Improving Electrical System Reliability with Infrared Thermography
Source : http://www.infraredelectrical.com/index.html
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.
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.
Why can we say all equipment? Because all equipment when 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.
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
within any type of equipment whether electrical, mechanical or process related.
No electrical system is 100% efficient. Current flowing through an electrical system will generate
a small amount of heat because of electrical resistance. With time the components and contact
surfaces of the electrical system will begin to deteriorate. With the deterioration comes increased
resistance and with resistance, increased heat. This course will continue until eventual failure.
Fluctuating and high loads, vibration, metal fatigue, age and specific operational environments
such as extreme ambient temperatures, wind, chemicals or dirt in the atmosphere will increase
the speed of degradation and the number of faults in electrical systems.
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.
Electrical Thermography
The main application for thermography has always been, and still is electrical system inspections.
Infrared thermography has been used as a condition monitoring tool to predictively maintain
electrical systems, even before the terms "condition monitoring" and "predictive maintenance"
were used. In 1965, the Swedish Power Board began inspecting approximately 150,000
components a year. In 1976, the UK Electrical Generation Board began utilizing infrared
thermography for predictive maintenance on the transmission lines. Ontario Hydro and BC Hydro
in Canada also became involved in infrared thermography during this time.
By the year 2000, virtually every electric generation and distribution company as well as every
major manufacturing and process facility will be using infrared thermography as a condition
monitoring technique to increase reliability and decrease downtime.
Why such an interest in electrical thermography? Simple. 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 and
losses of production.
Benefits of Infrared Electrical Inspections
Since most problems on an electrical system are proceeded 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 a
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:
1. Safety - failure of electrical components could be catastrophic, injuring or even killing
employees, maintenance personnel or the public.
2. Greater System Security - locate the problems prior to failure greatly reduces
unscheduled outages, associated equipment damage and downtime.
3. Increased Revenue - with more uptime, revenue is maximized. With less maintenance
on good components and faster repairs of faulty components, maintenance costs care
are reduced leading to a better bottom line.
4. Reduced Outage Costs - the cost of an emergency outage is ten times greater than
planned maintenance.
5. 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.
6. Improved and Less Expensive Maintenance -
a. precise pinpointing of problems minimize time required for predictive and
preventive maintenance,
b. maintenance efforts directed to corrective measures rather than looking for the
problem,
c. repair only what requires repairing, reducing repair time and replacement of good
components.
7. Reduce Spare Parts Inventory - with improved inspection techniques giving advanced
warning of failure, 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%?
8. 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.
In the first part of our article, we concentrated on what thermography is, how it works, and why
electrical inspections are the main industrial application for infrared thermography. Whether you
purchase an instrument, rent or hire an outside service company, the return on investment is
amazingly fast. The benefits of establishing an infrared inspection program at most facilities far
out weigh the investment, these are:
1. Safety
2. Greater system security
3. Increased revenue
4. Reduced outage costs
5. More efficient inspections
6. Improved and less expensive maintenance
7. Reduce spare parts inventory.
8. Reduced operational costs
Now we will look at the more practical side of infrared electrical inspections. We will discuss
the sources of thermal patterns on electrical systems. Thermographers beware!! Not all "Hot
Spots" are problems..... We will then look at a variety of uses and applications, return-on-
investment and training.
Sources of Thermal Pattern Variances on Electrical System
Thermal energy generated from an electrical component is directly in proportion to the
square of the current passing through it multiplied by the components resistance (I2R
Loss). As the condition of the component deteriorates, its resistance can increase and
generate more heat. Then as the component temperature rises the resistance increases further.
This self propagating process continues until the melting point of the weakest component is
reached. By utilizing thermography to inspect electrical systems and components under load
the faulty components can be identified and classified by severity. It is interesting to note that
because heat loss is proportional to the current, unbalanced or overload conditions can be
identified. (I2R Loss)
When performing an infrared inspection of an electrical system it is important to realize that
all of the radiation leaving a surface is not due solely to the temperature of the surface.
Unless knowledge, understanding and caution are applied during the analysis portion of the
inspection, documentation and interpretation may result in the false conclusion that a fault does
or does not exist.
Thermal pattern variations are normally referred to in two ways:
1. Real Temperature Differences - These are thermal patterns caused only by infrared
energy exiting the surface of the object.
2. Apparent Temperature Differences - they are patterns which are due to factors other
than variations of the target surface.
