## 8 Discussion  
No overflows of active power exceeding the normally permissible parameters of the equipment were detected during the measuring. However, spontaneous partial load discharges and emergency shutdowns of the LMs were recorded on 20 June, 16 July, 18 July, 29 July, leading to an emergency stop of the GTPS \"Ilyichevskaya\" power units. It is known that the average time for the resumption of the operating mode of the GTPS \"Ilyichevskaya\" is from 2 to 4 h, which causes an increase in emissions into the atmosphere with incomplete APG combustion on the flare. The analysis of the spectrum and levels of harmonic components showed that the recorded excess of the permissible values of the coefficients of odd harmonics from 11 th to 17 th is due to the presence of powerful converter equipment in the load, in particular, frequency converters [30; 31]. Furthermore, during the PQI measurements in the PSS of the GTPS \"Ilyichevskaya\", voltage dips and swells were registered. The maximum recorded voltage dip duration was 1250 ms, and the dip depth was 84.69% of the nominal value. The analysis of the registered dips and swells, as well as the absence of exceeding the permissible values of slow voltage changes, allows us to conclude that there are no uncontrolled overflows of reactive power along the main voltage harmonic during the period of the PQI measuring [32]. Analysis of the spectrum of harmonic components that go beyond the normally permissible values by the standard [28] and their distribution [33; 34; 35] allows us to conclude that the characteristic sources of the recorded deviations of the nth harmonic component coefficient in the PSS of the GTPS \"Ilyichevskaya\" are:  
* Soft-start devices BKM-1,2, 3, 4, 5 for 5 th, 7 th, 11 th, and 13 th harmonics, only during the start of the drive motor;
* Operation of the pulse-phase control system with non-sinusoidality of the supply voltage for 6 th harmonic;
* Operation in the main power system of 6-pulse bridge converters for 11 th, 13 th, 17 th, 19 th, and 21 st harmonics;  
Figure 9: The PQI profile from 00:00 am on 15 July to 00:00 am on 16 July. (**a**) Non-sinusoidal coefficient, (**b**) frequency, (**c**) phase voltage in the secondary measuring circuit, (**d**) zero and (**e**) negative sequence voltage unbalance. * Switching of vacuum breakers and resonant phenomena for short-term harmonic components of odd order 23 and higher. The reason for the recorded negative sequence voltage unbalance was a breakdown of the inter-turn insulation of the power transformer of the SS 35 kV \"Ilyichevskaya\", detected on 25 June and its subsequent asymmetric loading, since, after the repair work, no excess of the unbalance coefficient in the negative sequence of the normally permissible values was detected. The reason for the recorded voltage dips and swells in the PSS was unfavorable weather conditions (lightning discharges), as well as switching of vacuum breakers [36] during an emergency stop of one or more power units of the GTPS \"Ilyichevskaya\". In addition, an analysis of the influence of the operating modes of the GTPS \"Ilyichevskaya\" on the PQI was carried out, as a result of which the following was revealed:  
* When the load is dropped from 1.5 MW, even when working in parallel with the main power system, there is an emergency stop of the power units of the GTPS \"Ilyichevskaya\". * When BCM connected to the busbar, working in the local mode of generation, there was a slight (1%) fluctuation in the steady-state value of the voltage with a period of about 5 min. * More frequent fluctuations in the level of voltage in view of the measured current loads of the LM-3 indicate frequent assist switching devices of the LM's switchgear 0.4 kV that can be associated with the misalignment of the control systems of the GTUs and LMs. * The connection of LMs when entering the mode causes the frequency to decrease almost to the minimum permissible value in the presence of two GTPs or less in operation.