**6. Discussion**

<sup>0</sup> <sup>100</sup> <sup>200</sup> <sup>300</sup> <sup>400</sup> <sup>500</sup> <sup>0</sup>

NACF

samples

<sup>0</sup> <sup>50</sup> <sup>100</sup> <sup>150</sup> <sup>200</sup> <sup>250</sup> <sup>300</sup> <sup>350</sup> <sup>400</sup> <sup>450</sup> <sup>500</sup> <sup>0</sup>

monopole

samples

triangle

<sup>0</sup> <sup>50</sup> <sup>100</sup> <sup>150</sup> <sup>200</sup> <sup>250</sup> <sup>300</sup> <sup>350</sup> <sup>400</sup> <sup>450</sup> <sup>500</sup> <sup>0</sup>

samples

sphere

<sup>0</sup> <sup>50</sup> <sup>100</sup> <sup>150</sup> <sup>200</sup> <sup>250</sup> <sup>300</sup> <sup>350</sup> <sup>400</sup> <sup>450</sup> <sup>500</sup> <sup>0</sup>

samples

**Distance**

As it can be seen, the monopole and the spherical antenna preserve the pulse shape in almost similar way while the triangle's received signal is affected by noise and it is groped far from

**Monopole Triangle Sphere** 0.39 0.96 0.29

0.2 0.4 0.6 0.8 1

**Figure 22.** NACF of the PD current of Figure17.

0.5 1

198 Progress in Compact Antennas

0.5 1

0.5 1

**Figure 23.** NACFs of the transmitted signals of Figure21.

The table I shows that the most suitable probes for the identification of partial discharge signals are the monopole probe and the spherical probe. This evaluation was obtained using one of the simplest classification algorithms, certainly other more advanced algorithms may change this rating, and also the use of digital filters in the same implementation may overturn the comparison. The use of filters or the use of more elaborate techniques of signal processing goes beyond the intentions of this chapter. Therefore, the comments will be expressed only in relation to the analogical performance of probes.

#### **6.1. Monopole antenna**

The monopole probe has a high gain, superior to the others. This is one of the key aspects in the evaluation of partial discharge phenomena that makes it attractive: the discharges take place within structures often shielded, for which the outgoing signals are weak. The use of too attenuating probe could make the measurement insufficient and the monopole can solve this issue. However, the use of this probe in the industrial environment is not wise since it could involve the absence of higher harmonics. Indeed, their contribution can modify the shape of the signal and even changing the initial instant of the discharge. Such behaviour, in the diagnosis of PD phenomenon, is not acceptable, since the determination of the type of discharge (internal, surface, corona, etc..) is based on the presence of a greater or lesser occurrence of discharges at certain angles of the sine wave function. One way to change the behaviour of the monopole is to change its length, but this length cannot be sufficiently modified to remove the effect of resonance. A simple way to try to mitigate the effect of the resonance is to insert appropriate RLC circuits. UWB antennas are actually filters, which introduce dependences between the transmitter and the receiver frequencies. Therefore such kind of antennas can be treaded. Generally, antennas have linear and passive behaviour, and input impedance can be represented by means of the canonical forms of Foster [28-30].The structure shown in Fig.24 is suitable to represent electric antenna as the electric dipole and monopole.In order to modify the behaviour of the antenna, the electric model of the antenna is required. The numerical implementation of the antenna gives the complex impedance used in the equation 19. The equivalent circuit has to show a similar behaviour for all the harmonic of interest. By following the steps in [28] the value of C0 is set by taking the value of the capacity presented by the antenna at low frequencies; the value of L0 is initially set to cancel the imaginary part of impedance at the first resonance frequency. It is required that the first RLC parallel branch has a resonant frequency corresponding to the first maximum of the real part of impedance. By adding more RLC parallel branch the impedance profile can be easily reproduced. Once the circuital model of the antenna is reproduced, new real RLC parallel branch can be used to modify the behaviour of the antenna by mitigating the resonance effect. imaginary part of impedance at the first resonance frequency. It is required that the first RLC parallel branch has a resonant frequency corresponding to the first maximum of the real part of impedance. By adding more RLC parallel branch the impedance profile can be easily reproduced. Once the circuital model of the antenna is reproduced, new real RLC parallel branch can be used to modify the behaviour of the antenna by mitigating the resonance effect.

