**8. Discussion**

This article investigated the impact of using static capacitive compensation on energy consumption and payback period for energy efficient electric motors in a pumping application. Compared to the IE2 induction motor, motors such as the IE3 induction motor, direct-on permanent magne<sup>t</sup> synchronous motor and direct-on-line synchronous reluctance motor are considered.

The comparison considers not only the efficiency of the motors, but also their power factor, on which the losses in the cable and transformer supplying the pumping station depend. The possibility of installing static capacitors to compensate for the reactive power of motors is also taken into account. The analysis takes into account that the motors have different initial costs, and also takes into account the cost of capacitors.

Without taking into account the possibility of using capacitors, the DOL PMSM has the shortest payback period (1.549 years), despite the highest cost, due to its high efficiency and high power factor, which can significantly reduce losses in the cable and transformer. The payback period of the DOL SynRM (1.553 years) is approximately equal to the payback period of DOL PMSM due to its higher efficiency and lower initial cost. At the same time, the payback periods of the DOL PMSM and DOL SynRM are significantly lower than that of IE3 IM (2.75 years).

The analysis shows that considering the possibility of installing static capacitors can significantly affect the results of comparing different motors in the application under consideration. Capacitors have a low initial cost compared to the price of motors, however, they allow you to compensate for the reactive component of the motor current, eliminate losses from this component in the cable and transformer, and therefore significantly reduce total losses. When using capacitors, the DOL SynRM has the shortest payback period (1.07 years).

The use of static capacitors will shorten the payback period of all the motors under consideration. When installing them, the payback period for the IE3 IM decreases most significantly (from 2.75 to 1.75 years). The DOL SynRM payback decreases from 1.553 to 1.07 years. The payback period of the DOL PMSM also decreases, but only slightly (from 1.549 to 1.52 years), since the DOL PMSM has a high power factor even without capacitive compensation.

If a pumping station has an approximately constant flow rate without the need for frequent shutdown of individual pump units, then installing one capacitor bank at the common connection point of the motors is more profitable than installing separate batteries of smaller capacity for each motor.

It is also shown that in the absence of the possibility of replacing the IE2 motor with more energy efficient ones, installing static capacitors on the terminals of the IE2 motor can be a good energy saving solution with a short payback period. In this case, the payback period of the capacitors is only 0.38 years.

The results of this study can be applied not only to pumps, but also to other mechanisms in which electric motors are powered directly from the AC mains and operate for a long time with little changing load, for example, fans, blowers, compressors, mixers, etc.

**Author Contributions:** Conceptual approach, V.K. and V.P.; data curation, S.O. and V.D.; software, S.O. and V.K.; calculations and modeling, S.O., V.K. and V.P.; writing—original draft, S.O., V.D., V.K. and V.P.; visualization, V.D. and V.K.; review and editing, S.O., V.D., V.K. and V.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** The work was partially supported by the Ministry of Science and Higher Education of the Russian Federation (through the basic part of the governmen<sup>t</sup> mandate, Project No. FEUZ-2020-0060).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data are contained within the article.

**Acknowledgments:** The authors thank the editors and reviewers for their careful reading and constructive comments.

**Conflicts of Interest:** The authors declare no conflict of interest.
