VCB Closing and Opening Coil Inrush

What do YOU think?

Surely you have an opinion about running a coil rated at 110 VDC at TWICE that voltage.

If you are a student, do your own homework!

If you are applying for a job, don't bother.

If this is a work related question, quit your job now, before they fire you.

"...What happens when 110V Dc rated coil is energized with 220V DC?

"...The control circuit breaker to the VCB closing and tripping coil is tripping..."

See, you know the answer!!!

Call the manufacturer, buy the right coil, and have a qualified electrician install it.

You need to control the inrush current ...this will cause control failure....

http://electronicdesign.com/power/limit-inrush-current-ac-dc-power-supplies-and-rectifiers

Applying ohms law, a 110V DC coil energised at 220V will draw twice its rated current and dissipate 4 times the watts.

The coil will burn-out if connected continuously.

So the designer did a good job if the control circuit breaker operates before the coil fails.

It may be that 110V DC continuous coil is energised at 220V to give greater speed and pull. But it would be necessary that the coil was disconnected by an auxiliary contact after the breaker closed, else it will overheat and fail. It might be that the auxiliary contact operation inserts a resistor in the circuit which limits the current to less than the coil continuous rated current and holds the breaker closed.

So if the auxiliary contact is not working or the resistor is shorted you will get an excessive current and the control circuit overcurrent breaker operates.

Did the VCB close??

At this point my "magician's crystal ball" is a lot less reliable than your eyes and tools at the circuit/wiring diagrams and the breaker.

Read the Maintenance Manual. Please ensure all safety precautions like isolating, grounding and "checking dead" the HV supply are observed before working on the breaker.

A DC coil may have an "inrush" current which is that taken with only its own resistance limiting current and a "holding" current which is got by a ballast resistor once it is operated [switched into circuit by the auxiliary contact mentioned].

"Control circuit breakers" often have a thermal overload element and a magnetic instant trip which operates at about 5 times their rated current for short-circuit protection. I think it is likely to be the thermal element trip you have tripping - there would be a noticeable delay after pressing "VCB close" before thermal trip.

Please tell us what else you you find out, information like the measured resistance of the Closing coil and the type and rating of the "control circuit breaker" and circuit diagram would help.

67model

It sounds like the contactor was designed to operate with this equipment. It's not likely someone changed parts with some random voltage rating. Normally it is a full wave bridge (as you note), and the applied voltage is reduced with a resistor or electronic circuit once the contactor is proven closed. You may have missed this part, as the controls are often in a potted assembly with just wires coming out. A half wave rectifier would give you about the right voltage for the coil.

Once the dc coil has moved the load, it only requires about 20% of the voltage to hold in the mechanical load, where an ac coil requires over 60% of the normal voltage to hold in position. Your equipment then can more easily ride through power dips.

One of the reasons your control circuit breaker could be tripping is the armature of your contactor is not closing all the way. A small amount of contamination/rust paperclip or junk on the laminations, preventing full closure of the magnetic circuit, can cause large amounts of current to flow in the coil, tripping your breaker. Also not so good for your breaker, as the overtravel for the power contacts typically designed in may not happen, leading to local heating in the bottles.