CT NETA Test Question

[ATSman]

I am posting this for aa associate in the switchgear manufacturing industry.
Thanks in advance for any advice.:smile:

Just a quick question to field engineers I have had contact with over the last few years:

I would like to find out what method and/or equipment you and your associates use to test current transformers to meet the requirements of NETA Acceptance Testing Specifications, Section 7.10, specifically with regard to turns ratio accuracy.

As an OEM, we are not required to perform this test, but we use a Megger TTR25 handheld turns ratio tester as a quick check of polarity and ratio. I have recently been told by a CT manufacturer that this is not a recognized test method, so if you could answer this for me (at your convenience) I would appreciate it

Tony

 

[zog]

We use an older version of this model http://www.megger.com/us/products/ProductDetails.php?ID=1016&Description=

However, someone who really understands CT's can use any old adjustable current source, we used to give our new tech a fluke and a carbon pile and make them figure out how to test all sorts of stuff using just that. Then they "graduate" to the MS-1A set, then later they get the good stuff.

A TTR gives you limited data, there is a lot more needed to meet all the tests in 7.10. Have you read 7.10?

 

[brian john]

We use different currrent sources but also have a dedicated device that offers more features (I always use a current source when someone forces me to work)

 

[ATSman]

Thanks Zog and Brian,
I am old school also and think along the same lines. Abviously, the ratio accuracy depends upon the accuracy of the instruments you use to take the measurements. I've used an MS-2 for the primary source with a Fluke 87 DMM on the secondary for direct current measurement and get good results. Also, the dedicated sets work ok and you get polarity thrown in (AEMC makes one.)
The NETA version I have is dated 1989 and is not very specific. Where can I get the latest version? Do you guys remember the Flick Test for polarity?

Tony

 

[zog]

Thanks Zog and Brian,
I am old school also and think along the same lines. Abviously, the ratio accuracy depends upon the accuracy of the instruments you use to take the measurements. I've used an MS-2 for the primary source with a Fluke 87 DMM on the secondary for direct current measurement and get good results. Also, the dedicated sets work ok and you get polarity thrown in (AEMC makes one.)
The NETA version I have is dated 1989 and is not very specific. Where can I get the latest version? Do you guys remember the Flick Test for polarity?

Tony

www.netaworld.org , you can download the newest standards there.

 

[molotov27]

I've had great sucess with this one http://www.vanguard-instruments.com/products/cttesters/ezcts2.php
Very easy to use, completely automated, no need to do any calculations, etc. It is pretty much a "utility" rated instrument. It might be an overkill for some applications, so look at all the possibilities around, but this one gets my vote.

 

[72.5kv]

The Vanguard is very straight forward as mention on the earlier post. In situations where the Vanguard Ez CT Tester cannot be used, we used a variac and a fluke meter to verify CT turn ration.