The table I shows that the most suitable probes for the identification of partial discharge signals are the monopole probe and the spherical probe. This evaluation was obtained using one of the simplest classification algorithms, certainly other more advanced algorithms may change this rating, and also the use of digital filters in the same implementation may overturn the comparison. The use of filters or the use of more elaborate techniques of signal processing goes beyond the intentions of this chapter. Therefore, the comments will be expressed only in relation to the analogical performance of

The monopole probe has a high gain, superior to the others. This is one of the key aspects in the evaluation of partial discharge phenomena that makes it attractive: the discharges take place within structures often shielded, for which the outgoing signals are weak. The use of too attenuating probe could make the measurement insufficient and the monopole can solve this issue. However, the use of this probe in the industrial environment is not wise since it could involve the absence of higher harmonics. Indeed, their contribution can modify the shape of the signal and even changing the initial instant of the discharge. Such behaviour, in the diagnosis of PD phenomenon, is not acceptable, since the determination of the type of discharge (internal, surface, corona, etc..) is based on the presence of a greater or lesser occurrence of discharges at certain angles of the sine wave function. One way to change the behaviour of the monopole is to change its length, but this length cannot be sufficiently modified to remove the effect of resonance. A simple way to try to mitigate the effect of the resonance is to insert appropriate RLC circuits. UWB antennas are actually filters, which introduce dependences between the transmitter and the receiver frequencies. Therefore such kind of antennas can be treaded. Generally, antennas have linear and passive behaviour, and input impedance can be represented by means of the canonical forms of Foster [28-30].The structure shown in Fig.24 is suitable to represent electric antenna as the electric dipole and monopole.In order to modify the behaviour of the antenna, the electric model of the antenna is required. The

taking the value of the capacity presented by the antenna at low frequencies; the value of L0 is initially set to cancel the

**Author details**

of Palermo, Palermo, Italy

and Pietro Romano

search, PIER 84, 2008, 321–332.

search, PIER 85, 2008, 227–242.

sion (FCC), ET Docket 98-153, 2002.

Electrical Insulation2010; 17(1) 133-140.

trical Insulation 2003;10(2) 216-224.

Trans. On Power Delivery2006; 21(1), 528-530.

on Dielectrics and Electrical Insulation 2003; 10(3) 528-538.

In Electromagnetics Research, 2008, PIER 80, 337–348.

\*Address all correspondence to: fabio.viola@unipa.it

Department of Energy, Information engineering, Mathematical models – DEIM, University

Building Partial Discharge Signal Wireless Probes

http://dx.doi.org/10.5772/58840

201

[1] Yin, X.-C., Ruan, C.-L., Mo, S.-G., Ding, C.-Y., and Chu, J.-H. A compact ultra-wide band microstrip antenna with multiple notches. Progress In Electromagnetics Re‐

[2] Lamultree S., and Phongcharoenpanich, C. Bidirectional ultra-wide band antenna us‐ ing rectangular ring fed by stepped monopole. Progress In Electromagnetics Re‐

[3] Akhoondzadeh-Asl, L., Fardis, M., Abolghasemi, A., and Dadashzadeh, G. Frequen‐ cy and time domain characteristic of a novel notch frequency UWB antenna. Progress

[4] Notice of Proposed Rule Making, Revision of Part 15 of the Commission's Rules Re‐ garding Ultra-Wideband Transmission Systems. Federal Communications Commis‐

[5] B. A. Fruth and D. W. Gross, Phase Resolving Partial Discharge Pattern Acquisition and Frequency Spectrum Analysis. IEEE 4th Intern. Conf. Propertie, Application of

[6] Baker, P.C. and Judd, M.D. and McArthur, S.D.J.A frequency-based RF partial dis‐ charge detector for low-power wireless sensing. IEEE Transactions on Dielectrics and

[7] P. J. Moore, I. E. Portugues, and I. A. Glover, Partial Discharge Investigation of a Power Transformer Using Wireless Wideband Radio-Frequency Measurements.IEEE

[8] A. Cavallini, A. Contin, G. C. Montanari and F. Puletti, Advanced PD Inference in On-Field Measurements. Part.1: Noise Rejection. IEEE Trans. on Dielectrics and Elec‐

[9] A. Cavallini, M. Conti, A. Contin, G. C. Montanari Advanced PD inference in onfield measurements. Part 2: Identification of defects in solid insulation. IEEE Trans.

