Closing switches
Closing switches
(OP)
Heres a problem I have been working on and really can't find any data on. Under what conditions can you close a switch. My company has certain guidelines that we follow when closing a switch. Our maintenance departmeht claims we are destroying the switches ( and using there budget) by the way we switch them. I thought you could close any switch at any time as the stress exerted on the switch was when opening. I found nothing in ANSI and manufacturers seem to give contradictory answers. Before I begin I am going to give a basic primer of switching (as I understand it) so we are talking the same language.
De-energizing an overhead line
Open breaker at one end then de-energize with an Air Break switch (horn gap or arcing horn)
De-energizing a line with cable
Open Loop current switch (vacuum bottle) then de-energize with the breaker.
Re-energizing any line
Close breaker then close switch (air break or loop current). Since both sides of the switch are energized this only picks up loop current. This is not picking up load as I hear it commonly refered to.
Picking up load
By picking up load, I mean closing a switch that will energize a load that is de-energized. This only happens after a fault. The fault drops a substation, we sectionalize the line and close an Air Break switch to energize the sub. We do this so rarely now as we have breakers almost everywhere. My company had a policy not to use Loop current switches to pick up load. The funny thing was one of the rare places we had that a fault would drop a whole sub, we routinely picked up the sub with a loop current switch. It violated the internal policy but we would do it everytime.
Some of the contradictory statements from manufacturers are:
"The interrupter(vacuum bottle) is not in the circuit during closing. The switch can be closed quickly with a load."
"An airbreak switch should not be closed into a load."
One of the problems with the manufacturer statements was the engineering group did not differentiate 'load pick up' from 'loop current pickup'. I like the first statement because if its true for all vacuum bottle switches then we can treat our loop current switches as air break switches when closing. We have decades of experience closing air break switches to make up loops and pick up load. The second statement I dont like because it says we've been doing it wrong for decades.
Any standards, papers or personal experience in this matter would be greatly appreciated.
De-energizing an overhead line
Open breaker at one end then de-energize with an Air Break switch (horn gap or arcing horn)
De-energizing a line with cable
Open Loop current switch (vacuum bottle) then de-energize with the breaker.
Re-energizing any line
Close breaker then close switch (air break or loop current). Since both sides of the switch are energized this only picks up loop current. This is not picking up load as I hear it commonly refered to.
Picking up load
By picking up load, I mean closing a switch that will energize a load that is de-energized. This only happens after a fault. The fault drops a substation, we sectionalize the line and close an Air Break switch to energize the sub. We do this so rarely now as we have breakers almost everywhere. My company had a policy not to use Loop current switches to pick up load. The funny thing was one of the rare places we had that a fault would drop a whole sub, we routinely picked up the sub with a loop current switch. It violated the internal policy but we would do it everytime.
Some of the contradictory statements from manufacturers are:
"The interrupter(vacuum bottle) is not in the circuit during closing. The switch can be closed quickly with a load."
"An airbreak switch should not be closed into a load."
One of the problems with the manufacturer statements was the engineering group did not differentiate 'load pick up' from 'loop current pickup'. I like the first statement because if its true for all vacuum bottle switches then we can treat our loop current switches as air break switches when closing. We have decades of experience closing air break switches to make up loops and pick up load. The second statement I dont like because it says we've been doing it wrong for decades.
Any standards, papers or personal experience in this matter would be greatly appreciated.






RE: Closing switches
We have what I might call 3-1/2 versions of transmission line switches on our system. Arcing horns (for droping line charging current), Vacuum bottle switches (for breaking loop current), Combination - Joslyn LSI and Turner (to have the capabiltiy of performing both). The 1/2 are KPF high speed breaks that have some limited capacity to drop loop current and charging current.
When using a switch with arcing horns we remove all load including the transformer bank(s) prior to operating the switch. Prior to adding load we charge the line with the switch.
Load is dropped and picked up in the stations. For disturbution subs the feeder breakers are opened first then the switch on the high side of the bank is opened. With the reverse occuring when picking up load.
I hope this helps.
RE: Closing switches
RE: Closing switches
As far as the electrical properties of the switch goes, where I work, we always have the breaker pick up and drop actual loads or line charging current if lines are relatively long. Otherwise, we will break relatively small charging currents and such with the switches. I believe this is pretty much in line with most utilities policies here in the middle of the U.S. Although it is true that arcing horns or "whiskers" will become scarred and pitted over time due to breaking arcs from these small charging currents, most arcing components on switches I've seen in the last 20 to 25 years are replaceable just for that reason. Please keep in mind that I'm referring to standard, air break switches, both single pole disconnect, and gang operated 3 ph. that do not have "load break" capability, 69KV and up. To me, it sounds as though your rules for switching are not that much different from other places I've been.But, remember to CLA, and "operate with attitude!"
RE: Closing switches