Racking out breakers

[Waldo84]

I have an interview soon for a maintenance company on a drilling rig and 1 of the questions they asks is
when racking out a circuit breaker you hear crackling/arcing do you keep racking out or rack it back in?

 

[davesparks]

If you watch the videos from manufacturers demonstrating the use and features of their breakers you will see plenty being racked in and out without incident.

 

[Knobhead]

Because videos of breakers being racked out normally wouldn't be quite as exciting?!

It’s downright bloody tedious doing the same thing week in week out.

It’s not very often you get to do something out of the ordinary thats not covered in normal switching procedures.

 

[chlee-penang]

Normal practice the VCB shall be in "OPEN" position before any attempt is made to rack in/out, failure to observe this rule may lead to arcing and flash over. Not sure you are referring to arcing sound or hissing sound.

Certain design of switchgear uses a bar for racking which can rack in/out the breaker very rapidly and you can hardly hear any hissing sound, on the other hand, those gears using to hand crank to turn the worm gear as part of withdrawal assembly for racking, the motion is much slower, so it is normal to hear hissing sound.

For instance, the 33KV VCB I used to work on require to crank 84 turns for moving the VCB from service position to isolation position, when breaker begins to part from fixed contact, one can hear hissing sound, just need to keep turning till the VCB is latched in Isolation position.

If it is the arcing sound, I would rather rack it back in!

 

[Engineer54]

Normal practice the VCB shall be in "OPEN" position before any attempt is made to rack in/out, failure to observe this rule may lead to arcing and flash over. Not sure you are referring to arcing sound or hissing sound.

Certain design of switchgear uses a bar for racking which can rack in/out the breaker very rapidly and you can hardly hear any hissing sound, on the other hand, those gears using to hand crank to turn the worm gear as part of withdrawal assembly for racking, the motion is much slower, so it is normal to hear hissing sound.

For instance, the 33KV VCB I used to work on require to crank 84 turns for moving the VCB from service position to isolation position, when breaker begins to part from fixed contact, one can hear hissing sound, just need to keep turning till the VCB is latched in Isolation position.

If it is the arcing sound, I would rather rack it back in!

It's just not possible to rack in or out a VCB/GCB etc in the closed position, there are both electrical and mechanical interlocks to stop you doing so!!!

As for the actual manual racking in or out of MV breakers etc, you go as fast as your arms allow you, you certainly don't want to be hanging around during those operations!! lol!!

 

[Knobhead]

Normal practice the VCB shall be in "OPEN" position before any attempt is made to rack in/out, failure to observe this rule may lead to arcing and flash over. Not sure you are referring to arcing sound or hissing sound.

Certain design of switchgear uses a bar for racking which can rack in/out the breaker very rapidly and you can hardly hear any hissing sound, on the other hand, those gears using to hand crank to turn the worm gear as part of withdrawal assembly for racking, the motion is much slower, so it is normal to hear hissing sound.

For instance, the 33KV VCB I used to work on require to crank 84 turns for moving the VCB from service position to isolation position, when breaker begins to part from fixed contact, one can hear hissing sound, just need to keep turning till the VCB is latched in Isolation position.

If it is the arcing sound, I would rather rack it back in!

Are you for real?

The hissing is corona/capacitive discharge. Nothing to worry about unless there is internal damage to the breaker or the insulated bushings. This is where PM comes in.

I’ve had a breaker fail part open, no way could I rack the breaker out until the contacts had fully retracted.

If you’re that worried there are bolt on remote racking systems.