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TESTING OF NUMERICAL RELAYS 6

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521AB

Electrical
Jun 23, 2003
197
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 :)
 
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Let's try.
1. We also take in account digital relays, becouse I'm always separate digital and numerical relay.
2. Test of relays at commissioning time and at maintanance test.
3.Commissioning time, full test:
3.1 Analog inputs
3.2 Digital inputs ( include threshold voltage operation), outputs
3.3 Settings
3.4 Logics
3.5 power supply ( min and max thresholds).
4. Maintanence test, only 3.1, 3.2 and 3.5 (is very important test, electrolit capacitors into PS, off/on PS test).
Maintanence test depend on : relay is connected to SCADA or not, if yes pereodical test once per 6-7 years, if not per 5-6 years. Not needed test of settings and logics, only inputs and outputs. IRF/watchdog/selfsupervision not controlled Analog inputs ( I'm not say about AD converters), BI/O. I'm also recommend provide megger 500V to analog inputs.
OK, it's only start of topic.
Regards.
Slava
 
Now, continue.
Divide maintenance to periodic testing and preventive maintenance. Periodic testing for example per 3-4 years: what are include:
1. Visual inspection.
2. Front panel inspection.
3. Communication inspection.
4. Self-supervision inspection.
If you have SCADA, you can check many parameters via event/parameter list, compire settings with original, meas. with some power meters.
Preventive test: why is important, you have two groups of components: electronics with some life cycle influenced by themperature, hummidity,RF, etc and electromechanical with other life cycle influenced by corrsion, vibration, duct, etc. will be provide each 8-10 years.
Of course,preventive maint. is include CT/VT, swg test too.
 
Part III.
All relay mnf. today not provide any data about test of relays. You can see: free maintenance!!!! 5-10 years warranty!!!!. Sales slogans only. You must test relay.
I don't want say about advantages of digital/numerical relays, its clear. new technolgies open for us new option and possibilies w/o end. But don't forgot with new technologies also come new problems.
1. Serial faults, you can see this type of fault only after some time, possible after 6-7 years. Found it at test time: NO CHANCE.
2. SW problems, same as point 1.
3. Multifunction relay with tens protection functions
you put on the first step only 3-5 functions and after 5 years you add new functions, you must, must check whole relay again as at commissioning time. Why, you can see some problems in SW, like to tasks problems, longer time of trip, CPU overloaded, event overflow, etc.
4. I don't say about algor. problems, we found this type of problems also and not once.
Don't forgot, new relay is math. and possible mistakes.
You can check relay and after few years found that relay operated with 25-30% error. Actually it's another problem, what relays you bay" you get, what you pay for ".
 
Thanks for your dedication to this object, Slavag.

I would like first to define what "TESTING "means.

To my opinion, I will check Wikipedia later to see if I am right, and my using poor words, testing means "to carry a limited amount of 'experiments' with the system to be able to judge that it performs according tthe expectations"

Than we have to define "expectations".

But I hope you agree on that: ".. a LIMITED amount of 'experiments'..." that will allow me to judge the system. It the tests/experiments are not passed, we can say that there is something wrong.
If they are passed, we can say with a reasonable hope, that it should be correct.

We should also discuss on WHO is responsible to define the tests. Somebody who knows how it has been designed and know how it should perform. Somebody who knows where to put the "test points", like in the past (and still maybe today) with circuitry in the analog TVs, you had some test points on the printed circuit, where you were supposed to put your oscilloscope and somewhere else your signal generator and verify the correct waveforms... the test points were decided by the TV manufacturer! It was part of the design!

To my opinion, relay manufacturers today do not do it. The responsibility has moved away from manufacturers, and somewhere it should be brought to them, formally.






 
Let's go the e.m and static relays world. What happens there?

There is a measuring equipment and than a decision making equipment.
Both are made qith a technology that need "trimming", adjustment.
Simply, there is need to turn some potentiometers, trimmers, until the relay detects the correct point.

The correct point must be given from a signal generator (a calibrator generically. For "us" it is called test set).
You inject 1A (and you trust the test set that it is really 1A) and you turn the potentiometer until the relay trips or starts or whatever. Suppose that with this calibration, the potentiometer is set at 45 degrees. Another relay with the same name and manufacturer, will probably be set to 46 degrees, and another one maybe to 44 degrees. This because of tolerances in the components of the relay itself.

This is the basic of commissioning test. And this is the basic motivation that gave birth to test sets, Doble, Freja, Isa, Omicron etc. There was a clear need to have such equipments and we knew what they were supposed to do.

Then we know that there is drift in components/materials, so after a while we have to come back to the same relay and check that "it didn't move". The thresholds are verified again, and if there is need to adjustment, it will be done.

