VFDs vs Wye-Delta Starters

i feel that if all you want to do is start a large motor say 100hp and up that wye-delta is fine; assuming that motor just runs at one speed like a chipper, hog or something to that effect. i do maint. in a saw mill and we have TONS of vfds that are being used only for speed control operations for production. all of our chippers, hogs and other waste system conveyors have y-delta starters and some auto-transformer y-delta starters.

A bit confused., you just wish to compare between these 2 starting methods and a trade-off between VFD cost & maintenance and performance? What exactly is being asked here? Of course if the interest is mechanical - go for soft starter and not VFDs. VFDs to be only used if you need speed control for a majority of the time.

the question also depends the application

how many cycles per hour/minute/second?

what is mechanical connection to the equipment?

There can be other benefits to using VFD's beyond the soft start function

the more sophisticated metering, protection, networking....

VDF's are fine for different load patterns after initial startup, but the soft start is a fine torque reducing application that will save mechanical structure in the long run. We have cooling tower fans that had VDF's but replacement costs negated that application. The Y-delta start is the least expensive adaptation.

If it's affordable I'd always fit a VSD.

Besides the obvious speed control, you also get some other things for free.

Sophisticated motor protection

Monitoring & display of I, V & runtime

Handy I/O for interlocking, display & stop/start

If it is a 40HP centrifugal fan taking input from a bag filter, and having Winter exhaust air temperature of 10 'C and summer at 50"C , what would you prefer? The HP is based on Winter heavier load. In summer air will be less denser and so HP requirement will go down. What is better option VFD,Soft Starter, Star Delta? Every Shift it needs to be started twice from ambient temperature varying between 10Degree in winter and 45 Degree in summer. Exhaust air requirement is based on Summer requirements. But has been over sized for winter loads

For motors like this, direct on line starters are very common, at least in my experience -- in other words no attention is given to any form of soft start... unless couplings, etc are failing.

However, if you are thinking of optimizing running conditions for winter vs summer, then VFD is the only alternative -- the main concern being running efficiency rather than starting conditions. (The air density has a small impact on starting loads in comparison to rotating assembly inertia.) I am only guessing, but it seems that optimizing for the relatively small difference in air density would not justify the cost of a VFD, unless there were other reasons to use a vfd, such as those mentioned by ffej.

Let's be sure terminology isn't throwing us here. There is a family of devices referred to as "soft starts", and they are more than two coupled contactors in a Wye-Delta mechanical starter. The Soft Starts are electronic devices and can get fairly sophisticated. Sort of a VFD-light. For reference, the Square D ATS48 series is pretty fancy, but the list price for a 200HP @ 460V 3ph model is only $2900, compared with $10,366 for the equivalent sized ATV61 VFD.