Dielectr. Materials (ICPADM), Brisbane, Australia, paper 6207, 1994.

Fabio Viola\*

**References**

Figure 24. Foster's canonical form for an electrical antenna. **Figure 24.** Foster's canonical form for an electrical antenna.

**6.3. Spherical antenna** 

**6. Discussion** 

**6.1. Monopole antenna** 

probes.

#### **6.2. Triangle antenna 6.2. Triangle antenna**

The triangular antenna has a resonance similar to the one of the monopole and shares the same height. The triangular antenna presents an uninteresting behaviour already even used under the best conditions (propagation orthogonal to the surface, absence of high frequencies). Therefore, it is not useful to make changes to improve performances. The triangular antenna has a resonance similar to the one of the monopole and shares the same height. The triangular antenna presents an uninteresting behaviour already even used under the best conditions (propagation orthogonal to the surface, absence of high frequencies). Therefore, it is not useful to make changes to improve performances.

#### **6.3. Spherical antenna**

The spherical antenna is the true omnidirectional antenna and its performance does not vary by changing its inclination. Then, it presents suitable features to build the PD probes. However, it has a small gain, but this issue can be overcome by using appropriate amplifiers.

#### **7. Conclusion**

In this chapter the design of PD receiving antennas has been shown. Three different antennas were simulated by means of the method of moments. Received PD signals have been analyzed by the employment of the classification algorithm, based on the autocorrelation function (ACF) of the signals. The difference in the classification of the received signals has been explained by studying the aspects of the transmitted signals due to the shape of the receiving antennas. The best performances were obtained with the spherical antenna. Indeed, it exhibits an omnidir‐ ectional pattern and reliability for reproducing the shape of the partial discharge signal. Thus, this kind of antennas can be suitable to acquire PD pattern to determine the particular type of PD activity.

#### imaginary part of impedance at the first resonance frequency. It is required that the first RLC parallel branch has a resonant frequency corresponding to the first maximum of the real part of impedance. By adding more RLC parallel **Author details**

of impedance. By adding more RLC parallel branch the impedance profile can be easily reproduced. Once the circuital model of the antenna is reproduced, new real RLC parallel branch can be used to modify the behaviour of the antenna by mitigating the resonance effect.

Figure 24. Foster's canonical form for an electrical antenna.

The triangular antenna has a resonance similar to the one of the monopole and shares the same height. The triangular antenna presents an uninteresting behaviour already even used under the best conditions (propagation orthogonal to the surface, absence of high frequencies).

The spherical antenna is the true omnidirectional antenna and its performance does not vary by changing its inclination. Then, it presents suitable features to build the PD probes. However,

In this chapter the design of PD receiving antennas has been shown. Three different antennas were simulated by means of the method of moments. Received PD signals have been analyzed by the employment of the classification algorithm, based on the autocorrelation function (ACF) of the signals. The difference in the classification of the received signals has been explained by studying the aspects of the transmitted signals due to the shape of the receiving antennas. The best performances were obtained with the spherical antenna. Indeed, it exhibits an omnidir‐ ectional pattern and reliability for reproducing the shape of the partial discharge signal. Thus, this kind of antennas can be suitable to acquire PD pattern to determine the particular type of

it has a small gain, but this issue can be overcome by using appropriate amplifiers.

L1

Cn

Rn

**6.2. Triangle antenna** 

**Figure 24.** Foster's canonical form for an electrical antenna.

**6.2. Triangle antenna**

200 Progress in Compact Antennas

**6.3. Spherical antenna**

**7. Conclusion**

PD activity.