The causes for thermal pattern variations from electrical components are:
Of the real thermal pattern variations, only three will provide indications of a problem on an
electrical system:
1. I2R Loss
2. Harmonics
3. Induced heating
The other three (convection, thermal capacitance, and evaporation) will make a true
temperature change at the surface of the component, but it does not provide indication of an
electrical fault. In fact, they may actually provide false information by disguising or reducing the
amount thermal energy associated with the anomaly, or heat up a component and make it appear
to be a fault.
All of the real and apparent causes of thermal pattern variations are very important to
understand for anyone performing infrared inspections, especially electrical inspections!
Remember, the actual component temperature may change or may not change. The thermal
variations are not necessarily caused by the electrical components themselves but by outside
forces creating the thermal variations, creating or disguising problems. Many people say it is
easy to perform an infrared electrical inspection, be careful - it's easy to be fooled. Beware, IR
electrical inspections are one of the most difficult applications if done properly, not just being a "hot
spot" finder.
True Faults are Caused from
1) I²R loss
The most common loss of power in an electric circuit is the heat produced when current
flows through a resistance. The exact relationship between the three quantities of heat,
current and resistance is given by the equation:
P = I²R
Where P = Power and is the rate of doing work or the rate at which heat is produced. It can
see from the equation that the amount of thermal energy produced is increased or decreased
by increasing or decreasing the current or resistance.
This I²R heating, as it is often called, takes place in the circuit wires as well as in resistors.
The basic unit of Power is the watt, wattage is equal to the voltage (E) across a circuit
multiplied by
current (I) through the circuit. Below we have divided the effects of power under two headings,
since the reason for the power consumption provides an indication as to how the system or
components are operating.
1a) Load
As the load increases in a circuit the power output will increase as a square of the load, and the
temperature of the entire circuit and components on the circuit will increase. From a
thermographic point of view, load is usually looked at as a specific type of problem with specific
thermal indications. As the load on an electrical component rises, so does the temperature. An
even load on each phase of a three phase system for example, should result in uniform
temperature patterns on all three phases. An anomaly is identified when the overall component
and conductor temperature is too high, indicating an overload condition. An unbalanced condition
can also be a problem and is identified by the conductors not displaying a balanced or equal
thermal pattern and temperature.
Unbalanced or overloaded components can be identified thermally because the temperature
remains relatively constant along the conductor or component as long as the object size and
mass remains the same.
This Thermal image identifies a warm breaker. There is no problem with the breaker, there is just a load
variation between the three breakers.
1b) Localized Resistance
Here we consider a resistor. A resistor in any component in the electric circuit, this can be
connections, fuses, switches, breakers and so on. Under standard operating conditions each
component will have a certain "normal" resistance associated with it. It is when the resistance
deviates from this norm that the component begins to heat up and must be identified and
repaired.
Overheating of components can have several origins. Low contact pressure may occur when
assembling a connection or through wear of the material e.g. decreasing spring tension, worn
threads or over tightened bolts. Another source could be deteriorated conductors of motor
windings. As the component continues to deteriorate the temperature will continue to increase
until the melting point of the material is reached and complete failure occurs.
This type of fault can generally be identified because there is a "hottest point" on the thermal
image. What this means is, the heat being generated is greatest at the fault point with a tapering
off of thermal energy away from the point of highest resistance.
Remember, an increase in load will also have a significant effect on increasing the temperature of
a high resistance problem (I²R).
2) Harmonics
Harmonics are currents or voltages that are multiples of the basic incoming 60 HZ frequency
serving an electrical distribution system. Possibly the most damaging harmonics are the odd
harmonics known as triplens. The triplen harmonics add to the basic frequency and can cause
severe overvoltage, overcurrent and overheating. Frequency is not the enemy of the electrical
system. The real enemy is increased heat caused by higher frequency harmonics.
These triplen harmonics can create drastic overheating and even melting of neutral conductors,
connections, contact surfaces, and receptacle strips. Other equipment effected by harmonics are
transformers, stand-by generators, motors, telecommunication equipment, electrical panels,
circuit breakers and busbars.
3) Induced Heating
Alternating current in electrical systems naturally induce current flow and magnetic flux into
surrounding metallic objects such as conduit, metal enclosures and even structural support steel.
