The whole structure of MOA is vertical type with single column, consisted of components, grading ring (rated voltage: 192kV and upwards) and insulated base. The core component of MOA is nonlinear metal oxide resistors with excellent voltage-ampere characteristics. When atmosphere and switching over-voltage occurs, the resistance of the block is very small to limit the residual voltage within the permissible range and absorb the energy of over voltage, thus protecting power equipment and capacitor bank. Whereas, the piece being small resistance plays the function of insulation from power system by only allowing small current to pass.