why some Overhead cranes used Resistances (Resistance plates) connected in delta

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danishdeshmuk

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why some Overhead cranes used Resistances (Resistance plates) connected in delta to control the speed of the motor whether long travel or cross travel and some use VFDs to control the long travel and cross travel motors ?
 
I am rusty on these. I believe they are what was called "wound rotor". The motor guys will have more knowledge. They changed the voltage via the resistor banks which had to be fairly large to dissipate the heat.

I worked on them back in the mid to late 70s. I mean that literally. I rode on them throughout a local factory when i changed the lighting from MV to HPS.
 
ptonsparky said:
I am rusty on these. I believe they are what was called "wound rotor". The motor guys will have more knowledge. They changed the voltage via the resistor banks which had to be fairly large to dissipate the heat.

I worked on them back in the mid to late 70s. I mean that literally. I rode on them throughout a local factory when i changed the lighting from MV to HPS.
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When you brought up a wound rotor motor the rotor itself is wound and those winging are connect to slip rings at the end of the motor. The resistors are connected to those rings which when the resistors are varied will change the speed of the motor. I sold a 2300v, 800HP WRM that was designed to control the acceleration the which in turn ramps the starting current through the use of a series of stepping resistors which controlled the rotor resistance. .
 
templdl said:
When you brought up a wound rotor motor the rotor itself is wound and those winging are connect to slip rings at the end of the motor. The resistors are connected to those rings which when the resistors are varied will change the speed of the motor.
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(catching up with older topics)
I'm definitely not a motor expert, but before there were VFDs/etc, there were wound rotor and brush shifting motors for speed control. WRM grid resistors were duty-classed, smaller for starting duty and larger for continuous speed control. My introduction to them was running a large carousel for a summer job-- 10hp 900rpm motor belted and geared down to about 5 rpm at the carousel, 12-step GE manual drum controller. 35 years later, that carousel still has the same motor (from 1921, rebuilt mid 1970's) and controller (which replaced the original controller which was no longer repairable).

I've also seen them on railroad roundhouse turntables.
 
zbang said:
(catching up with older topics)
I'm definitely not a motor expert, but before there were VFDs/etc, there were wound rotor and brush shifting motors for speed control. WRM grid resistors were duty-classed, smaller for starting duty and larger for continuous speed control. My introduction to them was running a large carousel for a summer job-- 10hp 900rpm motor belted and geared down to about 5 rpm at the carousel, 12-step GE manual drum controller. 35 years later, that carousel still has the same motor (from 1921, rebuilt mid 1970's) and controller (which replaced the original controller which was no longer repairable).

I've also seen them on railroad roundhouse turntables.
Click to expand...


How the speed is increased or decreases automatically in slip ring motors with the help of resistances ? Especially in Overhead Electrical Cranes for Long Travel & Cross Travel Motors ?
 
danishdeshmuk said:
How the speed is increased or decreases automatically in slip ring motors with the help of resistances ? Especially in Overhead Electrical Cranes for Long Travel & Cross Travel Motors ?
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(I'm not at all an expert on rotating machines, but throwing caution to the winds and oversimplifying in the bargain....)

(BTW, 'automatic' would apply to any controls, not to the motor itself.)
When the rotor windings are shorted, the machine acts entirely like an induction motor. When an external load is connected to the rotor windings, the machine partly acts like a transformer with the resistors loading the secondary (the rotor). Because some of the energy in (watts) goes to heat the resistors instead of turn the output shaft, the machine has lower output (as rotational energy). Conservation of energy and all that. In this case, lower energy into a constant load translates into lower speed (and for an induction motor, higher slip).

This has a better explanation: http://www.allaboutcircuits.com/vol_2/chpt_13/8.html, or google "wound rotor motor".
 
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