2 or 3 phase control soft starter
2 or 3 phase control soft starter
(OP)
Do 2 ph controlled softstarters have higher harmonic content then 3ph controlled softstarter during ramp up period, i.e before bypass?
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2 or 3 phase control soft starter
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2 or 3 phase control soft starter2 or 3 phase control soft starter(OP)
Do 2 ph controlled softstarters have higher harmonic content then 3ph controlled softstarter during ramp up period, i.e before bypass?
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RE: 2 or 3 phase control soft starter
More important are other serious problems with them, in my opinion.
1) They inherently feed the motor with unbalanced voltage and current, which is heating the motor disproportionally to the current it is drawing, or looked at another way, the current draw is not all going toward acceleration, a larger portion is wasted as heat, which can increase your risk of failure or decrease the amount of current limitation you attain and still accelerate the load. That can have serious implications on all but the lightest of loads, so unless it is a centrifugal pump or fan, I would never use them.
2) In any SCR based AC controller, there is a slight risk that the right combination of shorted SCRs will allow for unrestricted current flow to the motor with no means of stopping it. For that to happen on a full 3 phase (6 SCR) designed soft starter, you need at least TWO shorted SCRs, and they must be in different phases, in order for there to be a valid path through the winding. This risk is generally accepted to be about the same as welding two sets of contacts in a contactor, which would have the same effect. However in the "2-phase" soft starter design, where there are only 4 SCRs and the center phase is just a bus bar, so therefore the first half of that failure path is ALWAYS present, meaning any single SCR shorting means losing the motor. So to avoid having that happen, you MUST use an up stream device with an air gap, such as a contactor, or if you use a circuit breaker, the breaker must have a Shunt Trip tied to the Fault contact of the soft starter. Many, if not most, of these 2-phase soft starters are sold as low cost alternatives, so they do not have a separate contact indicating that one of the SCRs has failed vs an Overload Trip or some other protective function. That then means that ANY time there is ANY sort of Fault, it will open the circuit breaker or drop out the contactor, and you will have no idea what the fault was.
So in my opinion, what you gain in getting a lower cost of the soft starter requires that you must sacrifice reliability or be willing to put your motor at risk, or both. Not worth it.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: 2 or 3 phase control soft starter
Normally we have two ships gens 480kw, in emergency we have a 420kw machine. It is 90kw standby fire pump that in bad situation may be called upon to run in emergency mode, currently AT starter. I've read of instances were soft starters cause problems during ramp up contary to all the literature saying otherwise. We didnt want to be one of those cases, especially when main generation failed on ship. Hence the question. We would do testing to find out if it will be a problem after install but dont would rather mitigate against it now if we can establish it would be a problem.
I had read on abb literature the first point you raised, but had not come across discussion on the 2nd point. A very good point you raise though. I will take those points back to designer.
RE: 2 or 3 phase control soft starter
A different firing circuit developed by a company called Vectrol, which became Westinghouse (and spawned most other soft starters on the market), used individual phase-locked-loop sensing on each phase to determine the firing angle of each one in turn, no ASSuming. So if the frequency started swinging from the AVR, the soft starter firing swung right along with it and just passed it on through to the motor, which couldn't care less. The Vectrol design (and all of their kin) never had that problem. But because Saftronics became very big in the 80s soft starter market, there were a lot of spectacular failures in generated power applications, such as marine fishing vessels (where I learned all this). It forced generator mfrs to look into it and solve the problem at their end. For a while in the early 90s, CAT even sold a retrofit kit for older AVRs, which was basically a filter for their sensing circuit. Now they have all revamped everything anyway and it's not an issue, plus almost all soft starters have gone to digital firing circuits anyway. It still used to come up once in a while when someone is using a very very old generator with an old soft starter, but it's been a long time now since I've seen it.
All that said, the cures were all based on the standard 6 SCR soft starter model, nobody was using the 2-phase design yet. No telling if that might raise the dead. I wouldn't, there is ZERO advantage, other than a slightly lower price, to using 2-phase.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: 2 or 3 phase control soft starter
I'd not heard of that before, it wasnt the generator i was thinking, more a case of anything sensitive that might be effected by distrupted waveform, like this case here. http://apps.geindustrial.com/publibrary/checkout/H...
RE: 2 or 3 phase control soft starter
Note also that the article mentions that the only thing that was really affected was the phase failure relay nuisance tripping, so they disabled it if the generator was running. I would have probably just tried a better phase failure relay...
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: 2 or 3 phase control soft starter
I guess we'll just have to sort out a fix during set to work if probs arise. Overall we are looking for safer switchboard and in the space constraints i think our only best option is softstarter. Hoping we can fit 3ph controller into the design of switchboard in that case.
RE: 2 or 3 phase control soft starter
Technically, a 2-phase control should have a contactor in series with the starter to isolate it when stopped. Some electrical codes even require it (specifically calls-out that it's not allowed to only switch 2-phases on a motor)
RE: 2 or 3 phase control soft starter
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington