zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Ah, I see what's going on.... in delta 1M and 2M are closed and thus sharing current. In wye, it's 1M and 1S where 1M carries full current but it's wye current so lower.
Contactors for 200HP Wye-Delta Motor Configuration
- Thread starter Cammando_Cool
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Cammando_Cool
Member
- Location
- US
- Occupation
- Electrical Engineer
Hmm, I think I'm starting to understand. So the current flows through two contactors allowing a lower rating than the motor?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The contacts may fail or weld closed if they are not sized to the motor starting current.
Those are the usual sizes most suppliers provide to customers of wye-delta starters.
Just follow what happens when your starter starts in wye-->the input voltage to the motor windings will be reduced to line voltage X 58%. That means the current passing the contactors will just be 33% of the line current, the case being that the motor torque will be directly proportional to the square of the input voltage; if you inputted 58%, the motor torque delivered (hence the current) will be (0.58)^2 = 33%. If the rated power was 200 HP, the delivered power will be = 0.33 X 200 = 66 HP. The 125 HP contactor (1S) is more than enough to carry a 66 HP power delivered.
During the transition to delta-run, the motor will be delivering whatever load requirement was thrown unto it. Say the motor is fully-loaded, 100%. But the arrangement of the delta contactor (2M) is that it is only carrying the equivalent amperes of 58% of the line amps (the phase current when in delta is 58% of the line amps). 58% of 200 is 116 HP! So your delta contactor of 150 HP is also more than enough to carry a load of 116 HP. The only question there is what size is the main contactor(1M)? It should be no smaller than the bigger contactor, 150HP because it is also carrying the same amps as the delta contactor (2M).
kwired
Electron manager
- Location
- NE Nebraska
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- EC
look at how current splits from the main supply lines - none of the contactors ever carry the full current carried by the main supply lines, but when using single contactor for across the line starting it will be carrying all teh current, plus starting current will be higher than with the wye-delta setup which it's main purpose is to lessen starting current, usually because of effects on the supply more so than because the motor can't take across the line starting.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I’m glad to see some good understanding, and great explanations, of Wye-Delta starting. In my experience, having multiple people in a group truly understand it is the exception, not the rule. Nice job guys.
I still dislike it as a reduced voltage starting scheme because as far as I’m concerned, the extra baggage is not worth the cheaper cost of the ticket. The ONLY reason why anyone chooses it over better alternatives now is because of the perception of it being the cheapest form of RV starting, but even that is no longer true if you really evaluate it properly. Costs of solid state soft (RVSS) starters have dropped over the years to the point where they are now so close to open transition Y-D that I would consider them actually cheaper. If you truly evaluate the LONG TERM costs if Y-D in terms of equipment damage, and realize that it should be closed transition, then RVSS wins every time.
I still dislike it as a reduced voltage starting scheme because as far as I’m concerned, the extra baggage is not worth the cheaper cost of the ticket. The ONLY reason why anyone chooses it over better alternatives now is because of the perception of it being the cheapest form of RV starting, but even that is no longer true if you really evaluate it properly. Costs of solid state soft (RVSS) starters have dropped over the years to the point where they are now so close to open transition Y-D that I would consider them actually cheaper. If you truly evaluate the LONG TERM costs if Y-D in terms of equipment damage, and realize that it should be closed transition, then RVSS wins every time.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
125% ... of what?
When you're starting from a dead stop, in Y configuration, your nominally 480-volt, 200 Hp motor is actually an 830-volt, (480√3) 67 Hp motor.
When making the transition from Y to Δ, it's already spinning. The transition pickup current is significantly less than the current of an across-the-line start from a standstill in Δ configuration.
If you don't have a rigorous understanding of this, it would be best to abandon the Y-Δ approach and use a soft starter or VFD.
On the other hand, If you do have a rigorous understanding, it would be best to abandon the Y-Δ approach and use a soft starter or VFD.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Of the running full load, just like any other conductor supplying a continuous load does.
Starting current isn't why we size them at 125%.
Intermittent duty motors is one place you may not have to size conductors @ 125%, they still have similar starting current as a similar output rated continuous duty motor. Depending on circumstances however there are cases where you need more than 125% for conductor ampacity.
Not only that!
