Infrared thermography

INFRARED THERMOGRAPHY

1. INTRODUCTION

Infrared thermography (IR/T) as a condition monitoring technique is used to remotely

gather thermal information for monitoring the condition of virtually all of the electrical

components on an entire system and from generation to end user. When equipments operating

under regular conditions, has a normal operating thermal signature which is typical of the

specific component being inspected. Infrared thermography presents this normal signature or

baseline to us. Once the baseline is established, IR/T will reveal the thermal variances

deviating from the norm this localized thermal deviation can either be caused by an

overheated condition or absence of heat. The information is reviewed and decisions are made

for repair or to plot the temperature change over time and repair the component at a more

opportune time. The information can be stored and fully analyzed at a later date providing

complete computer aided predictive maintenance capabilities and trending.

Infrared Thermography is currently experiencing rapid growth as more and more

electric utilities and industrial sectors are embracing the technology. The reason for this

growth is company personnel understand the benefits of this non-contact, nondestructive

method. The main benefit being,to find deteriorating components prior to catastrophic failure.

Thermography provides another set of eyes allowing a whole new level of diagnostic aid and

problem solving.

Infrared Thermography is simply a picture of heat, when you consider our natural

environment; everything is radiating a particular intensity of thermal energy. Our eyes are

unable to see this infrared energy unless the temperature of the object goes beyond 5000C.

With an infrared imaging instrument the thermal energy surrounding us can be detected,

imaged, measured and stored for analysis.Temperature and the resulting thermal behavior of

electric power generation and distribution equipment and industrial electrical systems and

processes are the most critical factors in the reliability of any operation or facility.

Temperature is by far the most measured quantity in any industrial environment. For

these reasons, monitoring the thermal operating condition of electrical and electromechanical

equipment is considered to be key to increasing operational reliability.

DEPT. OF EEE. KLEIT, HUBLI 1


In 1800, astronomer Sir William Herschel discovered infrared, and thus began the

exploration .of the science of thermography In 1800, astronomer Sir William Herschel

discovered infrared, and thus began the exploration of the science of thermography. Sir

William designed and created his owntelescopes – becoming very familiar with lenses,

mirrors and light refraction. His thermography research began with the knowledge that

sunlight was made up of all the colors of the spectrum, and that it was also a source ofheat, so

he set out to determine which color(s) were responsible for heating objects. The first

thermography experiment utilized a prism, paperboard, and thermometers with blackened

bulbs where the temperatures of the different colors were measured. As sunlight passed

through the prism, Sir William observed an increase in temperature as he moved the

thermometer from violet to red in the rainbow created by the light.Herschel noted that the

hottest temperature was actually beyond red light, and that the radiation causing this heating

was invisible. He called this invisible radiation "calorific rays." Today, we refer to the

light/energy as

Infrared, and the measuring of the heat emitted as thermal thermography Temperature

is one of the important parameters to tell the condition of internal Process, material and even

quality of the desired output. A qualitative but accurate conclusion can be drawn by observing

the temperature profile of any surface. On the other hand higher temperature also indicates

obvious loss of energy in the form of heat. Therefore temperature monitoring would give

ample indication of the condition of the material, process quality and explore the possibility of

energy conservation avenues. In recent years, many temperature monitoring techniques have

been in use in our industries. These techniques find their application based on the measurable

temperature range, sensitivity and ease in application. A comparison of various typical

techniques has been given in table no. 1. With the on-line condition monitoring technology

becoming an inevitable part of maintenance strategy in today’s scenario, non-contact type

temperature monitoring methods have become more popular. Infrared Thermography is such

a non-contact type technique which provides a fast, reliable and accurate temperature profile

of any material surface.

DEPT. OF EEE. KLEIT, HUBLI 2


2. What is Infrared Thermography

Thermography is nothing but the temperature profiling of a surface or point. As the

Name suggests, infrared thermography is based on Infrared (IR) technique. The principle

underlying t his technique is that every object emits certain amount of IR energy and the

Intensity of this IR radiation is a function of temperature. In an electromagnetic spectrum the IR

region appears between 0.8 micron to 1000 micron wavelength (See Figure 1).This wavelength

of IR spectrum is more than that of a visible spectrum. The IR energy which can directly

represent the surface temperature can be detected and quantified by the help of IR scanning

system.

