TESTING OF NUMERICAL RELAYS 6

[521AB]

I would like to consider again this issue:
What does testing a numerical relay mean? Why do we do it?
What happens if the relay fails a test?
Which kind of tests are required for digital relays and what is their purpose?
(for example: function test like overcurrent or distance protection tests; system test like communication schemes, A/R logics; maintenance test (purpose? )

Please let's try to figure out what we are asking and what we are expecting form a test of a digital relay. From scratch. I think that not even the relay manufacturers have a clear idea about that!

We should maybe start to list (that is easier) the arguments/needs/goals for the testing of the electromechanical relays, than remove what is not needed anymore because of technological change, and see what is new and needs to be tested, and why.
Try to make reference to your experience/troubles. Find out situations that have been detected thanks of the test.

Let's see if we manage this

 

[lz5pl]

521AB, relay protection is connected to one or another set of CT's via selector switch. Switch diagram was chosen correctly, the switch must maintain circuits closed during the switching from one position to another. Half of the switches were delivered OK, another were wrong, without such maintaining. Not Siemens designers mistake, it was mistake of the panel manufacturer.
Strange for me but Freja didn't react on so fast breaking of current circuits. Omicron's software has indicators on the right side of the screen which turn red even after short interruption.

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

 

[521AB]

Actually my experience with Omicvons is that it also did not detect some small interruptions, which only Doble was capable of. But after several investigations we understood that this fast reaction time (it was several years ago, don't remember what "fast" was but I can check at work) is not needed for "electrotechnical" applications, as inductive circuits will fix it by themselves, if the switch occurs on load. If it doesn't occur on load it is not a big problem if they cut-off.
I was working at that time with the "ASEA" test switches (I say ASEA because it comes from the old and good Combiflex time), that are designed to switch between main CT and test set while the substation is in operation, so under primary load.

 

[slavag]

521AB, Plamen, we will continue this topic or its all.
Slava

 

[veritas]

Hi All

I think mention should also specifically be made of Scheme Tests vs Relay tests. I quote seperately for a customer for these two items as a scheme tests involves the relay tests AND checking scheme circuitry - e.g. operation of switches, SCADA I/O, cb trip/close tests, etc.

With relay testing I am now referring to commissioning a new relay. I hardly do maintenance testing. I always test all protection functions, I/O and logics. I write my own macros for our test set and I verify results against manufacturer tolerances.

a) OC/EF relays - relay pickup and dropout and check three points on curve
b) Directional Relays - prove the zero torque line
c) Definite time - relay pickup and two points for timing test viz. at 2x and 5x pickup
4) Differential relays - verify minimum diff setting, slope 1, turning points, slope 2, diff hi-set, 2nd and 5th harmonic. Note that I actually test the EXACT throughfault stability characteristic of the relay and not just one shot inzone and one shot out of zone.
5) Distance relays - X reach, R reach, halfway up the right blinder and halway along the top line (quad). Need to modify depending on whether load encroachment used.

I also do the above for our local utility. I think it extremely important that an engineer who FULLY understands how the relay thinks, compile the test sheets. Modern relays have some very involved algorithms and the mathematics can be quite daunting. Just consider how modern digital distance relays do EF compensation for example or how to calculate test points for a current diff relay.

We thus have a policy here (at the utility) that the engineer accompany the technician for commission testing. Maintenance testing is performed by a technician and is more along the line of spot checks as mentioned above. For my industrial clients I prefer to do all commissioning myself. I do not believe it to be in the best interest of the client to subcontract the commissioning of a protection system when I was involved in the design and settings.

I am sorry to say but you can forget about getting expert technical support from your local supplier (rare if you do) - in this country at least. Most times when I analysie the relay my queries get routed to the designers in another country. In my experience many manufacturers do not have the indepth technical expertise and experience locally available to assist with detailed technical queries. The local agent is more a front end customer service rep. In the US it may be different I do not know. Very often they may be able to explain a setting but cannot give recommendations as to how the relay should be set as their power system knowledge/experience is rather limited.

There are exceptions I must add and I am very grateful for their assistance.

Hope this helps.

Regards.

 

[slavag]

Hey Veritas.
It's nice see,how we all think at the same direction.
I'm so happy. Not only with test procedure, also work with utilities and industrial clients.
For Plamen: If you write logic or change mnf. logic,original setting: it's your full responsible, same for protection, same for control, same for settings. Yes, I know, you not responsible for setting calculation, it's responsible of clients, but what you do, if you see mistakes. I always change it, but it's not good from one side, from other side I would like sleep at night.
This is another topic, where is a limit of our responsible on the site.
About local agents: yes, it's not so simple, usually are salesmans, but it's depend on country and companies.
Now, about why responsible for the test procedure.
Mnf, I don't think so. Commissioning eng of this mnf., yes, in lot of cases, but not always.
Client, if are utilities, yes 100%, only them.
Industrial clients, this is problem of problems:
1. Client, in lot of cases, havent any excpirience in protection,
2. Designer??????????? only if it's control function and simple protective functions.
3. We????designer and commissioning eng. I'm not sure, if it's right. We do this and always, but isn't correct. Need some another person or company.
I think about it, but haven't any solution.
Regards.
Slava

 

[slavag]

About new technologies in the test sets.
It's great, good, etc, etc.. Omicron, Frej, Doble ( with additional amplifiers) and other companies too.Great test sets, no words.
Only one not technical problems, new commissioning guys work with this Macros, according to Plamen's or Verita's or 521AB's test procedures and don't understand what them do!!
For this, before one year, we bouth some test set like to old Sverker 650,w/o communication and I'm request test all simple rely with this test set only, BTW I'm used it always.

