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CDAX 605High Precision Capacitance & Dissipation Factor Test Set

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Tan delta and capacitance measurements

V

A

Hi

Lo

Ground CHL

CL CH

Measure with AC test signal, use Ohms law to calculate:• Dissipation factor (tan delta)• Power factor• Capacitance

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Megger test sets for capacitance/tan delta testingApplication/Measurement CB100 CDAX605 IDAX/VAX DELTA4000

Power frequency tan delta/power factor Yes Yes Yes Yes

Capacitance measurements Yes Yes Yes Yes

External voltage source No Yes No No

High voltage tan delta/power factor No Yes Yes Yes

High power tan delta/power factor No Yes No Yes

Laboratory precision measurements No Yes No No

Dielectric frequency response No No 0.1 mHz-10 kHz 1-500 Hz

Moisture assessment No No Yes No

Individual temperature correction No No Yes Yes

Temperature dependence analysis No No Yes No

Tip-up testing No Yes Yes Yes

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CDAX 605 – General

High-precision impedance, capacitance and dissipation factor measurement instrumentUsed together with a high-voltage AC voltage source and a calibrated standard capacitor to form a complete setup for insulation testingIDAX605 can be used for high precision ratio measurements, e.g. calibration of voltage transformersTesting can be performed at any voltage level depending on the rating of the equipment, the power source and the reference capacitorIDAX605 performs measurements in all four quadrants – i.e. the instrument handles measurement of capacitive, resistive and inductive components (also in combination)

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CDAX 605 – Key features Direct readings of capacitance and dissipation factor, no balancing or calculation requiredDirect reading of measured ratioVery high accuracy

• Capacitance 0.02%• Dissipation factor 0.001%

Wide measurement range• Capacitance up to 100 µF• Dissipation factor 0-100

0-360° phase measurements. Reference and test objects can be capacitive, resistive or inductiveWorks with any reference value without any recalculationsMeasurements synchronized to power frequency or generator/reference signal (5-400 Hz) Measures UST-R, UST-B, UST-RB, GST-GND, GSTg-R, GSTg-B and GSTg-RB configurations using 3 inputs and two separate current measurement channelsIDAX605 SW + LabView and C# interfaces

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CDAX 605 Application – Capacitance & tan delta

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CDAX 605 Application – Ratio measurements

STANDARD CAPACITOR

- +GENERATOR

STANDARD CAPACITOR 2

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CDAX 605 Application – Ratio measurements

Test voltage is measured using a standard capacitor connected to the voltage sourceAnother standard capacitor (or resistor) is connected to the secondary output of the VTThe capacitance value is measuredVoltage ratio = Capacitance value/measured capacitance valueDirect reading of measured ratioExample:

• Test voltage 100 kV• VT ratio 230 kV/115 V = 2000• Capacitor value 10012.8 pF• Measured capacitance = 5.0067 pF• Measured voltage ratio 10012.8/5.0067 = 1999.9• Secondary voltage 50.002 V

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CDAX 605 - Software

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CDAX605 test modes

UST: Ungrounded Specimen TestingTest mode Measure Ground Guard

UST-RUST-B

UST-RB

RedBlue

Red and Blue

BlueRed---

Guard = Ground

GST: Grounded Specimen TestingTest mode Measure Ground Guard

GST-GNDGSTg-RGSTg-B

GSTg-RB

GroundGroundGroundGround

Red and BlueBlueRed---

---RedBlue

Red and Blue

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CHL: UST-R

A

CHL

CHCL

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CHL+CH: GST-GND

A

CHL

CHCL

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CH: GSTg-RB

2

A

CHL

CHCL

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CDAX 605 – Standard capacitors, 100-800 kV

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CDAX 605 – Test generator examples, 100-450 kV

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High Precision Ratio Measurements of

Capacitive Coupled Voltage Transformers

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CVT – General CVT/CCVT – Capacitive Coupled Voltage TransformerTypically used for voltages 69 kV – 765 kV (1200 kV in India?)Provides voltage potential for revenue meters and sometimes protection circuitsCapacitive divider down to 5-12 kV followed by a standard inductive step-down voltage transformer to typically 115 VSeries reactor connected from capacitive divider to step-down transformer.

