substation equipment testing
TRANSCRIPT
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Substation Equipment Testing
FECA Engineers ConferenceClearwater, Florida
June 12, 2013
Andre Lux
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Confidential Notice
Doble Engineering (Doble) hereby grants the recipient (you) the right to retain thispresentation and materials included within (the Presentation) for privatereference. No other rights, title, or interest, including, but not limited to, the rights tocopy, make use of, distribute, transmit, display or perform in public (or to thirdparties), edit, translate, or reformat any portion of the Presentation are hereby orotherwise granted and shall remain expressly reserved by Doble. Youacknowledge and agree that such limited license is expressly conditioned upon
your acceptance of the terms herein. You further agree that, in the event of yourbreach, Doble will suffer irreparable damage and injury for which there is noadequate remedy at law. As such, Doble, in addition to any other rights andremedies available, shall be entitled to seek injunction by a tribunal of competent
jurisdiction restricting you from committing or continuing any breach of these terms.
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Tests are Performed to confirm the integrity of the equipmentor a part of it. These are performed:
At various stages during the manufacturing process
At final factory acceptance
As on-site commissioning and acceptance
As part of routine maintenance and diagnostics
After system events
As part of end-of-life determination and de-commissioning
An important part of any equipments life cycle
Test Significance
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Average age (North America,typical utility) is 3540 years.
On order of book life On order of anticipated
design/expected life(whatever that means)
Condition varies from utilityutility, and from one
transformer to another, butmany are of marginalcondition and getting poorer.
Replacement programs cantkeep up with escalating ageand degrading condition.
Life extension programs aimto prolong life (age) evenfurther.
Why all this focus on transformers?
0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
375
400
0 -10 11 - 20 21 - 30 31 - 40 41 - 50 51 - 60 >60
NumberofUnits
Age Group
Typical Transformer Population, Large
North American IOU
Number of TD Transformers
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Potential Failure Impacts:
Personnel safety Environmental impact
Significant collateral
damage
Long outage times
Degrading reliability
Long lead times for
replacement
Significant monetary costs
associated with unplanned
outages.
Why all this focus on transformers?
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1. Overall (Transformer) Power Factor and Capacitance
2. Bushing Power Factor and Capacitance
3. Transformer Turns Ratio
4. DC Winding Resistance
5. Excitation Current6. Oil Quality
7. Dissolved Gas Analysis
8. Leakage Reactance
9. Sweep Frequency Response Analysis10. Partial Discharge
11. Visual Inspections
Typical Transformer Tests
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Each test targets a different area/component/accessory of the
transformer: Core
Winding
Insulating fluid
Solid insulation Tap Changer
Bushings
Controls
Tank
The main goal is to detect a developing condition (failure) andtake corrective action as appropriate.
Each test targets a particular potential failuremode/aging/deterioration mechanism
Test Significance
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Large IOU Failure History, 19882008 (96 failures)
What are the most common failure modes?
Through-Fault
Winding
Bushing
Gassing
Leads
Lightning
Tap Changer
UnknownVandalism
Leaking Valve
Design Problem
Overheating
26 %
20 %
15%
13%
8%
5%
4%^4%
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What is Power Factor?
Power factor is a measurement of the efficiency of
insulation system.
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Basic Power Factor Circuit
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The Term Power Factor Describes:
The phase angle relationship between the applied voltage acrossand the total current through a specimen.
The ratio of the real power to the apparent power.
The relationship between the total and resistive current
The efficiency of a power system in terms of real and reactive
power flow
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Insulation kV mA Watts % P.F.
CH + CHL 10 28.5 1.45
CH 10 7.05 0.38 0.39
CHL (UST) 10 21.5 0.95 0.32
CHL 21.45 1.07 0.36
CL +CHL 2 39.5 5.5
CL 2 17.65 2.85 1.18
CHL (UST) 2 21.5 3.55 1.2
CHL 21.85 2.65
FPE, 3-, 2-winding , -Y transformer
13.8/4.3 kV, 7 MVA
High CL % P.F. & disagreement between HV & LV CHL %P.F.s
Localized moisture/contamination in the L.V. winding
Problem Revealed in LV Winding
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Westinghouse, 3-Phase, 345/19 kV, 343 MVA Shell-Form Generator Step-up Transformer
Test Date CH (%PF) CL (%PF) CHL (%PF)
1972 0.50 0.59 0.47
1975 1.60 0.57 1.44
Routine Test Sister unit was tested & did not indicate a
similar increase.Other tests performed:
TTR, DC Winding Resistance, Exciting Current, TCG, DGA, Oil P.F. (No problems indicated)
Transformer Defect Oil-Pump Problem
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Transformer Defect Oil-Pump Problem
Results of Internal Inspection:
Oil pump No. 8 (located in the area of the - C H.V. bushing) wasseverely deteriorated. The outer bearing sleeve, the pump housing, &
1/2 the width of the impeller blade were destroyed.
