Looking for some feedback on solid state three phase contactors. I have an application in which a semi-conductive dust intrudes into a nema 12 equipment enclosure. This causes excessive and ware on the contacts of the numerous three phase starters. I understand this is steady money in replacing motors and contactors. Yet it is a known danger I wish to correct. I know the easy answer is to prevent the dust, but I'm not a dust preventer nor do i wish to sub this task out due to liability. I have used single phase solid state relays with the only potential problem being leakage such as found at a PLC solid state outputs. I am not specifically looking for who has the best solid state contactors. I am rather interested in short falls or unforeseen consequences of using three phase solid state contactors. I would also be interested in the results of using solid state contactors in a Y-Delta starter configuration. Thank you in advance...
To use or Not to use Solid State Contactor ?
- Thread starter VinceS
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GeorgeB
ElectroHydraulics engineer (retired)
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- Greenville SC
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- Retired
When I have selected or been told to use solid state contactors (they have been soft starts), there has been a bypass mechanical to eliminate the voltage drop and heat once stable. I would be concerned with heat in the running connection with Y-Delta as well. My applications have been motors, usually in the 5-150HP range, usually 460/3/60.VinceS said:
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
1st off, do NOT replace electro-mechanical contactors with solid state on a Y-Delta starter, they will not survive the first transition spike. But if you are going that way, just use a solid state soft starter and connect the motor in Delta permanently to it; no need for the Y-Delta any more with a soft starter, it's better.
But yes, heat is a definite problem. SCRs will reject 1-1/2 watts per running load amp per phase. You didn't indicate the size of your motor but Y-Delta makes me assume it is sizable. So lets say it's 150HP 460V, 220A 3 phase, that means the solid state starter will reject 4.5W/RLA or almost 1000W of heat into the box, about the size of a small baseboard heater!
So faced with that, you can possibly find a version that has a "fins out the back" design on the heat sink, but that will be limited to about 125HP. Above that, the SCRs are of a design that cannot be done that way because the heat sink needs to be part of the conduction path. A bypass contactor would solve the heat issue, but introduces a contactor again.
Honestly though, your best bet is to see if there is a better way to keep out the dust. Even with solid state, there are conductive paths inside and eventually the dust will build up and cause a short. Air purging systems are best for that.
But yes, heat is a definite problem. SCRs will reject 1-1/2 watts per running load amp per phase. You didn't indicate the size of your motor but Y-Delta makes me assume it is sizable. So lets say it's 150HP 460V, 220A 3 phase, that means the solid state starter will reject 4.5W/RLA or almost 1000W of heat into the box, about the size of a small baseboard heater!
So faced with that, you can possibly find a version that has a "fins out the back" design on the heat sink, but that will be limited to about 125HP. Above that, the SCRs are of a design that cannot be done that way because the heat sink needs to be part of the conduction path. A bypass contactor would solve the heat issue, but introduces a contactor again.
Honestly though, your best bet is to see if there is a better way to keep out the dust. Even with solid state, there are conductive paths inside and eventually the dust will build up and cause a short. Air purging systems are best for that.
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