Transient overvoltage transfer and amplification in a 400 kV network – A case study

•A realistic case study of overvoltage amplification in a 400 kV network is analysed and presented.•Energisation and fault inception involving new cables, led to overvoltage values at remote nodes that are close to switching withstand voltage.•Time and frequency domains analysis explained the causes of amplification.•Surge arresters are effective mitigation option for overvoltage amplification. The paper investigates overvoltage propagation in a 400 kV network within the National Grid Electricity Transmission system in the UK. The studies were triggered by a replacement project for two parallel 400 kV cables and the installation of an additional one. The network in the vicinity of the cables has historical issues of flashover and circuit breaker failures. Electromagnetic transient studies were performed to simulate energisation and fault inception and clearance for the three new cables to examine compliance against overvoltage standards and limits. Studies were performed using the DIgSILENT analysis tool. Studies show that due to resonance in a specific frequency range, switching overvoltage propagated and amplified at remote nodes to a level close to the equipment's rated switching voltage. As mitigation, surge arresters with characteristics different from the National Grid recommended surge arresters were proposed and found suitable to bring the overvoltage values within the design limits for temporary overvoltage.