This phenomenon will occur in areas of high electromagnetic fields such as high voltage
equipment, microwave transmitters, and induction heating equipment. This condition can be
induced in ferrous material when an electrically induced electro-magnetic field is present. The
field induces eddy current which causes subsequent heating and will create true surface
temperature changes. An example is ferrous bolts in aluminum electrical bus bar. This is a hard
condition to identify and it will appear as something between a faulty component and an
emissivity change.
Please Note: We will not go through the apparent thermal pattern variations, but it is just as important for a thermographer
to understand the entire ten reasons for real and apparent temperature variations that can be found on an electrical system If
the thermographer does not understand these, many false anomalies may be reported. Contact the author for more
information on real and apparent thermal variations and how they can be dealt with.
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:
• Power generation: hydro, thermal, and nuclear
• Power distribution: transmission, switchyards, substations, and distribution
• Industrial users: all process and manufacturing industries
• Commercial users: warehouses, office buildings, banks, schools, virtually all buildings
Baltimore Gas & Electric perform infrared electrical inspections on 40,000 miles of
distribution lines and 175 substations. The electrical test department is a firm believer in
using infrared condition monitoring as a program for increased reliability. 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".
Electrical Condition Monitoring
When considering remote diagnostic testing of electrical equipment, infrared
thermography is regarded as the most powerful of all diagnostic tools currently available. The list
of equipment to inspect is enormous since virtually every component from generation to low
voltage electronic boards, can and should be inspected.
It is very difficult to place a dollar value on the benefits realized from an infrared
inspection program because the faults are found and repaired before failure. However, power
companies such as Baltimore Electric, Insurance and Risk Management Companies has
noted the huge savings received from infrared CM programs.
Table 1 itemizes equipment inspected, and in some cases, indicating potential impact and
possible savings as reported by various power distribution organizations, industrial plants and
insurance companies.
APPLICATION CONDITIONS DETECTED POTENTIAL IMPACT
Power Distribution, Loose/corroded/improper Overheating, arcing, burning, fire,
Capacitors, connections and conductor strands broken - overhead
Lightning splices, line could come down. Inoperative
Arrestors, Circuit inoperative capacitor, capacitor causing lack of protection
Breakers, Conductors, failed from power surges and possible
Splices, Disconnect lightning arrestors, poor early failure of associated electrical
breaker connections, equipment, $1,000.00 -
overheating, $100,000.00. Defective
overloading, conductor lightning
strands arrestors leaking power to ground.
broken. Replacement " $5,000.00. Safety
considerations.
Miscellaneous Electrical Loose or corroded connections, Arcing, short-circuiting, burning,
Apparatus, poor contacts, unbalanced loads, fire. 25% of all miscellaneous
Switches, overloading, overheating. electrical apparatus failures are
Breakers, Load Centers, caused by loose
Motor Control Centers. electrical
connections. Average
main
switchboard or
MCC repair,
$10,000.00 -
$70,000.00;
replacement $80,000.00 -
$100,000.00. Safety considerations.
Transformers Loose/deteriorated connections, Arcing, short circuiting, burning,
overheated bushings, poor contacts fires. Rewind (5000 DVA)
(tap changer) overloading, $40,000.00 -
unbalanced 3-phase $70,000.00;
load, replacement $80,000.00 -
blocked/restricted cooling $140,000.00.
tubes, and fluid level.
Motors/Generators Overheated bearings, unbalanced Defective bearings causing damage
load, shorted or open windings, to iron and/or windings. Defective
heating of brushes, slip rings and brushes, causing damage to slip
commutators, rings or commutators. Resultant
overload/overheating, blocked damage to windings. Damage to
cooling passages. driven object. Motor rewind
(5000HP) $50,000.00 -
$100,000.00; replacement
$1000,000 - $200,000.00. Safety
considerations.
Emergency Poor battery terminal connections, Loss of stand-by power for essential
Power - dead cells in batteries, defective or services - hospitals,
Stand-By Generators, inoperative contactors or stand-by telephone
Batteries, Terminal switches. systems, computers, etc.
Connections,
In an issue
Contactors, of The Locomotive, by risk insurance company, Hartford Steam Boiler, they discuss
Automatic
statistics of Miscellaneous Electrical Apparatus (MEA) failures their clients have experienced over
Stand-By
Switches.
the previous fifteen years. Of the top ten causes of electrical failures, connection problems are
number one. The key method chosen to identify these problems is infrared thermography. They
say, "An infrared thermographic survey should be performed annually in commercial buildings as
well as manufacturing plants. All cable runs, bus ducts, distribution panels, motor control centers,
etc. should be checked for hot spots or heat imbalances". "This can identify loose connections,
overloads, unbalanced loads, and high neutral currents, that need to be corrected".
