34644 - Characterisation and Diagnostics of Electrical Equipment M

Learning outcomes

The course deals with the techniques used for condition assessment of electrical apparatus, with an emphasis on insulation systems. In particular, bulk and local diagnostic techniques of insulation systems will be dealt looking at both the microscopical nature of the degradation phenomena, as well as the macroscopical and measurable effects that the same phenomena cause in apparatuses (cables, generators, transformers and gas-insulated systems). The aspect of condition assessment of bearings (both journal and ball bearings) will also be dealt with. The use of artificial intelligence techniques as a mean to infer automatically the condition of an apparatus will be treated.

Course contents

1. Partial discharge (PD) measurements: the ABC circuit; apparent charge estimation; limits of calibration; guidelines to build a measurement circuit; use of PD detectors.

2. The physics of partial discharge (PD) phenomena in internal cavities as a key to understand and identify PD sources using the phase-resolved PD pattern; the use of fuzzy logic as a tool to identify PD sources.

3. Degradation phenomena occurring in internal cavities: physical and chemical observations; modeling.

4. Bulk diagnostic techniques: polarization/depolarization current analysis; dielectric spectroscopy; return voltage measurements.

5. Condition assessment of power cables: weak points and failure modes; PD detection and analysis; water tree; the use of bulk diagnostic techniques; working cases.

6. Condition assessment of rotating machines: structure of rotating machine insulation systems; weak points and failure modes; insulation resistance and polarization index measurements; other bulk diagnostic techniques; PD detection and analysis; working cases. Stress enhancement due to inverter supply: failure modes and related IEC standards.

7. Condition assessment of power transformers: characteristics of paper/oil insulation systems; degree of polymerization and its measurement; Dissolved Gas Analysis and other chemical analyses of oil; return voltage measurements; PD detection and analysis.

8. Condition assessment of gas-insulated systems: weak points and failure modes; PD detection using UHF techniques.

Readings/Bibliography

Notes and slides prepared by the teacher

Teaching methods

During the course, frontal teaching will be followed by lab experiences, where the student will be requested to build up the measurement circuit and interpret results in an autonomous and critical fashion.

Assessment methods

Oral exam, on a date arranged between teacher and student

Teaching tools

The lab owns high voltage transformers, coupling capacitors and partial discharge detection system, that can be used for testing artificial specimens as well as real objects. DC generators and pico-ammeters can be used to measure polarization/depolarization currents, as well as Voltage Return phenomena. Two test bench are available to reproduce and measure vibrations from ball and journal bearings.

Office hours

See the website of Andrea Cavallini