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Old 06-17-2017, 02:43 AM   #1
Edn
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Default Plugging old D.C. Equipment

At my job I have some very old 240v D.C. Equipment I'm trying to maintain. I have some questions about using plugging. I have a print I can share. I saw a PO for the equipment dated 1958. The equipment was not purchased new.
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Old 06-17-2017, 02:44 AM   #2
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Plugging... to me means phase reversal.

You can't mean THAT.
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Old 06-17-2017, 05:20 AM   #3
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Quote:
Originally Posted by Edn View Post
At my job I have some very old 240v D.C. Equipment I'm trying to maintain. I have some questions about using plugging. I have a print I can share. I saw a PO for the equipment dated 1958. The equipment was not purchased new.
What's the question?
Where's the print?
1958 was a mighty fine year.
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Old 06-17-2017, 05:44 AM   #4
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Plugging... to me means phase reversal.

You can't mean THAT.
D.C. motors can be plugged with the stator winding (reversal, or inserting a resistor). Also called "dynamic braking".
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Old 06-17-2017, 06:38 PM   #5
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I think at one stage they where using
a quick shot of reverse phase into the windings
as an emergency stop

i cannot imagine it is good for the motor
but it would stop it quick
which was the whole point !
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Old 06-18-2017, 01:31 AM   #6
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Plugging and dynamic braking are not the same thing. Old DC equipment is plugged by reversing the voltage across the armature. It was the designed way to stop the motor under normal conditions(like slowing down an overhead crane). There should be circuitry that limits the current while plugging. This circuitry (in old DC equipment anyway) prevents acceleration points from picking up past the slowest speed in the opposite direction of travel.
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Old 06-18-2017, 09:00 AM   #7
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Quote:
Originally Posted by ip246 View Post
Plugging and dynamic braking are not the same thing. Old DC equipment is plugged by reversing the voltage across the armature. It was the designed way to stop the motor under normal conditions(like slowing down an overhead crane). There should be circuitry that limits the current while plugging. This circuitry (in old DC equipment anyway) prevents acceleration points from picking up past the slowest speed in the opposite direction of travel.
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Old 06-21-2017, 10:18 AM   #8
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The equipment in question is made to handle hot metal ingots for forging. The equipment has two motors and drive trains for the bridge. The problem is we are breaking drive shafts in the gear boxes when the operator is changing directions. I suspect operator error but I need to ensure the plugging is working correctly. I'll send a copy of the print.
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Old 06-22-2017, 03:42 AM   #9
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Well to check the control side of things, run the machine at 3-Points forward (let it get to full speed), then throw the controller to 3-points reverse. Initially, all the should pick up in reverse, until the machine slows down (current drops), is the main line contactors, and the reverse contactors (M-A,M-B,1RA,2RA,1RB,2RB). If the plugging contactors (PA,PB) or accelerating contactors (1A-A,2A-A,3A-A,1A-B,2A-B,3A-B) come in immediately upon reversing direction to full 3-points, then you have a problem with plugging. Repeat, if the plugging relay or contactors immediately pick up upon reversing directions to full speed the opposite direction, then the system is not working properly.
Some other things to consider are grounds, and or shorts, specifically with the resistors. If a resistor bank is grounded you will get real hard plugging. Same if it's shorted (piece of scrap or something fell across it).
If they are the types of resistor banks that have multiple taps/tabs, look for the wires/cables to be going to the proper tab, especially if you see a bunch of burnt up tabs where someone has moved the cable to the next tab over (lowering the resistance). That assumes that the resistors are the correct values and hooked up properly.
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