DEPT. OF EEE, KLEIT, HUBLI 3


2.1 The Thermography Instrument

A thermography instrument can be a thermal pointer or a thermal scanner. The thermal

pointer reads the temperature of a specific dimensional point where as a scanner maps the

thermal profile of an area surface.

The basic IR system consists of an “IR energy detector” and a “Monitor”. The scanner is

an opt mechanical device which converts the IR energy received from an object surface to an

electrical signal. These signals are further fed into the monitor where it is processed and

presented in many forms like simple digital display to indicate temperature level and a video

display for thermal profile (See Figure 2).



2.2 Test Equipment

Hand held portable camera

I. Battery Powered

II. Operating at correct wavelength

III. Range…..-20°c to +1500°c

IV. Sensitivity…..0.1°c at 30°c

V. Real time display

VI. Image Recording capability



3. Electrical Thermography

Infrared Thermography is simply a picture of heat. All the bodies emit energy from their

surface as electromagnetic waves, which magnitude is directly related to their temperature. The

hotter the object is, the more energy it tends to radiate. Such temperature settles the wavelength

of the emitted energy; the colder the object is, the higher its wavelength will be, whereas the

hotter it is, the lower its wavelength will be. This last case, is the one of the infrared energy, non

visible to the human eye, but visible by means of an infrared camera. The radiation measured by

the infrared camera depends not only on the temperature of the object but also on its emissivity.

The radiation coming from the surrounding area and reflected on the object also influences the

measuring. Therefore, to measure the temperature accurately, besides the effects of different

sources of radiation that interact with the object, other variables such as emissivity, distance

between the camera and the object scanned, environment temperature and humidity, must also be

considered. In addition, due to the characteristics of the infrared radiation, to detect any

overheating by IR scans, the heat generated must be “directly” in sight of the thermographer. .

All electrical maintenance personnel know as soon as new electrical components are installed

they begin to deteriorate. With fluctuating and continual loads, vibration, fatigue, age, and other

things like operating environment, all of these will increase the probability of faults in electrical

components. These faults, if not found and taken care of, will lead to catastrophic failures,

unplanned shutdowns

3.1. Typical faults in electrical componentsAll electrical devices are usually rated for power, which indicates the amount of energy

that the devices can conduct without being damaged. If the device is operated at a power above

its speciecations, the excess power can reduce the device's life cycle and efficiency. Basically,

faults in electrical power system can be classified into few categories, i.e., poor connection, short

circuit, overloading, load imbalance and improper component installation. In most cases, the

major cause of overheating in utility components is the change in resistance due to lose

connection. The loose connection causes electricity to use smaller area of the defective

connection than required for proper current °o w and therefore, increases the resistance and



temperature of the connection. Any problem, which accompanies a change in resistance of the

equipment, causes it to consume more power than the intended load.

According to a thermographic survey conducted during the period of 1999 it was found

that 48% of the problems were found in conductor connection accessories and bolted

connections. This is mainly resulted from the loose connection, corrosion, rust and non-adequate

use of inhibitory grease. On the other hand, 45% of the thermal anomalies appear in

disconnections contacts.

Most of the anomalies are due to deformations, decent pressure of contact, incorrect

alignment of arms and dirtiness. Only 7% of the problems were found in electrical equipments.

Another major cause of overheating in electrical components within the structure is overloading. Through IRT camera, the sign of overloading can be seen clearly even if the cable was located

deep into the concrete

• Transformer

– Pad Mount

– Dry

– Overhead

• Service Entrance

• Distribution Panels

• Control Panels

• Rectifiers

• Drives

• Capacitor Banks

• Any Electrical Connection

• Main Switchgear

• Motor Control Centers Disconnects

Bus Duct

3.2 Electrical Inspection Items

4. Infrared Condition Monitoring



Temperature is one of the first observable parameters that can indicate the condition of

operating electrical equipment. Heat is a byproduct of all work whether is it electrical,

mechanical or chemical. All industrial processes operate with mechanical, chemical and

electrical energy being converted from one form to another. The natural byproduct of the

conversion process is heat. Heat generated either intentionally or unintentionally is transferred,

contained and otherwise being controlled to suit specific requirements. Thermal energy not in

control will cause problems

Universally, the electric industry understands that temperature is an excellent indicator to

the operating condition and hence the reliability and longevity of an electrical component.

