nuisance trips

[ww2]

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?

 

[ScottyUK]

ww2,

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.

 

[ww2]

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

 

[dpc]

If this is new equipment, I would complain to the supplier. The equipment in question is not adequately shielded for an industrial environment.

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.

 

[ww2]

Thank you dpc
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

 

[ScottyUK]

Hi dpc,

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.

 

[busbar]

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/description/relaying/C37.90.2-1995_desc.html

 

[dpc]

The cables could be shielded pretty easily.

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.

 

[electricpete]

dpc - wow that is quite an incredible fact that an electromechanical relay instantaneous element (plunger type) can be tripped by a radio. I guess that I am at a loss to understand the physical mechanism by which that would occur. After all a substantial spring force must be overcome over a distance. Inductive relay should resist any sudden rise in current. In fact normally a current circuit fed by ct secondary is very low source impedance virtually immune to emi noise. How do we explain it?

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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