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Topic Title: Replace Legacy Gantry Crane Slip ring Opotor Control system with VSD
Topic Summary: Crane hoist control
Created On: 28 March 2012 07:53 PM
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 28 March 2012 07:53 PM
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GlynnG

Posts: 3
Joined: 13 September 2002

Anyone any pointers or experience of repalcing an Opotor crane hoist control system with a VSD system.
"opotor" - opposite torque system is used on crane hoist control systems with slip ring motors, rotor voltages are used to bring in/out voltage relays.
These systems are on 60+ year old equipment , frequently are causing some control issues.?
 30 March 2012 02:35 PM
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dougflorence

Posts: 74
Joined: 25 July 2008

Many inverter suppliers produce inverter models or configurations for standard models specialised for winching duty. They are designed to give zero and low speed torque and a relay output to control a mechanical brake.

The problem with using inverters for winching is their poor ability to provide low speed torque to pick up loads so it can be difficult to design a system which will not drop heavy loads under some circumstances!
 31 March 2012 04:59 PM
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GlynnG

Posts: 3
Joined: 13 September 2002

Thanks for info.
We have other cranes that use standard induction motors with 4 quadrant inverters for hoist controls and they work fine. as these motors have no rotor or resistaance banks the VSD control is purley on the stator.
My questions woulb be then is it good practise to retorfit a VSD to a slip ring type motor , which would allow the removal of some or not all of the resistance banks and the control gear that goes with it , i.e the 5 stage contactors and voltage control relays.
 07 April 2012 02:15 AM
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rh2577

Posts: 164
Joined: 31 March 2006

Try contacting Master Control. They have years of experience with crane control systems. Another option would be to contact one of the main players in the crane industry i.e. Konecranes, Demag.
It sounds to me that your cranes may need a complete electrical refurb if the existing crane controls are Brook Hirst Igranic Opotor systems (I know these systems fairly well).
Good luck

p.s. there's no real problem using VSD's (variable speed drive) in hoisting applications, I have installed quite a few. The software needs to be configured for hoisting (usually a selectable option within the VSD) and you should always operate with speed feedback (motor shaft encoder). Speak to your VSD supplier.

-------------------------
Rob Heywood MIET

As you get older, three things happen, the first is that your memory goes and..........I can't recall what the other two things are!

Norman Wisdom
 08 April 2012 02:10 PM
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Jaymack

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Joined: 07 April 2004

Originally posted by: GlynnG
"opotor" - opposite torque system is used on crane hoist control systems with slip ring motors, rotor voltages are used to bring in/out voltage relays. These systems are on 60+ year old equipment , frequently are causing some control issues.?

These were made by Brookhirst Igranic (BHI), as I recall, we had 2 mast type, gantry cranes in a steel tube works with this method of control. They used overhaul of the the falling load, with plug braking for positioning steel ingots in piercers, prior to tube rolling in the pilger mill. The system was very reliable up to the late 80's when the plant closed. I remember checking/setting the relays to the manual, when "fettling" during maintenance. The motors were of the wound rotor type with banks of cast iron, grid resistors. These wound rotor motors, would probably require replacing nowadays, since they are very inefficient.

I suggest contacting one of the crane makers and discuss a solution with them

Regards
 30 April 2012 09:45 PM
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GlynnG

Posts: 3
Joined: 13 September 2002

Thanks for reply. Yes i have 2 remaing cranes with this control gear used in the steel works environment. One crane is dated 1905 and still going strong. The opotor system is robust to some degree and works well provided the sytem is set correctly and maintained. However i was looking to replace with vsd system to remove many of the parts that cost/require routine maintenace and no availabilty of spare parts is an issue. I put this on the forum to see if anyone had come across any difficulties with such conversions or give any pointers with old control gear like this.
Thanks
 25 May 2012 08:36 AM
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LesleyIlic

Posts: 1
Joined: 25 May 2012

Hi sir

I have seen your effective calculations for selection of slip Link removed/ motor resistance
I have still some confusion in my mind as I have following relation to calculate the resistance
Rotor coefficient is
K = U (lock rotor voltage) /I (rated current of rotor at rated torque). Root 3

in (ohm /phase)

And rotor resistance is then R = S. K (ohm /phase)

Slip = S =(Ns - N / Ns)

Therefore for motor rotor current = 224 A
Rotor V = 579v with rmp = 1477, 4 pole

The value is

K = 1.5

S = (1500-1477/1500) = 0.0153

R = 0.0153 * 1.5 = 0.022 ohm per phase

Plz help me in this regard


An advance thanks to all senior who will guided me.
 18 June 2012 04:16 PM
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phayton

Posts: 9
Joined: 03 January 2006

The rotor resistance will modify the torque / speed curve produced by the motor. Such that with no resistance in the rotor circuit the torque produced may be low or inadequate.
Even with a variable speed drive I recommend retaining the rotor resistance, possibly one stage permanently, to establish the effect during comissioning.
 05 July 2012 07:21 PM
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martra

Posts: 29
Joined: 25 July 2008

I used to work for a gantry crane refurbishment company and specialised in cranes for steel works. MH Automation Int LTD.
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