And if teh relay doesn't work? I mean, it does not trip, or I can't adjust it to the correct value, or I'll do it, and after 5 minutes it is far away from the given set point etc..
Nobody asked to the engineer (commissioning and/or maintenance) to take an oscilloscope and enter in the test points (if anyway available) of the electronic cards of the relay to try to understand why it doesn't work. Nobody asked the engineer to rewrap the coil of an e-m relay, or measure the magnetic field in the gap to see that it is really according to the design.

No, if relay does not do it's job, it was just declared broken or malfunctioning..

Of course today the problem is really this one: to be able to understand what means "if the relay does not do it's job", as the relay is today a complex system.

I don't want to enter already in the numerical world. I would like you to think about what above and eventually complete it, so that we have a clear panorama of the problematic in the "previous world".


 
OK, will back to the EM and static relays world.
I only one year worked with EM relays.
We had procedure difineded by mnf. for test those relsys, was included injection current/voltage and calibration of mechanical parts( springs, contacts,coils, etc).95% of work was calibration of mechanical parts. We also had special tools for calibrate them. As I remeber, for one single phase overcurrent relay we spend hours. As student, I worked at one commissioning company and get test protection of MV single speed motor. I worked on this about 4-5 days. Only test and calibration of 6-8 EM relays was about 3days. OK, I haven't excpirience too. Only one relay I tested fast,
static timer with knobs. EM relays was possible replace on the site or at some local lab.
Static world, good world, simple relays and simple test
No mechanical parts, tested exactly as you wrote. Calibration of knobs. Wat was problems , knobs in all cases is mechanical parts and those relays influenced by RF, mobiles phone and and .. havent connection to PC.
Before about three years we tested some generator protection with static and first digital relays( also with knobs). About 50% of relays was defected and reason was vibration of cubicles. I don't say about several unwanted trips becouse mobile phones. But in static relays you had "test points" also definded by relay mnf. and was possible tested them with scope and also possible repair them: replace some resistor, capacitor or repair at some local lab.
What is a big disadvantage of those relays: you test them put in operation and after 5 min you don't know it work or not, in static relay you see only one green led of PS.
One classical case: we tested EM diff relays and found all of them defected, but we tested them directly from terminals not from test plugs and after few hours we found that all CT's was shorted on the CT's terminals.
 
Ouf, how much I need write:), but this issue is very intresting and we have many discaussions on this topic with customers , with designers, with mnf and internaly at our team.
Next problematic point with analog injection, alsways you need some good Fluke for check your test set. Relay setting is 1A for 1s, you inject and have negative result. What is a reason, relay, test-set or wrong connection? What is a negative result: relay not work or you get trip after 1.3sec. Why, you don't know and start check all again. More problematic if it's angle, yes you can calibrate with knobs, but you don't know it's right or now. For exampe: we tested one reverse power static relay, relay passed w/o any problem, after one or two month was really reverse power and relay not operated. Why, we come again, test again this relay according to mnf. , all fine. Of course we found reason, solution was very simple: retrofit of protection relays.
 
Slavag,
I start from the point that the test set IS calibrated, so that it does what it is supposed to do. Ok with the Fluke of course, just in case you believe the test set is doing wrong. Instead of the Fluke you night consider the use of another test set (I am preparing myself for the discussion in numerical world, where the Fluke is difficult to have :) )


 
Hey 521AB, I see we have enouph time today for our dialog.
Today so rainy and windy...
But seems we think at the same direction:)
We will continue in the digital world and after this at the numerical
 
Let's wait until other will join the discussion, for E_M and/or STATIC relays
So far:

1) what's the meaning of testing an e/m or static relay.
2) what are we asking to relay manufacturer
3) what are we asking to the test set
4) which test do we perform and why
5) which decision we take if test is passed and/or failed

so that this point is clear

 
Slava, let's me share my opinion too. I have no much experience in maintenance tests, as all my professional life is with new projects - first company was pure commissioning, and my second job was design and commissioning of turn-key projects.

1. We also take in account digital relays, becouse I'm always separate digital and numerical relay.
=======
For first commissioning I cannot find much difference when testing of settings. May be I am wrong. Testing of logics is another story.

3.Commissioning time, full test:
3.1 Analog inputs
========
First point I test (and first table in my test report) is measurements test. Usually at the begining I inject current and voltages from terminal block where cables from CT's and VT's come, checking this way panel wiring. Next point is to inject from test blocks, if any installed. It is good to check whether short circuit facilities of test block operate without breaking the circuit. Sounds obvious, but last year I found that our Freja 300 cannot react on very brief breaks, during the switching of test switch. We found that wrong type of selector switch have been installed (without maintaining of closed circuit during switching) when tested second time relays using Omicron.

3.2 Digital inputs ( include threshold voltage operation), outputs
==========
Operation of DI's - OK, but threshold voltage check is not necessary according to me - there are factory tests for this purpose.

