Need a Latching Relay at No Power

Er, never mind the contactors, how are the motors to keep running when there is no power to them?

Motor restart without command is prohibited under many nations' electricity regulations!

u check the details provide by me COMPLETELY.hav a check at the link i have provided.u will understand the facts.

there are situations we need it.

and We need it right now.and we have decided to implement it.

the capacitors do provide that power when there is no power/power dip.

"We need it right now.and we have decided to implement it."

Then hire a local engineer who will do your bidding, right now and quit asking strangers to justify a decision you have already made.

Are these the same 500hp motors as the ones in this thread (the hyperlink won't open from here)?

http://cr4.globalspec.com/thread/75023

If so, then standby generation is needed, not capacitors or latching relays.

Hire an electrical designer locally.

Have you tried Wide Band Contactors and/or Wide Band Coils? Some wide band contactors can pick-up even at 50% of the coil voltage.

Heh heh, do you realise that you have given a hyperlink to a file in your own computer's H drive? How do you expect anyone to be able to access it?

As EE65 says, wide-band coils allow contactors to 'ride through' voltage dips. If the dips are of longer duration, there are mechanical latch units available for contactors from most manufacturers, you can use them.

What is the nature of the power dip you are talking about? Is there a total voltage loss and for how long? Such implementation must have provision to exclude ANY possibility of restarting if rhe dip time length is more than a pre-determined number of AC cycles AND be foolproof AND comply with local regulations. S.M.

Right, this seems to be a case of momentary voltage sag causing the voltage to drop below the coil holding voltage causing system shutdowns where system ride-thru would be prefered.

kindly let me know is there any other industrial practice used for this situation.

Power quality management springs to mind to ensure smoother grid supply and/or smoother end user supply to the equipment in question. I have never seen an application where this type of problem could not be solved this way cheaper, easier and safer, but again it depends on the particular application (and applicable standards).

The dip would have to be fairly large to cause contactor coils operating of the single or three phase AC voltage to drop below the coil holding voltage. Additionally, if you are using DC control voltage and contactor coils (eg- powered off DC power supplies as part of the control system) then these should already be protected from grid supply voltage drop by a UPS system(s) or similar.

Is this for a whole factory or portable motor application, etc (you do not say)?

It's not something to be taken lightly. Read this article from my local utility on the subject, it highlights some of the risks involved.

http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/voltagesag_ride.pdf

Reconnecting out of sysnch on a motor that slowed down during the sag or loss can create torque transients of up to 15X normal torque and it is well known to cause motor shafts to twist off. You need to be VERY careful with this. It's not for the casual user to undertake.

In that article, they mention one possible solution is to change to using DC coils on your contactors and having a capacitor installed to maintain the coil state. I have seen that used in some applications where the potential losses from shutting down at the wrong moment are well above the potential risks of motor damage. They then go on to mention the technology behind that "coil lock" product you say you are investigating. There are several suppliers out there besides them. I have never used any of them, I don't like the entire concept, but I recognize that sometimes you have to do what you have to do.

Latch type contactor is suitable for momentary voltage dip not exceeding 500 msec. Otherwise the motor will get slowed down and will take high inrush current when full voltage is restored. This may eventually trip the motor on over current protection. This depends on the size and type of the motor and the load being driven by the motor.

I had this problem too, dips how much or for how many cycles long I dont know.I connected a delay off timer across the contactor coils ( set at a very short time) it worked for me and is still working for me. You can use this only for DOL starters but for bigger motors you may have to use what you are currently looking for (coil lock) about which I am also keen about.

When I clicked the link it says "name changed or unavailable".