Distribution networks have undergone huge changes in recent years. Due to the increased requirements for the security of electricity supply, network operators have changed overhead lines into underground cable networks in large-scale and at a fast pace.
Due to the high phase-to-earth capacitance values of cables, uncompensated earth-fault currents have increased significantly, reaching magnitudes of hundreds of amps. For this, numerous new arc suppression coils (ASC) have been installed. When the structure and electrical characteristics of the network change, electrical safety and proper function of earth-fault protection must be verified.
This technical paper introduces the identified challenges for earth-fault protection and electrical safety due to large-scale underground cabling. ABBʼs new touch voltage-based earth-fault current protection function IFPTOC has been introduced to solve the identified challenges of traditional protection functions. With this new method both dependable and precisely timed protection operation can be ensured in compliance with the applied legislation during all possible operating conditions.