Power Outage - November 2021

[msimerson]

What happened

1. A tree came down of which the top 10 – 15 feet hit our power line between our fuse/disconnect, near the meter pole and the next one toward the Lodge. The tree (about 50 to 60 feet tall with dead branches about halfway, up with green branches to the top) shattered near the ground line. The tree likely broke due to wind which was thought to be in the 30-mph area. The top of the tree was removed and the rest of the tree was left to be dealt with later.

   

   
   

   

   
   

   

Photo’s courtesy of Jim Fahey

2. The outage was reported to PSE who patrolled the line and found the down tree and opened our fuse disconnects (Cutouts). They reported this to us.
3. We found both cutouts open and removed the cutout doors. The 100-amp (neutral) cutout fuse did not blow and should not have. The fuse in the hot wire did blow but the fuse door did not come open. We had to drill out the tube to get the fuse out of the door and replaced it with a new 65-amp fuse. The cutout was observed to be of an old style and should be replaced (it failed to open properly and may not have closed properly when we reenergized the power line).
4. The only damage we found was to the conductor. The poles and dead ending hardware all appeared to have survived ok.
5. The power line was repaired and returned to service.

What we know

1. We have had trees fall in the power line before, at least 4 times. Each time the sectionalizing fusing worked properly. The 25-amp fuse blew and the 65 amp did not when the tree/limb fell near the Lodge (twice). When the tree fell near the Tow Hut the 65-amp fuse blew. This time (the 5th time) however the 65-amp fuse did not work properly. It melted but the door did not come open.
2. On a summer work party, a tree was fell into the hot power line and the fuse took some time (15+ minutes) to blow but it eventually did.
3. The fuse on the transformer behind the Lodge blew for causes unknown (most likely a squirrel) the sectionalizing fuse did not blow, a proper operation.
4. The line wire has not failed due to ice loading event even though we have had ice loading conditions. To my knowledge the new line has not experienced an ice loading event.
5. It appears that PoTelCo used an all-aluminum conductor when they replaced the power line.
6. The wire PoTelCo used is apparently weak enough to break before damage occurs to the support structures when a tree comes down.
7. When the trees come down the damage has been limited to the wire only and no pole structures have been damaged as a result. To my knowledge no trees have come down in the summer months due to nature.
8. We have apparently found #2 splices and we purchased several. They are on their way now. We also have (2) #2 to #4 splices on hand as of this date in case we need them.

More details

Wire

1. The hot line wire was physically broken in the vicinity of where the tree hit it. It also had many flash marks for about 50 to 75 feet along the conductor with some of the strands burnt through and others melted a little. There were several splices in the down conductor at least 3 of which had failed. The conductor had partially pulled out of the splice.
2. The neutral wire was also physically broken in the vicinity of where the tree came down. It also had flash marks on it for some distance from the tree but not nearly the number or length as on the hot wire. The flash marks were likely due to the hot wire faulting to the neutral through the earth. The neutral also had a failed splice in it.
3. We had some difficulty getting the proper wire to splice in the line wire and did accidentally put some guy wire (11,000-pound strength) in the hot line instead of all aluminum wire. It is difficult to tell the difference between the guy wire and the line wire visually (they are physically the same size). You must try to bend it to tell and then you call tell.
4. It now appears that the line wire is all aluminum. The original line wire was #2 ACSR. When the power line was rebuilt by PoTelCo it appears that they changed the wire out to #2 all aluminum – actual type unknown.

Selecting a conductor

1. The wire selected must be strong enough to withstand ice/snow loading while breaking before the support structures are damaged due to a tree coming down. The wire we’re looking for is called, Aluminum Bare Transmission Cable and comes in flavors (2 gage):

   Type	Description	Amps	Strength Lbs.
   AAC	All Aluminum Conductor	185	1,235
   ACSR	Aluminum Conductor Steel Reinforced	140	2,850
   AAAC	All Aluminum Alloy 6201 Conductor	191	4,270
   ACCC	Aluminum Conductor Composite Core

2. Jim measured the wire and the sample we brought back. It is 7-strand with each strand at 3/32” (0.09375) and a total cable diameter of 5/16” (0.3125). Based on the physical measurements, I (Matt) believe that we have AAAC size 77.47 (~ 2 gage).

3. The approximate cost to buy 500’ (#2 AAAC), is $190 + $27 shipping for a total of $240.

4. Another thought is that ACSR conductor is now hard to recycle because of the steel core. As a result of this PSE may have shifted to AAAC.

