**4. Results**

### **4.1 Conducted emission**

The CD analyzed in the laboratories is identified in different ways. As already mentioned, one of the ways is by means of the conducted current. Therefore, we connected the CT to the return plane, and we observed in the oscilloscope the pulse. With this, we identified the presence of the discharge for an onset voltage of 12 kV ± 100 V. The current of corona pulse obtained of conducted way is shown in **Figure 2**, where **Figure 2a** corresponds to the pulse shape, and **Figure 2b** is the spectrogram obtained by WT.

In accordance with the spectrogram of **Figure 2**, the energies are concentrated at the range of 7 MHz and 16 MHz. In this last range is where there is the greatest amount of energy.

#### **4.2 Radiated emission**

The electromagnetic radiation of the CD generated by the short transmission line under test was measured in the time and frequency domain covering the frequency ranges in accordance with CISPR 16-1-1 (**Table 2**) [21]: band B, C, and D. For the time domain an oscilloscope was used, and for the frequency domain a signal analyzer in spectrum analyzer mode and an EMI test receiver were used. In both cases, the antenna factors were considered.

In order to cover the frequency intervals, three antennas were used, which are specified in **Table 2**. Whose frequency bands are the basis for displaying the results.

The results of the antennas are presented in dBμV vs. frequency, which can be converted to current, to predict the far field using the expression of a short dipole in the first instance [22].

#### **Figure 2.**

*Corona discharge pulse conducted. (a) pulse shape; (b) WT spectrogram.*


#### **Table 2.**

*Antennas and frequency band accordance with CSPR 16-1-1 [21].*

## *4.2.1 Frequency band B (0.3–30 MHz)*

In this frequency range, the loop antenna was used. The result corresponds to the total field formed by the three components (x, y, z). For the temporal part, an oscilloscope was used, whose data was processed using the WT to obtain its spectrograms; these results are shown in **Figure 3**. In the frequential part, we made two measurements: one with the spectrum analyzer and the other which EMI test receiver. The results are expressed in dBμV for both instruments, as shown in **Figure 4**, where graph (a) corresponds to the spectrum analyzer and graph (b) corresponds to EMI test receiver.

The results show that most amount of energy is concentrated in the 8 MHz, 11 MHz, 18 MHz and 25 MHz range; this agrees both in the temporal part and in the frequency part. At frequencies below 15 MHz, the EMI test receiver exhibits a higher signal level because it responds to the envelope and has a higher fall time constant on the input filter. An appropriate resolution bandwidth (RBW) in the spectrum analyzer allows a sweep so that the peaks of the RI are seen with greater definition, which makes the frequencies higher than 15 MHz the graphs of both instruments coincide.

#### *4.2.2 Frequency band C (30–300 MHz)*

The antenna used in this frequency range is biconical, which is recommended for this application by international standards. This antenna is basically a dipole with conical shape elements and has linear polarization. The results of the radiated emissions in the 30–300 MHz frequency range are shown for vertical and horizontal polarization. For the temporal response, the pulse with its spectrogram is shown in

*Electromagnetic Spectrum of the Corona Discharge and Their Fundamental Frequency DOI: http://dx.doi.org/10.5772/intechopen.101550*

#### **Figure 3.**

*Temporal answer of the corona discharge at B band (0.3–30 MHz) measured with a loop antenna.*

#### **Figure 4.**

*Frequency spectrum of the corona discharge at B band (0.3–30 MHz) measured with a loop antenna: (a) spectrum analyzer, (b) EMI test receiver.*

**Figure 5**. The frequency response measured with a spectrum analyzer and with the EMI test receiver are shown in **Figure 6**.

In this frequency band, we have the following:

In the spectrogram, it can be observed that the energy concentration for vertical polarization covers the range from 10 to 65 MHz. In this case, the measurement frequency range is not limited, and it is understood that the antenna responds outside its operating band.

