nuisance trips
nuisance trips
(OP)
We encountered numerous nuisance trips on a new 30ton/hour Kvaerner/ HDS/Saacke fire tube package boiler. After a number of alterations on the instruments, with little effect, we finally found out some of the instruments(6), in the lockout system, where susceptible to signals of the portable Motorola radios.
Improvements, by the vendor, on the PMV positioners and the earthling resistance, by us, mellowed it but not up to the necessary level. So finally, with success, we wrapped the instruments up with aluminum folio together with about 10 cm of there, in and out, cables.
This cannot be, of course, the final solution.
Could the forum experience help me to a acceptable professional solution?
Improvements, by the vendor, on the PMV positioners and the earthling resistance, by us, mellowed it but not up to the necessary level. So finally, with success, we wrapped the instruments up with aluminum folio together with about 10 cm of there, in and out, cables.
This cannot be, of course, the final solution.
Could the forum experience help me to a acceptable professional solution?





RE: nuisance trips
Are these radios the new-ish digital type, rather than the older analogue type? We upgraded our radio system to the digital type, and have noticed many previously reliable items of equipment have started misbehaving. For example, a battery charger output goes clean of the scale at 250A, dual-redundant control computers hang up, digital protection relays initiate trips for no obvious reason, fire panels initiate trips, again for no apparent reason... need I go on?
The problem with these radios is compounded by their apparent requirement to keep communicating at a system level to the base station even though the user is not actually talking on the radio. The only way we've found to avoid trips is to keep radios away from the susceptible equipment, which requires a lot of discipline from the users. We still get the occasional trip when someone forgets the rules.
RE: nuisance trips
Tanks,
The type of motorola’s causing the trip is at least 4 years on the market. The trips where triggered by sending I did not recall any while receiving. Coming to think of it I’m not so sure anymore we‘ve tested it.
koekoek
RE: nuisance trips
I'm not clear on the type of instruments involved, but installing them in a steel enclosure such as a small junction box would probably be as effective as the foil.
RE: nuisance trips
Initially we started of with a aluminium box, not completely surrounding the instrument though. But we found out that wrapping up the cables was also necessary.
koekoek
RE: nuisance trips
The equipment is all industrial design, in metal enclosures, and mostly from reputable suppliers who are, or were, leaders in their field. The plant is not so young, so the equipment manufacturers probably won't care about the problem after 12 years in service.
I think the field strength transmitted by the radio must be pretty high to cause this sort of problem. Most trips have occurred when the radio is within about 5' of the equipment. I find it interesting that the older (analogue)Motorola radios did not cause this problem to anywhere near this extent. I guess the power level is higher with the newer design.
RE: nuisance trips
Although primarily intended for qualification of control and protective components in the power-delivery biz, there is IEEE Std C37.90.2-1995 …Withstand Capability of Relay Systems to Radiated Electromagnetic Interference from Transceivers. TOC at http://standards.ieee.org/reading/ieee/std_public/descr...
RE: nuisance trips
A five-watt transmitter can pack a pretty good punch when it's within a few inches of susceptible gear. I've seen VHF FM radios trip an electro-magnetic instantaneous trip relay in an IAC relay.
RE: nuisance trips
Maybe it was fed by a new-fangled linear optical coupler thingy? Or perhaps there were electronic relays connected in series (perhaps caps on the input of those devices would provide a path for capacitive surge current through the relay).
Was the control circuit meggered afterwards? Any damage?
Would be interested to hear any more details and theories.
We have lots and lots of those GE IAC's and lots of radio's but I haven't seen this one (yet?).
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