Ensaios Em Alta Tensão e Diagnósticos de Cabos s506

Energy Cables and Systems - Utilities

High Voltage Tests and Diagnostics in Cables

Pietro Corsaro – PIRELLIGianCarlo Montanari – University of Bologna


Contents

• European Scenarios

• Overview on measuring technique

• Conclusions

• Case Study


European Scenarios

Various approach within Europe, due to:

• Adoption of different testing standard:–Quality insurance approach;–High Stress Test;– IEC Standards.


European ScenariosFrance

• Power systems and installation condition highly standardized.

• Few installers qualified by EdF.• Extremely long qualification process.• Installed Systems are therefore

considered a priori failure proof.• EdF therefore does not see the need of

field tests.


European ScenariosThe Netherlands - Germany

Cables and accessories are factory tested at high voltage level

Vtest = 2.5*U0

Customers do not feel the need of any further test due to the high test level.


European Scenarios Spain

- After-Installation test in agreement with IEC standard (withstand test 1 hour/off-line);

- Increasing demand of PD monitoring from major utilities due to contingency:– Abnormal failure rate in the last year with

consequent increased interest of utilities in preventive diagnostic.


European ScenariosItaly

–After-Installation test in agreement with IEC standard (withstand test 1 hour/off-line);

– Increasing demand of accessories with embedded PD sensors (from 275 kV and higher) for new systems.

– Increasing demand of PD monitoring at commissioning stage and after repair.


Pirelli-TechImp Cooperation

In 1999 Pirelli started a collaboration with University of Bologna / TechImp to develop PD sensors and testing techniques on power transmission systems, particularly focused on accessories, to provide reliable information for Condition Based Maintenance.


Pirelli-TechImp CooperationMain outputs

A wide range of PD sources has beencharacterized for testing reference:–Cavity–Misalignment–Protrusion–…

Thanks to Pirelli cable expertise and TechImp technological know-how.


Pirelli-TechImp CooperationMain outputs

A number of sensors has been developed:–HFCT– Inductive Clamps–Capacitive embedded

to be capable to test in reliable way both new and existing installations


Detectable defects

All those non conformities causing an high electrical gradient and lack of material and consequent partial discharge:– Air gap– Not-compressed cuts– Semi-conductive elements mispositioning– Electrical trees– Protrusion– …


PD: Testing method

Main difference on voltage test source:• ON LINE: System under test is

energized by means of the grid

• OFF LINE: System under test isenergized by means of mobile resonant test set.


PD: Testing method - Pro & ConsOff-Line On-Line

Potential problem on the grid in case of failure

Induced noise from the grid

Induced noise from adjacent phase

Test Voltage level

Released power in case of failure

Costs


Mobile Test Sets Fleet

2 x150 kV

220 kV – 440 kV50 kV

100 kV

260 kV260 kV – In progress

160 kV


Testing Procedure

–If power system does not have embedded sensors, external sensors are applied on it;

–Sensors are calibrated;–The system is then energized @ no

load;–PD activity, if any, can be then

monitored on one or more accessories at the same time.


PD: SENSORSHFCT

Can be used in the earthing connection of the termination Can be used with LINK BOXGood sensitivityObject measured has to be sectionalised (can not be used on stright joint)

INDUCTIVE CLAMP A.C.M.S. (Around Cable Metallic Sheath)No limit in application (need just the cable)Easy to be appliedLow sensitvity

INDUCTIVE CLAMP U.C.M.S. (Under Cable Metallic Sheath)No limit in application (need just the cable)Can be embedded during the accessory assemblingGood sensitivityThe cable metallic sheath has to be cut

CAPACITIVE “EMBEDDED”Very High sensitivity PD Located immediatelyCan be applied ONLY during the accessory assembling


PD: Sensors Sensitivity

Sensitivity

HFCT

UCMS

ACMS

Embedded Capacitive


PD: embedded capacitive sensor


PD: embedded capacitive sensor


Testing Procedure

Feasibility of on-line or off-line energisation depends on the sensors used.

It is not technically correct to guarantee a priori a sensitivity level for on-site monitoring applicable to every installed system.

Sensitivity level for on-site measurement must be defined case by case


PD: METHODS“JUST A CHECK”

Can use the earthing connection of the terminationMeasurements performed only from the terminationNot applicable to Long Link

SEQUENTIALCan use LINK BOXCan be applied to OLD link without any problemsBreakdown can happen without any PD evidence on jointnot “on measurement”

SIMULTANEOUSAll the accessories measured in “ONE SHOT”PD Location easiestNO data “LOST”On old link can be used only with Inductive or embeddedSensors

MONITORINGGive an evaluation of the PD PATTERN TRENDVery helpful for condition base maintenanceCan be used only with Inductive or embedded Sensors


Pirelli-TechImpHow we act

We are able to provide an optimised configuration for PD testing:

– Mobile test-set world-wide (to avoid influence to/from the grid);

– Sensors for PD detection with ultra broad band frequency acquisition

– Acquisition tool capable to manage a large amount of data.

– Professional data analysis for reliable condition assessment.


PD MEASUREMENTS

2451

70

150 152

300

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50

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250

300

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l leng

th o

f cab

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m)

Num

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f acc

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ries

2002 2003 2004 (first6 months)

Year

Partial Discharge MeasurementOn Site Activity: 2002÷2004

Cable lengthaccessories


PD MEASUREMENTS

0

10

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50

60

70

80

Total

leng

th of

cable

s (km

)

2002 2003 2004 (first 6months)

Year

Partial Discharge MeasurementsOn Site Activity: 2002÷2004

< 150 kV220 kV400 kV


In SummaryBest results in diagnostics for HV systems

are obtained by:energizing the power system with mobile test-set (off-line method) for both withstand test and PD measurement;Using PD measurement to detect a wide range of defect undetectable with other testing methods;Performing PD measurement at every single accessory;Performing PD using capacitive embedded sensors;


Cases StudyTechnical notes

and Real Application

OfPD measurements for Power System

condition assessment

Documents

Ensaios Em Alta Tensão e Diagnósticos de Cabos s506