PD is defined as a localised
electrical discharge that only partially bridges the insulation between
conductors and which may or may not occur adjacent to a conductor .
Thus, partial discharges are strictly related to insulation defects and
constitute cause and effect of degradation. Hence, PD measurements
constitute a powerful tool for guiding decision making in condition based
maintenance (CBM), as well as for quality control applications, as shown
by huge literature work.
Indeed, PD phenomena
manifest in a wide range of ways; for example, internal discharges within
the bulk of the insulation, surface discharges at the surface or at the
interfaces of two dielectric media or as corona discharges in air. The
severity of the effect that PD has on the insulation depends on the nature
and the location of the PD generating defect. Therefore, a key step in PD
analysis is the identification of the defect, through the characterization
of its PD activity.
The activities related to PD
measurements which are undertaken in LIMAT laboratory can be summarized as
carried out both in laboratory environment and on field.
Development of a
diagnostic database, to broaden knowledge about PD phenomena occurring
on different apparatus and components.
Development of expert
systems for automatic identification of PD generating insulation
defects, with the aid of artificial intelligence (AI) techniques.
Analysis of PD phenomena
through physical models and numeric simulations.
A fundamental contribution
in PD measurement and analysis carried out in LIMAT comes from company
which provides LIMAT researchers with the most advanced PD detection and
processing systems available. In particular, one precious feature of these
instruments consists of the possibility to distinguish and separate
different sets of acquired signals on the basis of the pulse shape.
Example of separation of
acquired data on the basis of the pulse shape (Subset A: disturbances,
Subset B: PD activity, Subset C: further PD activity ).
Measurement sessions are
carried out on artificial specimens in controlled environment, thank to
advanced HV equipments and a shielded room. In addition, measurements are
performed in the lab and/or on field on HV equipments as rotating machines,
power transformers (oil and resin-insulated), cables and cable
accessories, HF transformers, and capacitors.
Cable joint under test
of PD activity in cable joint
Example of automatic
Generator under test
of PD activity in a large generator
Example of automatic
Motor under test
of PD activity in a motor
Example of automatic
A database program has been
developed in Matlab environment, which is dedicated to PD acquisition
data. Such a program, beside usual database features, allows to perform
advanced data processing and to develop expert systems. Therefore, the
program itself is constantly updated and enforced.
Database / processing
Expert systems are developed, with the aid of AI techniques, e.g. fuzzy
logic, decision trees and concept learning. These systems have two main
purposes. The first purpose is to provide automatic tools for
identification of PD generating defects. The second purpose is to maximize
the information derived from PD measurements, thus allowing a deeper
investigation of PD phenomena.
 IEC 60270, Partial
Discharge Measurements, 3rd edition, March 2001.
A. Cavallini, M. Conti, A. Contin, G. C. Montanari, “Inferring partial
discharge identification through fuzzy tools”, IEEE CEIDP, pp. 698-702,
A. Contin, A. Cavallini, G. C. Montanari, G. Pasini, F. Puletti, "Digital
Detection and Fuzzy Classification of Partial Discharge Signals”, IEEE
Trans. on DEI, Vol. 9, no. 3, pp.335-348, June 2002.
 A. Cavallini, A. Contin, G.C: Montanari, F.
Puletti, "A new approach to diagnosis of solid insulation systems based on
PD signal inference", IEEE Electrical Insulation Magazine, Vol. 19, no.
32, pp. 23-30, April 2003.
A. Cavallini, A. Contin, G. C. Montanari, F. Puletti, "Advanced PD
Inference in On-Field Measurements. Part 1: Noise Rejection", IEEE Trans.
on DEI, Vol. 10, n. 2, pp. 216-224, April 2003.
 A. Cavallini, M. Conti, A. Contin, G. C.
Montanari"Advanced PD inference in on-field measurements. Part 2:
Identification of defects in solid insulation ", IEEE Trans. on
Dielectrics and Electrical Insulation, Vol. 10, no. 3, pp. 528-538, June
 A. Cavallini, M. Conti,
G. C. Montanari, A. Contin, F. Guastavino, F. Ombello, "Early detection of
electrical tree through advanced PD measurement inference techniques",
JICABLE, pp. 612-616, Versailles, France, June 2003.
 A. Cavallini, D. Fabiani, G. C. Montanari,
F. Ombello, F. Franchi Bononi, "Applications to cable diagnosis of new
methodology for partial discharge inference", JICABLE, pp. 659-664,
Versailles, France, June 2003.
 A. Cavallini, F. Ciani,
M. Conti, P. F. H. Morshuis, G. C. Montanari, "Modeling memory phenomena
for partial discharge process in insulation cavities", IEEE CEIDP, pp. ,
Albuquerque, USA, October 2003.
 J. Borghetto, A. Cavallini, A. Contin,
G.C. Montanari, M. de Nigris, R. Passaglia, G. Pasini, "Partial discharge
inference by an advanced system: analysis of online measurements performed
on hydrogenerators", IEEE Trans. on Energy Conversion, 2003.
 A. Cavallini, M. Conti, G.C. Montanari, C.
Arlotti, A. Contin, "PD inference for the early detection of electrical
tree in insulation systems", IEEE Trans. on Dielectrics and Electrical
Insulation, Vol. 10, no. 6, pp., December 2003.