Wait to reenergize following lightning? 3

[stevenal]

A rare thunder windstorm caused both 230 kV lines feeding a transco substation to trip open, causing a big outage. Transco found and removed a tree in one of the lines and stood by to reenergize. The wind had died down, but the lightning continued. Transco evidently has a strict policy of not reenergizing within 30 minutes of a lightning strike, so the restoration was delayed repeatedly. Does your company have a similar policy and why?

 

[System Protection]

Nope.

What would they do if a significant portion of their lines got hit with lightning?

Just leave half their lines out of service?

Its normal to go inspect a line that trips to lockout before attempting to re-energize but I've never seen one left de-energized after the problem was found/fixed.

 

[waross]

I'm guessing, based on general lightning shelter guidelines I have seen on large worksites, that the delay is for the safety of the work crews.
You don't want to be near a line when a second strike hits, let alone on the end of a hot-stick.
I am surprised that they didn't wait 30 minutes before removing the tree.
Same reason, a possible second strike.

 

[System Protection]

I'm guessing, based on general lightning shelter guidelines I have seen on large worksites, that the delay is for the safety of the work crews.
You don't want to be near a line when a second strike hits, let alone on the end of a hot-stick.
I am surprised that they didn't wait 30 minutes before removing the tree.
Same reason, a possible second strike.

This makes sense.

Maybe their policy got lost in translation somewhere.

 

[stevenal]

I doubt they were using hot sticks at 230 kV. Perhaps gang operated air break disconnects on the line sides of the circuit breakers at the adjacent substations. Can anyone cite a similar policy?

 

[waross]

Can anyone cite a similar policy?

Going from an imperfect memory;
In some of the construction projects at the large hydro-carbon plants in Northern Alberta;
When lightning is detected within a given radius, workers are instructed to leave the field and shelter in the lunch rooms until a given number of minutes after the last detected lightning strike.
The distance may have been in the range of 10 or 20 miles.
Shelter time in the range of 20 to 30 minutes.
It's been awhile.

 

[waross]

I doubt they were using hot sticks at 230 kV.

The policy may have applied to lower voltage lines as well.

 

[crshears]

stevenal: I doubt they were using hot sticks at 230 kV. Perhaps gang operated air break disconnects on the line sides of the circuit breakers at the adjacent substations. Can anyone cite a similar policy?

Tree removal at 230 kV? Sounds like forestry practices / R/O/W clearing operations were either not being performed or seriously behind schedule . . .

Practice when I was working was to confirm all infeed breakers open with Hold-Off / Hot Line Work Order tags [electronically] placed on all devices and, where possible, section confirmed off potential via metering; line section was then released to crew to proceed with tree removal on a "treat as live" basis, meaning 230 kV-rated hotsticks or other equivalent sufficiently dielectric devices were used to apply the necessary physical forces to remove the tree. If such effort was unsuccessful, full Work Protection / LOTO isolation [with or without grounding/de-energizing, depending on the circumstances] was applied, and the tree removed under Work Permit.

Either foregoing procedure was halted if a lightning strike was detected < 50 km from the crew work site by a suitable lightning monitoring/locating program, or if lightning was seen by the line crew, or if thunder was heard. Thirty minutes without lightning or thunder had to elapse before work could resume, double line outage or not, although if the tree could be confirmed as being only in contact with one of the two circuits and primary load was interrupted, restoration could be attempted on the "good" circuit without waiting for the lightning or other weather to clear, although the crew personnel would have to shelter in their vehicles during said attempt.

 

[stevenal]

Thanks all. I was able to find a few rules on line, and they deal with sheltering, not energization in particular. Lost in translation.

 

[davidbeach]

Tree removal at 230 kV? Sounds like forestry practices / R/O/W clearing operations were either not being performed or seriously behind schedule . . .

I don't know, 100ft right-of-way and a 150ft tall tree on the uphill side of the ROW. Fall-ins

I don't think I'd want to be dependent on those two lines in that weather...

 

[FPelec]

We normally adopt SPAR, so that the delay for re-energizing a 230 kV line after a lighting / flash over is about 0.5 to 2 s

 

[crshears]

SPAR: short period auto reclosure, or something else?

 

[System Protection]

SPAR: short period auto reclosure, or something else?

Single Phase Auto Reclosing

I don't think its that common below 500kV. At least that I've seen in the USA.

 

[crshears]

We didn't use that at all in my utility; all 500 kV breakers and thus their auto reclosure schemes were all three-phase.

 

[FPelec]

Yes, SPAR is Single Phase Auto Reclosing, here is widely adopted on 400 kV and 230 kV lines; it's instead much less common on 150 and 132 kV lines.
Our network code prescribes the following:

"Automatic Rapid Reclosing (RRA) and Automatic Slow Reclosing (RLA) of transmission lines
Automatic Rapid Reclosing (RRA) is required on all overhead lines in networks operating at voltages above 110 kV.
[...]
In active networks with rotating generation units, RRA shall always be unipolar. Conversely, in passive networks or active networks with static generation units, the reclosing scheme shall be either tripolar or uni-tripolar"
[...]
The Automatic Slow Reclosing (RLA) hase the same scope as the Automatic Rapid Reclosing (RRA). The device operates in a tripolar mode following the trip of line protections and is triggered after an unsuccessful or absent Automatic Rapid Reclosing RRA."


In practice, in networks with rotating generation, commonly found in 230 kV systems, single-phase automatic reclosing (SPAR) is performed first. If the single-phase reclosing fails, a three-phase automatic slow reclosing is then executed.
The waiting time for a single-phase automatic reclosing (SPAR) ranges between 0.5 and 2 seconds, with 1 second being the most common for 230 kV lines.
Even shorter waiting times, typically ranging between 0.3 and 0.4 seconds, are adopted for three-phase automatic rapid reclosing when fast single-phase reclosing is not applied.
In contrast, the waiting time for automatic slow reclosing (RLA) is several tens of seconds, typically around 30 s to one minute.

 

[crshears]

Thanks; interesting!