3.3 Settings
==========
Some manufacturers pretend that if measurements check is OK no need for detailed checking of setting values. I had a case when they required from me just to make shot test of one forward and one reverse point of distance relay characteristic and to sign commissioning report. I refused and never got other order from this customer. Anyway I don't regret.
For me initial commissioning must include checking of setting thresholds for each function. For numerical relays I don't see much reason to test PU/DO values - they are always good and are not dependable on ageing of some spring, for example. Of course more complicated functions require special programs, some of them included in test set software, some should be created by myself.
It is matter of discussion should test to be completely repeated if only some values have been changed during the test. Theoretically nothing wrong would happen, but we always have a risk something have been disabled and forgotten to enable again. According to me such risk should be accepted, but detailed review of printouts of final setting files must be done before energizing.

3.4 Logics
========
Most interesting point! This feature of numerical relays still keeps relay protection engineers necessary!
Actually I see here the biggest difference between numerical relays and all previous technologies. We cannot rely now on fully type tested configurations. Even when using typical configuration (like these ABB offers, for example) some minor changes must be set to adapt the relay to particular project. And main question is: Who takes the responsibility!? No answer for me.

3.5 power supply ( min and max thresholds).
============
According to me we should rely on factory tests here.



------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant
 
Plamen!!! Great!!!!.
I start from max requerements, you reduce all to gold optimum.
You wrote exactly procedure according to what we test relays.Logic it's other story, you are right, need decide case by case. About settings, in 10 years what I work with digital/numerical relay, we and our customers only once
found relay with errors in IDMT curve.
But, we have one customer with relays from some companies (w/o names) we tested those relay each year( some special requeremnts, critical object) and only on this years all relays passed, usually we was need replace one or two digital relays. Before , I think, one year we tested protection relays of one very serious company, four sets of diesel generator protection. We check all relays and after compaire results we didn't believe, same results for all sets with difference maybe 0.5% . crazy and this after about 8 years of operation.
Regards.
Slava
 
BTW, Plamen, I finished used test switches in design, only if it's special requerements, we start used Phoenix terminals URTK/S instead UGSK/GS, usually used for voltages, but possible ordered them with short slides. Don't like this test-switches and today with digital/numerical relay, from my point of view not needed.
 
".... It is good to check whether short circuit facilities of test block operate without breaking the circuit. Sounds obvious, but last year I found that our Freja 300 cannot react on very brief breaks, during the switching of test switch. We found that wrong type of selector switch have been installed (without maintaining of closed circuit during switching) when tested second time relays using Omicron...."

That's another example:

what does testing mean and what you do if the test fails ????????

I think you are talking about the test switches of "Asea type", where you enter the test handle and it automatically shorts the CTs, cuts the VTs and trip signals.

There is a potential flashover in those equipments, during the insertion/removal of the handle. The flashover is generated by the CT itself, which is a inductive circuit, and is not dangerous. Actually the flashover makes that the current circuit is not interrupted. No danger.
I think you have just tested the test switch in a no load situation, and used Omicron to detect a small and fast contact opening, which mechanically may happen, but the circuitry where it is inserted makes it correct. They are designed like that. You could have used an oscilloscope to sense the switching, but it was not -if I well understood- a realistic situation.

So I think your "old Freja" did its job, by not detecting it.



 
Slavaq, I also prefer to omit test switches. By the way they are not required anymore here in Bulgaria, but URTK/SP is standard terminal for current circuits (great for my good friend who is exclusive dealer of Phoenix Contact for Bulgaria!). No more BI-4 and BI-6 blocks in new panels!

521AB, I don't like to name the companies, but will make an exclusion now. It was Siemens design, but not the funny test sockets with selector switches which Siemens call "test switch". It was specific circuit, because primary design is double bus bar with transfer bus and it was necessary to switch CT's from the feeder and from the transfer bay to same relay protections. Design was OK, but in the factory they didn't order properly selector switches. Just mistake in delivery, it is good we caught it before energizing. Possibly operators never will switch them on-load, but I hate to miss such things anyway.
By the way I like these Asea/ABB test blocks and still keep test handles for both modifications. But I prefer switchable terminal blocks, test blocks according to me are just one more break point in a very sensitive circuit.

------------------------
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, when you say

"...Design was OK, but in the factory they didn't order properly selector switches. Just mistake in delivery, it is good we caught it before energizing. Possibly operators never will switch them on-load, but I hate to miss such things anyway...."

you mean that the current circuits were OPENED by the test switch? And it was not a short interruption? I wonder why Freja was not able to detect this.

Regarding companies, they do exist, and as long as we intentionally damage / favour them, I think it is not a problem in naming them.
Omicro, Freja, Doble are also companies, and I see that nobody has troubles in naming them.



 
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