After clean-up & repair, the unit was returned to service. It failed 4
months later. It is believed that the fault resulted from the magnetic
contamination introduced previously.
1 other pump was found to have appreciable bearing wear & the
remaining 7 pumps had varying, lesser degrees of bearing-wear.
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Dielectric Capacitance
C = CapacitanceA = area of electrodes = Dielectric constant
d = Distance between electrodesAll of these variables are Physical Parameters
AdC= Aed
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Significance
Indicate a physical change
Bushings - shorting of capacitive layers
Transformers - movement of core/coils
Arresters - broken elements Suggested Limits
+ 5% - Investigate
+ 10% - Investigate/remove from service
Changes in Current/Capacitance
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Significance of Measured Capacitance
Interwinding (CHT) capacitance of anautotransformer.
Test Date 20C % PF Cap (pF)
1965 0.20 2,650
1968 0.29 2,756
1974 0.29 3,710
1982 0.32 5,100
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Capacitance change can indicate movement and/or deformation of transformer windings.
C=Ae
d
What other tests would
confirm this?
Leakage Reactance
SFRA
Significance of Measured Capacitance
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Bushing Tests
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Condenser Bushing Components
Center Conductor
Sight-Glass
Liquid or Compound Filler
Insulating Weather shed
Main Insulating Core
Tap Insulation
Tap Electrode
Mounting Flange
Ground SleeveTapped Capacitance-Graded Layer
Lower Insulator
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Condenser Bushing Construction
Voltage is stressed equally across each condenser layer of
C1insulation
Relationship between C1and C2 dependent upon desired
voltage at the tap when in service
Main Insulation C1
CA = CB = CC = CD = CE = CF= CG = CH = CI = CJ
V1 = V2 = V3 = V4 = V5 = V6 = V7 = V8 = V9= V10 Tap
Electrode
CKCenter
Conductor
Line-to-Ground Voltage for Type A and T
Grounded
Layer/Flange
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Typical Condenser Bushing Construction
Core Wind
C2 Plate
Foil
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ABB O+C Construction
C2 Plate
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ABB O+C, 27 kV
Conductors
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Bushing Tests
Ungrounded-Specimen Test
Center Conductor to Tap, C1
Tap Insulation Test
Tap to Flange, C2
Hot Collar TestExternally Applied Collar to Center Conductor
Overall
Center Conductor to Flange
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Test kV I (mA) Watts 20C %PF
10 1.313 -0.007 -0.053
ABB Type O+C 230 kV bushing
Staining of the Lower Insulator
E it ti C t & L
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Excitation Current & Loss
Exciting Current and Loss Factory Tests at Rated Voltage.
Field Tests at the Lesser of Rated Voltage or Highest
Capability of the Test Set.
Simple measurement of single-phase current on one side ofthe transformer, usually the HV side, with the other side left
floating (with the exception of a grounded neutral).
The tests should be performed at the highest possible test
voltage without exceeding the voltage rating of the excitedwinding.
Magnetic Circuit and Winding Tests
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Excitation Current and Loss
Excitation Current Tests Can Identify Problems in the Iron Core, Windings ,
and Tap Changers
Core
Abnormal core assembly
Windings
Turn-to-turn shorts
Turn-to-ground shorts (groundedwindings)
High resistance turn-to turn or
turn-to-ground shorts
Tap Changers
Mechanical failures
Auxiliary transformer problems
C &
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Excitation Current & Loss
What is Excitation Current?
~E1
Iex
1:1
+
-E2
+
-
Excitation current is the current that flows when the winding of the
transformer is energized under no-load conditions. It supplies the energy
necessary to create the magnetic flux in the iron core.
E i i C & L
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Excitation Current & Loss
When there is a Fault on the Secondary Winding
1:11
H1
H0
+E1
-
HV
LV
The primary current increases due to the current through the short-circuited turns.
Excitation Current & Loss
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Excitation Current & Loss
Examine phase patterns
Typical pattern is two high similar results on the outer
phases and one lower result on the center phase
however there are exceptions due to core design, etc.
Residual magnetism can affect results DC tests can magnetize core
Can be a result of being de-energized from the
system
Subsequent tests should be performed at same testvoltage and with same connections
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Current (ma) Losses (watts)
H3-H1 H1-H2 H2-H3 H3-H1 H1-H2 H2-H3
Aug 7 2001 6.96 3.12 75.76 42.85 19.36 735.1April 10 2000 7.03 3.27 7.66 43.98 19.94 46.87
Jan 19 1999 7.172 3.4 7.36 44.69 20.64 45.67
May 5 1994 7.64 3.46 8.05 47.72 20.96 48.99
A raccoon came into contact with the H3 bushing
which took out the bushing and an associated
voltage regulator. The bushing was replaced,
regulator cleaned up and the equipment was putback into service after a series of tests. Shortly
thereafter, the transformer was noted to be running
hot.