Associations like IEEE, ANSI, IEC and manufacturers all publish standards and temperature

ratings for electrical components. It is well understood that the life of electrical components and

materials is drastically reduced as temperatures are increased. It is logical, then, that evaluating

the thermal signature of electrical systems with Infrared Thermography will provide the

maintenance department, from generation to the end user, with valuable information directly

related to operational conditions of virtually every item through which electric current passes.

Infrared condition monitoring is the technique capable of revealing the presence of an anomaly

by virtue of the thermal distribution profile that the defect produces on the surface of the

component. The defect will normally alter the thermal signature of the surface due to the change

in the amount of heat generated and the heat transfer properties of the component.

To determine an adverse operating temperature of a component it is necessary to first

determine a baseline. For electrical systems the baseline is established when the system is

operating under normal load and operating conditions. Once a clear understanding is obtained on

what the normal thermal signature is for the many electrical apparatuses and components, the

thermography technician will be able to quickly identify a thermal anomaly. On larger more

critical components such as transformers, circuit breakers, capacitors etc., the baseline images

and data will be stored and compared to new data collected from each inspection interval. It is

the job of the thermographer to identify record, analyze and diagnose indications of abnormal

heat transfer in the electrical equipment or components. It is important that the data collected is



accurate, repeatable and is properly analyzed. This depends on many variables, the main being

the thermographers level of understanding of infrared instrumentation, background theories and

the level of field experience.

For the classification of thermal abnormalities,

Three critical levels and their corresponding recommended maintenance actions were defined

I -Overheating ≥ 130°C (Serious): immediate outage of the equipment affected for the repairing

of the anomaly.

II - Overheating between 100°C and 130ºC (Priority): repairing of the anomaly as soon as

possible.

III - Overheating between 75°C and 100º C (Programmed): repairing of the anomaly when

possible Correction factors considering the effects of variables such as emissivity, environment

temperature and relative humidity, wind influence and distance to the object were established to

be considered in the measuring. Maximum admitted load ability for the whole facilities to be

scanned were set and tabulated (for instance identifying the equipment with the lowest load

capability of the bay). Therefore, the overheating measured at any level of load could be referred

to such maximum admitted loading level, so as to consider the most unfavorable conditions that

could be present during their operation. Thermographic Reports provide information that

identifies with certainty the item on which a thermal abnormality has been detected, together

with a picture and a thermographic image of the abnormality detected, to facilitate the repairing

tasks for the maintenance personnel. Besides, they add additional information, such as over

temperature registered and temperatures of reference, load level at the time of the scan and

maximum admitted load, overheating above the environment temperature referred to the

maximum admitted load and the real classification of the abnormality



Table 1: applicatoin of IR on Electrical elements



4.1 Exception Repair Priority Criteria

Hot Spot Temperature…...203F Repair Priority 3

Reference Temperature….156F Corrective Measures Required

Temperature Difference….47F As Soon As Possible


Priority 0

Temperature Difference 10F or LessNo Corrective Measures Required

At This Time.Priority 1

Temperature Difference 10F to 20FCorrective Measures RequiredAt Next Maintenance Period

Priority 2 Temperature Difference 20F to30F

Corrective Measures Required As Scheduling Permits

Priority 3Temperature Difference 30F to 100F

Corrective Measures RequiredAs Soon As Possible

Priority 4

Temperature Difference Over 100FCorrective Measures Required

Immediately


Contact failure

Faulty screw terminals

Faulty wrap connection Fig:5



5. Benefits of infrared electrical inspections

Since most problems on an electrical system are preceded by a change in its thermal

characteristics and temperature, whether hotter or cooler, a properly trained and experienced

thermographer is able to identify and analyze these problems prior to costly failure occurring.

Infrared electrical inspections provide many benefits to the recipient. The two key advantages

from which the others stem, are:

1. The reduction in disassembling, rebuilding or repairing components which are in good

operating condition. This type of repair is meaningless and costly and may lead to a 30 percent

reduction of production. Furthermore, it is not guaranteed that the component will be in better

condition after the repair, since the location of the problem or cause was not established. With

infrared thermography you identify and hence repair only what needs repairing.

