**3.1. PD pulse sensor**

Different sensors (optical, acoustic, electrical, etc.) are used for detecting the PD. For detecting the electromagnetic waves propagating in shielded dielectric cables, normally a high-frequen‐ cy current transformer (HFCT) and ultra high-frequency (UHF) sensor are used [18–21]. The HFCT is normally placed around the shielded cable or sometimes around the ground strip to collect the PD signals. The UHF sensor captures the UFH electromagnetic waves propagating in the shielded cable, which can be attenuated quickly depending on the loss characteristic of the cable. Figure 15 shows some typical configurations for using HFCT in the PD measure‐ ments. There are a lot of different other sensors such as coupling capacitor, inductively coupled probes, integrated partial discharge sensor, etc. that are used in PD electromagnetic pulse detections. Among them, the HFCTs are one of the most widely used sensors due to their high bandwidth and ease of use.

For processing the measured PD signals, different theories and algorithms have been proposed for optimizing PD testing results [18–21]. For partial discharge measurements, as stated in the above sections, the PD signals cannot be detected directly due to its nature as the PD is inside the insulation. The electromagnetic wave pulse signals we capture are indirect measurements of the PD and analysis needs to be done to extract useful information such as PD locations, PD magnitude, etc. Some PD detection technologies require an excitation voltage to produce a partial discharge signal pulse to find the PD location. For locating the PD location, two sensors are placed at two different locations along the cable and if the attenuation along the cable is the same, then when the two sensors reads the same level of PD, the PD source is in the middle of the two sensors assuming that the cable splices contribute little or few losses for the PD pulse propagation. Theoretically, the technology should work but an excitation voltage could damage the cable and the cable needs to be taken out of service. More and more PD detection systems have been developed for online real-time measurements as they don't require dangerous excitation voltages and can be used to assess the HV apparatus under more realistic conditions. However, the highly noisy environment caused by the high voltage and high current of the power cable makes extracting useful PD information difficult. To improve the signal-to-noise ratio for optimized measurement results, different technologies, such as noise filtering, digital signal processing optimization, signal amplifying, etc., are used.

**Figure 15.** HFCT used in PD detection.

The reader should keep in mind that the studied case is a simulation result based on some assumed shield dielectric properties. To assess the losses caused by the splices, some field measurements as well as further computations are necessary. Normally, the splices have

PD detection has been extensively used for high-voltage apparatus diagnostic and status assessment. This section focuses on electromagnetic PD wave detection as, due to its relatively smaller losses, the HF PD signal can propagate for a long distance and can be detected by the PD sensors located either at the termination or other appropriate locations of the power circuit

Different sensors (optical, acoustic, electrical, etc.) are used for detecting the PD. For detecting the electromagnetic waves propagating in shielded dielectric cables, normally a high-frequen‐ cy current transformer (HFCT) and ultra high-frequency (UHF) sensor are used [18–21]. The HFCT is normally placed around the shielded cable or sometimes around the ground strip to collect the PD signals. The UHF sensor captures the UFH electromagnetic waves propagating in the shielded cable, which can be attenuated quickly depending on the loss characteristic of the cable. Figure 15 shows some typical configurations for using HFCT in the PD measure‐ ments. There are a lot of different other sensors such as coupling capacitor, inductively coupled probes, integrated partial discharge sensor, etc. that are used in PD electromagnetic pulse detections. Among them, the HFCTs are one of the most widely used sensors due to their high

For processing the measured PD signals, different theories and algorithms have been proposed for optimizing PD testing results [18–21]. For partial discharge measurements, as stated in the above sections, the PD signals cannot be detected directly due to its nature as the PD is inside the insulation. The electromagnetic wave pulse signals we capture are indirect measurements of the PD and analysis needs to be done to extract useful information such as PD locations, PD magnitude, etc. Some PD detection technologies require an excitation voltage to produce a partial discharge signal pulse to find the PD location. For locating the PD location, two sensors are placed at two different locations along the cable and if the attenuation along the cable is the same, then when the two sensors reads the same level of PD, the PD source is in the middle of the two sensors assuming that the cable splices contribute little or few losses for the PD pulse propagation. Theoretically, the technology should work but an excitation voltage could damage the cable and the cable needs to be taken out of service. More and more PD detection systems have been developed for online real-time measurements as they don't require dangerous excitation voltages and can be used to assess the HV apparatus under more realistic conditions. However, the highly noisy environment caused by the high voltage and high current of the power cable makes extracting useful PD information difficult. To improve the

**3. Electromagnetic wave detection in shielded dielectric cables**

smaller losses compared with the long cable.

for the shielded power cables.

bandwidth and ease of use.

**3.1. PD pulse sensor**

108 Advanced Electromagnetic Waves

### **3.2. PD pulse detection data processing and transmitting**

Some PD detection systems detect PD at the hot spots identified by the utility companies and can't be used to monitor the system continuously due to the complicated data processing and communication. Due to the fact that the PD signals are normally HF signals which can attenuate quickly if a normal coaxial cable is used for connecting the PD detection sensor and the PD signal analyzer and also for safety concerns, sometimes, optical coupling [22] is used for long-distance data transmitting between the sensor and the PD data analyzer. After the field signals are received by data processors, which can be a wide-band oscilloscope or a spectrum analyzer, the PD data are processed for waveform, phase, span, etc. [28]. For better results, field signals can also be filtered and amplified and processed with specialized processing computers for trend analysis and alarm generation, etc.

With the advancement of modern wireless communication and digital signal processing technologies, real-time continuously online PD detection becomes more realistic [23-28]. Different wireless technologies have been used for transmitting measured processed data back to the controlling center. The processed output from the oscilloscope or other digital instru‐ ments can be fed into data transmitters using Ethernet, wireless LTE modem, Wifi, Zigbee network, etc. Ethernet is reliable and easy to use but sometimes it can be unavailable. Wireless LTE is flexible but can be expensive due to its common monthly data fee. Wifi is also a good option if it's available. Zigbee is a low-cost and low-maintenance method compared with cellular data service as it does not have a monthly fee. The Zigbee node is small and, if set correctly, it can run for a long time without maintenance. Figure 16 shows one customized Zigbee node [29]. However, its data rate is relatively low compared with Ethernet and Wifi. To monitor the PD in real time, the captured PD signals can be processed with a wideband local oscilloscope or other devices such as a spectrum analyzer and the output can be fed into one of the data transmitting routers. The PD measurements will lead to a lot of raw data and normally they can't be sent directly to the remote controlling center due to its high data volume. After processing, the data can be sent back to the controlling and data concentrator for appropriate actions such as cable maintenance, alarm generation, etc.

**Figure 16.** One Zigbee node.
