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]

Hello guys!
I just sent that bloody "Protection coordination study" which ate-up all my time and attention during the last week. So now I can add some new 50 cents on the topic.

Slava, I am not 100% agree with you about threshold testing. I believe they should be checked regardless of measurement test of the relays. Not that I don't trust type-tested algorithms which produce relay characteristics, but mostly to check how correctly setting values are entered. It is especially valid for Thermal Overload function and IDMT characteristics, where it is not so easy from the first look to determine tripping time for certain current.

Veritas specify almost the same amount of tests we do with one exclusion: for differential relays we do only threshold test, not slopes. The first reason is that we haven't equipment (6 current channels) for slope testing, but actually nobody have asked for this up to now. According to me it is not absolutely necessary, I rely on relay algorithms for that.May be I am wrong, but I prefer to keep the minimum necessary tests which are required by the customer and which also allow me to sleep well. If/when we can afford more expensive test set probably we will do slopes also, even to make test more "scientifically looking", as my professor in the university said. With automated procedure it will not take longer time and definitely will reduce understanding of my guys on the amplitude and angle compensation - now it is a bit tricky to determine expected operation values depending of vector group and CT-ratios!

I like most of comments of the Oldfieldguy, some of them (about manual the size of a metropolitan city's phone directory ) I often say with small language variations ;-). But it is high time to go home, otherwise my quite patient wife will became impatient

Could you give me some information regarding the legal side of relay testing in different countries. They put here in Bulgaria some requirement to establish in the company special Accredited Control Body for most of tests concerning safety - like insulation resistance, HV tests, earthing resistance, electrical installations, etc. And sometimes it is required that relay protections also to be tested only by accredited Control Body.
Problem is that accreditation is completely bureaucratic procedure, something like certification under ISO 9001, but much harder. According to me it is established only to take money from really working people, never mind how well it looks on paper. I am curious how this is arranged in other countries.

OK, have a nice day/evening depending of your location on the globe !

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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]

Of course, Plamen, you are right. Its really good discussion.
I wrote some extrimaly points and you correct me and correct right. I would like add, you must test all IDMT functions and "thermal" function like to: V/Hz, NPS curves, Overload. As Veritas wrote: 3 typical points:
at the begining, middle and end of setting. Its very important point, IDMT curves have differnt errors depending on the fault currents from 12% up to 3%.
And, I would like back to the begining of thread, I wrote:
at the new numerical relays important CPU load and right tasks and modules, for test this, you must provide some "type test" of your relay configuration and settings and correct SW or file.
Regards.
Slava