In article , Peter H. says...

Normally, for a "consequent-pole" motor, one five-pole and one three-pole
magnetic starters are required. Hardinge implemented this starter with one
three-pole magnetic starter, and a drum switch of unusual configuration.

In some of their machines (for example the older milling machines)
they simply use two drum switches. The first is a common
forward/off/reverse drum switch that is wired in the conventional
way, with center off and one pair of lines is interchanged in
one of the on positions, to reverse the motor.

The other drum switch does indeed have more poles, but it is
a bit more complicated in it's operation. The rotor in the
switch is special purpose to run a pole changing motor. Here
again center is off and no contacts ring through. Its
purpose is to correctly connect the three incoming power
lines to the six (for a single voltage motor) motor leads.

Consider the motor windings to be set up in star configuration,
with the center of the star all common. However each
winding has a center tap midway along its length. This
gives a total of six wires emerging from the motor, three
'ends' and three 'centertaps.'

In low speed the center taps are not connected to anything,
and the ends of the star windings are connected to the incoming
lines as in any regular three phase motor.

However in high speed the incoming lines are connected instead
to the centertap wires, and the ends of the star windings
are all tied to each other, and do not connect to any other
power lead. (this effectively halves the number of poles
and makes the motor run faster)

Switching is accomplished by hardinge in a variety of ways. My
milling machine for example has a single drum switch with
six rotors in it, and each rotor has internal connections
such that the three wipers on one side of the switch are
correctly commutated to the six wipers on the other side.
This thing has a vaguely enigma-like quality and it took
me about three nights of sweating before I married it to
the motor and got it all wired up right. It's not the stock
drum control for that machine btw.

In my DSM-59 they do it in another way: here is a photograph
of the switchgear for that machine:

http://www.metalworking.com/DropBox/_2001_retired_files/DSM5.jpg

Wherein you will see two separate drum controllers. The right
hand one is the normal forward/off/reverse type. The black
disks on the shafts are cams, and the bottom-most cam actuates
its switch in both positions, the upper two pairs operate
alternately in forward and reverse, and serve to reverse the
two remaining incoming lines.

The left hand drum controller does the speed control.
Unfortunately I took the photo from the wrong side so
you cannot get a good view of the jumpers on the extreme
left side of the switches, but one can see that the
wires that enter into the switches from the left are
(top to bottom) white, black, white; and white, black, white;
and then at the very bottom they are again white black white.

The lowest trio is there, take it on faith.

The black wires are the incoming power lines (suitably
rendered by the reversing switch) and the white leads are
the motor wires, which go off in greenfield conduit to
the motor itself.

If one were to label the cams, top to bottom, as 1 to 8,
they operate as follows.

High speed, cams 1, 3, 4, 6 and 8 actuate their switches.

Low speed, cams 2, 5, and 7 actuate their switches

The reason that the high speed has two extra cams, is
so that the ends of the star windings can be all
tied together. Otherwise the contactors either choose
incoming lines to go to either 'ends' or 'centertaps'
of each motor winding.

This is a good deal more complicated in the telling, than
in the reality. There is also a good schematic on the
inside of the door cover if anyone wanted a snapshot of it.

Jim

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