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LCM 500
LeakageCurrent
Monitor
Presented by
Michal Slodkiewiczwww.doble.no
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Overview of presentation
Motivation and background
IEC 60099-5 available diagnostic methods
Requirements
LCM 500 unit and attached accessories
Performing self-test of LCM 500 unit
Preparation database of surge arrester
Grounding of the LCM 500 unit
Deployment of LCM 500 accessories during measurement on-side
Risk assessment
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Motivation and background
The MOSA is a cheap and passive component, but protectingcrucial apparatus
Overlooked despite of severe consequences if it fails
MOSAs can age and fail due to a variety of reasons
May offer inadequate over voltage protection, especially ifthe rated voltage is selected to low.
Diagnostic indicator: Resistive leakage current increases withtime increasing risk of failure
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Why test Metal Oxide Surge Arresters?
Utilize the lifetime of the operating MOSAs.
Prevent arrester failures by replacing aged arresters
before breakdown.
Avoid disturbances and costly outages of the electric
power supply.
Reduce the risk for damages to other equipment, for
instance transformer bushings.
Increase the safety for the utility/maintenance staff.
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Mechanism for degradation of MOSA
Sealing defects
Discharging due to surface contamination
Overloading
Long term aging during normal service
Internal partial discharges
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Degradation of MOSA
One consequence of the degradation of the MOSA isan increase with time of the resistive component ofthe continuous leakage current
Increase in resistive leakage current will cause an
increase in power losses and hence increasedtemperature in ZnO-blocks
The resistive current may exceed a critical limitwhere the accumulated energy in the ZnO-blocksexceeds the energy capability of the arrester. Thearrester will then get thermally unstable and fail.
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An arrester failure may appear in different ways:
Arrester with porcelain housing may explode
The arrester can be causing an earth fault due to internalflashover
Aged or overloaded arresters may have reduced protectionagainst overvoltages, i.e. it is not protecting the apparatus
it is supposed to protect.
Degradation of MOSA
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Requirements for surveyed surge arrester
1. Metal Oxide Surge Arrester - MOSA
2. Separate grounding wire
3. Insulated base for each arrester
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Why use insulated base arresters and separate earth leads:
Gives complete control of arrester current leading to the ground
Allows an easy on-line in service condition assessment test of theMOSA. Without insulated base you have to take the arrester out ofservice for proper condition testing.
If a surge counter is present, the clip-on should be placed above thecounter to avoid circulating currents from the counter ground loop.
Requirements for surveyed surge arrester
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IEC 60099-5 Part 5 Selectionand Application Recommendation
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Method B2 is rankedto be the best fieldmethod for
evaluation of ageingand deterioration ofMOSA.
Properties of on-site leakage current measurements:
A HV-DC test iseffective but off lineand complex
IEC 60099-5:Available diagnostic methods
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If the MOSA is energized by a pure sinusoidal voltage
(fundamental frequency only), the capacitive leakage
current will show a fundamental component I1c only,
while the resistive leakage current will show both a
fundamental component and a 3rd harmonic
component (I3r) due to its nonlinear properties.
The resistive components are said to be generated
by the arrester itself (due to the not linear current-
voltage characteristic) and can therefore be used as
a measure for the arrester condition.
IEC 60099-5: Metal Oxide Surge Arresters
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IEC 60099-5: Metal Oxide Surge Arresters
If harmonics are present in the operating voltage, this will
generate a significant 3rd harmonic component in the capacitive
leakage current in the arrester.
This capacitive 3rd harmonic component will be added to the
3rd harmonic component resistive component and create a
measuring error.
The LCM 500 uses a compensation method where the capacitive
component generated by the operating voltage is eliminated.
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Typical Voltage - Current Characteristics
The resistive currentcomponent:
is typically 5-20% of the totalleakage current under normal
operating conditions
is a sensitive indicator ofchanges in the voltage-currentcharacteristic
depends on the voltage and
temperature
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Equivalent Circuit of ZnO -Varistors
It
Ic200-3000 A Ir
10-600AU
Ir=It-Ic
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Leakage Current Measurements
Measurement of the total leakage current example:
Itot increases with only 1,5%
when the resistive vector is
doubled
This small change in Itot is not
measurable at a mAmeter
I
U
Ic1= 100
Ic2=100
Usyst
Ir2=20
I2total = 102
Ir1=10
I1tot = 100,5
1
2
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Recalculation of leakage current
By using arrester system data and measuring the ambienttemperature and operating voltage at the same time as thecondition monitoring is performed, it is possible to recalculatethe leakage current data to a common reference of:
20 C and U/Ur=0.7
The resistive leakage current values will then beapproximately the same independent of the test conditions
by taking account of the ambient temperature and operatingvoltage, measurements performed under different conditions can
be directly compared, and the measured values will be a reliableindicator of the arrester condition.
