Surge arrester selection at 20(10) kV level and in the neutral point for the TS 110/20(10) kV Imotski
Abstract
The paper presents a detailed calculation and selection of parameters for metal oxide surge arresters in a distribution network grounded using a Petersen choke. The selection of surge arresters was carried out for arresters connected between phase and ground (grounding conductors) and for a surge arrester connected in the star point of the power transformer (zero point of the network) TS 110/20(10) kV Imotski (parallel to the Petersen choke). The expected voltage stresses were considered, of which the following types of temporary overvoltages can be mentioned: 1. overvoltages caused by sudden load failure, 2. overvoltages caused by switching on unloaded cable lines, 3. overvoltages caused by the occurrence of short circuits with the ground, 4. overvoltages caused by resonant effects, 5. overvoltages caused by saturation of the power transformer, 6. overvoltages transmitted by capacitive coupling through the power transformer: In addition, since the incident network of 20(10) kV is grounded using a compensating (Petersen) choke, the following (over)voltage conditions were considered: 7. increase in the voltage of the zero-point network due to the asymmetry of the domicile distribution network, 8. increase in the voltage of the zero-point network due to the disconnection or interruption of one phase on one of the cable lines of the domicile distribution network, 9. increase in the voltage of the zero-point network due to the design of the power transformer, when ground faults occur in the incident transmission network. The following maximum expected (switching and atmospheric) overvoltages were also analyzed: overvoltages that occur when switching on the incident cable lines, overvoltages that occur when a short circuit occurs and is disconnected, overvoltages that are transmitted through the power transformer from the incident transmission network. The energy stress of the aforementioned metal oxide surge arresters was also considered.
