Ok, I can kinda see how the controls see it... but I am having trouble wrapping my head around the Wye-Delta start sequence. I find myself staring at the schematics... looking for the answer.. but it is alluding me...
And the last time I stared.. I ended up with my youngest. ;-)
Anyone explain it (simply, I have been drinking) to me?
http://www.lmphotonics.com/star_delta.htm that website says it better than I can. Basically, two contactors, two windings in motor, but both wye and delta are never evergized simultaneously.
For wye-delta, you will need at least 3 contactors....4 if you have a closed transition type of starter.
Originally Posted by mr_guy
wye type motors have low starting amps but high running amps.
Delta type motors have high starting amps but low running amps.
This type of starter attempts to use the best of both worlds. I only skimmed that article and it seems accurate except for 1 item, the transition transient current will not exceed an across-the-line type of starter current. The transition current is very high, but not that high.
Is this the basic info you can handle for a brown-bottle brain?
LOL, I normally roll a brown bottom brain prety hard on weekends... but not THAT hard. LOL
With this link, and going through my CVHE1250 Schematic line by line, I feel I grasp what it is doing, and why things like transition resisters exist in the Closed Transition type (Seeing how you are basically shorting the motor out without them).
I assume open transition types do not exists on any Cent Chillers due to the lead being put on them.
I can tell neither my Tranes or McQuays have open types.
It's pretty simple.
Take three pens. Point them inward like the letter "Y" with the tips all facing inward. The knot is not connected to power. The outer branches are connected to power. A 480v motor that runs in delta only gets 277v in each winding when arranged as wye. This heats up the windings. You could think of it as a drum brake. the drum is spinning at the full RPM. The shaft attached to shoes are gradually pressed up against the drum and catch up slowly (heating up as doing so)
After a certain RPM is reached or a time limit is reached, the set of switches rearrange the three pens in a closed loop, tip-to-back so that they look like the recycling logo and power is applied on each corner. This pushes down the brake shoes harder onto the drum and the shaft will quickly begin to catch up in speed.
Across the line starting is like punching the gas to the floor and peeling out at every stop light. It's hard on the shaft and motor mount. The motor recoils pretty hard when started like this. Large blower wheel weighs a hefty amount. You know one of those 30 hp ones that takes like ten minutes to come to a stop. Standard AC machinery don't have a modulating gas pedal, so when you start those across the line, the motor lunges back and the sheave squeals for a second. This is hard on everything. Mount, bearings, shaft. etc starting in wye and letting it spin up to some before switching to delta is less stressful on parts.
Newer chillers with electronic motor drive acts much like how we normally drive our vehicles. You can coast down/pull up to speed without the tremendous drivetrain stress that goes with punching the gas.
The transition resistors does the same thing as springs on a clutch disc. If you didn't have them, it would lurch when it switches over which causes problem on mechanical side as well as electrical.
I believe that I am quite wel versed on wye delta starters and motors as used in this industry and the whole pen/brake/clutch analogies just made me confused!
You were discussing electrical impact. I was discussing mechanical reasons for using wye start, delta run.
Originally Posted by jayguy
Each pen represents each coil in the motor.