In rush current

[rcdallas]

Can any of you tell me a little bit more about it?

Let say you have a 750 kva three phase UG transformer, you get your stick and close the switch to energize, you hear that windings take charge at the same time you think your the shiznit, then checking to see if a little pee came out. :D

What kind of effects does it have on transformers? I can't remember exactly what I was taught, it was something like on power transformer at a sub it's possible that it could cause an breaker operation... just need to brush off the cobwebs on that one.

[Special ED]

Can any of you tell me a little bit more about it?

Let say you have a 750 kva three phase UG transformer, you get your stick and close the switch to energize, you hear that windings take charge at the same time you think your the shiznit, then checking to see if a little pee came out. :D

What kind of effects does it have on transformers? I can't remember exactly what I was taught, it was something like on power transformer at a sub it's possible that it could cause an breaker operation... just need to brush off the cobwebs on that one.

Are you talking about ferroresonance?

[rcdallas]

No sir. I'm talking about when you first energize the transformer and you hear the windings charging up...the kinda deep throaty but not a thumping sound, in rush current.

[lewy]

I think you are referring to cold load pickup (google it) & yes depending on the conditions it could cause the breaker to open.

[thrasher]

Technically inrush or energizing the coils (with no load connected) should not operate the highside fuses, relays or any other protective scheme. However if you are talking about energizing with load connected this is a whole different ball game. In normal operation there is diversity on the connected load, in other words not every motor, device, light etc. is normally on and drawing full power at the same time. However once a line has been out for more than a half hour in extreme weather that starts changing. An extreme case we lost an underground subdivision from a primary fault under a railroad crossing in 19 degree weather with a 25 mile wind blowing. Took us four hours to dig up the frozen ground repair and re-energize the cable. Had to pickup the subdivision one transformer at a time. We closed on 75kva serving 4 houses and picked up 27 amps on the 7200 primary for about 4 minutes then it started dropping. Still don't know why the bay-o-net fuse didn't go since that was 194 kva. Rule of thumb I was taught is load doubles in an hour outage at extreme temps and triples after three hours. The previous example didn't quite do that but it was to close for comfort.

[Special ED]

Technically inrush or energizing the coils (with no load connected) should not operate the highside fuses, relays or any other protective scheme. However if you are talking about energizing with load connected this is a whole different ball game. In normal operation there is diversity on the connected load, in other words not every motor, device, light etc. is normally on and drawing full power at the same time. However once a line has been out for more than a half hour in extreme weather that starts changing. An extreme case we lost an underground subdivision from a primary fault under a railroad crossing in 19 degree weather with a 25 mile wind blowing. Took us four hours to dig up the frozen ground repair and re-energize the cable. Had to pickup the subdivision one transformer at a time. We closed on 75kva serving 4 houses and picked up 27 amps on the 7200 primary for about 4 minutes then it started dropping. Still don't know why the bay-o-net fuse didn't go since that was 194 kva. Rule of thumb I was taught is load doubles in an hour outage at extreme temps and triples after three hours. The previous example didn't quite do that but it was to close for comfort.

Simialar thing happend to me in 2003 on the Kentucky ice storm..

Phase was out. Road the line out and found the downed wire. Opened the kyles tested, grounded, and got to work. Got everything done and went to energize. Now keepin mind this was a large feeder we was working on at about 3 in the morning temps were high teens. None of the kyles would pick back up.. Dropped the load sides and tested. They worked fine. Opened them up made up the load sides and tried again. This time the engineer made us hold the levers in till if picked up.. Needless to say it locked out the sub. So the engineers thought... "Close the kyles and we will pick up the sub again." Everyone here knows that didnt work. Then they had us ride the line out and drop alot of the URD taps which there was a ton of em! Went back and they got the bright idea of closing the solid blades and pickin up at the sub again only this time they chaned the fault settings in the sub so it wouldnt lock out.. Energized it and it held.. Solid blades on the kyles well they turned cherry red visibile from the round and the engineer started freakin out wanting to know whats gonna happen. Boss came back with a quick answer "Well bub, one or two things can happen. All that cold load we just picked up will stabilize and we will be ok, or them solid blades are gonna melt and then were in for one hell of a show." Couple mins later the solid blades glow faded and they decided we was done for the night and was gonna have their engineers and own hands look into it.

[Bear]

When you energise a transformer the inrush current will depend on the point in the mains phase the primary coil is energised. If it's at the zero crossing point then the current will gradually build up as the core is magnetized, but if it's anywhere else in the phase then there will be a high current spike as the back EMF from the core is at zero allowing a high current to flow as the core is magnetized.

Sometimes the inrush current is enough to trip a breaker that's on the borderline for the rating of the transformer, particularly if there is a load on the secondary.

Often throwing it in again strikes lucky.

[Bear]

they got the bright idea of closing the solid blades and pickin up at the sub again only this time they chaned the fault settings in the sub so it wouldnt lock out.. Energized it and it held.

