Service call this morning - the lathe won't start - trips breaker.... Low voltage 3 phase.
Lathe is a TOS (Chech Republic) - no real US dealer - they bought it used several years ago. It appears that it is set up for a manual changeover - operator says "We start it with this switch pointing toward the Y, and then flip it to the Delta (symbol) With pride, he says "It's a soft start.", and then hit the Start/Stop buttons - breaker trips.
One section of the the 4 section "drum switch" seems to be bad - found burned lead and the switch doesn't "feel right" -
If that's right, it gets 3 phase Y for start, and only 2 phase delta for run.
Thinking about replacing it with a US switch, but need the configuration - Chech diagrams not a lot of help.....Euro conventions for symbols and Chech notes.... It seems to be a 4 section switch, with each section having 2 pairs of contacts.
Anyone familiar with maual Y-Delta starting? Customer is chasing a new part thru the used equipment dealer.....but I'm doubtful.......
Thanks for your help / suggestions.
[This message has been edited by grover (edited 07-28-2006).]
The type of starting arrangement is common in European machines. The "Y" is used to bring the tool up to speed, than wwitched to the delta for actual operation.
I believe that, in motors, "delta" windings provide more torque, while "Y" come up to speed quicker. In any case, the motor actually has two sets of windings... think "two motors in one case." The "Y" set is often a much smaller gauge of wire.
Euro switches and such are somewhat standard- though they may look different to us! Why not post your ? in the Non-US forum- maybe someone has a link to a supplier of the correct switch?
The starting arrangement is fairly simple and designed to reduce the starting rush current. The very same windings are first connected in Y, only seeing (sqrt(3)) of the nominal voltage, getting the motor to speed. When it's running stable you switch to delta, getting full torque. I had to run a 3ph blower unit once. It had a Y/D switch and an old ampere meter going up to 6A I think (small 1.5kW 380V 3ph motor). Switching to Y made the ampere meter jump to the end of the scale. Then you waited until the needle went down (or listened to the motor picking up speed) and finally switched to D. The needle would give a short jerk to "full", go back to a few amps and the motor was running.
This is an aside from the original question; more about the theory of wye-delta starting than about finding the correct parts.
A motor configured for wye-delta starting is not so much two different windings in the same frame, but two different connections of the _same_ winding, to place different voltages on the coils.
In the delta configuration the windings are connected line to line, so each phase of the motor sees the full supply voltage. Say for example 480V line to line.
In the wye configuration, each winding is connected between a supply line and a common point. This common point is essentially a derived neutral. So with the above 480V line to line, each phase would 'see' 277V when the motor was connected wye.
The net result is essentially 'reduced voltage starting'. The motor will have _less_ torque and accelerate to speed more slowly in wye, however it will draw less stall current. Reducing the starting current, and perhaps the mechanical shock of too rapid acceleration, are the reasons for using wye starting.
Wow! When I was a kid we would take ear corn to a hammer mill downtown. The guy would throw a lever and the mill would slowly start turning. rrr rrr rrr About 5 sec later he would throw said lever the other way. whiiiiirrrr! I always suspected this was a manual Y- delta. Would LOVE to get my hands on one. Sadly the old mill is gone
Yup... I _love_ that old stuff! It was fun to work with that huge fan unit at school (we used it to perform air flow measurings with a damper)! Firing up that beast... go to Y. Needle hits end of scale, belts start screeching and sloooowly the motor starts turning... when it's up to speed, whack the swwitch to Delta and it's running (something like 25 seconds)... the control box was a good 40-50 years old with pretty crappy meters... the volt meter kept telling me it only saw 355 or 360V line to line... in reality it was 380 (still low).
In the US, manual Y-Delta starting was so rare as to be almost non-existent if it didn't come from Europe on a piece of machinery. There are serious problems with all Y-Delta starting, even if done correctly. There is IMHO, nothing worse for your motor. It is in fact usually less harmful to start across-the-line! Y-Delta is essentially a "cheap cheat" around the requirements for reduced voltage starting. It appears to do the job, but only because you can't see what is really happening. A phenomenon called a "transition spike" is occurring every time you switch from Y to Delta, and that spike can be out of phase with the motor when it happens, causing a torque transient of up to 3 or 4 times the rated torque of the motor. It's very brief, but it is always doing some incremental damage. On big motors, I have seen it twist the shafts right off. it also causes voltage and current spike, which is what damages the controller contacts, causes fuses to blow, breakers to trip and can damage other electronic components in the facility such as SCRs. All in all, not worth the trouble to figure out how to use them.
The old "1 armed bandit" type starters that Rabbit witnessed with the corn mill were "Manual Compensators", a form of manually stepped autotransformer or reactor starters. There was a big autotransformer or reactor on the bottom, and the crank handle on the side moved a double-throw switch from sending power through it (dropping the voltage) or directly to the motor after it got to speed. Those things were bullet proof and reliable. Unfortunately they relied heavily on the skill of the operator to work correctly, so as time went on, old timers retired and new workers were not interested in learning the "art" of starting a motor. So electrically controlled autotransformer starters replaced them, followed by electronic soft starters as they became cheaper.
[This message has been edited by jraef (edited 07-29-2006).]