Safety and operation efficiency of the particle accelerators strongly depend on the quality of the supplied electric current and is affected by the electric properties of all elements of the circuit. In this paper the capacitance of the superconducting bus-bars applied in the cryogenic by-pass line for the SIS100 particle accelerator at FAIR is analysed. The unit capacitance of the bus-bars is calculated numerically and found experimentally. A 2D numerical model of a cross-section of the cable is applied. The capacitance is found with three methods. The stored energy, electric displacement field and charge gathered on the surfaces of the device are calculated and analysed. The obtained values are consistent. Experimental measurements are performed using the resonance method. The measuring system is undamped using a negative conductance converter. Small discrepancies are ob- served between numerical and experimental results. The obtained values are within the requirements of the accelerator design.

The influence and the potential risk due to hidden faults of a relay protection system on power supply in distribution systems are paid more and more attention to. A probability analysis method is used to analyse fault characteristics and action mechanism of dominant faults, hidden misoperation and non-operation of the relay protection systems, and failure probability model of relay protection system is constructed and simplified. The effects of dominant faults, hidden misoperation and non-operation of the relay protection systems on the reduced power supply load power are analysed, and a probabilistic model for reduced power supply load power is constructed by three parts corresponding to dominant faults, hidden misoperation and non-operation. A probability calculation method of power supply risk occurrence due to hidden faults of relay protecttion system is proposed considering the fault probability of the relay protection systems, the frequency of the hidden faults occurring in operation period, the reduced power supply load power or load power outage, and the connection mode of the in-lines, out-lines and transformers in a substation. The feasibility and applicability of the proposed method for estimation of risk value probability of the relay protection systems is verified by two studied examples.