A DGA and TCG test was performed with very high
results. %PF did not show any major changes but the
Iex did.
Winding Resistance
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Winding Resistance
Check for abnormalities due to loose connections, brokenstrands, and high-contact resistance in tap-changers.
Interpretation of results is usually based on a comparisonof measurements made separately on each phase in the
case of a wye-connected winding or between pairs ofterminals on a delta-connected winding.
Comparison may also be made with original datameasured in the factory. Agreement to within 5% for any ofthe above comparisons is usually considered satisfactory.
It may be necessary to convert the resistancemeasurements to values corresponding to the referencetemperature in the transformer test report
Magnetic Circuit and Winding Tests
Transformer Turns Ratio
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Transformer Turns Ratio
Ratio of the number of turns in a higher voltage winding
to that in a lower voltage winding Factory and Field
Low Voltage Method
High Voltage Capacitance Reference Method
Confirm nameplate ratios Detect short-circuited turn-to-turn insulation
Find open-circuited windings
Find problems with tap changer connections (DETC &
LTC)
Mechanical Integrity Diagnostics
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Mechanical Integrity Diagnostics
Frequency Response Analysis (FRA)
Leakage Reactance
Capacitance
Excitation Current
These independent diagnostic methods have their place inascertaining transformer condition
Frequency Response Testing
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Purpose
Assess Mechanical Condition of Transformers (mechanical
distortions)
Detect Core and Winding Movement
Due to large electromagnetic forces from fault currents Winding Shrinkage causing release of clamping
pressure
Transformer Relocations or Shipping
Frequency Response Testing
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Test Sequence
Measures the response Voutfor a low voltage sign Vinthatvaries in frequency. For two winding three phase transformer 9 tests
Open circuit test: one per winding, per phase (6 tests)
Short circuit test: one per phase (3 tests)
The analysis plots the ratio of the transmitted voltage Voutwaveform to the applied voltage waveform Vinin db.
Low voltage Signal 20hz to 2Mhz
in
out
V
VdB
10log20
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SFRA - Sweep Frequency Response Analysis
Core Tap windings
Main windingClamping structures
Tap leads
< 2 kHz
2 kHz20 kHz 20 kHz100 kHz
100 kHz400 kHz
400 kHz2 MHz
Case Study: Close in Fault
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Case Study: Close-in Fault
Capacity: 25/33/41 MVA
Voltage: 112/14.4 kV BIL 450KV
Entered service 1996 (10 years old)
Transformer saw a number of close in
faults, while attempting to isolate a cable
problem
The bus attached to the low side caught fire No surge arresters on low side
Can the transformer be placed back
into service?
Overall Capacitance and Power Factor
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Overall Capacitance and Power Factor
PF Results are acceptable
CapacitanceUnknown because no precious overallresults.
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Exciting Current Results
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Per Phase Leakage Reactance
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3Ph Equivalent LR
O Ci i Hi h Sid
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Open Circuit High Side
O Ci it L Sid
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Open Circuit Low Side
Sh t Ci it
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Short Circuit
C St d L k R t
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Case Study Leakage Reactance
0.2 dB delta is significant here!
T Y L t
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Two Years Later
Fl id T t
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Fluid Tests
Why Measure Gases in Oil?
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Excellent indicators of incipient fault condition - Most
important diagnostic in the industry
Can help determine the materials involved
Severity of the condition - abnormal amounts
Detect of wide variety of conditions - most important test
Gas-in-oil analysis complex - not easily simplified for easyanalysis in all cases
Why Measure Gases in Oil?
K G A l i
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Key Gas Analysis
Condition
Key Gas
Arcing High concentration of hydrogen and acetylene, with
minor quantities of methane and ethylene.
Key gas - Acetylene
Corona Low-energy electrical discharge creates hydrogen and
methane, with lesser quantities of ethane and ethylene.
Key gas - Hydrogen
Overheated Oil Includes ethylene and methane, and lesser quantities
of hydrogen and ethane.
Key gas - Ethylene
Overheated Cellulose Carbon dioxide and carbon monoxide are evolvedfrom over-heated cellulose. Hydrocarbon gasses will
be formed if the fault involves an oil-impregnated
structure.
Key gas - Carbon Monoxide
Gases Produced during Overheating
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Gases Produced during Overheating
Temperature of Overheating Gas Chemical Symbol
Low Temperature (~120o ) Methane CH4
Ethane C2H6
Ethylene C2H4
High Temperature (>350oC) Acetylene C2H2
Combustible Gases Westinghouse 24 years old
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Combustible Gases Westinghouse 24 years old
Rating 115 kV, 40 MVA
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
1/1/89 9/28/91 6/24/94 3/20/97 12/15/99 9/10/02 6/6/05
Date
Concentration,p
pm
.
