Contactors holding due to induced voltages in cable

[johnbose]

WE have lot of Telemechanique LC1D09 to LC1D38 contactors in the MCCs . The coil voltage is 220V .Control wiring is standard wiring with Start stop buttons located in the field and hold on contact across start button. Many drives which have long control cables do not stop on pressing the stop. We find that the contactors do not drop off till below 80V across the coil, once picked up. Since the current in picked up state is as low as 14mA at about 100V, the motor contactors holding are on due to induced voltages on long (300- 500m ) cable cores as we are using 220V AC control supply. CAn ANYONE SUGGEST / advise how to overcome this problem. We have already tried the following with no success

1. Addition of RC ( 100ohm +470uF) across coil

2. Using a coil of 240V AC rating

[RalphChristie]

See if this pdf-file can be of help:

 

http://www.squared.com/us/products/nema.ns...FILE/M-379F.pdf

[johnbose]

could not access the shortcut

[GGOSS]

Hello johnbose,

 

I have found that if you click on the link it will be unsuccesful. However, I have just tried copying the link and pasting into the address line and it works fine.

 

Many thanks to RalphChristie for providing this link. The document contains some very good information. So much so that I have taken the liberty to also post the link in the "Library" forum.

 

Regards,

GGOSS

[Guest]

add a lighted top button so when it is pressed it is on,this should add enough load to drain the voltage

[Guest]

that should have read stop button.

[johnbose]

Thanks alot that was a superb article on the problem . Telemecanique themselves have advised addition of a resistance to coil. I am also considering to replace the control transformer with a centre tap earthed one which would reduce trhe net voltahe to earth by half . Then the induced voltage should be below the holding voltage of the contactor. I will get the outcome posted

 

Thanks again to Ralph and Geoff