 

[521AB]

Slavag, when you say

"... About new technologies in the test sets.
It's great, good, etc, etc.. Omicron, Frej, Doble ( with additional amplifiers) and other companies too.Great test sets, no words..............................For this, before one year, we bouth some test set like to old Sverker 650,w/o communication and I'm request test all simple rely with this test set only, BTW I'm used it always...:"

I must say I understand you. Problem is that test sets took their own way, without feedback/contacts with relay manufacturers, and this is not only their fault, it is ALSO their fault. Even relay manufacturers have their responsibility in this missed dialog, so the risk is today that you test one relay from company ABC by using test set and procedure XYZ and you ... have not tested the relay at all, or you have tested it wrong.

At the end, you get one SVerker.. I see the point and I enjoy this forum

 

[lz5pl]

Hi guys,
It is our National Day today, so I stay a bit outside of professional problems. Tomorrow may be (I have to complete some urgent order) I will be again on-line in this discussion.

Slavaq, BTW I have in my practice three distance protections tested only with Sverker 760. It was in Lagos and there was nothing more suitable around. It is possible to do the work this way, but I wouldn't like to repeat it again :-(

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

 

[slavag]

Plamen. Congratulation!!!!! Viva to Bulgaria!!!!!

Sverker 760...., isn't so intresting, it include phase angele(phi) change option and weight..., 650.. not;-). We check with this new test set only simple O/C, E/F or voltage relays. And don't forget, with Sverker possible inject up to 100A!!!! 20 or 100 Inom!!! .
521AB, btw, Combiflex is still goodest aux relays, when possible, I'm used only them, 30-40 years of product, like to ASEA RI relay, 67 years of product.

 

[slavag]

Hi 521AB.
Understand me right, not only Sverker, btw if someone need this type of injection module,I add link, it was additional,of course we work with "normal" test sets (I would like bay new Omikron, but it's depend on our "moneyman").And 521AB, what do yoy say, we can manage it?
Good day to you all.
Slava

 

[521AB]

Yes Slavag, I got your metaphor with Sverker....
And I think there is a lot of true in it. Test sets are getting complicated, and are starting to give non-realistic problems to customers and, as consequence, to relay manufacturer.

There should be a sort of high level decision (IEEE, IEC, ANSI? I don't know) to decide -at least the minimum requirements- on what should be test and how.
It should also be decided what is a commissioning test, what is a performance test. Today people test with steady state shots and believe to find "bugs" in the relays, while actually the relays find bugs in the test sets.
THIS was what originated my thread.

I don't thing we will manage because to my opinion, nobody has the answers to this. But let's see..

 

[slavag]

Great 521AB!!!!!!!!!!!!
Its remind me some test with customer:
We tested pole slip generator protection with new Doble, test was about one hour,50min was calibrations of test set and we check this test set with this generator protection
.
We will continue. and will manage it .And, if you found bug of relay with your smart test-set, check twice again,
99% it was your mistake.
I also would like say again, if I bay good relay and we bay only good relays, I check only meas, BIO , tripping and signalization logic, its all, not setting, not drop-out, nothing, no needed. But first time we check new type of relay tens time. Im not KEMA and not type test company, Im only commissioning eng. Sorry for metaphor, if I bay and believe to good car, what is a difference, need believe to relay mnf. too. I work only with two relays mnf. and believe to them, of course check and test relays, but not all parameters according to manual. Guys, today, with new concepts, double protection, back-up of back-up, chance of not operated about zero, unwanted trip is possible,so, is not good, but I have statistics for ten years of my work.
NO NOT TRIPPING CASES. ONLY TWO REALLY BFP OPERATIONS. ABOUT 10-15 UNWANTED TRIPS ( wrong setting or HW problems). About 10 UNWANTED trips becouse relays fault, its all. For my pinion is nothing. I told about 50 substations and about 6000 installations.
Regards.
Slava

 

[521AB]

what I really liked from your post, Slava:

1) "Im not KEMA and not type test company, Im only commissioning eng."

The same for test sets. What are we asking them? Commissioning/maintenance test. NOT TYPE test tests, NOT relay performance tests.

Or let me say better: test sets can do smarter things, like performance tests and/or type tests, but they should declare what they are for, and put all the tests together, and move all the responsibility to the test guy.

If we decide what a commissioning test is, we have done a good step, and I think you have some good ideas, otherwise you didn't write "I am not KEMA...".. Just try to formalize them!