Hydrogen (H2)
Methane (CH4)Carbon Monox. (CO)
Ethane (C2H6)
Ethylene (C2H4)
Comb Gas
Acetylene (C2H2)
Overheating of Support Structure
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Overheating of Support Structure
Main Clamping Top Beam
Water Content
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Water content of oil and paper are related and can be described
using equilibrium curves
Dielectric breakdown voltage of the insulation system
Ability to overload
Temperature water vapor bubbles evolve from solid insulation afunction of its water content, with 2% water in paper can go up to
140C without risk of bubbles
Aging of the solid insulation directly proportional
Susceptibility to high relative saturation of water in oil and
formation of free water
Water Content
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Power Factor - Measure of dielectric losses, dielectric
heating, indicator soluble polar, ionic or colloidalcontaminants or aging byproducts
Color - Rapid change indicator of accelerated aging of the
insulation system
Interfacial Tension - Detects deterioration of oil in the early
stages of aging, affected by the polar contaminants
Acidity - Aging byproducts, accelerates aging of paper andcorrodes metal
Physical Properties and Inhibitor Content
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Viscosity
Should not change with aging
Important characteristic for cooling
Takes gross contamination, aging, or over processing to change
significantly Relative density
Should not change with aging
Simple periodic measure
Takes gross contamination, aging, or over processing to changesignificantly
Inhibitor Content - replenish when handling the oil
Physical Properties and Inhibitor Content
Partial Discharge
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PD diagnostics can be used to trend changes in the level
and severity of insulation degradation Once presentit dominates as its own inherent stress
degradation mechanism
Its an early warning signal and precursor to completeinsulation failure and breakdown
Early detection of PD is critical in the prevention of in
catastrophic failures
Partial Discharge
Types of PD
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Types of PD
Void/Protrusions in solidinsulation, cavity in liquids.
Surface discharge
Corona
PD Insulation Model
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The voids
capacitance CCis
part of the overalldielectrics capacitance
which includes the
remaining series
capacitance CBandshunt capacitance CA
The void has a
breakdown voltage VS
that once reached
across the void Ccwill
spark over (PD)
VS
CC
CA
CB
CACC
CB
=
Partial Discharge
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Causes of PD in insulation system:
Voids in epoxy resins, polymers, paper Bubbles in liquids/oils
Metal deposits, irregularities such as protrusions,contaminants
Electrodes and insulation surfaces and interfaces
Can arise through:
Poor design and manufacture
Damage of equipment e.g. Transport damage Poor installation processespoor workmanship
General ageing or deterioration of materials
g
PD Measurement on Transformers
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ValveConnector
Tank
Sensor Application Measuring Impedance
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Se so pp cat o easu g peda ce
PD Measuring Impedance for Bushing Tap Installation
Acoustics
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Acoustics are a valid technique for locatingPD but its thewrong approach for detecting PD due to low sensitivity of
the AE method and the fact that PD imbedded in thewinding will not produce acoustic pressure wavesdetectable on the tank wall. So no Acoustic Signal does notmean no PD and detection via HF-CT on the star point endwill only work for strong PD.
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Why Monitor Bushings?
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Why Monitor Bushings?
Bushing MonitoringGradual Increase
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Gradual deterioration over several month span.
g g
Bushing MonitoringSudden Increase
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The bushing was one of a type which had several failures around the world
recently.
A sudden variation in leakage current raised an alarm. Operations took the bushing off line and replaced ita tear down indicated they
had just hoursbefore catastrophic failure
g g
Transformer Test Summary
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Each test is sensitive to certain types of issues.
Motivation for testing should always be determinedbefore arbitrarily performing a variety of tests
Routine testing should provide owner with a high levelof comfort with transformer condition
Investigative testing needs to be more focused andthorough
Test results should always be scrutinized and takenseriously
Transformer Test Summary
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Planning discussions for contingencies are important in
making good decisions There are cases where some tests will fail to identify a
problem.
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Confidential Notice
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Confidential Notice
Doble Engineering (Doble) hereby grants the recipient (you) the right to retain this
presentation and materials included within (the Presentation) for privatereference. No other rights, title, or interest, including, but not limited to, the rights tocopy, make use of, distribute, transmit, display or perform in public (or to thirdparties), edit, translate, or reformat any portion of the Presentation are hereby orotherwise granted and shall remain expressly reserved by Doble. Youacknowledge and agree that such limited license is expressly conditioned uponyour acceptance of the terms herein. You further agree that, in the event of your
breach, Doble will suffer irreparable damage and injury for which there is noadequate remedy at law. As such, Doble, in addition to any other rights andremedies available, shall be entitled to seek injunction by a tribunal of competent
jurisdiction restricting you from committing or continuing any breach of these terms.