Rapid expansion of electrical power system in recent years and

at the same time

the breakthrough of HVDC transmission technology and further defect prominent of AC power transmission has paved the way for the wide application of HVDC transmission system. As an important part of HVDC system

DC filter capacitor tower plays an important role

not only in filtering the harmonic in DC side

but also in reducing the adverse effects. The malfunction of the protection is often occurred in the actual operation of the capacitor tower and the problem cannot be detected with power off and the normal operation of the transmission line is affected by the repeating effect. Based on the above issues

the online monitoring scheme for capacitor tower is proposed in this paper to calculate capacitance of capacitor and real-time monitor the operation status of capacitor by way of monitoring end voltage and the flow current of capacitor. The operation trend of the capacitor can be analyzed in advance in accordance with the operation status of the capacitor

develop preventive work timely and avoid unnecessary loss.