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Influence of ambient temperature and system voltageon resistive leakage current.
Temperature andsystem voltage influence
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1. LCM500 unit2. Current Probe
3. Field Probe
4. 12V DC cable
5. Field Rod adapter6. Power supply cable
7. Antenna
8. Grounding cable
9. Current loop wire
10.USB A+B cabel
11.Field test cable
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LCM 500-Leakage Current Monitor
2
14
3
8
76
911
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5
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LCM 500-Leakage Current Monitor
Optional Accessory
Field Probe Rod delivered in separate transportcase. Rod is divided on 3 pieces for 1m each piece.
Cannot be used as a Hot Stick!
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Mains powersupply
Light diodes
LCD displayFour pushbuttons
Turning knob
External DCpower sypply
Power switch
Antenna input
Self test Communication ports
Select button
LCM 500 Front Panel
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LCM 500 Self-test outputs
FIELD
Simulated field probe signal to be
connected by coaxial cable (type RG58)
V.TRSF
Simulated voltage transformer signal to
be connected to the voltage transformer
adapter (optional accessory)
CURRENT
By connecting an electrical wire betweenthe two black connectors, a current loop
simulating total arrester leakage current
is created
Self-test outputs - perform function test of internal system
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LCM 500 Communication Ports
USB, RS232, Ethernet
By connecting data cables to one of above ports, the instrument cancommunicate with a PC using the enclosed Windows based data
management software LCMViewer.
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2-Clip-on current transformer CCT500:Measures the total current in thegrounding cable of surge arrester.
1-Field probe FP500 (antenna):Measures the capacitive currentfrom the electric field surroundingthe arrestor.
1
2
LCM 500 Wireless probes
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Performing self-test of LCM 500Circuit diagram
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MeasurementSystemTest
Teast:verifysystemSimul.:generatetestsignals
TestSimul. Main
LeakageCurrentMonitorLCM500
MeasSetupDbaseTest
MeasurementSystemTest
Connect arrester and
antenna test signalsto probe before startStart Main
Performing self-test of LCM 500
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LCM500
MeasurementSystemTest
Succeeded
Start Main
LCM500MeasurementSystem
TestFailedCONTACT
MANUFACTURERMeasured:Ir:205+/-8AIt:332+/-5A
Measurementin
progress
AquisitionstartedPLEASEWAIT!
>
Performing self-test of LCM 500
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Performing self-test of LCM 500
TROUBLE SHOOTING:
- Be sure that all connectionsbetween field test cablecrocodile clips are fastenproperly to Field Probe
- Observe that current loop is not invicinity or not around antenna
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Preparation of surge arrester inLCMViewer
i f i
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If you dont know therated voltage, thesoftware will recommend
a proper value based onsystem voltage andarrester type.
Define database of yoursurge arrester andtransfer this to the LCM500, use Add to LCMQueue button. Softwareautomatically will moveyou to Instrumenttab.
Preparation of surge arrester inLCMViewer
i f i
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Use Send Data to LCM
button in order send
data to LCM 500
instrument.
Preparation of surge arrester inLCMViewer
G tti ti
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1. Choose correct
ComPort for LCM 500
instrument.2. Use Test button to
check status of your
connection in Log
area.
Go to Instrument=>Setup, Logtab
Getting connectionbetween PC and LCM500
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Grounding of the LCM 500
The LCM 500 can be grounding in two ways:1.In laboratory testing or during charging battery by using
the power supply cable. Power supply plug has to be
connected to the local earth.
2.During field measurements grounding cable has to be
connected to local earth system in the substation.
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Grounding of the LCM 500
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Deployment of LCM 500 accessories
1. Gapless MOSA2. Insulated base
3. Grounding wire
4. Clip-on CT500
5. Counter
6. Field probe FP500
7. Arrester pedestal
8. Field Probe Rod9. LCM 500 unit
The Field Probe shouldNEVER exceed this limit
1
5
2
7
3
98
4
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Deployment of LCM 500 accessories
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LCM 500 Set-up Mode From Main Menu
LeakageCurrentMonitor
LCM500MeasSetupDbaseTest
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LCM 500 Set-up Mode From Main Menu
Language: only English.
Dump mode: ON is for use incontinuous measurements. Themeasurements will be dumpedcontinuously to the serial port. Whena PC with proper software is
connected the measurements can bedownloaded.
Time: battery backed real-time clock.
Backlight: time in sec. the light in the LCD display is turned on.
Baudrate: baudrate defines the data transfer speed duringcommunication with a PC and can be set to 9600 bit/sec. or 57600bit/sec.
