ds and dsl breakers

[hawkeye23]

I would like to ask if anyone can explain a little about these cb. westinghouse ds 840 and dsl206. There is 480v utility power, 120 v and 48vdc in this switchgear, some of the breakers need to be cranked up the spring from time to time. i though the motor did that automaticlly and why ?
There is a battery bank that supplies 48vdc but for what ? Is the 120 volt for the motor and where is this supplied from ?
Thank you to anyone who maybe able to help here.

 

[rcwilson]

For a good answer, we would need a lot more information and the switchgear wiring diagram. But here's some bad answers, worth what you paid for them.

120V probably comes off a 480V-120V control power transformer connected on the utility side of the main breaker. It may supply the spring charging motors. Or maybe it is 120V from a UPS to power digital meters or transducers so the signals don't go crazy during an outage. Or it could be to just power anti-condensation space heaters off a local panel.

The 48VDC is probably tripping power for a protective relay or ground fault system. During a fault, the AC voltages may be shorted out leaving no 120V AC for tripping. The 48VDC provides a secure tripping power source, if the batteries are maintained, etc, etc.

Spring charging motors could be 48VDC. That way , the closing springs could be charged when power was not available.

Maybe the 48VDC just runs indicating lights and some meters.

I have had designs that used each of the above options for various reasons.

 

[hawkeye23]

Thanks RC for your quick response , the 120 is for the motor i just don;t no when or why it charges or discharges the motor.The 48 volt is for shunt trip , are these for the switches on the front of the CB. Found this infomation on the label on the CB.
GREAT INFO. Thanks again.

 

[rcwilson]

If these breakers are like most of the ones I worked on:

1. Power to the charging motor comes through the auxiliary fingers that make contact as the breaker is racked into place.
2. As the auxilary fingers make up, the spring charging motor gets power and starts charging the spring. A "spring charged" limit switch or equivalent shuts off the motor.
3. The spring stores enough energy to do one close and one trip. Some have enough to do a close-trip-close-trip sequence. There is always enough spring left to trip after a close.
4. Pushing the manual "CLOSE" button on the breaker front or energizing the close solenoid releases a mechanical latch that frees the springs to close and latch the breaker contacts.
5. On some breakers, the charging motor immediately runs after closing to bring the springs back up to full charge. Other breakers only recharge after a trip.
6. When we push the trip button or energize the shunt trip coil or the breaker's internal overcurrent trip unit actuates, a trip latch is released and the springs slam the breaker open. If the spring motor has power it immediately recharges the springs.
7. When you rack out the open breaker, there is still energy stored in the spring. A safety interlock on the racking mechanism trips the spring latch and discharges the spring.
8. Most switchgear also trips the spring when racking in.
8. Some engineers or owners specify a disconnect switch to turn off the charging motor during racking. That prevents a breaker automatically closing as it is getting racked in but before it is fully connected. Other owners train the electricians to pull the closing circuit fuses before racking.
9. The handle or lever on the front of the breaker allows manual charging of the springs when control power is not available. The last crank on a large breakre is HARD.

I'm guessing your breakers are older units. If the latch checking or spring mechanisms get stiff from dirt, poor lubrication or abuse, maybe they don't work everytime and run the charging motor at seemingly ramdomn times.

One type of GE breaker did not have a closing spring release. When the "close" command was energized, the charging motor rotated a cam that slammed the breaker closed once the motor drove the spring past the cam's trip point. There was no precharging the spring. Closing took 1-5 seconds depending on breaker size after we hit the close switch. It did not work well when trying to synch generators.

 

[templdl]

When the spring is charged when the breaker is open you should get (2) operations, closing the breaker and tripping it.
If you charge the spring when the breaker is in the closed position you get (3) operations being able to trip, close and trip it.
If the breaker is electrically operated with a 120v spring charging motor the spring should always be kept charged. There is a switch on the spring that determines if the spring winding motor needs to recharge the spring.
The release of the stored energy is accomplished either manually by depressing a bar on the front of the breaker or electrically energizing a releasing solenoid.
With a manually operated breaker besides adding a shunt trip in order to trip the breaker remotely you can also add a electric close release where you can close a breaker remotely. But, the spring must be charged when the breaker is open but the closing spring must be manually charger first.
But,if you have motor operators the springs should never need to be manually charged if 120vac is available at the motor and spring relaease mech.

RCwilson has included some other things to look for should the charging motor not be rewinding the spring as intended.