With the frequency behavior, the measurement with the spectrum analyzer in vertical polarization shows that there are signal levels in almost the entire band, concentrating in the 30–60 MHz range. In EMI test receiver also the energy of RI is concentrating at 30 MHz and 60 MHz, but there is no signal at higher frequencies. For horizontal polarization, both measuring instruments present the same behavior, concentrating the greatest number of electromagnetic emissions in the 30–60 MHz interval; the energy is most high, around 40 MHz.

**Figure 5.**

*Temporal answer of the corona discharge at C band (30–300 MHz) measured with a biconical antenna. (a) Vertical polarization. (b) Horizontal polarization.*

According to the above, the highest amount of electromagnetic energy radiated by a corona discharge generated by a short transmission line is in the range of 30–60 MHz for both polarizations. In vertical polarization, some significant emissions at frequencies greater than 100 MHz, such as in 120 MHz, are only identified with the spectrum analyzer due to their higher resolution.

The noise floor of each instrument is an important part. In the case of the spectrum analyzer, the noise is greater due to the used span. In EMI test receiver, the noise is less and can not identify narrowband signals, because detect only the envelope and the filters are not able to resolve those signals. The signal levels in the high activity band of RI are almost equal, considering the background noise in both instruments.

#### *4.2.3 Frequency band D (300–1000 MHz)*

This frequency band is important because there are lots of portable radio communication services. For example, some of the services are the trunk radio, which

**Figure 6.**

*Frequency spectrum of the corona discharge at C band (30–300 MHz) measured with a biconical antenna. (a) Vertical polarization. (b) Horizontal polarization.*

is a typical means of communication used by those who maintain the high-voltage transmission lines, the open digital television, the first cell phone band that one continues to apply, systems 5G and others. Therefore, it is necessary to analyze the levels of electromagnetic emissions from the corona phenomenon. In this case, a hybrid biconical/log periodic antenna was used to cover the D band frequency range. The results in the time domain for vertical and horizontal polarization are

presented in **Figure 7**, including the spectrogram. For the frequency domain part at both polarities with the spectrum analyzer and the EMI test receiver, the spectra are shown in **Figure 8**.

From the temporal results in this band, it is observed that there is noise only for vertical polarization. Then, it is difficult to identify if this corresponds to the corona discharge. As the measurement is made with an oscilloscope, the time base that is set is where the maximum amount of energy of the phenomenon occurs. What we see corresponds to the distribution of the noise signal at frequencies related to the time base of the oscilloscope. However, for horizontal polarization, the energy is concentrated in the frequency bands where the corona is identified.

Regarding the frequency part, in this case, the measurement with the spectrum analyzer and the antenna at vertical polarization, the spectrum shows a signal at the frequency of 336 MHz and noise. The same signal of 336 MHz is present with the horizontal polarization and one at 960 MHz. These signals are not seen with the EMI test receiver because they are narrowband. Therefore, in both polarizations, only the background noise is seen.

**Figure 7.** *Temporal answer of the corona discharge at D band (300–1000 MHz) measured with a hybrid biconical/log periodic antenna. (a) Vertical polarization. (b) Horizontal polarization.*

*Electromagnetic Spectrum of the Corona Discharge and Their Fundamental Frequency DOI: http://dx.doi.org/10.5772/intechopen.101550*

#### **Figure 8.**

*Frequency spectrum of the corona discharge at D band (300–1000 MHz) measured with a hybrid biconical/log periodic antenna. (a) Vertical polarization. (b) Horizontal polarization.*

The difference in the levels observed in the graphs is because the background noise of the spectrum analyzer is high by the span, which does not happen with EMI test receiver.

### **5. Discussion**

The measurements of the electromagnetic radiation generated by corona discharge at media electromagnetically controlled (semi-anechoic chamber) give us information secure in time and frequency domains about the energy amount emitted by this

phenomenon to the environment. In such as environment, only the signal referring to the corona was present. We ensure the presence of the corona by measuring the conducted current, which is a well-known parameter. This current was monitored in all measurements. The emissions radiated in dBμV are indicated, and those are compared to observe the frequency behavior, where are shown the band of most activity of RI.

