LCM 500 –
Leakage Current Monitor
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Presented by Michal Slodkiewicz
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
•
Risk assessment www.doble.no
measurement on-side
Motivation and background • The MOSA is a cheap and passive component, but protecting crucial 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 if the rated voltage is selected to low. • Diagnostic indicator: Resistive leakage current increases with time 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. www.doble.no
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 is an increase with time of the resistive component of the continuous leakage current • Increase in resistive leakage current will cause an increase in power losses and hence increased temperature in ZnO-blocks • The resistive current may exceed a critical limit where the accumulated energy in the ZnO-blocks exceeds the energy capability of the arrester. The arrester will then get thermally unstable and fail.
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Degradation of MOSA An arrester failure may appear in different ways: • Arrester with porcelain housing may explode
• The arrester can be causing an earth fault due to internal flashover • Aged or overloaded arresters may have reduced protection against overvoltages, i.e. it is not protecting the apparatus it is supposed to protect.
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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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Requirements for surveyed surge arrester 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 the MOSA. Without insulated base you have to take the arrester out of service for proper condition testing.
•
If a surge counter is present, the clip-on should be placed above the counter to avoid circulating currents from the counter ground loop.
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IEC 60099-5 Part 5 Selection and Application Recommendation
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IEC 60099-5: Available diagnostic methods Properties of on-site leakage current measurements:
A HV-DC test is effective but off line and complex
Method B2 is ranked to be the best field method for evaluation of ageing and deterioration of MOSA.
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IEC 60099-5: Metal Oxide Surge Arresters 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 currentvoltage characteristic) and can therefore be used as a measure for the arrester condition.
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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 current component: is typically 5-20% of the total
leakage current under normal operating conditions
is a sensitive indicator of
changes in the voltage-current characteristic
depends on the voltage and temperature
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Equivalent Circuit of ZnO -Varistors
It
Ic 200-3000 µA U
Ir 10-600A
Ir=It-Ic
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Leakage Current Measurements Measurement of the total leakage current example: I Ir1=10
Ir2=20
Itot increases with only 1,5% when the resistive vector is
I1tot = 100,5
doubled
I2total = 102 δ1
Ic1= 100
This small change in Itot is not
δ2
measurable at a mA–meter
Ic2=100
Φ Usyst
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U
Recalculation of leakage current By using arrester system data and measuring the ambient temperature and operating voltage at the same time as the condition monitoring is performed, it is possible to recalculate the leakage current data to a common reference of:
20 °C and U/Ur=0.7 The resistive leakage current values will then be approximately the same independent of the test conditions by taking account of the ambient temperature and operating voltage, measurements performed under different conditions can be directly compared, and the measured values will be a reliable indicator of the arrester condition.
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Temperature and system voltage influence Influence of ambient temperature and system voltage on resistive leakage current.
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LCM 500-Leakage Current Monitor 4
1
3
1. LCM500 unit 2. Current Probe
2
3. Field Probe
5
4. 12V DC cable
5. Field Rod adapter 6
6. Power supply cable 7
7. Antenna 8. Grounding cable 9. Current loop wire 9
8
11 10
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10.USB A+B cabel 11.Field test cable
LCM 500-Leakage Current Monitor Optional Accessory
Field Probe Rod – delivered in separate transport case. Rod is divided on 3 pieces for 1m each piece. Cannot be used as a Hot Stick! www.doble.no
LCM 500 Front Panel Self test
Communication ports
Light diodes Mains power supply
External DC power sypply Power switch Turning knob “Select” button
Antenna input Four pushbuttons www.doble.no
LCD display
LCM 500 Self-test outputs Self-test outputs - perform function test of internal system 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 between the two black connectors, a current loop simulating total arrester leakage current is created
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LCM 500 Communication Ports
USB, RS232, Ethernet By connecting data cables to one of above ports, the instrument can communicate with a PC using the enclosed Windows based data management software LCMViewer.
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LCM 500 Wireless probes
1
1-Field probe FP500 (antenna): Measures the capacitive current from the electric field surrounding the arrestor.
2 2-Clip-on current transformer CCT500: Measures the total current in the grounding cable of surge arrester.
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Performing self-test of LCM 500 Circuit diagram
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Performing self-test of LCM 500
Measurement System Test
Leakage Current Monitor LCM500 Meas
Setup
Dbase
Teast : verify system Simul. : generate test signals Test
Test Simul.
Measurement System Test Connect antenna to probe
arrester and test signals before start
Start
Main
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Main
Performing self-test of LCM 500 Measurement in progress Aquisition started PLEASE WAIT! >
LCM 500 Measurement System Test Succeeded Start
Main
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LCM 500 Measurement System Test Failed CONTACT MANUFACTURER Measured: Ir:205 +/- 8µA It:332 +/- 5µA
Performing self-test of LCM 500
TROUBLE SHOOTING: - Be sure that all connections between field test cable “crocodile” clips are fasten properly to Field Probe - Observe that current loop is not in vicinity or not around antenna
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Preparation of surge arrester in LCMViewer
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Preparation of surge arrester in LCMViewer
Define database of your surge arrester and transfer this to the LCM 500, use Add to LCM Queue button. Software automatically will move you to Instrument tab. If you don’t know the rated voltage, the software will recommend a proper value based on system voltage and arrester type.
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Preparation of surge arrester in LCMViewer
Use Send Data to LCM button in order send data
to
instrument.
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LCM
500
Getting connection between PC and LCM500 Go to Instrument=>Setup, Log tab
1. Choose
correct
ComPort for LCM 500 instrument. 2. Use Test button to check status of your connection
area.
