Impact of superimposed direct and 50 hz alternating high voltage stress on current and voltage distribution along surge arresters

Summary

High voltage metal-oxide surge arresters (MO arresters) must protect electrical power devices by limitation of switching and lightning transient overvoltages which occur in the high voltage transmission system and in HVDC converter stations. The MO arresters which are installed either at AC-side or DC-side of the converter station or at a hybrid transmission system are stressed by non-ideal sinusoidal or direct voltage waveforms. The applied voltage constitutes as a composite voltage. These voltage waveforms affect the MO arrester in form of a higher power loss, higher operating temperature as well as unexpected and difficult phenomena. Additionally, it is known, that MO arresters are assembled of several metal oxide resistors (MOR) in serial and that the voltage and current distribution along the MO arrester is not uniform due to stray capacitances and unwanted parasitic conduction currents. This would imply that upper MOR in the arrester are stressed by higher harmonic frequencies and by a higher voltage and current amplitudes than the lower MOR, these electrical stresses result in higher conductor and dielectric losses which leads to a temperature increase of the MO column. Finally, the effect of increasing temperature can be checked on the basis of a typical optical temperature measurement system. However, this method has the disadvantage that only the time delayed resulting temperature is known – not the cause of it. The presented investigation focuses on how the current distribution is changed by different composite voltages (50 Hz UAC + UDC).

Additional informations

Authors

C. HIPPLER

Keywords

High-voltage, surge arrester, current distribution, metal oxide resistor