CT Ratio Limit in Siprotec 7UT613?

Have you phoned the manufacturer?

hello ramneet. i don't come with the solution! but i have some thing to ask u. can u help me how to calculated setting for transformer differential relay. the transformer is 4mva and assume its impedance is 8%. please help me to understand.

There is a manual for 7UT613 and also application manual for Siprotec relays.These manuals deal exhaustively on settings, applications with example. Please go through number of time to understand. It is not easy to explain in forums, because you have to understand the basics.

The TUT613 relay has a MULTIPLICITY of settings and you are likely NOT to have all of them set correctly.

To start with, . . . the power transformer voltage ratio is (HV/LV) 220/66 kV = 3.33, thus your CT ratio has to be the same (LV/HV) must be the same = 3.33.

If the ratios are NOT correct, then you have to use an auxiliary CT or ratio-matching features in the relay.

If you use the 800/1 CT on the HV side, the LV CT should be ~2,666/1.

If you use the 1000/1 CT on the LV side, . . . you need a 300/1 ratio on the HV side.

As the full load current on the HL side is in the order of 300 amperes, using the avobe suggested ratios would be correct. No ratio matching features are required when using this correct CT ratio.

By testing the relay with various CT ratios and different values of MVA, I have observed that relay goes into the blocking state if HV CT ratio> 2.5 * Full Load current.

Can anyone who has worked upon this relay suggest some remedy?

Thanks

Do you have any idea as to how the differential protection works on a power transformer?? Judging from your posts and comments - you have no idea - you do not know what you are doing.

So, get on the internet and read up on DIFFERENTIAL PROTECTION.

ONE OF THE THINGS YOU WILL LEARN IS THAT THE RELAY REQUIRES PROPER SETTINGS OF THE CT RATIOS - and that the CT ratios depend on the power transformer ratios.

Get it through your skull that it is not the HV ratio . . or the LV ratio . . . IT IS THE RATIO OF LV/HV THAT HAS TO BE CORRECT.

From the data you have posted . . the following ratios should work correctly:

150/1 & 500/1; 300/1 & 1,000/1; 600/1 & 2,000/1

Do don't have to match ct's for a 7UM613 dumbass. Don't be so rude

@Olehwi

I don't think u have worked with numerical relays.. One of the biggest advantages of the numerical relays is in terms of the flexibilty in settings (ICT are not required when numerical relays are used). I don't think you have worked on Siemens relay. I requested the people who have had hands on experience with Siemens relays only. So, please stay out of this.

You are correct . . . the "digital relays" have many advantages . . . unfortunately you appear not to know how to use them - how to set them up.

Using the "preferred ratios" simplifies the settings of older or newer relays.

Hi Ramneet

I did have have a similar problem with a 7UT613 relay where the configuration/settings issued caused the the relay to block.

My problem turned out to be a configuration error where there was a conflict with the UREF Settings.

I noticed that you experimented with different settings which is good.

Without seeing your configuration it is difficult to see what else there might be blocking the relay.

If you contact Siemens and email the file to them they will be very helpful in identifing the problem.

I would like to say that this is the worst web site to ask a question as most members are very abusive and not very helpful.

I can forward you the email address of a technician in Siemens but i will need your email address

I wish you good luck anyway

I am just wondering whether magnitude matching has been done appropriately.

Finally got the solution to my problem. Just wanna share for the benefit of others. Increasing the value of Pole Open Current Threshold Side 1 (No. 1111) doesn't block the relay anymore for HV side CT ratio 800/1.