LCM 500 Presentation - 2 [PDF]

Zitiervorschau

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 10-600A

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