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#146442 12/31/06 09:26 AM
Joined: Jul 2002
Posts: 8,407
Likes: 2
Trumpy Offline OP
Member
Ray(RODALCO),
I've got a problem with a sub-station that just won't go away!.
Earlier on in the week, the Hinds Sub was hit directly with a lightning strike, through a spike above the highest point in the sub-station.
It blew out a Gaseous Surge Diverter.
I replaced that upon finding it was blown.
I took out all of the ABS's and had a good look at the switchgear and what have you, it didn't seem to be damaged at all.
Went to put back in AH 36 and there was an almighty bang from the DDO's on the load side of the sub.
One DDO dropped, I meggered the tranny and it checked out OK.
I hence put it down to an old fuse link.
On Wednesday, the whole thing gave up the ghost knocking out most of Ashburton.
I got down there and saw the 3 of the DDO's dropped, I opened the ABS and replaced the fuses and had another go, they stayed closed until Friday night.
Ray,
Do you have any idea what could be wrong here?.
I should mention that 2 of the upstream feeds are locked out by me because of Earth Faults that we haven't the staff to fix.
Besides, this is not an overcurrent problem, it's short circuit current.

#146443 01/01/07 06:44 AM
Joined: Dec 2005
Posts: 866
Likes: 4
R
Member
Mike,

I'm not sure how you protect Ashburton area but in Auckland OHUG lines have surge arrestors fitted at the crusifix and at both sides of the new gas switches which are replacing the ABS switches.

The LA's are their to protect the cables and gas switches against excessive voltage surges.

Check all lightning arrestors on your outgoing lines which drop ddo's.
We have had the odd intermittand ones taken out a feeder on earthfault or sometimes overcurrent in Auckland.

Usually the LA's blow apart but sometimes they don't, and look ok from ground level, but require a close look and a bulged end or tear in the resin may be visible.
When temperatures change, the tracking across it may increase and cause a blow out.
For 11 kV we use LA's with MCOV value of 8.4 kV. which is adequate for the RMS value of 6350 Volts to earth.
Somehow we got also 7.65 kV MCOV LA's which tend to be more prone to spikes or lightning strikes.(perhaps these were cheaper)
It is not likely to be a cable fault because that will usually drop ddo's out immidiately after re energising, or within a couple of minutes.
A faulty insulator is also possible and then feedback from a local resident can be very helpfull re a bang or flash noticed along a line.

Good luck with fault finding.


The product of rotation, excitation and flux produces electricty.
#146444 01/01/07 06:57 AM
Joined: Dec 2005
Posts: 866
Likes: 4
R
Member
An other thing i forgot to tell is when the line is tested, de-energised and earthed after the fault is to megger or replace the other LA's as well.

I know their is alway pressure upon getting power back on but if i get called out then i take my time to test and record matters properly to avoid early call backs to the same job.

I forgot what voltage level we talking here
33 / 11 kV or 66 / 22 kV.
Most 11 kV LA's with a MCOV of 8.4 kV will give a 5 kV megger reading in the giga ohms ranges. 100 G.ohms or more.
33 kV LA's with a MCOV of 29 kV can read up to T. ohms.

It also depends upon moist conditions during testing. At night i have reclosed 11 kV polyloom cables feeding transformers with megger readings as low as 25 M.ohms without causing a trip or ddo blow out.

On the other side of the coin i have had polyloom cables blow out with megger readings of 1 G.ohm on one phase compared to the other 2 phases reading 100 G. ohms.

Part of the game of playing with the big stuff that the fireworks can be spectacular sometimes, and noisy too when a ddo blows under fault conditions.


The product of rotation, excitation and flux produces electricty.
#146445 01/05/07 05:09 AM
Joined: Jul 2002
Posts: 8,407
Likes: 2
Trumpy Offline OP
Member
Thanks a lot Ray!.
Your opinion really helped.

What I actually found, two days later was a 33kV line that was dropped by a couple of kids that had hit an insulator with an air rifle.
I'd never seen it at the time, but the kids mother made them come in and confess.
Makes sense now, the wire ran over the river here.
Us kids used to shoot all sorts of things with rifles of different calibres, but never a power line insulator.
Once again Ray, thanks for your help!. [Linked Image]

#146446 01/07/07 12:45 AM
Joined: Dec 2005
Posts: 866
Likes: 4
R
Member
Glad you got it sorted Mike, indeed feedback from a local resident is great.

The newest thing in Auckland now are the big party poppers.
These blow out a type of serpentine made from aluminium foil, which goes up about 12 to 15 metres.

Of course these occasionally get blown on purpose or winddrift into the 11 or 33 kV OH lines. BANG!! Feeder trip, reclose, all OK.
One day we will find someone fried near a HV line, when lines came down after a reclose.

You may get these issues down the line one day, teenage kids, cellphones, text messages The information travels fast.

Cheers

Raymond


The product of rotation, excitation and flux produces electricty.
#146447 01/07/07 03:44 AM
Joined: Jul 2002
Posts: 8,407
Likes: 2
Trumpy Offline OP
Member
Ray,
Like these?.
Party Poppers

#146448 01/07/07 03:56 AM
Joined: Jul 2002
Posts: 8,407
Likes: 2
Trumpy Offline OP
Member
Oddly enough Ray the new "Red Shed" is next door to work, that is where the kids buy this imported rubbish.
Oh well, what can you do?.

#146449 01/07/07 03:14 PM
Joined: Dec 2005
Posts: 866
Likes: 4
R
Member
Exactly MIKE!

These things are the trouble makers on the HV lines.

The red shed is one of the sellers of that rubbish.


The product of rotation, excitation and flux produces electricty.
#146450 01/08/07 05:30 AM
Joined: Dec 2004
Posts: 354
K
Member
I've never seen these "Party Poppers"! Probably because I only go to boring parties now. [Linked Image]

Are they a firework or are they like one of those popper things where you pull a string ?

Why do you need a 15m tin foil streamer ? A big paper streamer would do wouldn't it ?

I hate to be the "Party Pooper" but these things need to be banned.

By the way Trumpy I clicked on your link to the Ash-Vegas Guardian. Its a great Net Newspaper. It's the first time I've seen it. I've added it to my news favourites.

#146451 01/08/07 02:28 PM
Joined: Dec 2005
Posts: 866
Likes: 4
R
Member
kiwi
These you pull a string as far as i'm aware.
they are just a bigger version of the ones used at kids parties but they shoot up about 10 to 15 metres.

I haven't seen them myself but seen the aluminium foil remains after a feeder trip.

They trigger a spark between phases or across an insulator and Bang!! Feeder out.


The product of rotation, excitation and flux produces electricty.
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