Well that was either an educated action or a complete gamble. I'd say the latter. An unknown fault could have caused a spectacular outcome. :D

Either way it sounds like they really need to look at the loading in that area.

[Special ED]

Either way it sounds like they really need to look at the loading in that area.

Exactly...

[rcdallas]

When you energise a transformer the inrush current will depend on the point in the mains phase the primary coil is energised. If it's at the zero crossing point then the current will gradually build up as the core is magnetized, but if it's anywhere else in the phase then there will be a high current spike as the back EMF from the core is at zero allowing a high current to flow as the core is magnetized.

Sometimes the inrush current is enough to trip a breaker that's on the borderline for the rating of the transformer, particularly if there is a load on the secondary.

Often throwing it in again strikes lucky.

That's sounding more like the answer I was given back then.

It's not cold load pickup.

Thanks.

[Bear]

The cold load issue is a serious one though. All those freezer compressors , air conditioning units and heaters waiting patiently for power to be restored so they can instantly burst into life and cause one helluva current demand. When the power goes off the thermostats on those appliances will generally turn on after a while resulting in an abnormal load.

In some places they try to educate people to turn off major appliances in a power outage and just leave a light on as an indicator that power has been restored. That also helps avoid appliance damage if power is restored in a less than desirable manner.

[rcdallas]

The cold load issue is a serious one though. All those freezer compressors , air conditioning units and heaters waiting patiently for power to be restored so they can instantly burst into life and cause one helluva current demand. When the power goes off the thermostats on those appliances will generally turn on after a while resulting in an abnormal load.

In some places they try to educate people to turn off major appliances in a power outage and just leave a light on as an indicator that power has been restored. That also helps avoid appliance damage if power is restored in a less than desirable manner.

Oh I hear ya on the cold load pickup.

I got to experience it one night when I was on the service truck at the coop I worked for. Storm came through... I was the serviceman being trained in that area and I happened to be the only one on call that night as my senior lineman was out.

They sent another serviceman about an hour away to keep an eye on me. In the mean time the line super superintendent had me going around helping troubleshoot, etc. Found the feeder locked out. Crew called. Finally those damn guard lights actually did good, none of them were on. :)

Eventually after getting all the line picked up we went and closed in but the breaker kept reclosing due to cold load pickup. I learned then and there I do not like being around that breaker when it's thumpin' at the sub...

On that particular feeder we had two sets of OCR's downstream, so what we did was open up both sets. Closed in at the sub, waited about 15 minutes, went to the next set down stream, closed in, waited about another 15 minutes then eventually closed in at the last set. Everyone back on.

I'll keep in mind what you were saying about the time line you mentioned in the cold.

[Pootnaigle]

When picking up cold load( especially during an ice storm) you may hafta exceed the value of line fuses. when the powers been off a while and every hot water heater n every strip heater, plus all the lights are calling for power it will often cause the normal fuse to melt after a few minutes( resistance heat like strip heaters and hot water heaters take a while to build to max current)Often just long enough to get yer stick down and get back to the truck.Its important to be able to recognise wheter the fuse has blown( paper cylinder housing the fuse no longer intact) or has melted( Paper cylinder perfectly intact. and the portion of the fuse tail housing the actual fuse is also cleanly and clearly melted into) I overheard a linecrew once trying the fuses repeatedly and patrolling the line after each failure finding nothing. Bout the 3rd try I told em to overfuse it from a 65 to an 80 and that held. bad thing is they needa be put back to normal size to keep co ordination in the circuit once the customers stuff catches up and cycles.this requires a short outage or mechanical jumpers .

[Lineman North Florida]

:Not to high jack the thread, have you ever seen a jack jumper Poot? No outage necessary and no mechanical jumper, works on most jacks with loadbreak horns, pretty good idea from a lineman and easy to use.:D

[Electriceel]

Glad to hear someone else has used the jack jumper and likes it. Pretty nice tool and pretty nice for public relations.

Shouldn't be hard to tell the difference between an overloaded fuse and faulted fuse.LOL

[rcdallas]

When picking up cold load( especially during an ice storm) you may hafta exceed the value of line fuses. when the powers been off a while and every hot water heater n every strip heater, plus all the lights are calling for power it will often cause the normal fuse to melt after a few minutes( resistance heat like strip heaters and hot water heaters take a while to build to max current)Often just long enough to get yer stick down and get back to the truck.Its important to be able to recognise wheter the fuse has blown( paper cylinder housing the fuse no longer intact) or has melted( Paper cylinder perfectly intact. and the portion of the fuse tail housing the actual fuse is also cleanly and clearly melted into) I overheard a linecrew once trying the fuses repeatedly and patrolling the line after each failure finding nothing. Bout the 3rd try I told em to overfuse it from a 65 to an 80 and that held. bad thing is they needa be put back to normal size to keep co ordination in the circuit once the customers stuff catches up and cycles.this requires a short outage or mechanical jumpers .

