Message Board Thread - "What is best emissivity to use for electrical bus inspection?"

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What is best emissivity to use for electrical bus inspection? IRfriend 3/22/2004
My company is renting an IR camera for a month and I have been asked to do several electrical bus inspections. I used an emissivity of 1.0 and then 0.67 for oxidized copper. But in some places the copper is still shiny. I saw that this emissivity may be as low as 0.07. This will make a big difference in my readings. If I am only concerned about good connected on the busses, could someone tell me what they usually use for emissivity for these inspections?
 
Re:What is best emissivity to use for electrical bus inspection? IRJay 3/22/2004
First of all you must accept the fact that you cannot get an accurate temp reading from these surfaces. Now the image in the camera is not dependent on the surface emissivity. You will still find that the connections of the busbar are capable of showing the heating caused by a malfunctioning connections. What will be seen is not a true indication of the heat though. What you will have is an idea of concern in those parts but no ability to measure and compare.

Once those busbars are deenergized for any reason put some high emissivity material such as liquid tape or a vinyl label between the bolts. Now you have a surface for the future to measure from.
 
Re:What is best emissivity to use for electrical bus inspection? Thermoimagen Roberto Cruz 3/22/2004
i agree.
this part of "can't measure but i can see where the heat coming from" is called qualitative method. In effect, we are not able to have a good reading, just the idea where can be the a problem.

 
Re:What is best emissivity to use for electrical bus inspection? Tony Holliday 3/23/2004
Good points everyone, if you cannot remove the covers of your equipment to perform these scans then take a look at our infrared windows and ports. They will make you life faster and definately safer!

Tony Holliday
www.hawk-ir.com
 
Re:What is best emissivity to use for electrical bus inspection? RayS 3/23/2004
I have used emmissivity of 0.05 when looking at oxidized copper.

When the copper is polished, we have used emissivity of 0.78 all the way to 0.70.

I hope this helps.
 
Re:What is best emissivity to use for electrical bus inspection? IRfriend 3/23/2004
IRJay said "First of all you must accept the fact that you cannot get an accurate temp reading from these surfaces. Now the image in the camera is not dependent on the surface emissivity."

Why can you not get an accurate temp reading from these surfaces?

When I looked at these bus bar connections, I used emissivity of 0.67 or so and just looked for problem areas at the connections (i.e. a "hot" spot compared to all else in the breaker or substation). Is this the correct way to look at these connections for problems?
 
Re:What is best emissivity to use for electrical bus inspection? Tony Holliday 3/24/2004
Hi IRFriend,

I concur, the method you describe is certainly the method our service arm use.

When performing an infrared inspection they look for "hotspots" first, with approximate camera settings and more importantly load readings (where possible). Once a potential problem has been identified using comparative methods and gradients etc. then more time is taken to attempt to obtain a more accurate temperature reading at this point.

If the guys attempted to take into account the many variables required to obtain an accurate reading on each point of interest on a switchboard the job itself would be so time consuming that they would never complete one routine never mind going back every six months to do it again!

An example of this would be an air-circuit breaker. This equipment has three main areas of interest to an electrical engineer (an hence electrical thermographer);

1. Breaker section,
2. Busbar section,
3. Cable section,

As a typical Brit I remember these as the BBC..

Anyway, for each section there are again multiple points of interest;

The breaker section has feed and switched side breaker to bus stabs - where the breaker engages into fix bus connections aftering being racked out for service - (1 per phase making six points to monitor) an sometimes a neutral if the breaker is a four pole making eight.

The cable compartment has again at least three cable terminations to look at in addition to the point at which the glands(s) enter into the box making at least six potentially more if the phases are parallel fed, CT's etc..

The busbar section again has the bolted connections from the breaker clusters which is another three points in addition to the bolted sections of the bar which consitute the shipping breaks(not on all ACB's I known).

All these potential problem points make up a mass of images to be taken. Even if we discount the time taken relating to the health and safety requirements of performing such a survey the time rquired to scan a single ACB for all the above points is phenominal.

I would say that on a plant with hundreds of such pieces of equipment, not to mention motors, busduct, trasnformers etc. we should focus on finding a fault first and then attempting to quantify it. If we start factoring reflected temperature, humidity, angle, emmissivity etc. etc. into every point we will never get anywhere.

Sorry for my longwinded response, just my two (or ten!) pence worth from across the pond!

This is a point I am personally very interested in, so if you guys want to email me on how you do it I will certainly return the favour.

Thanks!


Tony
http://www.hawk-ir.com
 
Re:What is best emissivity to use for electrical bus inspection? Bob Berry 3/24/2004
I would strongly suggest a level 1 training course. What people have said is correct to a piont. Most of the time you are just scanning around and the emissivity setting is not all that critical, however busbars are a difficult application if not tackled correctly. It is easy to miss a hot spot completely if you dont know what to look for. Very often a hot spot will exist with very little signs even with the best equipment. You need to look for things like cavity radiators and a level 1 course will help you with this.