Connections- Poor connections are the most frequently found problem on an electrical system. It
has been found that routine preventive maintenance on connections does not cure the connection
problems, and normally creates additional problems. Routine inspection with a thermal imager
lets you know exactly where you problem is, and allows you to schedule maintenance on the real
problems.
Return on Investment
The cost of implementing an infrared condition monitoring program and as the return on
investment will vary with the size of facility, complexity of the program, and whether infrared
equipment will be purchased, rented or a service hired.
Most utilities and industries recognize that infrared electrical inspections are a key element to
providing electrical system reliability. For a large organization purchasing equipment and setting
up an in-house infrared condition monitoring program is economically justifiable. Many companies
report a complete payback the first time the instrument is used. For example, during the initial
inspection at a metal smelter, a hot contactor was found in their main substation which, if not
found, would have brought much of the process to a halt costing hundreds of thousands of
dollars. On the average, with a trained person, the return on investment is approximately 3
months to one year.
Smaller industrial facilities and commercial building owners can set up an infrared inspection
program by using an infrared service company. The return on investment in this situation is also
excellent. For example, at one hospital, a one day infrared inspection identified problems that
could have cost $12,800.00. Some of the problems were an overheated breaker supplying power
to the hospital data processing center; another breaker supplying two elevators; and a badly
corroded connection in the breaker of a 50 hp motor.
Another example at a plastics manufacturing plant where an infrared inspection revealed
numerous loose, dirty and corroded connections throughout the plants main electrical distribution
system. A "worse case" incident in this plant may have resulted in a $12-22,000 direct damage
loss, with a 25% production loss for 3 - 4 days, as compared with several hundred dollars for
minor repairs, and a few hours downtime for cleaning, replacing and tightening connections. If
this is compared with a typical rate for a one day inspection at $850.00, the payback is
substantial.
Start the Program off on the Right Foot
It is simple enough to purchase an infrared instrument, all vendors are willing to accommodate
you. There is much more to establishing an effective infrared condition monitoring program than
just buying a piece of equipment. We have found that most programs fail because the new
untrained and inexperienced operator goes into the plant, finds some "hot spots", misinterprets
them as problems, repairs are initiated only to find no problem exists. Both the operator and
management lose confidence and the equipment is shelved. For example, a newspaper hired an
infrared service company to evaluate the bearings on their printing press. A hot bearing was
found and the main printing press was shutdown, this severely interrupted production. The
bearing was removed and it looked was like new! Unfortunately infrared thermography took the
bad rap, not the untrained and unskilled thermographer.
In one of our recent Level I thermography courses, a student was showing some of his reports
with "hot spots" on an overhead line. At the end of the course, we asked the student to show his
reports again so that the class could evaluate them, he refused. The reason for refusal was he
realized most of the "hot spots" were not problems at all but were reflections, solar gain or
variations in emittance only. He had been doing infrared inspections for 2 years prior to taking the
course!
Training
If maximum benefits are to be achieved from your investment in this powerful, cost reducing
technology, a commitment must be made to provide proper training for the operator. If you are
going to hire an outside service you must make sure their operators have received and are
continuing to receive training and upgrading, just as you would expect from any one coming to
your facility to perform other inspection procedures such as x-ray, ultra sound, liquid penetrant
etc. Many companies now require thermographers to have a Level II thermographer standing.
Elements of a typical training course include infrared theory and principles, basic heat transfer
theory, operation of infrared equipment, how to conduct inspections in facilities and temperature
measurement techniques. Training in how to conduct inspections should include what false
anomalies to look out for, how to analyze the information and to prepare a report.
With a properly trained individual your infrared condition monitoring program will be off to a great
beginning. A trained thermographer will be able to properly diagnose temperature related
equipment problems and develop trends to predict equipment failure.
Conclusion
Even though there is effort involved in establishing a program such as this, the benefits are well
worth it. Properly implemented and maintained, infrared condition monitoring as a part of a total
predictive maintenance program can increase reliability and improve operating profit. Infrared
thermography will assist in determining equipment and facility maintenance priorities, enhance
operational safety and contribute to a stronger bottom line.
