CDAX 605 High Precision Capacitance & Dissipation Factor Test Set 1 Tan delta and capacitance measurements Hi V Lo A C HL Ground Measure with AC test signal, use Ohms law to calculate: • Dissipation factor (tan delta) C C L H • Power factor • Capacitance 2 Megger test sets for capacitance/tan delta testing Application/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 3 CDAX 605 – General „ High-precision impedance, capacitance and dissipation factor measurement instrument „ Used together with a high-voltage AC voltage source and a calibrated standard capacitor to form a complete setup for insulation testing „ IDAX605 can be used for high precision ratio measurements, e.g. calibration of voltage transformers „ Testing can be performed at any voltage level depending on the rating of the equipment, the power source and the reference capacitor „ IDAX605 performs measurements in all four quadrants – i.e. the instrument handles measurement of capacitive, resistive and inductive components (also in combination) 4 CDAX 605 – Key features „ Direct readings of capacitance and dissipation factor, no balancing or calculation required „ Direct reading of measured ratio „ Very 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 inductive „ Works with any reference value without any recalculations „ Measurements 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 channels „ IDAX605 SW + LabView and C# interfaces 5 CDAX 605 Application – Capacitance & tan delta 6 CDAX 605 Application – Ratio measurements - + STANDARD CAPACITOR 2 GENERATOR STANDARD CAPACITOR 7 CDAX 605 Application – Ratio measurements „ Test voltage is measured using a standard capacitor connected to the voltage source „ Another standard capacitor (or resistor) is connected to the secondary output of the VT „ The capacitance value is measured „ Voltage ratio = Capacitance value/measured capacitance value „ Direct reading of measured ratio „ Example: • 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 8 CDAX 605 - Software 9 CDAX605 test modes UST: Ungrounded Specimen Testing Test mode Measure Ground Guard UST-R Red Blue UST-B Blue Red Guard = Ground UST-RB Red and Blue --- GST: Grounded Specimen Testing Test mode Measure Ground Guard GST-GND Ground Red and Blue --- GSTg-R Ground Blue Red Ground Red GSTg-B Blue GSTg-RB Ground --- Red and Blue 10 C : UST-R HL A C HL C C L H 11 C +C : GST-GND HL H A C H L C C L H 12 C : GSTg-RB H „ 2 A C HL C C L H 13 CDAX 605 – Standard capacitors, 100-800 kV 14 CDAX 605 – Test generator examples, 100-450 kV 15 High Precision Ratio Measurements of Capacitive Coupled Voltage Transformers 16 CVT – General „ CVT/CCVT – Capacitive Coupled Voltage Transformer „ Typically used for voltages 69 kV – 765 kV (1200 kV in India?) „ Provides voltage potential for revenue meters and sometimes protection circuits „ Capacitive divider down to 5-12 kV followed by a standard inductive step-down voltage transformer to typically 115 V „ Series 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) 17 Typical CVT design (ABB) 1. Primary terminal 2. Expansion tank 3. Porcelain 4. Expansion tank for multi-section capacitors 5. Low-voltage terminal switch 6. Compensating reactor 7. Main primary windings 8. Secondary windings 9. Trimming windings 10. Damping device 11. Ground terminal C1 High voltage capacitor C2 Intermediate voltage capacitor 18 Typical CVT schematic diagram (Trench) 1. Series reactors 2. Intermediate voltage transformers 3. Harmonic suppression filter 4. Sealed protective gap 5. Secondary terminal board 6. Faraday shield 7. Potential ground switch 8. Choke coil and gap assembly 9. Drain coil, gap and carrier ground switch assembly 19 CVT testing – Factory „ Dielectric (insulation) tests – designed to verify the CVT’s insulation integrity „ Accuracy tests – designed to verify CVT’s compliance to a specified accuracy class „ Leak tests (unit is pressurized and checked for leaks) 20 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 21 CVT ratio measurement factory setup (bridge) 22 CVT ratio testing with traditional bridge „ High accuracy by using bridge technique „ Manual 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 23 CVT ratio measurement factory setup (direct) Can be exchanged for a reference resistor 24 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 current „ Accuracy in line with traditional bridge technique 25 Summary – CVT ratio measurements „ CVT 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 use „ Traditional 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 26 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 ratio „ Possibility to use a resistor reference on LV „ Calibration of CCVTs up to highest accuracy grade, with support for full automation using LabVIEW and/or C# 27 CDAX605 – Demo box „ Easy to demonstrate „ Both capacitance and ratio „ Adjustable ”output voltage” 28 CRD605 – HV resistor „ 20 MΩ „ Max 2 kV (100 µA) „ To be used for ratio measurements „ Or in any other application requesting a stable high-voltage resistor… 29 30