2. Problems that truly exist will be identified quickly, giving time to repair the problem before

failure. In most cases, the problem is identified well before the problem becomes critical.

Depending on the temperature and criticality of the component, the decision can be made to

repair immediately, repair at the first opportune time, or monitor on a continual basis until the

critical temperature is reached or until the repair can be scheduled. Identifying true anomaly,

scheduling the repair, and eliminating the actual cause of the problem within a proper time frame

is the most efficient and cost effective way to maintain the system. The other advantages of an

infrared inspection program are based on the above overall advantages, yet are no less important.

They are:

Safety - failure of electrical components could be catastrophic, injuring or even killing

employees, maintenance personnel or the public.

Greater system security - locating the problems prior to failure greatly reduces unscheduled

outages, associated equipment damage and downtime.

Increased revenue - with more uptime, revenue is maximized. With less maintenance on good

components and faster repairs of faulty components, maintenance costs are reduced leading, to a

better bottom line.



Reduced outage costs - the cost of an emergency outage is ten times greater than planned

maintenance.

More efficient inspections - since all common electrical problems announce themselves as an

increase in temperature, they are easily detected in a minimum amount of time. No service

interruption is required for infrared inspections.

Improved and less expensive maintenance -

a) Precise pinpointing of problems minimizes time required for predictive and preventive

maintenance,

b) Maintenance efforts are directed to corrective measures rather than looking for the problem,

c) repair only what requires repairing, reducing repair time and unnecessary replacement of good

components.

Reduce spare parts inventory - with improved inspection techniques giving advanced fewer

spare parts are required in inventory. What would it mean to the bottom line if your spare parts

inventory could be reduced by 10 per cent?

Reduced operational costs - with the system up and running for longer periods of time, the

reduction and improvement of inspections, maintenance, spare parts inventory and outages will

reduce the overall cost of operations.



5.1. Advantages & Disadvantages of IR Thermography

The following points spell the advantages and disadvantages of this technique.

Advantages :

I. It is a non-contact type technique.

II. Fast, reliable & accurate output.

III. A large surface area can be scanned in no time.

IV. Presented in visual & digital form.

V. Software back-up for image processing and analysis.

VI. Requires very little skill for monitoring.

VII. Non Intrusive

VIII. Can work at a distance

IX. Portable

X. Convincing Results

Disadvantages :

I. Cost of instrument is relatively high.

II. Unable to detect the inside temperature if the medium is separated by

i. glass/ polythene material etc.

III. Non Intrinsically safe.

IV. There must be a temperature difference for certain surveys

V. Operator experience is essential

VI. Filters may be needed for certain applications

VII. Sensitivity and Resolution reduce with distance and angle of view



5.2. Electrical Applications

This could be an enormous list of equipment and processes since virtually every

component from Generation to low voltage electronic boards can and should be inspected.

Suffice it to say, the Applications fall within four categories:

I. Power generation: hydro, thermal, and nuclear

II. Power distribution: transmission, switchyards, substations, and distribution

III. Industrial users: all process and manufacturing industries

IV. Commercial users: warehouses, office buildings, banks, schools, virtually all

buildings

In the April 1991 article of Transmission & Distribution, the supervisor says “the infrared

equipment allows on-line Maintenance with no interruption to service, resulting in continuity of

service that avoids about 150,000 customer out-of-service hours a year. The annual inspection

tour yields an average of 400 to 450 reports that call for either immediate repair or investigative

action, gathered in all types of weather".

Described below are some of the application areas of IR thermography with illustration of some

real life case examples.

5.2.1. Cooling Efficacy of Radiator Fins of a Power Transformer

Thermography survey of the radiator fins of a power transformer indicates the total

temperature profile as shown in Figure 6. A temperature gain of around 7-8 0C would indicate

good cooling effect of the transformer oil along the fins. Here an average gain of about 2 0C in

few of the fins indicates that fins may be having internal deposition or choking resulting in

ineffective cooling.



