Device to hold starter coil in

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jtester said:
I have a client who experiences numerous equipment outages from what he describes as voltage sags. Motor starters often drop out, and they have to restart processes. Does anyone have experience with either of these devices?
http://www.scrcontrols.com/products.asp?productName=KNOW TRIP
http://www.pqsi.com/

Thanks in advance for any thoughts.
Jim Tester
Click to expand...

Yes.
These devices work as advertised, but if the sag is low enough and or long enough duration other issues will surface.
If the sag condition is severe enough to dropout the contactor coil, I would want to perform a PQ study with a recorder to determine the cause, severity, duration and frequency of events.
 
No experience with them but it seems like a bad idea to me for a couple of reasons...
1) If the voltage has sagged enough to drop out the coil, it has also sagged enough to potentially damage the connected load. Best to let the contactor drop out and protect the load IMHO.
2) The literature seems to suggest that the coil will not drop out until voltage reached 30 VAC but will automatically restart if the voltage picks back up to 70 VAC. What happens to the guy troubleshooting the system or the guys who was just say, stepping into an area he should not be in because a machine was not operating at the time when he decided to step into harms way when the machine automatically restarts?

Just me 2 cents worth
 
I recall a job 40yrs ago when I was a young field engr for Westinghouse
It was a series of pump stations that were burning up motors due to voltage sags.
The MCC motor contactors were AC powered. After consulting the factory, we installed rectifiers and DC coils on the contactors and the problems went away. So it was a matter of ridding thru the voltage sag time for the contactor to stay closed to correct the problem. DC voltage stays energized longer than AC on a sag of line voltage. Not sure this applies to your application since I did not read the details.
Tony










knowing the
 
jtester said:
I have a client who experiences numerous equipment outages from what he describes as voltage sags. Motor starters often drop out, and they have to restart processes. Does anyone have experience with either of these devices?
http://www.scrcontrols.com/products.asp?productName=KNOW TRIP
http://www.pqsi.com/

Thanks in advance for any thoughts.
Jim Tester
Click to expand...

(I realize that this answer goes beyond the complexity of the issue the OP addressed, but it can be useful reference at other times.)

Theare are several other ways this is adressed.

  • AB makes a mechanical TDUV attachment that fits their NEMA size contactors and actually holds the armature in place for a preset time period. 3 second used to be the utilities standard reclose rate so that used to be a favored number.
  • AGASTAT makes a true TDUV relay - eg. no external power source is required for re-energization - and it became rather expensive after the TYCO takeover of that product line.
  • Several manufacturers now make electronic true TDUV relays that are a cost effective alternative to the above. Siemens, Telemechnaique.
There are several problems ot ponder.
  • All these relay have basically analog adjustments. What that results that when you are close to your set time some of your equipment may or may not restart.
  • When you are dealing with an entire substation and your motors inertia had slowed down long enough, you may be dealing with a mass inrush that can collapse your bus voltage and nothing can be succesfuly restarted and you've lost your production.
For the above we have utilized PLC control, bus voltage monitoring and prioritizing group restart while monitoring the restart voltage level availability.
 
Last edited:
jtester said:
I have a client who experiences numerous equipment outages from what he describes as voltage sags. Motor starters often drop out, and they have to restart processes. Does anyone have experience with either of these devices?
http://www.scrcontrols.com/products.asp?productName=KNOW TRIP
http://www.pqsi.com/

Thanks in advance for any thoughts.
Jim Tester
Click to expand...

We have a "demo board" for the longest time for these two devices. worked well as long as only contactors are involved.



weressl said:
AB makes a mechanical TDUV attachment that fits their NEMA size contactors and actually holds the armature in place for a preset time period. 3 second used to be the utilities standard reclose rate so that used to be a favored number.
AGASTAT makes a true TDUV relay - eg. no external power source is required for re-energization - and it became rather expensive after the TYCO takeover of that product line.
Several manufacturers now make electronic true TDUV relays that are a cost effective alternative to the above. Siemens, Telemechanique.
Click to expand...

thanks for the info. will research this and see if we can add this to our list of available sag solutions
 
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