• Reactor impedance is designed so its impedance cancels the impedance of the capacitor

• Full intermediate voltage to the step-down transformer

Typical ratio range: 500 to 5000• Capacitive: 10-100• Electromagnetic: 50-100

Accuracy down to 0.1% (revenue metering)

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Typical CVT design (ABB)

1. Primary terminal2. Expansion tank3. Porcelain4. Expansion tank for multi-section capacitors5. Low-voltage terminal switch6. Compensating reactor7. Main primary windings8. Secondary windings9. Trimming windings10. Damping device11. Ground terminal

C1 High voltage capacitorC2 Intermediate voltage capacitor

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Typical CVT schematic diagram (Trench)

1. Series reactors2. Intermediate voltage transformers3. Harmonic suppression filter4. Sealed protective gap5. Secondary terminal board6. Faraday shield7. Potential ground switch8. Choke coil and gap assembly9. Drain coil, gap and carrier ground

switch assembly

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CVT testing – Factory

Dielectric (insulation) tests – designed to verify the CVT’s insulation integrityAccuracy tests – designed to verify CVT’s compliance to a specified accuracy classLeak tests (unit is pressurized and checked for leaks)

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CVT ratio testing LV measurements (100 V TTR)

• High ratio – very low secondary voltage. May be difficult to measure accurately, especially in the field…

• Test voltage from TTR instrument is stepped down 10-100 times in the capacitive divider

– Very low test voltage to step-down transformer – Impedance error risk…

• Inaccuracy is generally > 1%HV measurements (2-5 kV TTR)

• Higher test voltage reduces accuracy issues• Inaccuracies < 0.5% is achievable

HV measurements (10-500 kV) – capacitance method• Very high test voltage (up to rated voltage) removes accuracy issues• Final accuracy is pending accuracy of standard capacitors (as well as

test equipment)• Inaccuracies < 0.1% is achievable

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CVT ratio measurement factory setup (bridge)

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CVT ratio testing with traditional bridge

High accuracy by using bridge techniqueManual instrument

• Needs balancing• Manual data collection, interpretation and reporting• Difficult to create an automated test… No computer interface

Can only measure capacitance• Reference capacitor on LV circuit• Higher capacitance (>1000 pF) is desired to get higher test current –

Expensive and limited number of suppliers

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CVT ratio measurement factory setup (direct)

Can be exchanged for a reference resistor

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CVT ratio testing using direct measurements Processor based instrument

• No balancing• Direct readings• Automated data collection and interpretation• Computer interface to standard lab SW

Can measure capacitance, resistance and inductance in combination

• Possibility to use a reference resistor on LV circuit• Less expensive and can easily be designed for higher measurement

currentAccuracy in line with traditional bridge technique

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Summary – CVT ratio measurementsCVT ratio needs to be verified in factory tests (and sometimes also in the field…)CVT’s with 0.1% accuracy class needs to be tested with a test setup that provides an inaccuracy well below 0.1%.

• Only HV methods are possible to useTraditional tan delta and capacitance measurement bridges provides very good accuracy but

• Needs balancing• Have manual data collection, interpretation and reporting• Are difficult to integrate in an automated test setup• Reference components are limited to capacitors

Direct voltage-current measurement instruments can measure capacitance, resistance and inductance in combination and provides

• No balancing, direct readings, automated data collection• Computer interface to standard lab SW e.g. LabView• Possibility to use a reference resistor on LV circuit• Accuracy in line with traditional bridge technique

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CDAX605 Application example – Ratio measurements on revenue class CCVT:s

Ratio and insulation measurements on revenue class CCVTs (0.1% accuracy)Direct replacement of CB-605 (old Multi-Amp measuring bridge)Direct reading of measured ratioPossibility to use a resistor reference on LVCalibration of CCVTs up to highest accuracy grade, with support for full automation using LabVIEW and/or C#

-

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CDAX605 – Demo boxEasy to demonstrateBoth capacitance and ratioAdjustable ”output voltage”

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CRD605 – HV resistor

20 MΩMax 2 kV (100 µA)To be used for ratio measurementsOr in any other application requesting a stable high-voltage resistor…

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