Electrothermography en

Electrical thermography
Product application

2/37Testo AG, Electrothermography
Introduction
Electrical thermography is used to detect thermal
conspicuities.
A load current flows through electrical
installations and equipment:
• “Natural” internal resistance
• Transfer resistance at the connection points
Depending on the voltage, the electrical current
can be life threatening.
 Special safety aspects
Thermal load in a switch cabinet
Caution! Electrical installations can
be life threatening.

Measuring tasks
Thermographic measurements at all voltage levels:
• Low, medium and high voltage switchgear systems
• Overhead power lines
• Transformers
• Compensation systems
• Electrical drives
• Control cabinets
• Electric drives
Main measurement tasks: Locating faulty electrical connections and detecting
any overloads on lines and motors.

Target groups
The mentioned measuring tasks can be allocated to the
areas of activity of certain people:
• In-house technicians
• Electrical experts
• Company electricians
• General electricians
This results in the following Testo target groups:
• Facility management services
• Professional services
• Other contractors
• Industrial plant maintenance
• Plant maintenance high energy industry
• Electrical trade (TASC 431 „electricians‟) An electrician at work

Reasons for measurement
The aim is to inspect electrical systems in process and production plants to detect
thermal irregularities at an early stage in order to:
• prevent damage
• reduce operational disruptions
• prevent downtime and ensure system availability
• reduce maintenance and follow-on costs (avoid
urgent contracts)
• reduce energy costs
 Increased system safety
 Improved fire protection
Fire damage
caused by electrics
Low voltage main distribution board under load

Maintenance strategies
• Reactive maintenance („fire brigade strategy‟)
• Use of the resource until it fails
• In case of damage, it is necessary to react to unplanned events
• Technical diagnostics: Meaningless
• Preventive maintenance (time-dependant)
• Replacement of the resource at certain intervals
• It is often an uneconomical strategy: poor utilisation risk of failure
• Technical diagnostics: subsequent analysis of the resource‟s condition
• Condition-based maintenance
• Precise analysis of the resource‟s condition
• Maximum utilisation and events with greater cost-effectiveness
• Technical diagnostics: Key role

Eletrical basics – Electricity grid
(1) generate the power,
(2) transform the voltage,
(3) supply industrial companies with medium voltage,
(4) transform the voltage to the supply voltage
for small companies and residential homes (5) and (6)
Highest and high voltage
Supra-regional energy
transmission
Distribution of electrical energy
Medium voltage
Distribution into the low
voltage grid or supply of
large companies
Low voltage
Lowest voltage level
Supply of the
households
Power supply based on
Germany as an example

Electrical basics – Electricity grid
Substation:
• Transmits electrical energy over several voltage levels
• Connects power lines with different voltage levels
Transformer station:
• Components: Transformer, medium voltage switchgear system
and low voltage distribution board
• Transforms the electrical medium voltage of the regional
distribution grid into the low voltage used by the local grid
 Difference: Size of the system
Substation
Transformer station

Electrical basis – Electricity grid
Distributor:
• Known as junction boxes or fuse boxes
• Closable boxes containing fuses and switch elements for
distributing electrical power
• Main distributors and sub-distributors
Home junction box:
• Connects homes to the public power grid (local grid)
• Transmission point from the grid operator‟s
distribution grid to the consumer system
Junction box at
the roadside
Main distributor Sub-distributor
Home junction
box, old
Home junction
box, new

Switch cabinet:
Electrical components of a system that are not
directly attached within or to the machine
Bus bar:
Arrangement of cables for the central
distribution of electrical energy
Contactor:
Electrically-controlled switch
for large amounts of power
Circuit breaker:
Special switches that also
withstand extreme loads
Electrical basis – Electrical installations

Standards and directives in Germany
DIN VDE 0105-100: ‘Operation of electrical installations’
All matters relating to the operation of and all work on, with or near electrical installations
BGV A3: The accident prevention regulation
Inspection of the electrical devices used in the companies
Successors: TRBS 2131 and BetrSichV
TRBS 2131: The Technical Rule on Operational Safety
Specific information about how the requirements of the Operational Safety Ordinance
(BetrSichV) can be observed
BetrSichV: The Operational Safety Ordinance
Regulation of the provision of resources by the employer