2) "...if I bay and believe to good car, what is a difference, need believe to relay mnf. too."
Exactly! I was discussing this with some friends of mine (and colleagues).
When you buy a new car, do you start to test the ABS functionality? Or you ask for the report of the Otto cycle of the engine?
No, but on the other side, you perform some tests, even if not formally.

3) ".... NO NOT TRIPPING CASES. ONLY TWO REALLY BFP OPERATIONS. ABOUT 10-15 UNWANTED TRIPS ( wrong setting or HW problems). About 10 UNWANTED trips becouse relays fault, its all. For my pinion is nothing. I told about 50 substations and about 6000 installations...."

This is an interesting statistics. What voltage level? Do you have a main voltage level or you "run everywhere?"

 

[521AB]

And another question. Sorry but I have to ask. What is this pink star close to my name all the time?

 

[slavag]

Hi 521AB.
Pink Star near to your name: THANK YOU FOR YOUR POST!!!!.
My statistic is include voltage level from 3.3kV up to 400kV. But lot of relay are MV level and generator and transformer protection.
About commissioning. I would like ask:
We bay not satnd-alone relay, we bay some BBP.BFP system for
28 bays with tripple buses with 12 protection zones and additional aux. bus, with couplers are included six disconnectors in distribution version. Folks its example only. What I can do, check each unit as stand alone relay, connected 20 synch. test-sets for check stability and performence of relays. Check again all zone configuration.
Of course no. FAT of this system is maybe two days. That means I must believe to relay mnf and to test eng. On the site, I provide only small testing for check AI, BIO and statuses of HW eqp. Its all. And of course primary stability test. Now, what is a difference with alone OC relay, no difference. In many cases no needed any smart test sets on the site. Simple Sverker enough also for distance, pole slip, loss of excitation, NPS, AR and diff protection!!!!!. Problem is only function like to ROCOF, freq, etc.
I always say to my bosses, customers and to my team:
Commissioning of relay on the site is connection of this relay to the system (CB,CT,VT, Alarm Panels, SCADA). NOT PERFORMANCE TEST OF RELAY.
Regards.
Slava

 

[slavag]

And additional Q. If I check on the site billing meter with class 0.2S, I need get to site test-set with class 0.1 or 0.05 and I need bay it ( approx 100k$ price!!!).
Of course NO!!!.

 

[oldfieldguy]

Not do start a history lesson, but...

I'm in the USA. When I started in this business, everything was electromechanical. If you needed overcurrent, you had three overcurent relays (or maybe four). If you needed phase current balance, that was another relay. Undervoltage? Another relay. A large motor or transformer had aalmost a dozen different relays, all made with clever configurations of iron and copper, and when it was time to test them, you dutifully pulled each relay out, did careful inspection, cleaning, contact burnishing. You knew the realy worked per the manufacturer's manual.

If you wanted to see how the relay functioned int he circuit, you rolled out the drawings and saw how the input currents and voltages came in, and where contact action would affect the circuit, and it was ll right there on the drawing. Life was good.

Fast-forward to today. Instead of that dozen relays protecting my transformer, I have ONE GE UR T-60. It has all those old functions: primary and secondary overcurrents, neutral, ground overcurrents, much more ocnfigurable differential and restraint characteristics. The siring is much simpler: Two sets of currents and a set of potentials in, contacts out.

But information that used to be on the drawings as to how the different protection elements interacted int eh control circuit, that information is not on the drawing as it was. It's in the relay's programming. Where it used to take a real effort to add wiring or cut connections to change the function of relays in a control circuit, now it's a matter of an ambition, if mis-informed engineer or technician with a laptop computer to foul things up. I've seen that done.

I've also seen setpoint programming that was incorrect, i.e., essential elements not included in the trip logic statement, or the incorrect implementation of the elements included resulting in misoperations.

All this means that our job got both easier, install one box and we have just about every function a protection engineer could dream of, and it got harder, we had to make sure we did our work with a manual the size of a metropolitan city's phone directory, and anybody with a laptop could mess things up without any external evidence of future problems.

And all that takes us back to the original post: What do we do about periodic maintenance testing of digital relays?

I am of the opinion that the most important things are to verify that the relay is still properly processing inputs, in other words, it properly reads voltage and current inputs, that the outputs still react properly, i.e., a contact closure results in the proper action the control circuit, and finally, that there have been NO changes in the programming of the relay since the last intentional changes.

Note that I said "periodic maintenance testing". Obviously, commissioning and type testing require a much different approach.

old field guy

 

[slavag]

Thank you Old field guy for your opinion.
One US guy with us, one Australian and three from Europa. Not bad statistic.
We still wait to other.
I think, we dont need discuss about type test. Only commissioning and maintenace.

 

[oldfieldguy]

slava--

We are a pretty good cross-section of the electrical power business, aren't we?



old field guy

 

[521AB]

I like this free discussion, and if we go sometimes out of the main subject, we discuss about something that brings us back, so feel free to brain storm.
Thanks oldfieldguy for coming in.

Regarding the star: is it possible that as soon as I write a post, like this now, somebody clicks on "Thanks 521AB for this valuable post"?.
There must be a bug somewhere!