978-1-5386-6635-7/18/$31.00 ©2018 IEEE. Applicability of the risk assessment in international standards to HVDC converter stations J. Hernandez-Guiteras HVDC ABB Ludvika, Sweden joan.hernandez@se.abb.com L. Arevalo HVDC ABB Ludvika, Sweden liliana.arevalo@se.abb.com H. Hammarsten HVDC ABB Ludvika, Sweden harvey.hammarsten@se.abb.com Abstract—The risk assessment is a methodology to assist during the design of lightning protection systems. However, the available standards do not have clear guidelines for its application to HVDC converter stations. This results in unfeasible expectations and misunderstandings between designers, utilities and insurance companies, among others. This paper highlights some of the practices of the industry and discusses their relationship with actual international standards. The publication is expected to highlight the areas of improvement in future editions of the standards to include HVDC converter stations. Keywords: Lightning; Risk; Power Systems; HVDC; I. INTRODUCTION The design of the lightning protection systems for substations and transmission lines is based on measurements and statistics of data collected historically of lightning discharge characteristics [1]-[2]. Based on such statistics empirical models were proposed to describe the striking point of the discharges [3]-[7]. Based on the different proposals available in the literature, some of them have been accepted and recommended in international standards such IEEE [8] and IEC [9]. HVDC converter stations consist of outdoor and indoor environments. Outdoor environments are commonly referred as yards, e.g. AC yard or DC yard. Indoor environments are divided in high voltage and low voltage systems. The high voltage system contains high voltage equipment for power transmission and commonly known as hall e.g. valve hall or DC hall. The low voltage systems contain medium and low voltage systems used to control the converter station operation and are commonly known as building, e.g. control and auxiliary system building. Consequently, the lightning protection of HVDC converter stations requires a coordination between outdoor and indoor environments to warranty faultless protection of living beings and equipment against direct lightning strikes. To be able to perform a lightning protection of HVDC converter stations, it is required to combine protection principles available some of them summarized on international standards, such as IEEE 998 [8] for outdoor yards and IEC 62305 [9] for indoor halls and buildings. However, a clear guideline regarding the risk assessment to design lightning protection stations for electrical substations with indoor and outdoor environment is not available in the literature, and it has not been addressed in the international standards such as IEEE or IEC. Therefore, with the great increase of the use of HVDC interconnections worldwide, it raises the necessity to clarify the applicability of different standards for the protection against direct lightning strike. II. LIGHTNING PROTECTION DESIGN PRACTICE FOR HVDC CONVERTER STATIONS An HVDC converter station comprises two different environments, outdoor and indoor. The equipment on the AC and DC sides of the station are located outdoors. The location where converter valves are located is indoors and known as valve hall. The low voltage systems are located in the control and auxiliary system building. Figure 1. Aerial view of HVDC converter station. A. Converter station outdoor switchyards The lightning protection system of a converter station outdoor yards against direct lightning strikes have been done with methods described in IEEE 998 [8]. The lightning protection system can be achieved with overhead shield wires or with the use of masts.