We do need to constantly be aware of reflected temperature, humidity, angle, emmissivity and most importantly we need to account for any convection that may be present. You cannot just disregard these factors when surveying and walk away. Thermography is not yet an Olympic event, we need to do a good job, not a high speed survey.

Finaly, even when you find a hot spot you will never be able to achive accurately consistant and repeatable measurements. All this of course assumes you are looking at bare copper busbars.
 
Re:What is best emissivity to use for electrical bus inspection? Tony Holliday 3/24/2004
Hi Bob,

I sure do agree that we need to bear in mind what is happening around us (I have long since taken my level I course by the way!) however I simply do not think it is feasible to expect that all of the parameters you list, can be taken time and again for every measureable point, with enough repeat accuracy to provide comparable readings. In fact, I would say that the overriding variable (and something that you do not mention) is the load on that particular circuit. Convection and airflow inside the gear in general is of course important, but minor when compared to the lack of a load reading. If you are unaware of this invaluable parameter then any temperature rise must be looked at very carefully before we begin shutting down equipment and pulling things apart.
With any indicated temperature rise regardless of the actual number shown, the load should be documented. As we all know as load increases so does the power in the system and hence the heat radiated. I have seen many infrared reports in the past that profess to diagnose faults with not even a passing mention to load on the system!

Too many false hits (or hots!!!) are bad for the industry after all, as they create a lack of trust in this fantastic technology.

You are of course quite correct in that infrared is not an Olympic sport, however of the hundreds of thermographers I have spoken with during my travels - including many of the predominant training bodies - most do advise that actual temperature measurement is only performed when a potential fault is discovered. Yes we may only see a small increase in "indicated" temperature due to low emissivity values and yes this may actually be far far higher if we had another means of measurement however this may not be possible and with live copper bus - even you would agree with me on this - that contact measurement is not a good idea!

As an hourly paid contractor it is nice to say that we need to take the time to get an accuarate measurement of each point and coming from a company with a service arm, I wish it were commercially possible! However, I say better to cover everything across the plant and then go back and concentrate on the potential faults found rather than try and measure everything, everytime and only do a quarter of it. Maintenance budgets are not an open cheque book as I am sure you are aware.

From a personal point of view, I would be interested to know how for example you make sure that the angle of your imaging device in relation to the target is guaranteed to be consistant time and again, year after year and how you measure this angle. Also, how does this relate in measurement terms to the angle of your imaging device and the comparative phases? What is the potential error in your readings if this angle is incorrect and how does this compare in severity to for example errors in emissivity at low values (under 0.6)? Also, how do you document this angle in your reports such that the guy after you can follow your work?

Sorry for the questions. I sincerely appreciate your input Bob, I may disagree but I do respect your opinion.

For all reading, we are performing tests back in our UK factory on the relationship between infrared measurement and angles, with specific reference to switchgear. If anyone would like to get hold of this data or has any supplementary information that they can share please drop me a line.

Many thanks!



Tony.
http://www.hawk-ir.com
sales@hawk-ir.com
 
Re:What is best emissivity to use for electrical bus inspection? Bob Berry 3/25/2004
Just to clear something up for you Tony, the angle you measure has little bearing on your measurement. Where the angle is important is on the effect of the reflected background temperature this will vary with the angle viewed.

I agree with most of what you say, when it is applied to high emissivity targets, but on low emissivity targets like bare copper busbars you do need to take your time and do it right, the emissivity setting you use will not really matter as the temperature measurement is unreliable anyway. I am sure you are already aware that you can view two pennies of different temperatures side by side and not be able to tell which one is hotter ( unless there is a very significant difference). If people attempt this application with no training whatsoever, they may miss even a significant problem as it may not be visable to the untrained eye.

I know false hits undermine the industry, but not as much as hits that have been missed completely.
 
Re:What is best emissivity to use for electrical bus inspection? Azar 3/29/2004
You mentioned you are renting the camera for a month. Is it a FLIR IR Camera that you are renting? If it is a FLIR camera and you rented from FLIR Systems there should be an emissivity table in the back of the manual that may assist you with your application.

Please contact me directly if you have any questions or if you are missing the manual.

Azar Louh
Inside Sales Manager
978-901-8206
 
Re:What is best emissivity to use for electrical bus inspection? jsharp 4/1/2004
I am concerned with the temperature rise above ambient . I leave the camera set to one E value to compair temperature rise between bus sections . For an individal temperature value , the correct E value for object being measured should be used .
So , I will perform my inspection with one E value set in the camera and will then correct the E value in the inspection report .
 
Re:What is best emissivity to use for electrical bus inspection? MS 4/1/2004
I mostly do substation inspections and leave the emissivity set at .95. I have had success with quick scans and then coming back to problem areas. The substations I inspect are small so I can almost see any hot spots before even opening the gate. What is nice in a three phase substation, is there are two other phases to compare a problem area to. I have not had any problems with overlooking a hot spot on shiny new copper or oxidized copper. I am not concerned with the exact temperature but rather comparison with other components and the amount of load. I guess expierence plays a part with how concerned I would become over a hot spot.
 


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