In substation environments usually multi lead cables are used to transmit signalling voltages. Due to substation conditions these signalling cables are often exposed to disturbances that can not be allowed to get into the cable conductors, thereby causing possible malfunctions in the connecting equipment. Therefore, these cables are typically shielded and armoured, and in such applications it is important to know exactly the shielding effectiveness of shielding and/or armouring.
As a part of my thesis I have done measurements on the shields of signalling cables. This meant measuring the shield’s inner and outer surface impedances in the function of frequency and current. I used the measured impedances to define the inner protective factors, which describes the effectiveness of the shielding on given frequency, or on given current. I also defined the resultant protective factors for three typical cases, which are the function of the soil resistivity.
It is possible, that inside the cable some wires are emitting disturbances towards the other wires, so it is worth to examine the disturbance coupling between the cable wires. Therefore, in the second part of my thesis I studied the inductive coupling between the leads of signalling cables. At first, I examined if the cable leads could be considered as tubular conductors and I did measurements according to this. Finally, in the knowledge of the results, I made a model capable of calculating the inductive coupling between the cable leads, and I compared the results provided by the program with the measured values. According to this, the developed model can calculate the mutual inductivities accurately, even at high frequencies, by taking the skin effect into consideration.