Single-Phase Cylindrical Capacitor

In a single-phase low-voltage power distribution system, the switching operation of Single-Phase Cylindrical Capacitors is like that of a dancer who needs to precisely control the rhythm. The inrush current generated by the capacitors at the moment of switching could potentially become a latent disturbance that affects the stable operation of the system. A thorough understanding of the unique characteristics of the inrush current of the Single-Phase Cylindrical Capacitors and the mastery of effective suppression strategies are the important technical foundations for building an efficient and reliable compensation system.

Compared with the surge current behavior of the three-phase system, the surge current generated when a Single-Phase Cylindrical Capacitor is switched on or off shows more significant randomness and unpredictability. When the capacitor is connected to the power grid at the peak voltage, the energy stored inside it is almost zero. At this moment, the grid voltage will exert a sharp charging effect on the capacitor through the line impedance, causing the instantaneous current to potentially reach several times the rated current. This high-frequency, high-amplitude transient current not only causes a sudden drop in system voltage, but also generates a huge electrodynamic force inside the capacitor. The long-term accumulation of this electrodynamic force will lead to fatigue and damage of the metallized film electrodes. Especially in systems where some capacitors are already in operation, the later-connected capacitors will also be subjected to the reverse discharge impact from the already-charged capacitors. This multi-source superimposed surge current phenomenon is more complex than that of the three-phase system.

To suppress the inrush current of Single-Phase Cylindrical Capacitors, efforts should be made from two aspects: timing control and impedance management. The most effective way to eliminate the inrush current is to adopt the synchronous switching technology based on voltage zero-crossing detection, which fundamentally avoids the voltage step at the charging moment and enables the single-phase capacitor to smoothly connect to the power grid at the zero-crossing point of the voltage. For systems without the condition for synchronous switching, the most economical and practical choice is to connect a specific reactor in series to each capacitor. By increasing the circuit impedance through the reactor, the current rise rate is effectively limited, and the inrush current ratio is controlled within five times the rated current. In the case of multiple capacitors connected in parallel, a minimum switching time interval should be set to ensure that the previous group of capacitors complete the charging process before the subsequent capacitors are put into operation, avoiding mutual impact between the capacitors.

Geyue Electric has comprehensively optimized the inrush current characteristics of the BSMJ(Y) series Single-Phase Cylindrical Capacitors. By improving the internal connection structure and electrode design, our company has significantly enhanced the mechanical strength of this series of capacitors in withstanding inrush current impacts. The dedicated current-limiting reactor provided by us has been precisely parameter-matched, and it can limit the inrush current within a safe range without affecting the normal compensation performance. For customers with special requirements, we can also provide intelligent capacitor modules with built-in solid-state relays, enabling true no-inrush switching for the customers.