Investigation of transformer tap-changers for thyristor-based electrolyzer system

Green hydrogen without carbon-gas emissions is playing an important role in the decarbonization of industry. To expand electrolyzer installation, low cost and high efficiency AC/DC rectifier is a crucial component, among which the thyristor rectifier is a widely adopted solution considering its high current capability and economic benefits. To cope with the AC voltage variation as well as the DC operation range of electrolyzer, the transformer tap-changer is often required in combination with thyristor rectifier to regulate voltage at different loadings. However, transformer tap-changer configurations, namely on-load tap-changer (OLTC) and no-load tap-changer (NLTC) will have different implications on the system design and power quality performance. This paper compares OLTC and NLTC solutions for thyristor rectifier based electrolyzer plant in terms of reactive power consumption and harmonic currents through theoretical calculations and simulation validations. From the results, OLTC solution shows obvious advantage over NLTC in terms of reactive power and harmonic currents when connected to MV system with large AC variation; however, for a stable power grid with smaller AC variation, NLTC solution could perform similar power quality as OLTC but with lower cost and simpler configuration.