Standards on electrical thermography
DIN 54191: ‘Non-destructive testing – thermographic testing of electric installations’
• Specifies how a thermographic system inspection should be carried out
• Defines terms within the field of electrical thermography
• Defines the minimum requirements on IR cameras
• Regulates the classification of inspection results
• Defines the minimum contents of an inspection report and describes how to handle
the inspection results
CNPP DTG.06.090 - Thermographie Infrarouge - Controle d'installations electriques
Risk assessment, risk evaluation and development of safety regulations and
procedural instructions
 Minimum technical and functional requirements for the thermal imagers

German Property Insurers’ Association
(VdS) Directives (CFPA)
Directives on electrical thermography
VdS 2858: „Thermography in electrical installations‟
Leaflet: Benefits, typical fields of application and
importance of thermography
VdS 2859: ‘Directive for the accreditation of experts for electrical
thermography (electrical thermographers)’
• Qualification requirements for electrical thermographers and
minimum technical requirements for suitable camera systems
 Certification is possible

VATh-Richtlinie: Electrical thermography
• Training requirements for electrical thermographers as well as requirements relating to
health and protective equipment
• Description of how to conduct an electrical thermographic measurement
• Minimum requirements for thermal imagers used for electrical thermography
• Minimum contents of the evaluation document
• Fault groups and temperature classes
SK 3602: ‘fire clause’
Instruction that electrical installations must be inspected using an infrared thermometer or a
thermal imager to check for any conspicuous temperature values
(The Directive on the fire clause is VdS 2871 - „Inspection guidelines according to clause 3602‟)

Application knowledge
Several influencing factors and important application basics:
• Influences on measurements
• Limit temperatures
• Defect definition
• Defect classes
• Measurement of small objectives
• Calculation of the measurement spot
Basic safety rules:
• Workplace safety
• Protective distance
Safety always plays a decisive role!

Workplace safety
When inspecting an electrical installation, the
following points must therefore be observed in all
cases:
• ONLY approach electrical equipment IF ACCOMPANIED
by an electrician
• Familiarize yourself with the safety regulations on site
• Keep a SAFE DISTANCE from all electrical installations
• DO NOT TOUCH! Work on electrical installations must
only be carried out by authorized specialists.
Proper thermographic
inspection
Basic rules of
operational safety
Electric arc injury

Protective distance
VDE, employers‟ liability insurance associations, DIN:
Definition of safe distances  Ensures safe work with energized parts
Safe distance
= Minimum required distance between
the energized part and the
thermographer
Nominal
voltage
Safe distance to be
kept by electricians
< 1.000 V 0,5 m
1 kV - 30 kV 1,5 m
30 kV - 110 kV 2 m
110 kV - 220 kV 3 m
220 kV - 380 kV 4 m
Info: When using thermography on overhead power lines,
a consultation with the line operator is essential.

Influences on measurements
Surface of the measuring object:
• Object’s surface properties
Measurements are often taken on bare metals (cables)
 The emission level must be carefully determined.
If necessary, an emission tape can be used.
• Specular reflections
Reflection?
Real
temperature?
Scanning the measuring
object with thermal imager
Emission tape
This method only works
if the installation is not
energized!

Practical information for the measurement
• Measure on the isolator – this usually has an emission level of e = 0.9
• Measure the „cavities‟ (e.g. the gaps next to the terminals) – these behave
similarly to black body radiators (e = 1)
• Measure painted, dusty, smudged or otherwise dirty points – these usually have
a good emission level (e = 0.95)
• Use stickers that are already available (e.g. type plates) as a
reference radiator for determining the emission level
• Most important rule: NEVER measure the bare terminal
– this produces nearly all the time a false measurement result!
Influences on measurements

