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In the US, a dual-rated CT is one that has a protection class and a metering class, and should be tested to verify both at the factory. A "two-core" is referred to as a dual-core CT which is two separate cores contained in one housing.

When using portable CT test sets keep one thing in mind - what are you accomplishing with it?? I will tell you that the IEEE C57.13 and IEC 61869 standards require testing be performed at rated current at rated power frequency. Manufacturers are mandated to assure extreme accuracy and many...

The Siemens article is referring to placement of conductors in general when there is plenty of space which is not really same as in your condition. In your case however, all conductors fill the window area and as long as the conductors are rated for the CT class, 0.6kV for example, then you...

They are mounted inside the tank in IEEE-land as well. BCTs in general, are indoor type construction and the environment depends on the device they are going on. For example, in a power breaker they are dry-type mounted external of the interrupter but always under a protective shell/cover. In...

OK Scott, so you are playing the RF game. If this were a dry-type CT I would tend to agree with you. However, this is a GSU so the BCT will be under hot transformer oil at 80C average and possibly higher. So with class A insulation and trying to limit a BCTs rise to 20-25C under those...

Hey Scott, just curious ... why would metering making it any different?? From a technical perspective, metering and/or protection class wouldn't change a thing except how I would test it. Unless you are looking for a more "preferred" ratio??

It is often better to select the CT ratio to be higher than the max rated current it is measuring. in this case there is nothing wrong with specifying 7000:5 or higher ratio. The Rating Factor (RF) of the CT should be coordinated with the rated continuous current of the bushing, not exceeding...

As part of Class X spec is also the secondary winding resistance. And when determining the desired operating knee voltage the interal IR drop of the CT must also be considered. So to add to Scott's exapmle, Vk > 40 X (Rs + 4 Ohms). I agree with Scott that the exciting current is seldom a...

From A CT manufacturer's perspective... With low ratio window-type CTs that are used strictly in a core balance scheme (all 3 conductors passing thru window), let the buyer beware!! I encountered the DOs and DON'Ts of these CTs long before that GE article was written and I can tell you that...

What ratings are you speaking of?? Voltage transformers made to IEEE C57.13 for 600V class (and less) have a 10kV BIL requirement.

Greetings Scottf, The words Jimmy used to describe the test are verbatim as in C57.13.1, in fact it is entire 16.3 as published. My question to you is in the test itself. At what levels of induction do you take the CT while performing this "inter-core coupling test"?? The standard doesn't...

Hello JimmyXWang, Let me first comment on the referenced thread from Nov 10, 2010 - It looks as if the OP was not performing the test correctly and may not have been using a high-Z voltmeter like C57.13.1 suggests, but who really knows as there was very little discussion on the method. As for...

Veritas is exactly correct. And I might add to assure saturation you can take it up to the rated secondary current times its rating factor. That induction level should be high enough to remove any significant residual magnetism that may be in the core. If you want to test that theory then...

Bushing CTs made in USA, in general, do not have a ground connection from the core. The core is fully insulated from the secondary winding. Dry-type BCTs which are found on HV power circuit breakers are usually installed under the bushing flange and protected by an aluminum shell isolated...

zimmerDN, I cannot speak for all CT makers but I can speak for those that I have personally been involved with - with regards to zero sequence GF CTs they are wound in a different manner than a typical CT. In ZSGF all three phases pass thru the window, and it is possible to have unequal line...

My educated guess based on CSA (Canadian) and older IEEE/ANSI (USA) standard nomenclature for protection class CTs: 5 = composite error (5%) at the accuracy limiting factor (ALF) which in this case might be 20 L = low leakage design, i.e., ring-type core with fully distributed windings 400 =...

derek22 - "...in case that the CT secondary is opened accidentally". Are you refering to the aux CT's secondary circuit here??

derek22 - A CT works best with minimal burden, therefore a short circuit provides its best accuracy performance. I am confused as to why the aux CT is there, is it not connected to anything other than the main CT secondary?? And you mentioned easy removal without disturbing the main CT - you...

Hello 111R, With regards to metering CTs don't always assume they too, will saturate at fault levels. That depends on the type of CT (wound-type or window-type) and the current ratio. Many window-type CTs have enough capacity to drive a low burden well over 20 times rated current without even...

Hello Scottf, I figured you would figure it out sooner ot later. I did talk to a few of your colleagues in Orlando this last week but did not get to meet you face to face. Maybe some other time?? It's funny you bring up routine testing because the standard does not say to test at Vse or...