Dielectric Response Measurements Using DC Voltage

Transcription

1 Dielectric Response Measurements Using DC Voltage Jean-François DRAPEAU Researcher Expertise Équipement électriques IREQ ICC Spring St Pete Education Session

2 OUTLINE Introduction DC charging & discharging current components DC Leakage Current Measurement Technique Converting DC current values to loss spectral data - Hamon approximation Time Domain Spectroscopy VLF Hamon Approximation Method ICC S11 - St Pete - Education Session - J.-F. Drapeau 2

3 INTRODUCTION It is possible to perform cable system diagnostic using DC supply sequences Diagnostic information will come from the measured current 3 methods: - DC leakage current measurement - Time Domain Spectroscopy (TDS) - VLF Hamon approximation ICC S11 - St Pete - Education Session - J.-F. Drapeau 3

4 DC CHARGING & DISCHARGING CURRENT COMPONENTS Charging current in a dielectric has 3 components: i pol t i t i t i t i cap cap abs Capacitive charging current C0 U0 t qc K 1 e - t t Diagnostic issues Absorption (or Polarization) current i abs C 0 U 0 f t K 2 t - Quasi-conduction (or Conduction) current i qc C0 U 0 = 0 n constant value --> associated to dielectric loss --> associated to local weakness or defect ICC S11 - St Pete - Education Session - J.-F. Drapeau 4

5 DC CHARGING & DISCHARGING CURRENT COMPONENTS Charging current in a dielectric has 3 components: Linear Graph ICC S11 - St Pete - Education Session - J.-F. Drapeau 5

6 DC CHARGING & DISCHARGING CURRENT COMPONENTS Charging current in a dielectric has 3 components: Log-Log Graph ICC S11 - St Pete - Education Session - J.-F. Drapeau 6

7 DC CHARGING & DISCHARGING CURRENT COMPONENTS Charging current vs discharging current: i i pol t i t i t i t cap abs t -i t i t dépol cap - abs qc --> For the discharging current, since the test sample is not energized anymore, the "quasi-conduction" (or conduction) component is absent ICC S11 - St Pete - Education Session - J.-F. Drapeau 7

8 DC LEAKAGE CURRENT MEASUREMENT TECHNIQUE METHOD About 2 X peak value of rated line-to-ground voltage ICC S11 - St Pete - Education Session - J.-F. Drapeau 8

9 DC LEAKAGE CURRENT MEASUREMENT TECHNIQUE METHOD DC current is measured during each step and during the hold phase Interpretation guide: No signs of deterioration Middle signs of deterioration Marked signs of deterioration Ref.: CDFI Phase 1 Final Report, Neetrac ICC S11 - St Pete - Education Session - J.-F. Drapeau 9

10 CONVERTING DC CURRENT VALUES TO LOSS SPECTRAL DATA - HAMON APPROXIMATION Hamon approximation: This is a "point-to-point" transformation For each current value acquisition taken at time, we can use the formula : t i pol ( t ) tg i t t where f = 0.1 / t C' = capacitance U 0 = voltage ICC S11 - St Pete - Education Session - J.-F. Drapeau 10

11 TIME DOMAIN SPECTROSCOPY (TDS) TDS principle for measuring dielectric loss DC charge-discharge sequence The charging (polarization) current is measured during the application of a DC voltage step. The discharging (depolarization) current is measured when the DC supply is turned off, and the sample is grounded. These two currents can be converted into two dielectric loss components, using the Hamon approximation. ICC S11 - St Pete - Education Session - J.-F. Drapeau 11

12 TIME DOMAIN SPECTROSCOPY (TDS) IREQ's TDS system V 1 - V 2 - V 3 ICC S11 - St Pete - Education Session - J.-F. Drapeau 12

13 TIME DOMAIN SPECTROSCOPY (TDS) TDS principle for measuring dielectric loss Example of current measurement 200 s pol 500 s depol ICC S11 - St Pete - Education Session - J.-F. Drapeau 13

14 TIME DOMAIN SPECTROSCOPY (TDS) TDS principle for measuring dielectric loss Application of the Hamon approximation ICC S11 - St Pete - Education Session - J.-F. Drapeau 14

15 VLF HAMON APPROXIMATION METHOD In this case, the Hamon approximation is used for a situation where the test sample is energized with a VLF Cosine Rectangular wave: Ref.: "Dielectric Loss Measurement of Power Cables Using Hamon Approximation", Conference proceedings of CMD2010, Seba KMT ICC S11 - St Pete - Education Session - J.-F. Drapeau 15

16 VLF HAMON APPROXIMATION METHOD Picture of the system: Ref.: "Dielectric Loss Measurement of Power Cables Using Hamon Approximation", Conference proceedings of CMD2010, Seba KMT ICC S11 - St Pete - Education Session - J.-F. Drapeau 16

17 VLF HAMON APPROXIMATION METHOD Observations: Provides dielectric loss in polarization regime only Voltage steps correspond to 2 X V max The upper bound of available Tan spectrum is set by the charging time of 0,3s VLF(0.1Hz) --> f max = 0.33 Hz The lower bound of available Tan spectrum is function of the VLF frequency: VLF(0.1Hz) --> f min = 0.02 Hz VLF(0.01Hz) --> f min = Hz ICC S11 - St Pete - Education Session - J.-F. Drapeau 17

18 Thank you for your attention! ICC S11 - St Pete - Education Session - J.-F. Drapeau 18