Figure 7 : Thermal Figure 8 :hot-spot in LT MCC terminalImage of a Radiator Fins

5.2.2. Power Circuit of Electrical Drives

It is essential that good power circuit be there to ensure proper functioning of electrical

motors. Sometimes loose contacts at Motor Control Centres(MCC) or at terminal boxes lead to

introduction of high resistance in the circuit. So voltage is dropped across this loose contact and

a severe voltage unbalance is obtained at the motor terminal end. This results in malfunctioning

of the motor. It may so happen that aggravation of such loose contact (thereby high temperature)

will eventually lead to single-phasing situation. Figure 5 indicates a thermography survey of a

415 volt 75 KW induction motor having high temperature (101 0C) at MCC breaker terminal

with ambient about 30 0C in R-phase resulting in a voltage unbalance of about 4.7% at motor

terminal



Fig:9: a typical industrial drive

6. CASE STUDY6.1applications in distribution systems

Infrared thermographic inspection of electrical distribution system in Thermal image

camera has the ability to produce a visual representation of thermal patterns as heating systems

components are identified and recorded. Maintenance strategies are then planned and carried out

before system breakdowns occur. Heating components are generally noted as white or lighter

colored areas in an infrared image. Transformer secondary connections, transformer overheating,

ground currents, fuse connection or internal heating, transformer bushing heating, utility

connection box break and breaker connection heating are several examples of unwanted

conditions that thermography can locate and provide early warning signs for maintenance

departments.

(a) A typical electrical distribution system consists of a number of isolators, circuit

breakers, Current Transformers, Potential Transformers, Distribution Transformers, bus bars etc.

Most faults are encountered in the form of hot-spots at contact terminals which may be due to

lose contact, corrosive nuts & bolts, broken conductor strands etc. These hot spots are indicated

by high surface temperature. Higher is the current flow, more severe is the fault. On-line thermal

scanning of these contact terminals will identify the hot-spots and severity of the fault (See Table

2). Attending these fault points will, of course, reduce the breakdown of the system and

reliability can be improved



Fig 11:

Another case also justifies the applicability of the IR thermography technology in a

switchyard of a captive power plant of an aluminum company. With increasing the frequency of

application from 2 to 3 times a year, the reliability of the switchyard could be achieved to nearly

100% as no shutdown is reported. In addition to this, the base line of the critical point has also

come down drastically (See Figure 6).

Figure 12 : Consequence of Application of Thermography in a switchyard of a Captive Power

Plant

(b) The thermal scanning of about 400 first switching sub-stations (11KV/415 volt) of a power

distributing company of a metropoly city of India could reveal very critical points. Necessary

corrective action could lead to save frequent interruption in power supply and huge downtime.

Maintenance activities could be streamlined more appropriately



CASE STUDY NO.1

Thermal image camera can also identify overheating components such as transformers as

shown in figure 6. Transformer overheating increases transformer losses , weaken the insulation

and may result in reducing transformer life. The principal reasons for transformer overheating

are classified as follows:

I. Excessive transformer loading.

II. Excess current in the neutral of the transformer.

III. Problems in the cooling system.

IV. High harmonic content in the power supply.

V. Sustained overvoltage which exists for a long period of time.47.2°C

Since transformers are a critical and expensive component of the power system so that it

must be protected against faults and overloads. The type of protection used should minimize the

time of disconnection for faults within the transformer and to reduce the risk of catastrophic

failure to simplify eventual repair. Any extended operation of the transformer under abnormal

condition such as faults or overloads compromises the life

of the transformer, which means adequate protection

should be provided for quicker isolation of the transformer

under such conditions.


• Electrical connections

• Insulators

• Thermal profile

• Operating temperature

• Liquid Level


Fig.13: transformer in distribution system

6.2 applications in overhead transmission lines

Overhead transmission lines (O.H.T.L) in order to decrease the number of transmission

failures that can be occurred at all connection points as follows: non-tension sleeves, sleeves,

jumpers, disconnecting switches and overhead ground wires in order to improve power quality.

The following are two examples of unwanted conditions that thermography can Locate and

provide early warning signs for maintenance departments.

CASE STUDY NO.1

.

A high-temperature spot is found at the connector of phase-T conductor at the jumper of

the riser pole. This means that phase-T connector has high temperature due to using

inappropriate equipment and tools; use of a machine bolt instead of hexagon bolt without a

spring ring has caused a bad electrical connection so that it is proposed to make a replacement

using the appropriate equipment and installation.



Fig.14: transmission lines


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Infrared thermography

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