Limit temperatures
Limit temperatures:
• When analyzing the condition of equipment with a thermal imager, component-specific limit
temperatures must be considered.
• These are stipulated in standards, directives and technical specifications
Thermal weaknesses should be defined and allocated to defect classes.
Examples:
PVC- insulated cables (in acc. with VDE 0207):
Limit temperature ≤ 70 °C
Copper bars (in acc. with DIN 43671):
Limit temperature ≤ 105 K
Ambient temperature ≤ 50 °C
Plastic and other non-metals:
Limit temperature ≤ 50 K
Ambient temperature ≤ 40 °C

Defect definition
Depending on the type of installation to be inspected,
there are different “normal conditions”.
When defining possible defects, it is also important to
determine the current load under which the
installation is inspected (operating current lb).
The „nominal current‟ (ln) of the installation is usually
defined as a reference.
Example criteria that can be used to evaluate the
condition:
• Permissible temperatures according to the relevant
product standards
• Visually detectable areas of weakness or damage
• Temperature differences of any kind
Evaluation criterion: „Temperature
difference between the cables“

Defect classes
Defect classes:
When defining the defects, the possible defects are divided into
several classes:
 For further procedural instructions for external
thermographers
 and as a yardstick for in-house electricians
Defect classes in acc. with VdS criteria (see also VATh Directive):
Defect class 1 0 K < ∆T < 10 K
Defect class 4 ∆T > 70 K
No measures
Rectify weakness on occasion
Maintenance within six months
Acute danger, isolate and rectify the defect as
soon as possible, reduce load if necessary

Measuring small objectives
Particular field of application: Electronics development
• Electronic components are becoming ever smaller and therefore being positioned on circuit
boards more compactly
• Heat development plays an important role
 Can impair their ability to function in the long term
• When used on microelectronic components in particular, the resolution (determined by the
detector size and lens) is decisive:
The testo 890 can be used to measure
the smallest structures of just 113 μm
(that equates to 0.113 mm!).

The following generally applies to thermography:
The (real) measurement spot should never be larger than the object to be measured.
The size of the measurement spot depends on the field of view (IFOV) and the distance
from the measuring object.
The IFOV value is determined by the used imager
system and is indicated in mrad.
For example, an IFOV of 3.5 mrad, specifically means:
At a distance of 1 m, the imager can still measure an
object with an edge length of 3.5 mm.
For the smallest measurable
object (IFOVmeas), there is a rule of thumb:
IFOV x 3 ≈ IFOVmeas
In our example, the smallest measurable
object has an edge length of
3 x 3.5 mm = 10.5 mm.
Calculating the measurement spot

Measuring technology
The following device requirements have proven in practice to enable good
measurement results for electrical thermography:
Spectral range 8 - 14 μm
Temperature measurement range - 20 … +500 °C
Range of application - 10 … +40 °C
Design
A rotating fold-out display is beneficial as measurements can be
taken in installations that are difficult to reach.
Lenses
Different lenses are required depending on the measuring task. For
measurements on high voltage installations, telephoto lenses of
between 12° and 7° must be depending on the measurement
distances and imager technology
Thermal resolution ≤ 100 mK
Geometric resolution ≤ 2 mrad
Measuring accuracy, absolute: +/- 2 K

Measurement preparations
The following points should be considered in preparation for the measurement:
1.Is the area to be inspected visually accessible?
2.Check whether there are temperature specifications or comparative measurements for
the measuring object that describe its normal condition.
3. Put on personal protective equipment. Other
equipment such as ladders or a power supply
may also be required.
4. Thermographic inspections must be reported:
a safety briefing and approval for the work
must be provided by the company
management or responsible departmental
manager.
5. Set the right emission level and RTC on the
measuring instrument to minimize
measurement errors.
With glass pane
Without glass pane

Measuring tasks
Typical measuring objects in the field of electrical thermography are:
• Junction boxes
• Contacts/ connections
• Resistances
• Cables
• Contactors
• Power distributors
• Transformers
• Substations
Typical reasons for temperature spikes and deviations are:
• Uneven load distribution
• Overloaded systems/ excessive power consumption
• Increased resistance in the electrical circuit due to loose contacts or rusty connections
• Defective isolators
• Wiring faults
• Undersized components (e.g.: fuses)