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in
Log
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 MOSA
1
2. Insulated base 3. Grounding wire The Field Probe should NEVER exceed this limit
2
4. Clip-on CT500 5. Counter 6. Field probe FP500
3 4
7. Arrester pedestal
5
8
9
8. Field Probe Rod
7
9. LCM 500 unit
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Deployment of LCM 500 accessories
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LCM 500 Set-up Mode From Main Menu
Leakage Current Monitor LCM500 Meas
Setup
Dbase
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Test
LCM 500 Set-up Mode From Main Menu
Leanguage : English Dump mode : OFF Time : 10:30:45 Date : 2011.06.14 Backlight : 40 Baudrate : 57600 Serial # : 205039 Netw. Radio
<
Main
Language: only English. Dump mode: ”ON” is for use in
continuous measurements. The measurements will be dumped continuously to the serial port. When a PC with proper software is connected the measurements can be downloaded.
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 during communication with a PC and can be set to 9600 bit/sec. or 57600 bit/sec.
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LCM 500 Measuring mode
Leakage Current Monitor LCM500 Meas
Setup
Dbase
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Test
LCM 500 Measuring mode
Station/Loc/Arrester: No station chosen No location chosen No arresrer chosen Installation # Run
Auto
Setup
<
Main
By pressing the “MEAS” button in the main menu, the screen presented on the left appears. When database is transferred from the software, you will get access to it in this menu.
If you press ”Setup” in the above menu, you will enter the measuring set-up mode
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LCM 500 Measuring set-up mode
Station/Loc/Arrester: No station chosen No location chosen No arresrer chosen Installation # Run
Auto
Setup
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<
Main
LCM 500 Measuring set-up mode Mode Temp Line Transf
Meas
: 3-phase : Auto 24 C : Man 245 kV : 1:1000
<
Mode: In field test 3-phase mode should be set. 1-phase mode is for use in lab tests. Temp: Choose between manual automatically setting of the temperature.
Main
or
Line: The line-to-line operating voltage. Choose between manual or automatic. Manual setting is the most common. Automatic is for connection 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 set from 1:1 up to 1:10000 in steps.
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LCM 500 Auto measurement
Station/Loc/Arrester: No station chosen No location chosen No arresrer chosen Installation # Run
Auto
Setup
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<
Main
LCM 500 Auto measurement
Auto measurement Start :2011.02.10 < 16:11:25 Interval : 00:00:15 90005 STA A1 PH R Abort
Run
STA A1 PH R Ir corr. 198µA ±5µA It : 567 µA Ir:172µA 24 C 68kV AUTO, next measurement 2011.02.10 16:11:40 Abort
Main
Function allows performe long-term monitoring of an surge arrester. The time and date for the first measurements can be set than by press button ”Run” subseqent measurements will begin.
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LCM 500 Perform a Measurement
Station/Loc/Arrester: No station chosen No location chosen No arresrer chosen Installation # Run
Auto
Setup
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<
Main
LCM 500 Perform a Measurement If the measurement runs ok, the measuring result will be shown in the LCD display like the example below. 90005 STA A1 PH R Ir corr:
Ircorr-total corrected resistive leakage
159µA
Ant. 3rd harm. : It: 587 µA Ir: 24 C Run Store New
0.8% 89 µA 68 kV Main
current with standard deviation (corrected value with regard to ambient temperature and line voltage).
It-total leakage current Ir-total uncorrected resistive leakage current.
In addition the ambient temperature and the line voltage used during the measurement are displayed. To save your measurement, press the ” Store” button
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Download the measurements Go to Instrument=>Measurement from Instrument tab 1. Click
the
Read
Measurements LCM
to
from
make
the
transfer take place 2. Mark
your
Arrester
than
Surge use
Apply Measurements (Auto
only),
all
performed measurement will be add to existing Surge Arrester data. www.doble.no
Structure and data analysis Leakage Current Plot The LCMViewer lets you create a graphical statistical presentation of your Surge Arrester measurements. Easy way to compare measurements for groups of arressters.
Test Conditions You can observe factor of temperature, voltage and containing of 3th harmonic from taken measurements.
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Structure and data analysis
Arrester Test Reports
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•
LCMViewer will generate an arrester report in either Excel or pdf files.
•
You can select content of information to be included in the report.
•
You can use your company logo.
Doble LCM - Your best choice! You should choose: A simple in-service method Doble LCM – takes less then 5 minutes per arrester, in service Reliability method verified by independent sources LCM method recommended by arrester IEC standard Convincing references Developed together with ABB! Now in Siemens surge arrester monitoring catalog! www.doble.no
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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 34 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, the situation of overvoltages, quality of the apparatus etc. www.doble.no
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 in order. Circulating currents??
2. If Ir is higher than expected: •
Temporary heating of the ZnO-blocks inside?? Consider to retest in approximately 1 day to confirm the value.
•
If surge counter is present: is the clip-on CT connected above it?
3. If high reading is stable and confirmed, consider monitoring continuously or proceed with step 4. 4. Contact the arrester manufacturer and consider replacing www.doble.no
Leakage current trend Excample • Three different arresters with almost the same leakage current
200 %
•Which of them is the most dangerous?
150 %
100 %
1
2
3
4
5
6
Years with measurements
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7
8
Leakage current trend Excample • The same three arresters as above, with measurements over 8 years.
200 %
•Which of them is most dangerous?
150 %
•The yellow has increased its leakage current from ~85% to 95% in 8 years
100 %
•The red one from 65% to 100% in 8 years 1
2
3
4
5
6
7
Years with measurements
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8
•The blue from 25% to 95% the last 3 years!
