Home » English riddles » Protection » Protection Riddle No.18 – Generator Stator Earth-Fault Protection at Low Frequency Injection » Reply To: Protection Riddle No.18 – Generator Stator Earth-Fault Protection at Low Frequency Injection Reply To: Protection Riddle No.18 – Generator Stator Earth-Fault Protection at Low Frequency Injection 2021-08-03 at 11:08 am #1632 Hamid why 20 HZ? Why 10,25,30,40,… HZ cannot be suitable?