1. 1 Dielectrometry Measurements of Moisture Diffusion and Temperature Dynamics in Oil Impregnated PILC Cables Zachary M. Thomas Wolf, Greenfield & Sacks P.C. Markus Zahn Massachusetts Institute of Technology

2. 2 Presentation Outline Motivation Dielectrometry Sensors Sample Materials and Setup Constant Temperature Measurements Transient Measurements Summary

3. 3 Motivation Develop technology for cable health monitoring. What can dielectrometry sensors tell us about the electrical properties of PILC insulation? Cable Aging Mechanisms Temperature Fluctuations –Temperature varies with loading conditions. Moisture Ingress –Cracks and corrosion provide sights. –Aging of cellulose releases water. Partial Discharge (PD) –Formed in gaps and voids formed during temperature cycling in the cable insulation. –Regions of low oil content.

4. 4 Dielectrometry Sensors Capacitive sensing technique. Requires access to one surface of MUT (material under test). Sensor response determined by MUT effective permittivity Periodicity i.e. wavelength determines sensors depth perception. Frequency domain measurements taken from mHz to kHz. 3 λ Sensor

5. 5 Sensor Excitation

6. 6 Sensor Theory

7. 7 Field Line Results

8. 8 Sample Materials and Setup Sample Materials –PILC – Paper insulated lead covered cables –Teflon –Wood (Birch & Oak) –Polycarbonate –Polyethylene –Acrylic Experiments conducted in a vacuum chamber.

9. 9 Single Conductor Cable Constant Temp. Measurements Feedback capacitance is 5 nF on all channels.

10. 10 Arrhenius Temperature Dependence Observe: Changes in temperature cause a frequency shift of the permittivity. Dependence described by activation energy. MaterialWavelengthE a eV Single Conductor Cable 1.0 mm0.8981± 0.0137 2.5 mm0.9083 ± 0.0136 5.0 mm0.8909 ± 0.0138

11. 11 Transient Moisture Measurements We wish to observe moisture moving through test materials. Moisture prevented from entering everywhere except the exposed front surface. Transient moisture measurements are taken at a single temperature. Before time zero chamber is typically dried. At time zero moisture admitted into the chamber. Sensor is monitored at several frequencies during the diffusion process.

12. 12 Maple Rod Measurements (130 F, 30% RH) Time, days

13. 13 Maple Rod Mapping at 1 Hz

14. 14 Maple Rod Moisture Profiles at 1 Hz 0.3

15. 15 Single Conductor Cable Measurement Time, days

16. 16 Single Conductor Cable Mapping at 1 Hz

17. 17 Summary Theoretical solutions have been derived and tested for new geometries. Steady state measurements detail the permittivitys dependence on temperature. Arrhenius temperature dependence is characterized. Transient moisture measurements provide insight into moisture dynamics in woods and cables. With the lead sheath in place, dielectrometry is not practical for manhole measurements. Dielectrometry sensors could be used as an inexpensive method for utilities to assess cable health. Future measurements should focus on comparing dielectric properties of failed and failing cables to healthy cables.