Haven't dealt with having to over fuse yet Poot. I'll remember that.

[rcdallas]

Glad to hear someone else has used the jack jumper and likes it. Pretty nice tool and pretty nice for public relations.

Shouldn't be hard to tell the difference between an overloaded fuse and faulted fuse.LOL

Any pictures? Where you get one?

[Electriceel]

http://www.utilitysolutionsinc.com//utilitycatalog/catalogAllSC.cfm?CatID=17&CN=Overhead Distribution

Go to the utility solutions website, really works well. And yes made by a lineman.

[Special ED]

http://www.utilitysolutionsinc.com//utilitycatalog/catalogAllSC.cfm?CatID=17&CN=Overhead Distribution

Go to the utility solutions website, really works well. And yes made by a lineman.

Thats pretty slick! I've never seen or heard of them but damn they seem like they would be pretty effin handy!

[johnbellamy]

An excellent tool to have, some guy got sick of macks on fuse cordination, a draw back is, one guy can do it, so don't let where you work send a serviceman out to be by-passing cut-outs by himself.

As far as cold load, what I do is have my amp stick ready after closing a cut-out in the winter or on storm, I can see for myself how many primary amps for the "cold load", then fuse accordingly. The draw back again is alot of guy's over-fuse, then drive away, screws up your fuse cordination on that system, things do not open as they should, so stick around and mack or jumper jack, put the right fuse back in, or at least let the utility who's property you are on know to change it later.

[wtdoor67]

How's that thing constructed? Some kind of spring steel alloy or some with a copper outter layer to carry the amps? Good idea, looks like. Does it have a usuage life as such or can you just use them on and on?


What happens when you put it into a fault?

Used to use a gizmo a little like that. I think it was from the 50's. Kinda like a cutout tube with a bolted clamp at the bottom and a hotclamp like top. Had them in some real old installations. Mostly on old rural applications. Lift them off with a shotgun, put a fuse in them and then cram them back on. Wasn't no extendo application. If blown, you had to climb the pole, lift it off and shotgun it back on. Better wear your rubbers. We always changed them out to a cutout as soon as possible. Locals called it a fusetapper.

Never saw a new one. We carried some for cutting jumpers and testing a section of line. It was okay, just a little outdated.

[Pootnaigle]

Ummmmmmm Nope I recon I am from the dark ages never seen er hurda a Jack jumper, sounds handy tho

[johnbellamy]

A simple spring, dont work on some style cut-outs, designed for your newer non load break cut-out.

Only used to by-pass a cut-out already energized, so you can change fuse sizes rather than using a mechanical.

An example, fuse cordination, you have to change a 50T to a 65T, it goes on the side, you can now open the door without interuption, change your fuse size in your door, simple but handy, or like ya say, you put in a larger fuse for cold load, check with your amp stick, it settles down, use your jumper jack, put the proper fuse size back in.

Different sizes for smaller or larger cut-out, can pack the load.

They can slip if not properly installed.

Not used for picking up load.

Hope the guy made a mint, sometimes ya get something useful, this is a good one.

[Bear]

What happens when you put it into a fault?


Your pants turn brown.

[wtdoor67]

It'd be a turkey shoot with a stick. I've crossphased 13 and ground faulted 7.2 with rubber gloves. Didn't even get a sun tan.

[Lineman North Florida]

We went from KS fuses to K fuses and I changed thousands of fuses out with a jack jumper, very safe tool to use, as is with other tools after much use I could tell the spring was getting weaker and it was not as secure as when I first got it, I ordered another one and trashed the original, I have macked out plenty of pots and laterals and I can tell you first hand it'll take you longer to put your stifflegs down than it will to change 3 fuses with this tool, oh yeah there must be several different designs as the one I have can only be used on jacks with loadbreak horns.

[wtdoor67]

Whatever happend to just a piece of wire with 2 hotclamps? These sissie linemen, always looking for an easy way to do things. Get in their little bucket and put on a little sissie gizmo. Heh.

[Special ED]

Whatever happend to just a piece of wire with 2 hotclamps? These sissie linemen, always looking for an easy way to do things. Get in their little bucket and put on a little sissie gizmo. Heh.

Done that many times. Make up a lil spring jumper and away ya go. Tough to cover it though. And alot of the risers around these parts ya really dont wanna even touch unless you have load off of it.. Some ding alings built alot of risers with hard drawn #6 and as old and brittle as it is it dont take shit to break it.

[Lineman North Florida]

Whatever happend to just a piece of wire with 2 hotclamps? These sissie linemen, always looking for an easy way to do things. Get in their little bucket and put on a little sissie gizmo. Heh. If the jack is a sissie gizmo I like it, and you aint fooling me none door,you would to.:D