Siemens 7UT513 XFMR relay

[marks1080]

Has anyone ever experienced a missoperation with this relay during the deenergization of a transformer in respect to the relays algorithim for calculating 2nd harmonic current?

I've heard of a trip over the weekend at one of our stations where deenergizing a transformer at a tapped station cause the entire line to trip off. I have not seen the reports but I am hearing that it was due to the 2nd harmonic from the DE-energization of the unit and that current being detected as a zero sequence current through the primary nuetral. There were duel protections in place, only the Siemens 7UT513 relay sent the trip, the other protection relay is a GE (multilin of some kind - not sure exact type).

This should not of tripped, obviously. People are initially saying its due to the way the 513 calculates 2nd harmonics... This is not my problem, nor my station, but I am curious.

I would appreciate any insight or discussion of similar experiences other people may have had with the 7UT513.

Best Regards,
Mark

 

[AMBMI]

It could be interesting to know the level of 2nd harmonic measured by the 7UT513 just before the trip.
I know that for new transformers the generated 2nd harmonic level during the energization is lower so a typical value of about 10% should be used to inhibit the differential trip.
Perhaps the relay was simply set with a too large inhibit threshold.

 

[marks1080]

I am still getting more information on this. Looks like there have been several misoperations with 513 devices in our stations. We had one yesterday at a station during energization of a XFMR. The companion protection (GE Multilin) did not trip. Still compiling information at this point. It's still too early yet to know if it is a problem with the 513 or something else we are not seeing. It's very easy to blame hardware when something unexplained goes wrong. Too often that is not the case.

If this turns out to actually be an issue with the 7UT513 I will try to post details.

Note: We have not had similar problems with schemes using the 7UT613/33 relays.

 

[slavag]

Mark.
We have a tens of 7UT513 from 1996, no problems.
Could you please check, if its same relay or few relays.
Not seems good, that it happened in teh de-enegrazing mode.
Good Luck.
Slava

 

[marks1080]

Yes it is very strange indeed Slava. There is a group working on this now. I believe there were five misoperations that are as of yet unexplained - all with the 7UT513. We have also been using this relay for quite sometime, although the new standard we use is for the 613/33 model. It doesn't look like we are going to get an answer anytime soon. If it is a hardware issue I will be sure to post.

 

[marks1080]

Update: I've gotten a report written by one of our phds. Looks like AMBMI was on the right track!

The report has compiled over a dozen previously unexplained trips on transformer energization and deenergization over the past year or so. They weren't all just 7UT513 relays either. Some T60s and 7UT613s as well. The report describes how newer transformers have different 2nd harmonic characteristics than older ones - i assume because of different construction/materials for the core. It can take slightly longer for the common 2nd harmonic characteristics to show themseleves with these units - about 5 cycles or more in some cases.

The report is very interesting. I wish I were able to post it for you guys, but at this point it is still in Draft and is an internal document. I think the solution will ultimately be in reducing the % of 2nd harmonic current for pickup. Most of the units that tripped were set to 15%.

I think it is safe to say this is was not a relay issue at all.

 

[lz5pl]

marks1080, do you have "cross-blocking" function enabled? I have the same problem with AREVA MiCOM P633 differential protection. Transformers were very old (around 1963), Chinese made, and second charmonics during energizing lasts sometimes about 800 ms ! Initially I didn't set "Cross-blocking" enabled and protection tripped in about 3 from 5 enerizings. After setting up of crossoblock problem was solved.
It is good that in numerical relays is possible to see oscillograme of the disturbanse. Our customer suspected problem with this old transformer (the second one from same type didn'd trip) and was ready to switch it off permanently and look for some repairing company!

------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[marks1080]

Cross blocking seems to be the solution to this problem that is being proposed in the report I had.

 

[slavag]

Hi.
Cross blocking is good solution, not only at the energazind time, at AR time too. Im not sure if its help at the de-energizing situation :-(.
But, in all cases you can check setting of 2-nd harmonic block, and option of de-block in the internl time fault.

Mark, maybe were replaced CT on this transfromers? I had such problem in the de-eneragizing mode with big motors.
Trip was occurised in the end of opening time of CB on the low level of current.

Please try found any DR file. Its very intresting and helpful.

Good Luck.
Slava

 

[marks1080]

Wasn't just a single unit. The report that came out listed over a dozen trips assoicated with this. I know some of the units had their 2nd harmonic restraint set at 15%. I can't vouch for all of them.

They were all 'newer' type transformer.

These are power transformers that are connected to the main system. We have to respect clearing time of about 3 cycles for instantaneous tripping. From what I understand, just implementing cross blocking could jeopardize this. I think some of our design engineers are working on new logic that will ensure the cross blocking won't slow down instantaneous tripping for a true fault.

Again, it's too bad I can't post the report that was produced.