Leanguage:English
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LCM 500 Measuring mode
LeakageCurrentMonitor
LCM500Meas SetupDbaseTest
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By pressing the MEAS button inthe main menu, the screenpresented on the left appears.
When database is transferred fromthe software, you will get access to
it in this menu.
If you press Setup in the above menu, you will enterthe measuring set-up mode
Station/Loc/Arrester:Nostationchosen
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Station/Loc/Arrester:Nostationchosen
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LCM 500 Measuring set-up mode
Mode: In field test 3-phase mode should beset. 1-phase mode is for use in lab tests.
Temp: Choose between manual orautomatically setting of the temperature.
Line: The line-to-line operating voltage.
Choose between manual or automatic. Manualsetting is the most common. Automatic is forconnection to a PT combined with an adapter.
Transf:This ratio defines the voltage divider ratio of the voltage transformer
that can be connected for automatic voltage measurements. The ratio can be setfrom 1:1 up to 1:10000 in steps.
Mode:3-phase
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Station/Loc/Arrester:Nostationchosen
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AutomeasurementStart :2011.02.10
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Station/Loc/Arrester:Nostationchosen
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LCM 500 Perform a Measurement
If the measurement runs ok, the measuring result will be shown in
the LCD display like the example below.
Ircorr-total corrected resistive leakagecurrent with standard deviation(corrected value with regard to ambienttemperature and line voltage).
It-total leakage current
Ir-total uncorrected resistive leakagecurrent.
In addition the ambient temperature and the line voltage usedduring the measurement are displayed.
To save your measurement, press the Storebutton
90005STAA1PHR
Ircorr: 159AAnt.3rdharm.:0.8%It:587AIr: 89A24C 68kVRunStoreNewMain
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1. Click the Read
Measurements from
LCM to make the
transfer take place
2. Mark your SurgeArrester than use
Apply Measurements
(Auto only), all
performed
measurement will be
add to existing Surge
Arrester data.
Go to Instrument=>Measurementfrom Instrumenttab
Download the measurements
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Leakage Current Plot
The LCMViewer lets youcreate a graphical statisticalpresentation of your SurgeArrester measurements.
Easy way to compare
measurements for groupsof arressters.
Test Conditions
You can observe factor oftemperature, voltage andcontaining of 3th harmonicfrom taken measurements.
Structure and data analysis
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Arrester Test Reports
LCMViewer will generatean arrester report ineither Excel or pdf files.
You can select content ofinformation to be includedin the report.
You can use your companylogo.
Structure and data analysis
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Doble LCM - Your best choice!
You should choose:
A simple in-service method
Doble LCM takes less then 5 minutes perarrester, in service
Reliability method verified by independentsources
LCM method recommended by arrester IECstandard
Convincing references
Developed together with ABB!
Now in Siemens surge arrester monitoring catalog!
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Risk Assessment
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Evaluation of the Arrester Condition
Based on the level and development of resistive leakage current
Ir over time: Trend analyses
In general look for increasing trend
Perform a baseline reading when the arrester is new. If Ir increases by 3-4 times(typically), it is indicating severe aging
Compare the value to maximum recommended leakage current values
given by arrester manufacturers ABB and Siemens provide max values
Compare Ir to arresters of same design and type
The three phases in a line or bay
All similar arresters in the grid
Test interval
In beginning once a year to get knowledge about trend. Later on each 3-5 year
It depends on age of the arresters, the regional lightning activity, thesituation of overvoltages, quality of the apparatus etc.
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Eliminating possible sources of error
Some steps to consider in the final evaluation:
1. If total current It and resistive current Ir are unrealistically high:
Check if the arrester base and the arrester grounding is inorder. Circulating currents??
2. If Ir is higher than expected:
Temporary heating of the ZnO-blocks inside?? Consider to re-test in approximately 1 day to confirm the value.
If surge counter is present: is the clip-on CT connected aboveit?
3. If high reading is stable and confirmed, consider monitoringcontinuously or proceed with step 4.
4. Contact the arrester manufacturer and consider replacing
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150 %
200 %
Years with measurements
100 %
1 2 3 4 5 6 7 8
Three differentarresters with almostthe same leakagecurrent
Which of them is themost dangerous?
Leakage current trendExcample
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Years with measurements1 2 3 4 5 6 7 8
The same threearresters as above,with measurementsover 8 years.
Which of them ismost dangerous?
The yellow hasincreased its leakagecurrent from ~85% to95% in 8 years
The red one from
65% to 100% in 8years
The blue from 25% to95% the last 3 years!
Leakage current trendExcample
www doble no
150 %
200 %
100 %