Duplex Motor Control for Crane Bridge Drive
Duplex Motor Control for Crane Bridge Drive
(OP)
I have a question concerning the motor system for a crane bridge drive. I'm writing a spec. for a 15 ton upgraded to 25 ton (by mechanical means with reconditioned motors) overhead electric crane. Presently the bridge has a duplex drive (for 2 DC mill type 800 series motors), series wound, magnetically controlled system. A spec. that I downloaded from the Army Corps of Engineers states that they must be connected in series. Does this mean that the motors must be electrically connected end to end to form one large motor, i.e...25hp +25hp = 50hp? Or does this mean something else...perhaps a misprint, where series connected was used in place of series wound?
Also, what is meant by duplex control?
Nick
Also, what is meant by duplex control?
Nick





RE: Duplex Motor Control for Crane Bridge Drive
I think that in this case duplex refers to the two drive motors on the bridge, one on each side. The Corp spec requires the motors to be electrically connected in series so that each motor has the same current the there for the same speed.
15ton up to 25ton, what are you doing to the bridge structure to carry the extra load?
RE: Duplex Motor Control for Crane Bridge Drive
So, in your opinion, the bridge motors operate at the same time? Is this to keep the bridge going straight or not developing twisting torques?
RE: Duplex Motor Control for Crane Bridge Drive
RE: Duplex Motor Control for Crane Bridge Drive
RE: Duplex Motor Control for Crane Bridge Drive
If you have upgraded the controls with a PLC and variable speed drives then your service tech's may need a couple of days to get their head around the new systems.
RE: Duplex Motor Control for Crane Bridge Drive
RE: Duplex Motor Control for Crane Bridge Drive
Connecting both motors just in series will produce equal torque in each motor but would still allow 1 motor to turn faster than the other motor. If 1 motor turns a little faster the bridge could derail. The pieces of steel plate that you see keep the bridge from falling off of the runway rails if there is a derailment.
Streetcars that ran off of a 1200 volt catenary usually had the traction motors connected in series pairs with the fields connected in series and the rotors connected in series. There was no serious consequence if one traction motor tried to run a little faster especially if both motors were on the same truck.
RE: Duplex Motor Control for Crane Bridge Drive
That would provide the load sharing discussed above, it seems to me.
RE: Duplex Motor Control for Crane Bridge Drive
For compound wound generators that have independent prime movers the wiring diagram is quite different because you want equal load division in spite of slightly different speeds.
In this application, you want torque sharing but you also need equal speed so that the bridge does not derail. Best way to do this is to have equal voltage on both rotors and equal current in bothe field coils. This means that the series field coils need to be in series with each other. The rotors need to be in parallel with each other and then in series with the series field coils.
If the motors were compound wound, the shunt fields would need to be in series with each other and then operated from the same field resistor and power supply so that each shunt field has theoretically equal current.
In this application you might need a shunt resistor around one of the series field to tweak equal torque output. This is because each motor will have slightly different air gaps among other things that make the motors slightly nonidentical.