Microprocessor Relay Testing
Microprocessor Relay Testing
(OP)
Hello Everyone,
I would like to ask everyone's opinion and references on the frequency of testing microprocessor based and solid state relays. The type of testing is using a relay test set, not just the self-test feature of the relay.
With electro-mechanical relays, I've been testing them on a yearly cycle but the others I have been depending on the self-test feature.
I'm also limited by the test set (Multi-Amp SR-76) and am trying to get in the budget a newer test set and need some justification.
Thank You in advance.
wbd
I would like to ask everyone's opinion and references on the frequency of testing microprocessor based and solid state relays. The type of testing is using a relay test set, not just the self-test feature of the relay.
With electro-mechanical relays, I've been testing them on a yearly cycle but the others I have been depending on the self-test feature.
I'm also limited by the test set (Multi-Amp SR-76) and am trying to get in the budget a newer test set and need some justification.
Thank You in advance.
wbd






RE: Microprocessor Relay Testing
RE: Microprocessor Relay Testing
What I have been recommending to clients who are moving from an electromechanical to a microprocessor environment is that they start with a two year interval and then increase that as they get comfortable with the new technology and see the trend of test results over time.
You didn't say what type of relays you are testing, but I would infer from your use of the SR-76 test set that they would be mainly overcurrent and maybe differential relays. The basic tests for these won't change much whether they are electromechanical or microprocessor, so a test set with more bells and whistles may not be warranted on that basis alone. On the other hand, if you are getting into some more exotic areas such as playback of fault recordings from microprocessor relays, then a high tech test set is definitely in order (I recently isolated a transformer differential trip application problem using fault recording playback on a Pulsar test set - great feature, with a lot of practical utility).
jghrist - while I have the greatest respect for SEL as an ethical company and for their products, I don't think that I would take any manufacturer's say-so to replace prudent engineering practice for calibration checks. I agree with you in principle (it's all firmware and monitored hardware when you get past the analog/digital conversion), but I will continue to recommend calibration testing. As an aside, I recently came across some older (1994) SEL relays that had to be replaced because of drift that could not be corrected by calibration - admittedly, this is a rare exception involving slightly older analog-based technology rather than today's all-digital relays, but it does make the point.
RE: Microprocessor Relay Testing
It's hard to break old habits even if they may not be completely rational. It is possible that the increased probability of a relay error and outage while testing and depending on backup (although extremely small) may be greater than the probability of a relay error causing a problem if left untested. Not really worth figuring out.
RE: Microprocessor Relay Testing
All of these factors may dictate a shorter maintenance interval than would be required for the relays alone.
RE: Microprocessor Relay Testing
One approach may be to get a basic two-channel amplifier-driven test set with manual control, and add a similar second and third later. One consideration not to leave behind is the instrument having adequate compliance to fully test existing electromechanical relays. Some reps are given new equipment by their manufacturers—a 14-30 day loan may be a negotiable proposition, especially if the rep senses your serious interest.
Software is a major commitment for a number of reasons. Although relatively expensive, rental of test sets may allow for ‘evaluation’ of sorts. It’s not real common, but used equipment becomes available at times, and sometimes changes hands rather quickly, so you may have to convince procurement to be a bit more flexible to accommodate this.
Whether your management cares or not, a variac/tapped-transformer test set can drive you mad trying to test numerical relays.
RE: Microprocessor Relay Testing
We test at 3 year intervals, cycling an operational check with a full calibration. A properly cleared fault is taken as an operational check. All watchdogs are monitored via SCADA. All checks exercise full system from instrument transformer secondaries to CB trip.
BTW, we now use the SEL contact arc suppression devices, and have had no further problems with relay contacts.
Bung
Life is non-linear...
RE: Microprocessor Relay Testing
For microprocessor relays, my approach has been:
1. One test to confirm that the logic is functioning correctly (eg a timing test)
2. Test all of the A/D conversions. This is basically current / voltage injection and noting the displayed currents / voltages.
3. Trip test - confirm the relay trips its final device.
4. Test of instrument transformers.
RE: Microprocessor Relay Testing
In any case, personnel safety is still only a secondary function of protection - it is there to get the fault off before it becomes any more of a problem to personnel and plant than it already is. If the person was the source of the fault, well sorry mate, but he's probably dead anyway. So attaching meaningful numbers here is pretty haphazard.
I have tried to do these kinds of calculations, but I believe that they are ultimately only useful as one of the factors used to guide you to a decision - to illuminate the problem, not as teh sole basis of any decision.
Bung
Life is non-linear...
RE: Microprocessor Relay Testing
http://www.selinc.com/techpprs/6000.pdf
The nowadays digital relays have self-testing feature, monitoring, reporting, etc., therefore, their routine testing is less significant. The electromechanical and solid state relays routine testing and maloperations were indicators of potential problems.
RE: Microprocessor Relay Testing
Relay testing and relying upon the relay to let you know if it is in trouble:
Only trouble with self testing by the relay itself is that we had a P44x series Alstom relay that had the potential to stop working after a few weeks from maintenance testing, without making the internal relay failure contact operate. (It was a firmware problem). So we only became aware of the potential problem courtesy of Alstom letting us know.
Of course this can happen with other relays by other manufacturers. (We appreciated Alstom letting us know in advance of any potential relay failure).
RE: Microprocessor Relay Testing
I would disagree that protection of people is a secondary function of protection. It is well documented that a persons chances of survial are improved if the exposure time to voltage decreases. A relay failure that requires back-up relaying to clear a fault is much more likely to kill someone.
RE: Microprocessor Relay Testing