Local open/close/trip pushbuttons 2

[Mbrooke]

What is local control used for in circuit breakers, motor operators and tap changers? I see some projects specify it, but honestly the ones I'm used to specifically ask to leave it out. In these all switching and operation is done in the control hut via mimic board / bay control unit. Open/close testing initiated via walkie-talkie. What am I missing?

 

[davidbeach]

Maintenance. The easier the steps during maintenance the quicker it will be completed.

 

[Mbrooke]

Gotcha- but still looks like a poor and redundant idea on my end. Yes I know its generally the norm rather then the exception at most other utilities.

 

[waross]

Local control of a large breaker may be a remnant of a bygone era.
Most arc flash protocols will prevent the local operation of a large breaker unless it is interlocked so as to be only functional when the breaker is racked out to the test position or isolated.
That would leave the condition where a trip control was not functional during normal opertion.
Better to omit the local controls.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Mbrooke]

@Waross: This is exactly the reason I was given for rack out breakers: Arc flash protocols. I have to agree on this one.

 

[crshears]

Depends on breaker size and type; for large 500 kV SF6 circuit breakers that don't rack out but are isolated with disconnects on either side, our EMD personnel find local pushbutton control is quite handy for breaker timing tests, repetitive breaker operations when bleeding hydraulic systems after overhaul, etc., etc., and would not want to have to tie up an extra person sitting some distance off in a control hut or relay building just for this.

Same thing for large trafo's; for ratio tests etc. they much prefer to have the controls right there.

This is considered less of an issue for motor operated switches as they typically are not operated repetitively.

Another issue that may arise is when due to EMFs walkie-talkie use becomes problematic, cel phones get temperamental, and the company doesn't want to have a permanent telephone pair daisy-chained throughout the switchyard with a jack at each device, which ironically is often the most reliable method out there despite its being seriously old technology...

Hope this helps.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[thermionic1]

In addition (and agreement) to the comments from crshears, when maintaining apparatus in a utility environment, certain groups are authorized to operate the "101" or Trip/Close switches in the control panels, while others are not(switching qualified). The Local Trip/Close buttons are a separate function, which allows non "101" qualified personnel to operate the apparatus for commissioning or maintenance purposes, during a hold off or clearance. Some local control panels have a "Local/Remote" switch for this that can be monitored by SCADA. This is of course, for outdoor equipment.

For metal clad switchgear under current arc flash rules, I can't see a safe reason to have the controls right in from of the door. Most MVCB OEM's offer some kind of wall mounted test panel that can control a breaker that is fully withdrawn and connected via the umbilical cord to the test panel.

 

[davidbeach]

For the last several years the 52CSR being installed on our switchgear doors includes a walkaway timer. In addition to the control handle there are open and close push buttons; push and hold for a couple of seconds and then walk away. About 10-15 seconds later the breaker operates. There's a clear relationship between switch and breaker but no need to be in the gear enclosure when the breaker operates. Even with that, most routine switching is performed from the control center with on-site personnel well away from the breaker.

 

[Padlock01]

In the old days it was Fire suits worn in the substation for close/tripping breakers (Oil breakers Yuck!) here in RSA we have been using
the remote pendant (5 metre cable)for Close/Tripping breakers for +/- 30years even though we use vacuum or preferable SF6 one never knows whether one is closing on an internal fault (Vermin) or external faults. Authorised personnel safety is paramount.

 

[bacon4life]

Crshears nailed the reasons local controls are handy for LTCs and outdoor standalone HV circuit breakers. Also, switches in the control cabinet are helpful during initial commissioning so that one crew can install circuit breakers prior to the control house equipment being wired up. Sometimes during short outages there is one crew replacing relay racks in the control house, one crew pulling cables between the breaker and the control house, and a third crew installing/filling the SF6 circuit breaker.

 

[Mbrooke]

Great replies, not much more I can say other than thank you.


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