Vertical angle offset
The Leica TS16i is great for this. The imaging capabilities make it easy to aim at the lines. Just put it on reflectorless and continuous mode. This way even if the line is bouncing in the wind, you are sure to get it. And with Leica's data overlay on the live image, you know you got the shot in the right place.
As others have said, either shoot directly with reflectorless, or shoot to the rod man and turn the angle up.
Larry Scott, post: 431187, member: 8766 wrote: Intersecting 2 HA at the low point can be a problem.
Position the insultaors on the poles by intersection. Then, measure a single HA/VA to to the low point in the sag of the power line. The low point is a brg/brg intersection between the insulators.
This is the most accurate and reliable way unless you are willing to rely on the reflectorless readings for the cable/
I do the maths using a spreadsheet and it will calc the height at any point with an "angles only" reading.
The HA gives you the E and N of intersection with the line between the insulators. The HD follows by trig and thus the VA gives you the VD.
There are onboard applications that wiil do it if you need an answer in the field.
If you don't have a reflectorless EDM then the insulators will need to be measured by intersection from 2 stations.
paden cash, post: 431173, member: 20 wrote: I've used a reflectorless TS (SET4) for years to shoot conductor elevations.
I'm not sure kind of project you're working on, but all power-power crossings I locate for my power company clients usually also include locating the attachment points and heights at each end of the conductor, a low-wire elevation (bottom of the sag, if determinable) and the outside air temperature at the time of the measurement.
I have also had to add wind speed and direction to this deliverable
Licensed Land Surveyor
Finger Lakes Region, Upstate New York
Larry Scott, post: 431187, member: 8766 wrote: Intersecting 2 HA at the low point can be a problem.
Position the insulators on the poles by intersection. Then, measure a single HA/VA to to the low point in the sag of the power line. The low point is a brg/brg intersection between the insulators.
As Squowse says, this works best, and is applicable in all circumstances, even where you can't get a scanner in. I'd add a comment which, on the face of it, goes against normal survey practice.
For the actual conductor sags viewing square to the line and from a considerable distance is better, as the sightline tends to be more horizontal and is not affected by any conductor sway in wind. Typically I use at least a span length away from the line, so for a HV line perhaps 3-400 metres. Because the arc of view is fairly small then any refraction errors tend to be the same for all shots, which are all of similar length. I normally take a number of intersections along the lowest conductor, as this will highlight any poor reading - with a single shot you have no check.
If the tops of the towers have all been fixed by separate survey they can be used as resection control points (use the span you are interested in plus one tower on either side). Observe the conductors, top of tower, suspension and attachment points from your set up and for that span they should all be in sympathy. Instrument height calculated from the two tower tops - refraction errors more or less cancel out.
Calculate sag as described by Squowse.
For lines with twin or quad conductor bundles then the spacers between the conductors can be used as intersection targets from a two station baseline.
I've used this successfully over many years with distances from the line of up to 1 km. While you still need ground survey under the line it often means the conductor observations can be taken from places you can drive to without further walking.
paden cash, post: 431173, member: 20 wrote: I'm not sure kind of project you're working on, but all power-power crossings I locate for my power company clients usually also include locating the attachment points and heights at each end of the conductor, a low-wire elevation (bottom of the sag, if determinable) and the outside air temperature at the time of the measurement.
Paden, do you not also get asked to also take the tower leg steel temperature (on the shady side, using a magnetic clamp on thermometer). Under normal line load conditions this temperature, when combined with the air temperature, gives a good indication of the temperature the conductors are probably running at. Exact time of observation is also often asked for, as this can be compared with the line load record to determine the current being passed at that moment.
chris mills, post: 431224, member: 6244 wrote: Paden, do you not also get asked to also take the tower leg steel temperature (on the shady side, using a magnetic clamp on thermometer). Under normal line load conditions this temperature, when combined with the air temperature, gives a good indication of the temperature the conductors are probably running at. Exact time of observation is also often asked for, as this can be compared with the line load record to determine the current being passed at that moment.
We do report the time of the observation but I've never been asked to measure the structure temp. There are a variety of structures up in the air around here too. Wooden, lattice tower, self-supporting with concrete foundation and direct-bury metal. Some of the bigger transmission towers (<250kV) have restricted access to the tower bases also.
paden cash, post: 431189, member: 20 wrote: Before I got the Leica SET4 130R3 I used a Nikon. Although it wasn't reflectorless, if you took a shot on the reflector then moved the barrel up to sight the conductor, the displayed elevation would also change. This all happened BEFORE you hit the record button. It made it really slick and easy to get heights on objects you couldn't get to. You just had to make sure you were DIRECTLY underneath them.
You also have to be very careful of the rod height that was stored in the TS....;)
I was disappointed the Leica did not work the same way as the Nikon. Gawd those were good guns.
I still have a Nikon DTM-322, and I agree it works great for this application.
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BushAxe, post: 431227, member: 11897 wrote: I still have a Nikon DTM-322, and I agree it works great for this application.