Measurement on switch cabinets
Measurement on switch cabinets, junction boxes and
fuse boxes
• The object to be measured must be „thermographically
accessible‟.
• This means that any switch cabinet to be inspected has to
be opened for the measurement
• and any contact protection muss be removed so as to
provide an unobstructed view of the components to be
inspected
• Only surface temperatures can be visualized using
thermography
• It is not possible to detect the heat sources behind glass
or plastic panes.
• When inspecting the switch cabinets, weak points on
sensitive components are indicated by increased
temperatures known as „hot spots‟.
IR image for a switch cabinet

Measurements: Fuse boxes
Medium fuse under load
(normal mode):
hot spot = 25 °C
∆θ ≤ 7 K
 no unusual heating,
everything fine
70,0°C
142,0°C
80
100
120
140
Inspection of a
fuse box
Fuses on a 500 V
distribution board
Super-heated fuse block,
T ≤ 145 °C (∆θ ≤ 49 K)
Ib = no measurement
(Ib = operating current)
 Defect class 3
(maintenance within six
month)

Measurements: LV HRC fuse, power distribution
Faulty lower fuse contact
„L2‟: T ≤ 129 °C (∆θ ≤ 72 K)
Ib = 112 A (90 % In)
(In = nominal current)
 Defect class 3
LV HRC fuse block,
plug-in 500 V main
distribution board
Faulty output terminal
„L1‟: T ≤ 49 °C (Δθ ≤ 18 K)
Ib = 139 A (75 % In)
 Defect class 2
Be careful with reflections
on bare metals!
(See arrow)Output cable on
500 V main
distribution board23,0°C
49,0°C
25
30
35
40
45

Measurements: Junction boxes, cable floors & vaults
Thermography on a
transportable
junction box
Result: faulty cable
coupling,
T ≤ 142 °C (Δθ ≤ 86 K)
Ib = 137 A (69 % In)
 Defect class 3
22,0°C
39,0°C
25
30
35
Cable temperature
T ≤ 40 °C
Cable vault low
voltage switch room

Measurements: EMCR systems, electric motors
Diode overheats:
T ≤ 97 °C (∆θ ≤ 22 K)
 Defect class 2
Operating temperature:
T = 40 °C
 Normal condition
Pump motor for the
hot water circuit
51,0°C
96,0°C
60
70
80
90 Control card in an
EMCR switch cabinet

Measurements: High voltage systems, transfomers I
Tension terminal:
the „current loop‟ is
connected to the current
cable via a terminal
connection
 Inductive heating of the
bushing
1,5°C
42,0°C
5
10
15
20
25
30
35
40
14,5°C
31,0°C
15
20
25
30
Transformer (110 kV on 6 kV)

Measurements: Transfomers II, circuit boards
Circuit board
13,5°C
65,0°C
20
30
40
50
60
Transformer
20 kV / 0.4 kV
Damaged bus bar
connection „L3‟ on the
secondary side:
T ≤ 70 °C (∆θ ≤ 46 K)
Ib = 73 A (50 % In)
 Defect class 3

Measurements: Photovoltaic systems
Solar energy systems deliver their
maximum performance in bright
sunshine.
Thermal imagers can be used to
monitor photovoltaic systems of all
sizes in a way that is wide-ranging,
contact-free and exceptionally
efficient.
Photovoltaic systems

Evaluation: Testo IRSoft
Testo IRSoft reporting software
• Comprehensive analysis options
• Clear structure and intuitive layout
• Several templates for report generation
• Report designer
 Thermographers and the system
operators can prove that the
measurements have been conducted

Evaluation: Report generation
A standard report for electrical thermography should
contain the following information:
1. Name of the thermographer conducting the
measurements and the other people involved
2. The imager system used
3. The inspection date
4. The site of the inspected company
headquarters, plant or energy supply company
5. The aim of the work
6. For outdoor measurements: the weather
conditions (including relative humidity in %, wind
in m/s and global radiation in W/m²)
7. Evaluation and results
Note:
The Testo IRSoft PC software contains
a report template that is specially
tailored to industrial and electrical
thermography for the quick and simple
creation of thermographic reports.

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