- Scanning for Hot Spots - Criteria for Response · – Thermography Physics and Heat Transfer –...

Fluke Thermal Imaging Company Confidential 1

Thermal Imaging - Scanning for Hot Spots - Criteria for Response

Presented by:

Alex Johnson

Fluke Corporation


Agenda

• Thermography

– What, Why and Where

• Applications

• How a Thermal Imager works – How Does an Imager Measure Temperature

– Thermography Physics and Heat Transfer

– Resolving detail and capturing a good image

• Additional training & support

• Questions?


What is Thermography?

• It is the science of “seeing” temperatures by measuring the radiation emitted from a given surface and converting this data to a corresponding digital, or visual image

• Infrared radiation is emitted by all objects based on their temperature

– The amount of radiation increases with temperature

• Thermal imagers measure apparent surface temperatures


Why use Thermal Imaging?

• Hot or cold areas, or thermal anomalies, often are a strong indicator of equipment health.

• Allows maintenance personnel to work safely becoming more proactive and less reactive.


What to look for?

• Perform preliminary scan prior to entry.

• Follow applicable safety guidelines: NFPA 70E, OSHA 1910.269

• Follow recommended procedures: NFPA 70B

• Transformers

– Bushings

– Elbows

– Cooling tubes, fans

– Connections

• Splices

• Breakers/fuses/clips

• Contacts

• Buss and stub connections

• Fan motors, pumps, belts

• Measure and document loading


Possible causes

•Transformers and components overheat due to: – Loose or contaminated connections

– Unbalance

– Overloading

– Harmonic distortion

– Restricted oil flow in cooling tubes

– Failed cooling fans/pumps

– Insulation failure


Document findings

• Create inspection routes

• Save images and track temperatures over time.

• Compare baseline images to later images.

• Validate corrective actions with additional scans.


What represents a “red alert”?

• Equipment conditions posing safety risk receive priority

• Transformers operating above max. ambient temperature – Typical max. operating ambient temp is 40°C (104°F)

– Typical temp rise at full load: 80°C for dry type and 55°C for liquid-filled

– A 10°C (18°F) rise above max. operating temp reduces xfmr life by half

• NETA* guidelines on equipment and connections: – ∆T exceeding 15°C (27°F) should receive immediate attention

• For similar components and loading conditions

– ∆T between components and ambient air exceeding 40°C (72°F)

*InterNational Electrical Testing Association


Suggested action guideline*

Temperature difference (ΔT)

between similar components

under similar loading.

Temperature difference (ΔT)

between component and

ambient air temperatures. Recommended Action

1°C - 3°C 1°C - 10°C Possible deficiency; warrants

investigation

4°C - 15°C 11°C - 20°C Indicates probable deficiency;

repair as time permits

------ 21°C - 40°C Monitor until corrective

measures can be

accomplished

>15°C >40°C Major discrepancy; repair

immediately

* Based on NETA guidelines


T & D application examples


Substation regulators

Note

temperature

difference


Substation transformers

13


Hot bushing


Some cooling

tubes appear to

be plugged

Transformer Cooling


Transformer elbows Note temp difference

~30 F


Vault phase conductors


Pad-mount transformers

Look for consistent

temperatures across

all elbows


20

Transformers elbows

Look for problems in both internal and external

connections


Vault fan motor

Internal motor temp is ~36 F hotter


Pole transformer


Transformer

problem easily

identified from a

distance using

telephoto lens

Pole transformer connection


Utility Connection


Electrical panels and circuits

• Overloaded systems or

excessive current

• Loose or corroded

connections

• Component failures

• Wiring mistakes

• Under-specified components

• Power quality problems like

phase unbalance, overload

or harmonic distortion

• Insulation failures

Image shown here is Picture-In-

Picture (PIP) mode where center ¼

of image is IR surrounded by ¾

visible


Thermography helped distinguish between

loose connection and overloaded circuit

Overloaded

circuit fuse

hot on both

ends

Loose

connection,

fuse hot on

one end only

•Courtesy of Snell Infrared


IR inspection windows

IR windows provide faster, safer equipment inspections

• High-voltage Switchgear

• Medium-voltage Switchgear

• Dry-Type Transformers

• Motor Control Centers

• Other areas where Arc Flash Hazard exists


Infrared Radiation

• Infrared radiation is electromagnetic radiation with wavelengths longer than visible light but shorter than microwaves