In frequency band B, we measure one decade from 0.3 MHz to 30 MHz. The antenna used is a loop, so its three components (x, y, z) were measured. In the time domain, the current pulse was obtained, and the wavelet transform was applied in order to obtain information on the energy distribution. In the frequency domain, measurements were made with a spectrum analyzer and an EMI test receiver with the peak detector. In this case, the information coincides with the frequency. At frequencies lower than 6 MHz, what is observed is the background noise in both instruments. The spectrum analyzer presented less noise since the span and RBW were conditioned for this decade, which implies less bandwidth in both parameters. In this regard, the frequency peaks are matching.

For the C frequency band that corresponds to 30–300 MHz, a biconical antenna was used. The answer of the time domain that corresponds to the current pulse was processed by the transform wavelet, which is shown the energy distribution. For this case, the major amount of energy is below that of the 70 MHz. The vertical polarization presents more activity of emission than polarization horizontal, which is also shown with both the spectrum analyzer and the EMI test receiver. The answers at both instruments are similar, where the greatest amount of energy is found. In vertical polarization, the spectrum obtained with the spectrum analyzer shows two peaks at 120 MHz and 260 MHz, which are not shown in the measurements with EMI test receiver. For the horizontal polarization, the spectrums of both instruments have the same performance.

Measurements in the D frequency band (300 MHz–1GHz) with vertical polarization, only a signal in the 335 MHz frequency was obtained, with a low amplitude level; the rest is the background noise. This is corroborated with the EMI test receiver and with temporal measurements, where the distribution in the spectrogram is observed. In the case of horizontal polarization, in the temporal part, a more defined signal can be seen with respect to the corona, keeping the energy concentration at 16 MHz and 32 MHz, as observed in the spectrogram. In the response of the spectrum analyzer, there are two signals, one at 335 MHz and the other at 960 MHz; the first is also presented with vertical polarization, the rest is background noise. Measurements with the EMI test receiver in this frequency range do not present information; only the background noise is seen.

As an important part of this work analysis, we can say that the measurements of the electromagnetic radiation of corona discharges are concentrated below 70 MHz, which has already been reported. However, it does not present a spectrogram like we do, which gives information on the distribution of radiation both in time and in frequency. It was also determined that, for frequencies greater than 30 MHz, the most appropriate is to use a spectrum analyzer since the bandwidth resolution can be adjusted to obtain more frequency components. With the EMI test receiver, the envelope of the signal is obtained by its filter; it has a large recovery constant.

The measurements of the corona discharge in a semi-anechoic chamber and safely verify the presence of the phenomenon gives the certainty that the emissions only correspond to this discharge and that it can also be ensured that there are no interfering signals in the band from 300 MHz to 1 GHz. Therefore, radio communication systems that are highly sensitive cannot be affected by this phenomenon. This leads us to ensure that the measurements that have been reported regarding this problem both on-site and the development of antennas have a complete spectrum of partial discharges where corona discharge may be included.

*Electromagnetic Spectrum of the Corona Discharge and Their Fundamental Frequency DOI: http://dx.doi.org/10.5772/intechopen.101550*

For measurements of radiated emissions in open spaces, the fact of identifying the corona with an ultraviolet camera does not indicate that only the corona discharge is present, it may be the main discharge with frequencies of partial discharges, but as the corona has been verified, it does not emit high-frequency signals (UHF).

In HV systems greater than those used (>12 kV) in this work, of course, the corona discharge has levels of radiated emissions higher than those obtained. In the bands with higher activity (<60 MHz), their presence is significant, but at high frequencies (UHF and microwaves), this phenomenon is not a problem for radiocommunication systems.