C0

C1

R1

**6.3. Spherical antenna** 

Therefore, it is not useful to make changes to improve performances.

The table I shows that the most suitable probes for the identification of partial discharge signals are the monopole probe and the spherical probe. This evaluation was obtained using one of the simplest classification algorithms, certainly other more advanced algorithms may change this rating, and also the use of digital filters in the same implementation may overturn the comparison. The use of filters or the use of more elaborate techniques of signal processing goes beyond the intentions of this chapter. Therefore, the comments will be expressed only in relation to the analogical performance of

The monopole probe has a high gain, superior to the others. This is one of the key aspects in the evaluation of partial discharge phenomena that makes it attractive: the discharges take place within structures often shielded, for which the outgoing signals are weak. The use of too attenuating probe could make the measurement insufficient and the monopole can solve this issue. However, the use of this probe in the industrial environment is not wise since it could involve the absence of higher harmonics. Indeed, their contribution can modify the shape of the signal and even changing the initial instant of the discharge. Such behaviour, in the diagnosis of PD phenomenon, is not acceptable, since the determination of the type of discharge (internal, surface, corona, etc..) is based on the presence of a greater or lesser occurrence of discharges at certain angles of the sine wave function. One way to change the behaviour of the monopole is to change its length, but this length cannot be sufficiently modified to remove the effect of resonance. A simple way to try to mitigate the effect of the resonance is to insert appropriate RLC circuits. UWB antennas are actually filters, which introduce dependences between the transmitter and the receiver frequencies. Therefore such kind of antennas can be treaded. Generally, antennas have linear and passive behaviour, and input impedance can be represented by means of the canonical forms of Foster [28-30].The structure shown in Fig.24 is suitable to represent electric antenna as the electric dipole and monopole.In order to modify the behaviour of the antenna, the electric model of the antenna is required. The numerical implementation of the antenna gives the complex impedance used in the equation 19. The equivalent circuit has to show a similar behaviour for all the harmonic of interest. By following the steps in [28] the value of C0 is set by taking the value of the capacity presented by the antenna at low frequencies; the value of L0 is initially set to cancel the

branch the impedance profile can be easily reproduced. Once the circuital model of the antenna is reproduced, new real

RLC parallel branch can be used to modify the behaviour of the antenna by mitigating the resonance effect.

Ln

L0

surface, absence of high frequencies). Therefore, it is not useful to make changes to improve performances.

**6. Discussion** 

**6.1. Monopole antenna** 

probes.

Fabio Viola\* and Pietro Romano

\*Address all correspondence to: fabio.viola@unipa.it

Department of Energy, Information engineering, Mathematical models – DEIM, University of Palermo, Palermo, Italy

## **References**

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	- [6] Baker, P.C. and Judd, M.D. and McArthur, S.D.J.A frequency-based RF partial dis‐ charge detector for low-power wireless sensing. IEEE Transactions on Dielectrics and Electrical Insulation2010; 17(1) 133-140.
	- [7] P. J. Moore, I. E. Portugues, and I. A. Glover, Partial Discharge Investigation of a Power Transformer Using Wireless Wideband Radio-Frequency Measurements.IEEE Trans. On Power Delivery2006; 21(1), 528-530.
	- [8] A. Cavallini, A. Contin, G. C. Montanari and F. Puletti, Advanced PD Inference in On-Field Measurements. Part.1: Noise Rejection. IEEE Trans. on Dielectrics and Elec‐ trical Insulation 2003;10(2) 216-224.
	- [9] A. Cavallini, M. Conti, A. Contin, G. C. Montanari Advanced PD inference in onfield measurements. Part 2: Identification of defects in solid insulation. IEEE Trans. on Dielectrics and Electrical Insulation 2003; 10(3) 528-538.

[10] A. Contin, S. Pastore, Classification and separation of partial disharge signals by means of their auto-correlation function evaluation. IEEE Trans. On Dielectrics and Electrical Insulation2009; 16(6)1609-1622.

Drives. Bologna, 5-8 September 2011, 451-455, IEEE, ISBN: 978-1-4244-9303-6, doi:

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