals of Current Transformer. This module consists of three parts, each building upon your knowledge based on previous ones. Get 𝟗𝟎% 𝐎𝐅𝐅 on 𝐂𝐮𝐫𝐫𝐞𝐧𝐭 𝐓𝐫𝐚𝐧𝐬𝐟𝐨𝐫𝐦𝐞𝐫 𝐅𝐮𝐧𝐝𝐚𝐦𝐞𝐧𝐭𝐚𝐥 𝐂𝐨𝐮𝐫𝐬𝐞: bit.ly/Current-Transformer-90OFF

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[@MegaRonin777]

Absolutely wrong. I install and test ct's for a living.

[@Generalpac]

+MegaRonin777, Im no expert but I like to share what I know so others can learn and I get a better understanding in the process. Do you mind sharing what is incorrect? I'd like to investigate and correct my mistake so I don't lead people in the wrong direction. Thanks! Looking forward to your response.

[@MegaRonin777]

My apologies, my comment should have been framed in a more positive, constructive manner. Rule one, all protective relay ct’s are wound subtractive. I have run into an occasional additive auxiliary ct but it is not common. Understanding positive and subtractive is important and in the case of protective relaying it is imperative. With understanding the subtractive rule you can assess the orientation of the ct and how to connect it to your equipment correctly. Of course as an installer, you will thoroughly test the ct to prove its orientation (polarity), saturation and ratio.

[@Generalpac]

hi @MegaRonin777 -- thanks for explaining your comment. I did some research and found that CTs are almost always wound subtractive as you have said. But I couldn't find any specific IEEE standards that confirmed this assessment. There wasn't any relevant material in IEEE Standard C37.110 nor C57.13. Also, to make commenting easier, I created a thread on GPAC Forum with more detail. Please reply here: generalpac.com/forum/index.php?threads/current-transformer-subtractive-polarity.12/ --- Thanks @MegaRonin777 --- looking forward to your response on the forum.

[@kiamick]

@@MegaRonin777 You seem English, Fancy teaching me a thing or 2 about HV protection? Most of the stuff on youtube is in Hindi. At this rate i'm thinking it could be quicker to learn Hindi than it would be to find a decent English teacher who knows CTs etc.

[@RogerCillion]

@@MegaRonin777 It is all a matter of reference. Because in the real world the electrons flow in the opposite direction. But that is another subject. I tend to see it as voltage transformer... or better put, the secondary current is a "resisting" current that always travels in the opposite direction. We never create a current, it is the material that is resisting the magnetic field. But you can label it positive or negative, depending on how you install the transformer. Or the angel, better put. Compared to the label of the terminals.

[@satyanarayanamurthy3245]

background ground music is very harassment to viewers.please switch off back ground mudic

[@Generalpac]

This was one of our first videos... and YES, we hear you loud and clear. All of our new videos have the background music at a severe minimum. Thanks

[@Generalpac]

We're also redoing this series with additional info and content!