• Infrared radiation is radiated heat that cannot be seen by our eyes but can be sensed by our skin

• All objects, whatever their temperature, emit infrared radiation

• The intensity of infrared radiation depends on the temperature and a surface property termed “emissivity”

• When an object reaches approximately 644 C(1200 F) visible light is emitted


Infrared spectrum

IR atmospheric transmission bands

Long-wave 8-14µ Mid-wave 2-6µ

Infrared µwave Radio Ultra-

violet X-rays

Gamma-

rays

Visible light


Three Modes of Heat Transfer

• Radiation is the transmission of electromagnetic rays through space

– Each material that has a temperature above absolute zero (-460°F) emits infrared radiation,

• Conduction is direct heat flow through matter

– Fun fact: Notice how metal feels cold? We perceive this as “cold” as the metal takes energy away from your hand.

• Convection is the transport of heat within a gas or liquid

– Cold air drops so A/C vents are high

– Warm air rises so heating vents are usually down low


Reflection, Absorption and Transmission

•What happens when IR radiation strikes a surface?


Reflection, Absorption and Transmission

• When IR radiation strikes an object surface only three things can happen

– Some can be reflected ( )

– Some can be absorbed as heat ( )

– Some can pass through the object ( )

• From 1st Law of Thermodynamics

+ + = 1

• From Kirchhoff’s Law: emissivity ( ) = absorptivity ( ) Therefore + + = 1, for opaque surfaces = 0

ρ


Radiometric measurements Radiosity

• Radiation can be transmitted through a surface

– Our IR camera lens, for example

– Does not change the temperature of the surface!

• Radiation can be reflected off a surface – Remember our glass window example?

– Does not change the temperature of the surface!

• Radiation can be absorbed and re-emitted – Amount of energy absorbed = re-emitted

– This is what we measure with our IR camera!

• Reflected + Absorbed + Transmitted = 1 – Known as the RAT law

– Can also say R+E+T=1 Reflected

Transmitted

Absorbed

Re-emitted


Radiometric measurements

0.03 Reflected

0.97 Re-Emitted

T=0

0.60 Reflected

0.40 Re-Emitted

T=0

• The camera sensor detects infrared radiation

• Only the emitted radiation tells us about surface temperature.

• Different surfaces absorb and emit radiation differently – this is called “emissivity”

• Adjusting emissivity value and background temp improves accuracy.


Emissivity (ε )

•Pronunciation: "Em`is*siv"i*ty ”

•Definition: scientific measurement of the ability for absorbed heat energy to radiate (leave) an object as compared to a black body at the same temperature

– a true black body radiates 100% of its absorbed energy (nothing is reflected or transmitted) so the ε = 1

– A perfect reflector would have an ε = 0

•Materials that are not black bodies only radiate a fraction of the radiation as a black body at the same temperature and wave length so the ε is <1


Selecting the Correct Emissivity Value

• Rules of thumb – Use 0.95 for all painted target surface independent of color

– If unpainted or un-corroded metal use 0.2 or lower

– Reliable measurements when emissivity is > 0.6

– Known or controlled background temperature

– Apply tape or paint to increase emissivity

• Values for common materials are found in the imager owners manual, in the PC software, internet sources and on some Imagers

• If the target emissivity is unknown use the Imager to measure it

– Use the tape method


Emissivity of Target Surfaces

Emissivity Values (samples)

Aluminum, polished 0.05 Platinum 0.08

Brick 0.85 Rubber 0.95

Bronze, polished 0.10 Snow 0.80

Bronze, porous 0.55 Steel, galvanized 0.28

Copper, oxidized 0.65 Steel, rolled 0.24

Copper, oxidized to black 0.88 Steel, rough 0.96

Skin 0.98 Tin 0.05

Nickel 0.05 Tungsten 0.05

Paint 0.94 Water 0.98

Paint, silver finish 0.31 Zinc, sheet 0.20


Thermal Capacitance

• The amount of energy an object needs to absorb or release in order to change temperature

– Water heats and cools slowly because of its high heat capacity

– Air heats and cools rapidly because of its low heat capacity

• How quickly this change takes place depends on thermal capacitance and thermal conductivity – not time.