If you fail to consider the infinitesimal transition period from the wye-mode to the delta-mode, your contactor contacts can get damaged due to a possible "short-circuit" when the parting contacts of the wye contactor still have an arcing connection and the delta-mode contacts make!
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
Yes, yet another reason to relegate the Y-Δ approach to the dustbin of history. A well-integrated, well thought out controller would have considered all that, and included delays & sequencing to assure that it doesn't happen. But if I recall correctly, the original post was asking for assistance cobbling something together from a basket of loose parts.
Yes, for the conductors feeding it, for complying with code. But if I recall correctly, the original post expressed concerns about the contactors being too small for the current they'd be carrying.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Which is fine but the 125% applies to conductors, selecting appropriate contactors is sort of a different game.
conductors between the controller and motor I would presume can be smaller than the supply conductors as well, none of them will ever carry same current as the main supply conductors do at any given time, well at least not while in run mode, in wye start mode they will but it will be only very short duration and still will be less current than the starting current for across the line starting is.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree with those who say that this type of starting scheme should be sent to the museum. With modern methods using them is rare. The only time in my career that I've seen this is when an engineer specified this type of starter for a fire pump. Another problem that I see is that finding an electrician who actually can correctly wire these is not easy.
ptonsparky
Tom
- Occupation
- EC - retired
Electricians can be found, but they need to be willing to do the research required & someone needs to be willing to pay for that research.
Yes, not easy.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I've encountered part winding and auto transformer starting methods but never actually seen wye-delta in the wild.
ptonsparky
Tom
- Occupation
- EC - retired
Only once for the W-D.
I could stand in the enclosures for the part winding starts I worked on. Still small in comparison to what many here have worked with.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
My experience is that wye-delta is a very common starting method through Europe and maybe the rest of the world except North America. It seems every IEC contactor manufacturer has premade busbars and interlocks in their catalogs.
But in 40 years, I don't think I was ever involved in much more than 20 installations of them.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I think maybe partly because their motors are more likely to be wound with necessary leads made available to do so. They also seem to mostly have delta wound motors where it seems there is a lot of wye wound motors in North America, with no ready access to the wye point. Even delta wound motors often don't have access to every individual winding end lead, just enough to make them dual voltage capable most the time. Though under ~100 HP not many are using reduced voltage starting for utility impact reasons but do use electronic soft starters or VFD's in those lower HP motors for mechanical shock reasons.
A lot of 100+ HP motors I've encountered are only single voltage and have six leads leaving the options for old school reduced voltage starting methods more open.
Dzboyce
Senior Member
- Location
- Royal City, WA
- Occupation
- Washington 03 Electrician & plumber
Back in the 1980's and 90's I worked for an irrigation company. We drilled wells, installed lineshaft turbine pumps, centrifugal pumps, pipelines, and center pivot sprinkler systems. I remember some old pump panels then that were referred to as "shotgun panels". They were propably 20-50 years old back then. I never worked on one or even opened the cover. But when you started it the motor would run at reduced speed. Then there was a lever on the dide of the panel, similar to the handle on an old slot machine. You would pull that lever and with a bang the motor would accelerate to full speed.
Would these shotgun starters have been a wye-dekta starter, with a manually operated mechanism to switch from wye to delta?
Back then we installed across the line pump panels up to about 125 hp. Abovethat we used RVAT panels, or Robicon Mark4 VFD's.
Would these shotgun starters have been a wye-dekta starter, with a manually operated mechanism to switch from wye to delta?
Back then we installed across the line pump panels up to about 125 hp. Abovethat we used RVAT panels, or Robicon Mark4 VFD's.
Back in the 80s, every air compressor we sold into Europe had Y-D starters. ATL were supposedly not allowed above a certain HP.
So I’ve seen my share.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
FWIW, in 40 years I think I've seen three or four of them- one on a hydraulic elevator pump (not touching that, Thyssen maintains the machine) and curiously enough the rest on pipe organ blowers (maybe 5-10ph and 60+ years old by now). They still work.
Did anyone do a single-phase equivalent (parallel/series connection)? I can't think of reading about any in the old books, seems like an autotransformer would work better there.
Did anyone do a single-phase equivalent (parallel/series connection)? I can't think of reading about any in the old books, seems like an autotransformer would work better there.
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