5. Tension calculations by Mike L. The actual tension is made up of many factors which include temperature, initial sag (which I estimate at 3 to 4 feet) and initial tension which I estimate about 100 to 150 pounds. The chart below should be used to give you some thought as to what loadings we could be looking at.

   Span (ft)	Sag (ft)	Diameter Ice Inches	Cable tension Pounds
   150	2	1	475
   150	3	1	325
   150	2	2	1900
   150	3	2	1275
   150	4	2	950

I (Mike L) used clear water ice since that has a known density. I have seen much thicker rime but have no way of judging density other than it is less. One inch diameter is .34 and 2” is 1.36 plf.

Fusing

1. Our current fusing is a 15 amp for the transformers, 25 amp for the sectionalizer in the swamp and 65 amp for the one near the PSE meter. All most likely “T” fuse speed which may now be PSE standard.
2. Fusing the 50 Kva transformers, which at full load draws approximately 7 amps, is fused at approximately one and a half to two times full load to take care of momentary overloads like motor starts etc. The fusing chart shows that to be a 15-amp fuse although a 10-amp fuse could be used. The criteria here is you do not want the transformer fuse to blow for an issue with the transformer or beyond that (like a panel fault) before the sectionalizer fuse blows.
3. The 65-amp sectionalizing fuse at the meter pole sees approximately 7 amps if you are keeping the total load at the Lodge complex under 50 Kw and if it is allowed to go as high as 75 Kw it would then see approximately 10 amps, clearly below the 65-amp rating of that fuse. We could put in a lower capacity fuse but would sacrifice coordination between fuses. I believe this is a topic for discussion at our lunch.
4. Available fuse sizes are small, 6,8,10,12,15,20,25,30.40,50, 65 and larger, in T and K speeds. T speed is slow (I think this is the PSE standard) and K speed is faster (Seattle City Light standard). If you want to know more on overhead cutout fusing, go to S&C Electric web page.
5. Fault current levels. Here is where the rub comes, we do not know the actual level of the fault current available on our high voltage system, but we know it is low (we are a long distance from the PSE substation). Likely it is the area of 1000 +/- amps. Perhaps even lower. The actual level of the fault is determined by available fault duty modified by the resistance to the fault namely the resistance in the tree (which is high) and the earth as well as in the neutral conductor and various grounds. In our case it is likely quite low likely in the area of 100 amps +/- which allows the conductor to lay on the ground and burn for some time like minutes and even longer and the fault can be interment. But we do know that our 65-amp fuse has cleared past line to ground faults -- eventually. An area for discussion.

Ray Nelson December 3, 2021

[msimerson]

Meany Linemen Team

Shortly after successfully repairing the line on November 26, 2021.

[msimerson]

Today the MLT met at the monthly Fossil Luncheon and discussed the "what next" phase. Considerations were brought up:

• the hot cutout failed to disconnect, leaving the hot conductor to lie on the ground and arc until PSE disconnected it
  • if this had happened in the summer, it could have started a forest fire
  • using an insulated hot could greatly reduce this risk ("tree wire", runs ~$3.50/ft, so about $4k)
  • we've never had a tree fall on the line in the summer. Trees tend to fall in the fall and winter during wind storms.
  • after some failures, hot dripping insulation has started fires
  • insulated overhead wire is much heavier
• max system load with all (3) 50KVA transformers fully loaded is ~20A
  • the fuse size of 65A on the hot cutout is 350%, consider downsizing it
  • each transformers is rated for 7A and we have 15A fuses on them. Consider downsizing.
  • transformer fuses could be sized closer to 7 * 125% = 9A
• which type of wire, AAC or AAAC?
  • Ray remembers previous version of the line was ACSR, suggesting that AAC wasn't strong enough
  • measurements taken of the strands and conductors suggest current line is AAAC
  • 2-gage AAAC is rated at 191A, at max we push 20A. Plenty of headroom
  • maintain 2-gage in order to provide tensile strength for ice loading
• to simplify future repairs
  • [x] have only 2-gage Auto Splices on hand (make it harder to mess up)
  • [ ] discard existing short pieces of wire
  • [ ] assemble a repair kit with all the needed tools
  • isolate guy wire from conductors
  • after breaks, aim to replace pole-to-pole segments
• TODO:
  • [ ] contact PSE and ask them to replace cutouts
  • [x] buy a supply of 2-gage Auto Splices
  • [x] buy a supply of 2-gage AAAC overhead wire
  • [x] walk the line and note the precise locations of fuses
  • [x] measure pole to pole distances

[msimerson]