###### Abstract  
Reliability and safety are crucial for the operation of a dynamically tuned passive power filter (DTPPF). Safe performance of DTTPFs implies complete normal filtering without failure within a specified period. To prevent potential disaster or economic loss, it is desirable to achieve early warning of any core device faults in a DTPPF based on its running state and to optimize its harmonic mitigation performance. In this paper, we explore effective methods for identifying core device faults in DTPPFs. First, we summarize the characteristic parameters of faults, running state parameters, parameters required for fault monitoring, and fault type parameters. Then, a cloud server-assisted remote monitoring and fault identification system for DTPPF is proposed, which consists of monitoring system's architecture and cloud servers' software architecture as well as software design of the back-end service layer and functional design of the front-end application layer. Our experiments demonstrate that the proposed system can monitor the real-time operational status of the DTPPF, enabling remote diagnosis and identification of core device faults. Moreover, it is user-friendly, as it is capable of optimizing equipment maintenance schedules and utilizing manufacturers' service capacities. Therefore, this research provides a theoretical foundation for harmonic mitigation in low-voltage distribution networks and is valuable for practical engineering applications in industrial power grids. cloud server; dynamically tuned passive power filter; fault identification; monitoring system +
Footnote †: journal: Applied  
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harmonic, and can absorb the harmonics current. In this way, they reduce the corresponding harmonics current into the distribution network, achieving the purpose of filtering. PPFs are widely used in many industries because of their high reliability, simple structure, large capacity, and low costs. The filtering performance of PPFs depends on the parameters of the grid and the load. In contrast, active power filters (APFs) have complex structural and control requirements, making their operation conditions more demanding [8]. The main impediments for the development of PPF technology are the difficulty of continuously adjusting parameters, the need for a better understanding of the working mechanism of dynamic tuning, and challenges in optimizing the design and implementation of key components that cannot meet the requirements of practical engineering [9]. After ten years of research, the dynamic tuning power filter (DTPPF) was developed. DTPPFs consist of an electromagnetic coupling filtering inductor and multiple filter capacitors connected in series, which can effectively filter out the harmonics current. Recent studies have shown that DTPPFs are capable of harmonic suppression and energy saving. They can absorb the harmonics current and reduce the current RMS, thereby improving the power quality and the security of the power supply. DTPPFs can effectively achieve dynamic tuning and suppression of power harmonics in industrial applications [10; 11; 12]. However, long-term operation can affect the core devices of DTPPFs. For example, the harmonics current can cause aging or short-circuit failure of the filter capacitor, resulting in damage or reduced capacity. Additionally, it can lead to the breaking of the thyristor in the secondary winding of the electromagnetic coupling filter reactor(ECFR), rendering the primary-side inductance of the ECFR unable to be continuously adjusted. Both of these faults cause the resonant frequency of the DTPPF to deviate, resulting in a poor filtering effect. There have been many studies on the capacitance and dielectric loss of capacitors [13; 14]. The temperature of the capacitor case can be obtained by temperature sensors, while the temperature of the internal core can be inferred through estimation methods [15].