## 2 Design and Implementation of On-Line PD Monitoring System
### Modules of Server Software  
In the firmware of the monitoring system server, the following software modules were implemented: virtual data concentrator (VDC), analytic module, the module of graphic data presentation, and reporting module. In the monitoring mode, the VDC module receives from the MPD-001 concentrator notifications of the PD pulse occurrence. This causes that information about the event with calculated partial discharge parameters (number of pulses, their energy, and amplitude) is saved to the database on the server. In turn, in the diagnostic mode, VDC enables direct access to the transmitted data frames, including the preview in real-time the PD waveforms of the registered in particular channels. This functionality also enables gathering the samples to perform further, more advanced analysis, including the elaboration of PRPD patterns. Based on the data gathered in the database parameters, the analytical module regularly checks if the threshold values of the PD parameters have not been exceeded. Additionally, using the least square method, a linear trend estimation is conducted for the data from the last week and the last month. All information is shared with the user through the module of the graphic data presentation, which displays in the application window, i.e.,  
* the number of detected PD pulses and the average value of their energies and amplitudes,
* the result of self-diagnosis of measurement channels,
* warning or alarm state after exceeding the threshold values for the sum of registered pulses, their average energy, and amplitude for various time intervals: 15 min, 60 min, 24 h, and 30 days,
* the warning or alarm state when the values of PD parameters collected during last week and last month show a rising trend. Figure 22: Schematic diagram and photograph of developed multi-channel data concentrator module MPD-001. The functions of the reporting module enable elaborating summary reports or details for the PD parameters registered in the database and events description. As it was mentioned before, the system in the diagnostic mode functions as a multichannel partial discharges detector allowing to observe the PD waveforms or PRPD pattern images. PRPD images are created based on the 20 ms aggregation of data frames from HFCT and UHF sensors and voltage sine wave registered by the current/voltage transformer (CVT) on the substation. The system also provides the possibility to wirelessly measure the high voltage in a power transformer, which is realized with the use of a special capacity probe. The structure of the probe and assumptions of the measuring method is discussed in detail in [105]. The signal from the probe is registered with an additional, A/D converter of sampling frequency equal to 4 MS/s dedicated exclusively for this task. This converter is placed in the circuit of every analog-to-digital signal processing module. The angular resolution of the created PRPD patterns is 1\({}^{\circ}\), whereas the amplitude resolution equals 16 bits for the output voltage range equal to 0-3.6 V. The software function responsible for preparing PRPD patterns was tested in the laboratory conditions. For this purpose, the comparative research, during which PRPD patterns were simultaneously registered with a standard partial discharges detector type Doble PD-Smart and monitoring system under test. A schematic diagram of the measurement setup was presented in Figure 23.  
The PRPD images obtained during the research were the effect of about 60-90 min registrations of the partial discharges pulses. In this case, instead of pressboard samples, glass samples with a thickness of 6 mm were used. This change was caused by the fact that the pressboard samples quickly degraded under the influence of the action of high-intensity surface discharges with the apparent charge of a few nC. This, in turn, led to PD extinction or breakdown.