• Which has the highest thermal capacitance?

– Copper

– Steel

– Brick

– Wood

– Water


Be aware: wind can effect temperature

85F 76F 72F

15 mph wind T = 13F

117F 95F 81F

No wind T = 36F


Best practices for a good image

• Composition

• Focus

• Level and Span

• Palette

• Distance – IFOV/IFOVmeas

• System load

• Camera settings

• Calibration


Qualitative vs. Quantitative Inspections

Qualitative

• You don’t need to know the temperature to see there is a problem

• Very intuitive

• Easy to see variations from the norm

Quantitative

• Requires radiometric (temperature reading)

• Ability to compare to established limits

• Track even slight variations

• Must measure under known loading conditions




Focus is CRITICAL

• IR imager focus is less sharp than a visible camera

• Best focus is critical for accurate temperature measurements

• Anything but focus can be modified/optimized later with PC software

• Look for edges

• Use IR-Fusion


Thermal imagers vs. Spot radiometer

It’s like having Thousands of infrared thermometers in one instrument

When a thermal imager captures an image, all the background data is also saved along with the picture allowing in-depth post processing analysis.


IR thermometer Distance-to-Spot ratio

1’

30’

Distance-to-Spot Ratio (D:S) is distance from instrument to the object compared to the size of the spot being measured

30:1


Imager IFOV or Spatial Resolution

• Smallest detail seen by imager.

• Determined by imager’s optics and detector.

• Specified in milliradians or mRad (1 mRad = 0.0573°)

• D:S = 1/IFoV (in radians)

Example: IFoV= 1.25 mRad (0.072°) per pixel

30’

0.45”

800:1


FOV, IFOV, IFOVmeas

• 320x240 imager


FOV, IFOV, IFOVmeas

• 160x120 imager


Checking calibration

• Routinely check basic calibration before each scan.

• Here are a few simple test you can perform

– Check the tear duct of a work partner (recommend the same person)

– Check an ice bath to verify camera performance at 0º C

– Check boiling water to verify camera performance at 100º C

– Acquire a blackbody reference in one of your common temp ranges


Choosing an IR Camera

•Where will it be used?

•How will it be used?

•Considerations: – Detector Size (Pixels)

– Thermal Sensitivity (NETD)

– Ease of Use

– Ruggedness & reliability

– IR Fusion Technology

– Screen Size & FOV

– Software

– Total Cost of Ownership


Selecting the Detector Array Size Depends on the Application

•Target size needed in a single image

•Target distance

•Spatial resolution (spot size)

•Temperature measurement accuracy

•Budget


What is IR-Fusion® ?

• IR-Fusion links the Thermal Image with the Visual Image

– Easier to understand what you are looking at

• See the context

• Read any markers/labels/text

– Easier to report findings to others

• No need to also take a picture with a normal camera

– Helps you focus the Thermal Imager better

• The Thermal Imager is focused correctly when the Thermal and Visual images are completely aligned


Thermal Imagers for Industrial Applications

Performance

Ti32

Ti27

Ti29

Ti125

Ti110

Ti100 (160x120)

(240x180)

(320x240)

(280x210)

(160x120)

(160x120)

Pri

ce

$2k

$8k


PC Software - SmartView

Software provides image:

– analysis

– enhancement

– annotation

– archiving

– report generation


Additional training and information

• Fluke Thermal Imaging Training Center

– www.fluke.com/titraining

• Hands-On Seminars

• The Snell Group:

– Online Training

– Level 1, 2 & 3 Thermography Training

– Application Specific Training

– www.snellgroup.com

• Application Notes

http://www.fluke.com/titraining

http://www.snellgroup.com/


Thanks for attending!

Questions?

- Scanning for Hot Spots - Criteria for Response · – Thermography Physics and Heat Transfer –...

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