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Leica instruments generally do work like that. Sometimes there is a setting that needs to be changed that's all.
I was doing it with TS16 just today.
paden cash, post: 431189, member: 20 wrote: Before I got the Leica SET4 130R3 I used a Nikon. Although it wasn't reflectorless, if you took a shot on the reflector then moved the barrel up to sight the conductor, the displayed elevation would also change. This all happened BEFORE you hit the record button. It made it really slick and easy to get heights on objects you couldn't get to. You just had to make sure you were DIRECTLY underneath them.
You also have to be very careful of the rod height that was stored in the TS....;)
I was disappointed the Leica did not work the same way as the Nikon. Gawd those were good guns.
Leica instruments generally do work like that. Sometimes there is a setting that needs to be changed that's all. (on the 700 and 800 instruments for example)
I was doing it with TS16 just today.
I. Ben Havin, post: 431166, member: 6834 wrote: Got a power transmission line project coming up where intersecting cross power lines will need to be measured up for height of wire. Looking for ideas on quick ways to obtain power transmission wire heights.
Thanks for any ideas.
Trimble makes a program called Powerline if you are using Access. Shoot the attachments and the rest is automated trig. Just point and record. No distances required for the conductor shots.
If you aren't running Access, then reflectorless conductor shots are the next easiest. It is best to be as perpendicular to the conductor as possible. The only drawback is obstacles such as branches or other conductors in the line of sight.
If you don't have reflectorless, use a rodman for vertical angle offsets to the conductor attachments, then record HA and VA to points along the conductor. This method works well but is office time intensive. The line is fixed by the attachment shots, then use HA to intersect it and VA to calc the elev. (this is what the Trimble Powerline program does).
I would suggest 5 shots per conductor plus the attachments in case one or two shots are bogus. The engineers can usually live with 3 shots plus the conductor attachments.
If you need real time info, such as working with the line crew to set the sags, there is no such thing as quick. You will be there for awhile.
chris mills, post: 431223, member: 6244 wrote: As Squowse says, this works best, and is applicable in all circumstances, even where you can't get a scanner in. I'd add a comment which, on the face of it, goes against normal survey practice.
For the actual conductor sags viewing square to the line and from a considerable distance is better, as the sightline tends to be more horizontal and is not affected by any conductor sway in wind. Typically I use at least a span length away from the line, so for a HV line perhaps 3-400 metres. Because the arc of view is fairly small then any refraction errors tend to be the same for all shots, which are all of similar length. I normally take a number of intersections along the lowest conductor, as this will highlight any poor reading - with a single shot you have no check.
If the tops of the towers have all been fixed by separate survey they can be used as resection control points (use the span you are interested in plus one tower on either side). Observe the conductors, top of tower, suspension and attachment points from your set up and for that span they should all be in sympathy. Instrument height calculated from the two tower tops - refraction errors more or less cancel out.
Calculate sag as described by Squowse.
For lines with twin or quad conductor bundles then the spacers between the conductors can be used as intersection targets from a two station baseline.
I've used this successfully over many years with distances from the line of up to 1 km. While you still need ground survey under the line it often means the conductor observations can be taken from places you can drive to without further walking.
In a major power line survey, dozens of spans of high tension line, we had one control point per span, about 90?ø to the low point, and far enough offset to keep the vertical angle below 25-30, and a strong intersection to the insulators. It's really not high precision but high accuracy. The sag varies by load, air temp, season, and sunlight. So the power company didn't need hundredths, but did need reliable. And given time of day, they figured additional sag due to peak summer load, and safety factor.
However, if you're just working with a street crossing, 2-3 spans, just pick it off a couple of times, quote the minimum.
Positioning a rod man directly under the line and a vertical angle to the line is easy, but not the best. But is the project miles? or just a road crossing.
When performing these surveys with a reflectorless instrument to determine the sag (it works great), as stated above, it is extremely important to note the temperature and the time of day. The reason for time of day; you don't know what kind of load the line is carrying at the time you mapped it and an electrical inspector on the last overhead survey I did told me a 500kv line can sag as much as 9' under certain circumstances.
Howard Surveyor, post: 431242, member: 8835 wrote: When performing these surveys with a reflectorless instrument to determine the sag (it works great), as stated above, it is extremely important to note the temperature and the time of day. The reason for time of day; you don't know what kind of load the line is carrying at the time you mapped it and an electrical inspector on the last overhead survey I did told me a 500kv line can sag as much as 9' under certain circumstances.
Here's a 250kV line that belongs to one of my clients...they've nicknamed her "Saggy Betty". The vertical clearance in the hot summer (high load) in the hay field to the left can get close to '25. This pic was taken in August. We've measured this span several times; winter and summer. The difference in the seasonal clearances far exceeds 9'.
A tornado 4 years ago completely wrecked this run about 3 miles west of this location. The engineers were wishing the storm had wrecked these spans also so a replacement or an added structure could have been charged to "disaster repair"....
