the power company changed over the transformer at the street from 208 to 480 and we changed over the switch gear and also added an additional transformer to bring the voltage back down to 208 for the 208 loads. The 480 is used to feed the new 208 transformer and for the motor loads in the building. I was told the motors were dual voltage with a star or delta hook up. I am not sure of how they were previously wired because I didn’t switch them over. The customer is now complaining that they are spinning too fast. I’m not sure if switching from a delta to a star setup would do that. I thought it was mainly hertz that controls the speed? I don’t have all the details but am just looking for places to start looking after I find out all the info tomorrow, thank you and if I didn’t explain it well tell me and I will try to clarify
Motor speed change after voltage change
- Thread starter Jnewell
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
If the motors are 208-230/460, then they're running now on 480v as they would have on 240v as opposed to 208v, as long as they were re-wired correctly (and were wired correctly before).
I'd say the customer's issues should be addressed to whomever re-wired the motors.
I'd say the customer's issues should be addressed to whomever re-wired the motors.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If the motors were running at a reasonably low slip rate before (i.e. plenty of torque at close to synchronous speed) then the only thing that could significantly change the speed would be using windings with a different pole count. But if the slip rate was high, and it is lower now, there must have been a problem with the original setup that produced too little torque. As Larry said, the voltage per turn on the windings should not have changed.
P.S.: Is it the loaded or no load speed that is "wrong", or both?
P.S.: Is it the loaded or no load speed that is "wrong", or both?
So they are only fan motors for an oven and only push air from the furnace and I believe they are only on or off, so I believe they are always technically loaded.
if I remember right delta creates more torque than wye setup?
Right about the voltage per turn because it just changes to series or parallel depending on the voltage that is being fed.
so if I'm tracking we want to find out how it was wired either delta or wye before we changed it over compared to now and if it’s been switched switch it back to the previous configuration at the right voltage?
But if that doesn’t fix it what would be the next step cause the us didn’t change neither did the number of poles in the motor?
if I remember right delta creates more torque than wye setup?
Right about the voltage per turn because it just changes to series or parallel depending on the voltage that is being fed.
so if I'm tracking we want to find out how it was wired either delta or wye before we changed it over compared to now and if it’s been switched switch it back to the previous configuration at the right voltage?
But if that doesn’t fix it what would be the next step cause the us didn’t change neither did the number of poles in the motor?
- Occupation
- Licensed Electrician
You got a few things mashed up.
Three phase motors are dual voltage 208-230/460. NEMA motors are wound internally wye, or delta, but don't worry about that, it doesn't matter. You change voltages by putting the windings in parallel or series. IEC motors voltages are changed by connecting the winding leads in a delta or wye configuration. In neither case does the speed change when the applied voltage changes, you would need a multi speed motor for that.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I'm actually saying that there might be a difference in speed between 208v and 240v for some motor types, and that the same speed difference ought to happen between 416v (theoretical) and 480v.
- Occupation
- Licensed Electrician
Not in any practical sense. There might be a few hundredths of a difference in rpm
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
Maybe they could be 2-speed Dahlander motors, which have 6 leads. It would be helpful to know what the motor nameplates show.
Metallicbeing
Member
- Location
- Visalia, CA
- Occupation
- Electrician
I agree (with Synchro). This goes back to what type of motor is there. We need more info.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If it is six leads and delta for low volts/wye for high volts, OP was applying 208 volts across each coil initially. After switching to wye configuration and applying 480 you will get 277 volts across each coil. This is a change in V/F ratio and may seem to work initially but probably will let smoke out of windings eventually. Should still have same synchronous speed if frequency stays the same, might change the amount of slip some, but probably not enough to notice without measuring devices.
If it is a six lead two speed motor and was designed for the 208 system it probably lets the smoke out in little time if connected to 480 volts.
If it is a six lead two speed motor and was designed for the 208 system it probably lets the smoke out in little time if connected to 480 volts.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
So if the transformer was put in there for the 208V motor loads, why was the motor change from star or delta done? If they worked on 208V before, and you gave them 208V from the new transformer, what is different? I'm thinking they did NOT use the 208V transformer for the motors, because they could just change the winding connection patters.
When you say "star or delta hookup", that implies an IEC dual voltage motor, in which case the Delta connection would be 230V 50Hz and the Star connection would be 400V 50Hz. If they were using them at 230V 60Hz here in the US, the V/Hz ratio was already wrong, and the motors would have been significantly under fluxed, resulting in LOWER torque and higher slip, meaning the motors have been running SLOWER than they should have been (which was likely stressing them too by the way). If they changed to Star connections and fed them 480V (i.e. not powering them from the 208V transformer), the V/Hz ratio for 480V 60Hz is exactly the same as 400V 50Hz, so the motors would change to having FULL rated torque, instead of running a LOW torque as they had been. That may have "fixed" their excessive slip problem, resulting in the appearance of the motors turning faster than before.
Metallicbeing
Member
- Location
- Visalia, CA
- Occupation
- Electrician
Jnewell, you said "Star"; which is foreign talk for "Wye", so Jraef used that to explain since "Star" was used instead of "Wye", the motor must of been running slower due to it being in that 50hz "Star"setup instead of our 60hz "Wye". He being funny.
Yeah, we still need more info on the motor.
Yeah, we still need more info on the motor.
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kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
But also as Jraef mentioned, star-delta for dual voltage purposes is typical for 50hz IEC motors. If you see wye-delta in NEMA motors is usually for reduced voltage starting methods and not for dual voltage run ability. NEMA motors are typically 9 or 12 lead for dual voltage and you connect windings in series for the high rating and in parallel for the low rating.Jnewell, you said "Star"; which is foreign talk for "Wye", so Jraef used that to explain since "Star" was used instead of "Wye", the motor must of been running slower due to it being in that 50hz "Star"setup instead of our 60hz "Wye". He being funny.
Metallicbeing
Member
- Location
- Visalia, CA
- Occupation
- Electrician
Hey Jreaf, I'm sorry about that last post. I left my browser open and my son (an Apprentice) found it and thought he'd add his two cents. I've explained the difference to him, and he also says he's sorry.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Lol. I shudder to think what my son might post in the same situation... at least yours understands how a motor works!
No offense taken. I was going to respond that I wasn’t joking, but it wasn’t that important.
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