Characteristics of four typical ash deposition forms is analyzed.
Ash belts form at low voltages and will overlap to form ash ribs when T ⩽ 500 °C.
Smooth slope type ash layer forms at high voltages when T ⩾ 500 °C.
Thickness growth rate of a given point decreases with the increasing time.
Back corona discharge onset voltage decreases with ash layer thickness lineally.